Front Cover A giant ejection of matter from the sun (blue color) as observed by the Solar Maximum Mission. Each eruption ejects about one billion tons of matter into interplanetary space. These clouds of matter travel at speeds of about three million kilometers per hour and cause global magnetic storms on Earth that produce intense auroral displays over the poles. A typical aurora viewed from the Dynamics Explorer satellite is shown in the larger inset to the left. Up to one hundred billion watts is deposited in the upper atmosphere during such displays. The solar atmosphere is so hot (over a million degrees) that it blows away from the sun as a steady wind at about a million kilometers per hour past all the known planets. The presence of this wind was originally inferred from comet tails, which always point away from the sun. The lower inset shows the first man-made comet, formed recently by a release of barium from one of the Active Magnetosphere Particle Tracer Explorers spacecraft.

Back Cover The trajectory of Solar Probe superimposed on a picture of the sun taken during an eclipse. The pearly- white streamers are shaped by the sun's magnetic field and the solar wind and, in some eclipse pictures, can be seen to distances of over 7 million kilometers from the sun. The red prominences visible over the moon's shadow are cool gas condensations suspended in the corona, which is one hundred times as hot. The Solar Probe spacecraft would explore the sun's vicinity for the first time and approach to within about 2 million kilometers of the solar "surface." The time marks on the trajectory show that the near-sun traversal would last for 10 hours, with the spacecraft traveling at a speed of some 300 kilometers per second (over a million kilometers per hour) at closest approach. The probe would intersect many of the closed and open magnetic field structures, as is evident in the picture. The total flight time could be as short as 2.7 years, depending on available propulsion systems. AN IMPLEMENTATION PLAN FOR PRIORITIES IN SOLAR-SYSTEM SPACE PHYSICS

Committee on Solar and Space Physics Space Science Board Commission on Physical Sciences, Mathematics, and Resources

NATIONAL ACADEMY PRESS Washington, D.C. 1985 NOTICE: The project that is the subject of this document was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee that cosponsored the workshop were chosen for their special compe- tences and with regard for appropriate balance. These proceedings contain papers presented at the workshop, which was arranged and con- ducted by the sponsoring agency. The subject matter and content of the papers, as well as the views expressed therein, are the sole responsibility of the authors. In the interest to timely publication, the papers are presented as received from the authors, with a minimum of editorial attention.

The National Research Council was established by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of further- ing knowledge and of advising the federal government. The Council operates in accordance with general policies determined by the Academy under the authority of its congressional charter of 1863, which establishes the Academy as a private, nonprofit, self governing membership corpora- tion. The Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in the conduct of their services to the govern- ment, the public, and the scientific and engineering communities. It is administered jointly by both Academies and the Institute of Medicine. The National Academy of Engineering and the Institute of Medicine were established in 1964 and 1970, respectively, under the charter of the National Academy of Sciences.

SPONSOR: This project was supported by Contract NASW 3482 between the National Academy of Sciences and the National Aeronautics and Space Administration

Available from: Space Science Board National Academy of Sciences Washington, D.C.

ii CONTENTS

FOREWORD ...... vii

PREFACE ...... ix

1 INTRODUCTION ...... 1

2 GUIDING PRINCIPLES ...... 4

3 SCIENCE STATUS AND OBJECTIVES ...... 5 Solar Physics ...... 5 Physics of the Heliosphere ...... 5 Magnetospheric Physics ...... 7 Upper-Atmospheric Physics ...... 7 Solar-Terrestrial Coupling ...... 10 Comparative Planetary Studies ...... 10

4 IMPLEMENTATION STRATEGY ...... 11 Rationale ...... 11 Program Mix in Solar and Space Physics ...... 11 Resource Requirements for Recommended Programs ...... 12 5 SUMMARY OF RECOMMENDED PROGRAMS ...... 14 Introduction ...... 14 Major Missions ...... 16 Explorers ...... 18 Spacelab/Space Station Payload Evolution ...... 18 Suborbital Program ...... 19 Theory and Computer Modeling ...... 19 Mission Operations and Data Analysis ...... 20 Research and Analysis ...... 21 Technology Requirements and Instrument Development ...... 21 6 SCIENCE HIGHLIGHTS AND ACCOMPLISHMENTS ...... 22 Skylab ...... 22 P78-1 ...... 22 Solar Maximum Mission ...... 23 Orbiting Solar Observatory-8 ...... 23 Heliosphere Missions ...... 23 International Sun-Earth Explorer ...... 24 Dynamics Explorer ...... 24 Shuttle/Spacelab--Space Plasma Physics ...... 25 Planetary Magnetosphere/Atmosphere Missions ...... 25 Atmosphere Explorers ...... 26 Nimbus-7 ...... 26 Solar Mesosphere Explorer ...... 27 Pioneer Venus ...... 27 Theory Program ...... 28

7 DETAILED MISSION PLANS-SOLAR AND HELIOSPHERIC PHYSICS ...... 29 Introduction ...... 29 Program Descriptions ...... 29 Priorities ...... 37

111 8 DETAILED MISSION PLANS--PLASMA PHYSICS ...... 39 Introduction ...... 39 Program Descriptions ...... 39 Priorities ...... 49 9 DETAILED MISSION PLANS--UPPER ATMOSPHERIC PHYSICS ...... 51 Introduction ...... 51 Program Descriptions ...... 51 Priorities ...... 58 10 PERSPECTIVES ...... 59 Introduction ...... 59 Data Management ...... 59 International Cooperation ...... 59 Mission Costs ...... 59 Facility Management and Operation • 60 Computer Facilities and Modeling ...... 60 Space Station ...... 61 Planetary Exploration ...... 61 11 ORGANIZATIONAL STRUCTURE ...... 63 APPENDIX: LEVELS OF INVESTIGATION ...... 65

iv SPACE SCIENCE BOARD COMMITTEE ON SOLAR AND SPACE PHYSICS

Stamatios M. Krimigis, Applied Physics Laboratory, The Johns Hopkins University, Chairman R. Grant Athay, High Altitude Observatory J Daniel Baker, Los Alamos National Laboratory ,' ' Lennard A. Fisk, University of New Hampshire Robert W. Fredricks, TRW - John W. Harvey, Kitt Peak National Observatory Jack R. Jokipii, University of Arizona _ _ _ • Margaret Kivelson, University of California, Los Angeles Michael Mendillo, Boston University Andrew F. Nagy, University of Michigan ...... j,, • Marcia Neugebauer, Jet Propulsion Laboratory Konstantinos Papadopoulos, University of Maryland Susan Solomon, Aeronomy Laboratory, NOAA Darrell F. Strobel, The Johns Hopkins University George L. Withbroe, Center for Astrophysics LIAISON REPRESENTATIVES C.G. Flthamrnar, Royal Institute of Technology, Stockholm, Sweden Melvyn L. Goldstein, NASA Goddard Space Flight Center James Russell, III, NASA, Langley Research Center EX-OFFICIO Thomas M. Donahue, University of Michigan Devrie S. Intriligator, Carmel Research Center Robert M. MacQueen, National Center for Atmospheric Research EXECUTIVE SECRETARY Richard C. Hart

v

\ \ SPACE SCIENCE BOARD

THOMAS M. DONAHUE, University of Michigan, Chairman DON L. ANDERSON, California Institute of Technology RAYMOND E. ARVIDSON, Washington University JACQUES M. BECKERS, University of Arizona DANIEL B. BOTKIN, University of California ANDREA K. DUPREE, Center for Astrophysics FREEMAN J. DYSON, The Institute for Advanced Study RICCARDO GIACCONI, Space Telescope Science Institute JAY M. GOLDBERG, University of Chicago DONALD M. HUNTEN, University of Arizona STAMATIOS M. KRIMIGIS, The Johns Hopkins University ROBERT M. MACQUEEN, National Center for Atmospheric Research HAROLD MASURSKY, Center for Astrogeology CARL E. McILWAIN, University of California, San Diego BERNARD M. OLIVER, Hewlett-Packard Company RONALD G. PRINN, Massachussetts Institute of Technology J. WILLIAM SCHOPF, University of California, Los Angeles EDWARD C. STONE, JR., California Institute of Technology ANTHONY L. TURKEVICH, The University of Chicago RAINER WEISS, Massachusetts Institute of Technology GEORGE WETHERILL, Carnegie Institution of Washington DEAN P. KASTEL, Staff Director

COMMISSION ON PHYSICAL SCIENCES, MATHEMATICS, AND RESOURCES

HERBERT FRIEDMAN, National Research Council, Chairman THOMAS BARROW, Standard Oil Company ELKAN R. BLOUT, Harvard Medical School BERNARD F. BURKE, Massachusetts Institute of Technology GEORGE F. CARRIER, Harvard University HERMAN CHERNOFF, Massachusetts Institute of Technology CHARLES L. DRAKE, Dartmouth College MILDRED S. DRESSELHAUS, Massachusetts Institute of Technology JOSEPH L. FISHER, Office of the Governor, Commonwealth of Virginia JAMES C. FLETCHER, University of Pittsburgh WILLIAM A. FOWLER, California Institute of Technology GERHART FRIEDLANDER, Brookhaven National Laboratory EDWARD A. FRIEMAN, Science Applications, Inc. EDWARD D. GOLDBERG, Scripps Institution of Oceanography MARY L. GooD, UOP, Inc. THOMAS F. MALONE, Saint Joseph College CHARLES J.MAN_, Okiahoma Geological Survey WALTER H. MUNK, University of California, San Diego GEORGE E. PAKE, Xerox Research Center ROBERT E. SIEVERS, University of Colorado HOWARD E. SIMMONS, JR., E.I. du Pont de Nemours & Company, Inc. ISADORE M. SINGER, Massachusetts Institute of Technology JOHN D. SPENGLER, Harvard School of Public Health HATTEN S. YODER, JR., Carnegie Institution of Washington vi RAPHAEL G. KASPER, Executive Director LAWRENCE E. McCRAY, Associate Executive Director FOREWORD

For the last several years the Space Science Board has been developing strategies for guiding future research programs in the various scientific disciplines involved in space research. This report, however, has a somewhat different character. While it does specify the scientific objectives of the field (thereby updating the previous report, Solar-System Space Physics in the 1980"s"A Research Strategy, NAS, 1980), it goes further and describes the plan for implementing the objectives. In this sense, the report more closely follows the methodology of two recent reports that have received wide acclaim for establishing priorities in related fields of research, Astronomy and Astrophysics for the 1980"s (NAS, 1982) and Planetary Exploration Through Year 2000 (NASA, 1983). The Space Science Board (SSB) adopted this different approach for this report for two reasons. First, with the appearance of the astronomy and planetary priorities reports, a need was established to do something similar in solar and space physics. Secondly, with NASA currently involved in preparing a priorities report for the Earth Sciences, it was decided that the SSB could provide a valuable service for this broad-based effort by undertaking a part of the subject matter for which the Board was admirably suited through the Committee on Solar and Space Physics (CSSP). NASA concurred in this decision. Thus, in November 1983, the Board directed the CSSP to develop a priorities-based study of solar and space physics, using the 1980 Research Strategy as a basis. The Committee produced the following report, which was reviewed and approved by the Board in November 1984.

Thomas M. Donahue Chairman, Space Science Board

vii

PREFACE

In carrying out the charge of the Space Science Board, stated above, the Committee on Solar and Space Physics (CSSP) proceeded by organizing three separate panels as follows: solar and heliospheric physics under George L. Withbroe; magnetospheric plasma physics under Robert W. Fredericks; and upper atmosphere physics under Darrell F. Strobel. Each panel was asked to solicit inputs from the scientific community in each discipline area on what constitutes the highest priority science and the optimum means for carrying it out. The resulting sets of science objectives and programmatic priorities, along with estimated costs, were organized on a tirneline from FY 86 through the year 2000 by each panel. The full committee examined critically the work of the panels and, after several iterations, a compos- ite Implementation Plan was agreed upon. This preliminary plan was presented by committee members to several scientific groups beginning in the spring of 1984; during these sessions comments and suggestions were solicited. The inputs thus received were considered by the committee, and a draft version of the report was circulated to over 70 colleagues representing most institutions active in the field of solar and space physics. Comments and suggestions were received from about half, and the committee redrafted the document in October 1984 for presentation to the SSB's November meeting for approval. This extensive interaction with the community has produced a prioritized Implementation Plan that is supported by most mem- bers of the scientific disciplines involved. Our report is published in two parts, the Executive Summary and the main body. The Executive Summary presents the prioritized program, summaries of the scientific objectives and recommended missions, near-term budget decisions, and connections to basic physics, astrophysics, and earth system studies. This part is intended to quickly familiarize the reader with the substance of the science being addressed and the essential conclusions and recom- mendations of this study. Although it can stand alone, it should be read in conjunction with the main body. The main body of the report describes the detailed science objectives for future research, the most significant accomplishments of the past research, the way in which the Implementa- tion Plan was constructed, the detailed mission plans of each of the major sub-disciplines of solar and space physics research, and some additional thoughts on the general health and conduct of our science. An undertaking of this magnitude required the assistance of many individuals and institu- tions, too numerous to mention. We owe special thanks to Marshall Space Flight Center for hosting one of our meetings, to Goddard Space Flight Center and the Jet Propulsion Labora- tory for assistance on cost estimates for some projects, and, most importantly, NASA Head- quarters for providing the background information necessary for putting together the Imple- mentation Plan. We are grateful to Drs. J.D. Bohlin and S.D. Shawhan of NASA who participated in some of our meetings and provided important information whenever needed. Dr. T.M. Donahue, Chairman of the SSB, gave us important guidance in the formulation of this plan. Many of our colleagues commented on several drafts of this document. We are especially grateful to Dr. D.i Williams for assistance in the selection and placing of figures included in this report. The work of Mrs. Carmela Chamberlain and Mrs. Pat Johnson in typing the innumerable drafts of this report is most appreciated, as is the work of Mrs. Angelika Peck, who did the design and layout for the Executive Summary. Finally, we are grateful to our Executive Secretary, Dr. Richard C. Hart, whose untiring efforts and advice were invaluable to the completion of this report.

S.M. Krimigis, Chairman Committee on Solar and Space Physics

ix PRECEDING PAGE BLANK NOT FILMED

1 INTRODUCTION

Man's wonder at the manifold phenomena cally conducting plasma permeated by the in the environment and the drive to under- Earth's magnetic field. It is called the "mag- stand and use them have led to modern sci- netosphere" because its structure and many ence. To understand the relationship be- of its processes are controlled by the mag- tween natural events on the Earth and netic field. Since the early years of the changes in the Sun has been one of man's space program, we have learned that the lasting intellectual quests. The scientific Sun has its own magnetosphere consisting discipline we now know as solar system of a hot (million-degree Kelvin) magnetized space physics is the modern culmination of plasma wind (the solar wind) that extends efforts to comprehend the relationships beyond the orbits of the planets and fills among a broad range of naturally-occurring interplanetary space, forming a distinct cav- physical effects including solar phenomena, ity in the nearby interstellar medium--the terrestrial magnetism, and the aurora. Un- "heliosphere." derstanding the solutions to these basic Using knowledge gained over the past 25 physics problems requires the study of ion- years, we can now begin to identify some of ized gases (plasmas), magnetohydrodynam- the physical mechanisms linking the Sun to ics, and particle physics. our near-Earth environment. For example, Space physics as an identifiable disci- motions in the convective layers of the Sun pline began with the launch of the first are believed to generate the solar magnetic Earth satellites in the late 1950s and the field and solar wind variations; these in discovery in 1958 of the Van Allen radiation turn affect the Earth's magnetosphere and belts. The phenomena associated with this regulate the amount of plasma energy inci- field of study are among the earliest re- dent on the Earth's polar caps. Associated corded observations in many parts of the magnetospheric activity drives strong winds world The ancient Greeks were puzzled by in the upper atmosphere and may influence "fire" in the upper atmosphere that we now the dynamical and chemical composition of call the aurora; there are several possible the mesosphere and stratosphere as well. references to the aurora in ancient Chinese The upper atmosphere, in turn, is the major writings before 2000 B.C.; there are also source of heavy ions in the magnetosphere. passages in the first chapter of Ezekiel with Further, current research suggests that vivid descriptions of what we now recognize small percentage changes (about 0.5 per- as auroral formations. cent) in the total energy output of the Sun The observation of sunspots by Galileo in (the solar "constant") may influence short- 1610 led to the eighteenth century discovery term terrestrial climate. These and other of the 11-year solar sunspot cycle and the speculative suggestions should be ad- recognition that there was a connection be- dressed as part of a comprehensive re- tween sunspot variability and auroral activ- search program in solar-terrestrial physics ity. The large reduction of sunspots during because of their potential importance for the the second half of the seventeenth century Earth. Indeed, the Earth and its space envi- during a period of unusually cool weather ronment contain coupled phenomena and in Europe suggests a tantalizing connection need to be studied as a system--from the between some aspects of solar activity and Sun and its plasma environment to the climate. Earth's magnetosphere, atmosphere, This possible link between solar activity oceans, and biota. and terrestrial phenomena could not be Discoveries in solar and space physics studied in detail until this century. We now over the past 25 years have inspired a num- know that, in addition to the atmosphere ber of developments in theoretical plasma that surrounds us, there exists a region, at physics. Concepts in charged particle trans- higher altitudes, consisting of an electri- port theory, developed to describe the be- havior of energetic particles in the solar Even though space plasma physics is a wind and magnetosphere, are routinely mature subject, new observations continue used in studying extragalactic radio sources to reveal facets of the physics not recog- and laboratory plasmas. Magnetic field re- nized previously. For example, observations connection (involving the explosive conver- of "spokes" in Saturn's rings seemed to sion of electromagnetic energy into particle highlight the importance of electromagnetic energy), coliisionless shock waves, electro- forces on charged dust particles. Similarly, static shocks, and hydromagnetic turbu- the interaction of dust and plasma in com- lence are also among the fundamental ets is thought to be a central element in plasma phenomena first studied and eluci- understanding the formation of comet ion dated in analysis of solar and space plas- tails. Such observations have given rise to mas. the study of "gravito-electrodynamics" in Subsequently, these and other concepts dusty plasmas, which in turn has important have found application to related branches applications to the understanding of the for- of plasma physics, such as nuclear fusion. mation and evolution of the solar system, as The development of space plasma physics pointed out by Alfven some years ago. since the 1960s has influenced nuclear fu- The understanding of the near-Earth sion research. Pitch-angle scattering and space environment is not only a basic re- magnetic reconnection are now tools of lab- search enterprise; it also has extremely im- oratory plasma theory, while ideas devel- portant practical aspects. Space is being oped in fusion work have influenced space used increasingly for many different scien- plasma science in important ways, Thus, tific, commercial, and national security pur- the language of plasma physics links two poses. Well-known examples include com- very important scientific endeavors-the munications and surveillance satellites and search for a limitless supply of clean energy such scientific platforms as the Space Tele- through thermonuclear fusion and the explo- scope and the Space Station. These space ration and understanding of our solar sys- vehicles must function continuously in the tem environment, most of which is in the near-Earth environment, subject to the dy- plasma state. namic variations of the heliosphere, the New concepts developed in studies of so- magnetosphere, and the upper atmosphere. lar and space plasmas find important appli- It is well-established that many spacecraft cations to astrophysical problems as well as systems and subsystems exhibit anomalies, to laboratory plasmas, For example, the or even failures, under the influence of structure of collisionless shock waves can magnetospheric substorms, geomagnetic be resolved only by spacecraft instruments. storms, and solar flares. Processes such as Such shocks are invoked in some current spacecraft charging and "single-event up- models of star formation. Furthermore, the sets" (owing to highly ionizing energetic study of propagating interplanetary shocks particles) in processor memories make the has contributed to understanding and mod- clay-to-day operation of space systems diffi- eling of acceleration of cosmic rays by cult. Finally, these aspects of the near-Earth shocks. Particle acceleration via direct elec- environment become particularly important tric fields, observed in the Earth's magne- in view of the planned long-term presence tosphere, has been invoked in acceleration of man in space. The complement of pro- models of pulsar magnetospheres. The sub- grams outlined in this report will allow us ject of cosmic-ray transport owes much to to model the global geospace environment detailed in situ studies of the solar wind. and will thus allow us to develop a global Some stellar winds are thought to be associ- predictive capability. This, in turn, should ated with stars that, like the Sun, have con- permit substantial improvements in our vective outer layers, while winds of more abilities to operate all space-based systems massive stars are driven by radiation pres- in the near-Earth region. sure. Explanations of physical phenomena We have advanced well beyond the ex- in astrophysical objects that will remain for- ploratory stages in solar and space physics, ever inaccessible to direct observation rest with some notable exceptions--the solar in- heavily on insights obtained through stud- terior, the environment near the Sun where ies of solar system plasmas accessible to in the solar wind is accelerated, the atmos- situ observations. pheres of some of the planets, and the boundaryof the heliosphere. The phenome- is intrinsically an important branch of sci- nological approach appropriate to a young ence." The Kennel report (Solar-System science still in its discovery phase has pro- Space Physics in the 1980"s: A Research gressed to a more mature approach where Strategy, NAS, 1980) laid out the scientific focussed and quantitative investigations are goals and objectives for the field. Other re- made, where interactive regimes are stud- ports (Solar-Terrestrial Research in the ied, and where theory and modeling play a I980"s, NAS, 1981; National Solar-Terrestrial central role in advancing understanding. Research Program, NAP, 1984) integrated the The future soJar and space physics pro- ground-based segment of the field and gram will require tools and techniques sub- stated priorities for its implementation. The stantially different from those of the past. Physics of the Sun (NAP, 1985) reviewed the Continued progress will require develop- scientific content of solar physics and de- ment of complex, multifaceted, experimen- scribed future research directions. A Strat- tal and observational projects that will be egy for the Explorer Program for Solar and technologically challenging. We believe Space Physics (NAP, 1984) emphasized the that the anticipated scientific contributions need for a revitalized Explorer program for fully justify the proposed undertakings. solar and space physics and outlined sev- The purpose of this report is to develop an eral specific examples of scientific investi- overall program of space research that will gations. address the most significant scientific prob- In addition, two other recent reports have lems, that will clearly define the priority of developed prioritized programs in related investigations, and that will be affordable sciences: astronomy, Astronomy and Astro- by NASA. physics for the 1980"s (NAP, 1982); and plane- Several other reports that are related to tary science, Planetary Exploration Through this document have appeared in recent Year 2000 (NASA, 1983). Our report is similar years. The Colgate report (Space Plasma to these in that it is intended to develop the Physics: The Study of Solar-System Plasmas, implementation plan for NASA's solar and NAS, 1978) reviewed the status of the field space physics program that will accomplish and concluded that "space plasma physics the aims of our scientific strategy. 2 GUIDING PRINCIPLES

The scientific goals established by the Ken- pheres, ionospheres, and upper atmos- nel report remain the guiding force of this pheres of the Earth, other planets, and com- science. The two principles that served as ets. the foundation for the design of the strategy • Studies of the interactive processes that remain extant: generate solar radiation and link it to the • "The objectives of solar-system space re- Earth should be emphasized, because they search are to understand the physics of the reveal basic physical mechanisms and have Sun, the heliosphere, and the magnetos- useful applications .... " 3 SCIENCE STATUS AND OBJECTIVES

The following summary of the status of the how solar-flare energy is released to the he- subject and the scientific objectives are liosphere; and adapted from the Kennel report (Solar-Sys- • the energy sources and composition of tem Space Physics in the 1980"s: A Research the solar atmosphere and corona and the Strategy, NAS, 1980) with appropriate physics of the Sun's large-scale weak mag- changes and updates. netic field.

Solar Physics Physics of the Heliosphere

Major advances in our understanding of the The Sun is the only stellar exosphere where Sun were made in the 1970s and the early complex phenomena common to all stars 1980s (see Figure 1). Most, if not all, of the can be studied in situ. Observations of the magnetic flux that emerges from the convec- Sun and the heliosphere, the plasma enve- tive zone is subsequently compressed into lope of the Sun extending from the corona to small regions of strong field (1200-2000 G), a the interstellar medium, provide the basis process that is still not understood theoreti- for interpreting a variety of phenomena cally. Observations confirmed earlier pre- ranging from x-ray and gamma-ray radia- dictions that the 5-minute photospheric os- tion to cyclical activity and long-term evolu- cillation, discovered in the early 1960s, is a tion. The Sun, together with the heliosphere global phenomenon. This discovery has and planetary magnetospheres and atmos- made "helio-seismology" possible, by which pheres, comprises an immense laboratory the depth of the convective zone and the that exhibits complex magnetohydrodynami- rotation below the photosphere have been cal (MHD) and plasma physical phenomena inferred. In addition, by ruling out the clas- whose study enhances our understanding of sical model of coronal heating by acoustic basic physical laws as well as our under- waves, observations from the ground and standing of the influences of the Sun on our from OSO-8 raised anew the question of terrestrial environment. what maintains the corona's high tempera- The solar wind has been studied near the ture. Coronal holes were among the major Earth since 1961. At the present time, meas- discoveries of the 1970s. White-light, EUV, urements of the solar wind have been ex- and x-ray observations suggested how co- tended to within Mercury's orbit (0.3 AU) and ronal holes are related to the convective past Pluto's orbit but have been confined to zone and to the solar wind. Skylab observa- near the ecliptic plane. Quantitative models tions unambiguously identified magnetic of high-speed solar-wind streams and flare- arches as the basic structure of coronal produced shocks have been developed and flares. This perception altered our theoreti- tested against data obtained near the eclip- cal picture of solar flares and clarified the tic. The realization that high-speed streams need for a coordinated multi-instrument at- originate in the rapidly diverging magnetic- tack, which was initiated with the Solar flux tubes of coronal holes has reoriented Maximum Mission (SMM). much solar wind research. The sector struc- To better understand all the processes ture of the solar wind has been unambigu- linking the solar interior to the corona, we ously related to a magnetic neutral sheet of need to study (see Figure 1B) the following: solar-system scale that connects to the • the Sun's global circulation, how it re- large-scale magnetic field of the rotating flects interior dynamics, is linked to lumi- Sun. Finally, microscopic plasma processes nosity modifications, and is related to the have been shown to regulate solar wind solar cycle; thermal conduction and diffusion and, pos- • the interactions of solar plasma with sibly, local acceleration of particles in solar strong magnetic fields---active regions, sun- wind structures. spots, and fine-scale magnetic knots-and To understand better the transport of en- A SOLAR PHYSICS--RECENT ACCOMPLISHMENTS

IMPORTANCE OF STRONG

_T_, _o ,_o_o_,o_... /__" o,_._.o_ __

______'d°_°_ _._, _

IDEN HELIOSEISMOLOGY SOLAR FLARE GEOMETRY

B SOLAR PHYSICS-OBJECTIVES

How Do Global Circulation and Surface Osciilations How Is Solar Reflect Interior Dynamics? \ Wind Generated? / WohratArse Ehn:r gy_'_ }4>

/ How Does Solar Plasma / What Is the Physics of / Interact with Strong the Large Scale Weak Magnetic Fields? How Is Magnetic Field? Solar Flare Energy Released?

C SOLAR PHYSICS-REQUIRED MEASUREMENTS

_ / j OFCORONALPLASMA / PROCESSES NEAR SOLAR

._TICA L SURFACE

I. HIGH RESOLUTION (0.1") SHUTTLE OBSERVATIONS 3. SU RVEY OBSERVATIONS OF OF ACTIVE REGIONS, SURFACE OSCILLATIONS, SMALL SCALE FIELDS LARGE SCALE MAGNETIC AND FLARES FIELD, LUMINOSITY VARIATION

FIGURE ] Solar physics: status, objectives, and recommendations. In this series of sketches ot the Sun and its coronal magnetic field we illustrate some recent accomplishments in solar physics (A), questions that can be fruitfully attacked in the 1980s and 1990s (B), and the principal research programs needed to answer these questions (C). Shown here is the Sun and solar corona within 5 solar radii, The influence of the processes occurring within this region extends throughout interplanetary space via the solar wind. ergy, momentum, energetic particles, across the magnetopause, through the mag- plasma, and magnetic fields through inter- netosphere and ionosphere and into or out planetary space, we need to study the fol- of the upper atmosphere; lowing: • the storage and release of energy in the • first and foremost, the solar processes earth's magnetic tail; that govern the generation, structure, and • the origin and fate of the plasma(s) variability of the solar wind; within the magnetosphere; and • the three-dimensional properties of the • how the Earth's magnetosphere, iono- solar wind and heliosphere, and sphere, and atmosphere interact. • the plasma processes that regulate the transport and acceleration of energetic par- Upper-Atmospheric Physics ticles throughout the heliosphere.

The upper atmosphere has traditionally Magnetospheric Physics been divided into the stratosphere, mesos- phere, thermosphere (and ionosphere), and New processes regulating Earth's magnetic exosphere, in order of increasing altitude. interactions with the solar wind were dis- Recent research makes it clear that these covered in the 1970s and early 1980s (see layers and their chemistry, dynamics, and Figure 2A). For example, unsteady plasma transport are coupled (see Figure 3A). For flows that apparently originate deep in the example, downward transport from the ther- geomagnetic tail and deposit their energy in mosphere can provide a source of nitrogen the inner magnetosphere and polar atmos- compounds to the mesosphere and possibly phere were observed. Observations of im- to the upper stratosphere. The catalytic re- pulsive energetic particle acceleration sug- actions of odd hydrogen, nitrogen, and chlo- gested that the cross-tail electric field is rine compounds destroy ozone, thereby al- also highly unsteady. The discovery of ener- tering the absorption of solar ultraviolet getic ionospheric ions in the near tail and radiation. Results from three Atmospheric inner magnetosphere forced a reevaluation Explorers (AE), which largely quantified the of our ideas concerning the origin and circu- photochemistry of the thermosphere and lation of magnetospheric plasma. ionosphere, also illustrated the strength of Our understanding of many individual the electrodynamic coupling of the thermos- processes became more quantitative. The phere to the magnetosphere. Finally, under- coupling of magnetospheric motions and en- standing how the upper and lower atmos- ergy fluxes to the thermosphere was ob- pheres affect each other will be necessary served and modeled. Currents flowing to complete the description of the chain of along the Earth's magnetic field and con- solar-terrestrial interactions. This will re- necting the polar ionosphere to the magne- quire considerable improvement in our un- tosphere were found to create strong local- derstanding of the chemistry, dynamics, ized electric fields at high altitudes. These and radiation balance of the mesosphere fields may accelerate the electrons responsi- and stratosphere, as well as of troposphere- ble for intense terrestrial radio bursts and stratosphere exchange processes. auroral arcs. Thus, the problem of auroral To understand fully the entire upper at- particle acceleration is nearing quantitative mosphere and its interaction with the sun understanding. By contrast, the relationship and the magnetosphere, we should study between energy circulating in the magne- the following (see Figure 3C): tosphere, the energy dissipated in the at- • the radiant energy balance, chemistry, mosphere, and the concurrent state of the and dynamics of the mesosphere and strato- solar wind has not been unambiguously sphere and their interactions with atmos- quantified even today. pheric regions above and below; To understand better the time-dependent • the worldwide effects of the magnetos- interaction between the solar wind and phere's interaction with the polar thermos- Earth we need to study the following (see phere and mesosphere and the role of elec- Figure 2B): tric fields in the earth's atmosphere and • the transport of energy, momentum, space environment; and plasma, and magnetic and electric fields • the effects of variable photon and ener- A MAGNETOSPHERIC PHYSICS-RECENT ACCOMPLISHMENTS

ELECTRIC FIELDS ACCELERATING AURORAL PARTICLES i- I" DISCOVERY OF ENERGETIC / //1 IONS OF IONOSPHERIC ORIGIN ,_-f IN MAGNETOSPHERE. ./_" ]H>

MODELLING OF ___

THEI_MOSPHERIC \'_-----_ __

WIND GENERATION / "'" "_ ]1"{> shocked solar wind

UNSTEADY PLASMA FLOWS, Col/is'_._.-.." ELECTRIC FIELDS AND tO/,-H'ess_. --.. PARTICLE ACCELERATION IN b°_sh_'- GEOMAGNETIC TAIL

B MAGNETOSPHERIC PHYSICS-OBJECTIVES

J What is Origin and Fate of 1- .// Magnetospheric Plasmas? 7 "/ How Does Solar "__--_"=

Wind Couple to _use Magnetosphere?

"_/' -- --_-_ __T_ How is Energy Stored

P_.._ Magnetic Tail? __ andReleasedin solar wind

How Does Magnetosphere c_"o _ Couple with Atmosphere °'si°o'_rs_'-_b and Ionosphere? _' Shoc"_

C SIX CRITICAL REGIONS OF MAGNETOSPHERIC PHYSICS

AURORAL FIELD -/ ON THE LINES/ _" GROUND / j7

/ /'_pause ..... _ _ _ DEEP IN SOLAR _#'_;_=__ ..,_ ...... GEOMAGNETIC WIND _X_"-'_ .... TAIL

MIDMAGNETOSPHERE "_ c_,,>.. EOUATORIAL PLANE- _ "°"'_n_,_o_.." I N TH E PO LA R hoc_ UPPER ATMOSPHERE

FIGURE 2 Magnetospherlc physics: status, objectives, and recommendations. Shown here is the Earth's magnetosphere--the cavity formed by the interaction of the solar wind with the Earth's magnetic field. A collisionless bow shock stands upstream of the magnetopause, the boundary separating shocked solar wind from the magnetosphere proper. The Moon is 60 Earth radii from the Earth; the Earth's magnetic tail is thought to extend some thousand Earth radii downstream. A illustrates some recent achievements in magnetospheric physics; B, objectives that can motivate research programs in the 1980s and 1990s. C illustrates the six critical regions where simultaneous studies are needed to help construct a global picture of magnetospheric dynamics. A UPPER ATMOSPHERIC PHYSICS-RECENT ACCOMPLISHMENTS

IMPORTANCE OF ELECTRODYNAMIC GENERAL REALIZATION COUPLING OF IMPORTANT COUPLINGS ATMOSPHERE EXPLORERS BETWEEN LAYERS AND _ .,,_v_ QUANTIFIED THERMOSPHERE _o._ u._e,o._..... _...... PHOTOCHEMISTRY ABOVE THEIR CHEMISTRY, _ .... ,_

DYNAMICS AND TRANSPORT t/ j,'_' 130km ( _ma

UPPER ATMOSPHERIC PHYSICS-OBJECTIVES

How Do Variable Photon and Particle Fluxes Affect the Thermosphere, Mesosphere, and Stratosphere?

How Do Energetics, Chemistry, _o_ "_ What Are the World-Wide and Dynamics Interact to s_=,,,, Effects of the Establish the Structure and _ M._e,o._,_ p_,,_,.__ Magnetosphere's interaction Variability of the Middle // "_='&i_ f/ with the Upper Atmosphere?

Atmosphere? _tric, winds

C UPPER ATMOSPHERIC PHYSICS-REQUIRED MEASUREMENTS

A SERIES OF SPACE OBSERVATIONS mesosphere and stratosphere

MONITOR SOLAR LUMINOSITY So4av ullr av_ _o_s u=0-.,os_,,_ o_ AND SPECTRAL IRRADIANCE, SELECTED HIGH RESOLUTION _ "'" _" LONG-WAVE RADIATION CHEMICAL OBSERVATIONS FROM \l _ COMPOSITION, DYNAMIC'S, AND FREE FLYERS , PLATFORMS ' _ , ENERGETIC PARTICLE INPUT AND SHUTTLE _ _ _ ,.

l_[GD11E 3 Upper-atmospheric physics: status, objectives, and recommendations. Sketched in these figures are the layers into which the atmosphere has traditiona]|y been divided. Our studies of these kryers, and the interacting processes occurring within them, are becoming more inte- grated. Solar ultraviolet photons deposit their energy |arge|y in the stratosphere and above. The magnetosphere interacts with the upper atmosphere both through energetic plasma deposition and through electric fields, which are generated by magnetospheric motions. Plasma heating and electric fields both couple to upper-atmosphere winds. 9 getic particle fluxes on the thermosphere Comparative Planetary Studies and on chemically active minor constituents of the mesosphere and stratosphere. Comparative studies of the interaction of the solar wind with planets and comets highlight the physics pertinent to each and Solar-Terrestrial Coupling put solar-terrestrial interactions in a broader scientific context. The solar system Solar-terrestrial coupling is concerned with the interaction of the Sun, the solar wind, has a variety of magnetospheres sufficient to make their comparative study fruitful. Be- the Earth's magnetosphere, ionosphere, and cause the planets and their satellites have atmosphere with particular emphasis on the different masses, magnetic fields, rotation response of the system to solar variability. For example, a solar flare produces both a periods, surface properties, and atmos- pheric chemistry, dynamics, and transport, strong solar-wind shock, which initiates a comparative atmospheric and magnetos- magnetic storm when it passes over the pheric studies can help us to understand magnetosphere, and energetic protons that these processes in general and possibly to penetrate deep into the polar atmosphere. Studies of such solar-terrestrial phenomena identify terrestrial processes that might otherwise be missed. can be of considerable practical importance. To understand better the effects of the so- In the 1970s, Pioneer and Voyager space- lar cycle, solar activity, and solar-wind dis- craft made flyby studies of Jupiter's atmos- phere and magnetosphere, the largest and turbances upon Earth, we need to most energetic in the solar system. Pioneer • provide to the extent possible simultane- ous measurements on many links in the 11 and the Voyagers encountered Saturn in chain of interactions coupling solar pertur- 1979, 1980, and 1981. Mariner 10 flybys dis- bations to their terrestrial response; and covered an unexpected, highly active mag- • create and test increasingly comprehen- netosphere at Mercury. Pioneer Venus re- sults suggest that the strong interaction sive quantitative models of these processes. between the solar wind and Venus' upper Whereas 10 years ago it was generally atmosphere plays a significant role in the believed that significant effects of solar var- evolution of its atmosphere. iability penetrate only as far as the upper To understand better the interactions of atmosphere, some scientists now believe the solar wind with solar-system bodies that they also reach the lower atmosphere other than Earth, and to learn from their and so affect weather and climate in ways diversity about astrophysical magnetos- not yet completely understood. For example, pheres in general, we need to it has recently been suggested that the • investigate in situ Mars' solar-wind in- mean annual temperature in the north tem- teraction in order to fill an important gap in perate zone has followed long-term varia- comparative magnetosphere and upper-at- tions of solar activity over the past 70 centu- mosphere studies--previous missions pro- ries. vided little such information; To clarify the possible solar-terrestrial in- • make the first in situ measurements of fluence on Earth's weather and climate, we need to the plasma, magnetic fields, and neutral gases near a comet; • determine if variations in solar luminos- • increase our understanding of rapidly ity and spectral irradiance sufficient to mod- rotating magnetospheres involving strong ify weather and climate exist and under- atmospheric and satellite interactions; and stand the solar physics that controls these • determine the role of atmospheres in variations, and substorms and other magnetospheric proc- • ascertain whether any processes involv- esses by orbital studies of Mercury--the ing solar and magnetospheric variability only known magnetized planet without an can cause measurable changes in the atmosphere. Earth's lower atmosphere.

10 4 IMPLEMENTATION STRATEGY

Rationale term. Thus, it was the task of the Committee to establish priorities and to select among The status of solar and space physics, its the many exciting scientific programs that science objectives, and the associated have been identified, by ordering the se- measurement objectives presented in the quence of mission implementation within an previous chapter have remained largely un- envelope of about $400M/yr (in FY 85 dol- changed since they were first published in lars). The proposed implementation plan the Kennel report (NAS, 1980). Although sig- contains only those scientific programs that nificant progress has been attained in some address the highest priority objectives. They areas [ionosphere-magnetosphere coupling are arranged in such a sequence that most following the launch of the Dynamics Ex- would be accomplished before the year plorer (DE) satellites in 1981; active experi- 2000. In the process, several programs con- ments in the solar wind with the recent sidered of lesser importance have been de- launch of the Active Magnetospheric Parti- ferred (e.g., Heliosphere Boundary Probe), cle Tracer Explorer (AMPTE)], most of these while even those of high scientific priority objectives have remained unfulfilled. have had to be scheduled for implementa- As is evident from the preceding chapter, tion at a time later than that dictated by the scientific content of solar and space either the maturity of the subject or the tech- physics is broad, involving several impor- nological readiness of the proposed meas- tant regions within the solar system--the urements [e.g., Solar Terrestrial Observa- Sun, heliosphere, and the terrestrial magne- tory (STO)]. In all but two of the programs tosphere, ionosphere, and upper atmos- [the Solar Probe and Solar Polar Orbiter phere and the complex interactions among (SPO)] the technology for implementation is them, solar-terrestrial relations. To advance already at hand. Thus, the budget ceiling our understanding in each of these subjects was the determining factor throughout the and the chain of interactions among them, a strategy. broad scientific attack is necessary, which translates into a major thrust in each of the Program Mix in Solar and Space central disciplines (i.e. solar/space, plasma, Physics and atmospheric physics). In the near term these thrusts are embodied in major space The diversity of environments represented missions--the Solar Optical Telescope (SOT) within the discipline of solar and space and the Upper Atmosphere Research Satel- physics demands a broad mix of programs lite (UARS), already approved, and the Inter- to implement the stated science objectives. national Solar Terrestrial Physics Program There is a need for major missions for de- (ISTP), currently a new start candidate. tailed studies on a global scale, as well as These programs together with the base pro- for exploration of previously unexamined re- gram (research and analysis, mission opera- gions (e.g., the environment near the Sun); tions and data analysis, shuttle science, for moderate missions (Explorer-class) to at- theory, etc.) result in a level of funding of tack specific, detailed problems; for quick about $400M/yr.* response techniques such as balloons, rock- The important scientific measurement ob- ets (Spartans), and experiments of opportu- jectives that have been outlined in the pre- nity best accommodated on the Shuttle; and vious chapter could add up to a level sub- for facility-class instruments that are devel- stantially higher than $400M/yr in the long oped for Shuttle use but that will evolve towards space platforms that can best be *The funding for solar and space physics in 1964 was accommodated as part of the Space Station $527M/yr (in FY 85 dollars); funding for the decade 1964- 1974 averaged $377M/yr (in FY 85 dollars). concept.

11 FUNDS REQUIRED FOR SOLAR AND SPACE PHYSICS

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FIGURE4

Resource Requirements for The MO&DA budget pays for the opera- Recommended Programs tion of missions after launch [currently Inter- planetary Monitoring Platform (IMP)-8; Inter- The science priorities outlined in the pre- national Sun-Earth Explorer (ISEE) 1, 2, and vious chapter and the rationale in program- 3; Solar Maximum Mission (SMM); Solar Me- matic considerations given above have re- sosphere Explorer (SME); DE; and AMPTE], sulted in an implementation plan with including science team support and data resource requirements over the next 15 analysis while the data are proprietary to years as shown in Figure 4. The total is the the selected teams (roughly, one year after sum of three separate budgetary require- acquisition). The budget for development of ments: resources for research and analysis flight projects supports approved projects (R&A), for mission operations and data anal- through launch and currently includes Inter- ysis (MO&DA), and for development of flight national Solar Polar Mission (ISPM), Com- projects. The R&A budget supports a spec- bined Release and Radiation Effects Satel- trum of activity including balloons and rock- lite (CRRES), Tethered Satellite System ets, laboratory experiments, analysis and (TSS), UARS and SOT, and Shuttle instru- interpretation of data from prior spacecraft mentation under various programs. missions, and the Solar-Terrestrial Theory In the budget projections presented in Fig- Program (STTP). The R&A budget addition- ure 4 the Committee has sought to achieve ally includes the resources to plan future a responsible and attainable funding plan missions through the pre-project definition that can be implemented within the funding stage and to undertake early development ceiling outlined previously. This program of instrumentation for such missions. envisions the launch of the recommended

12 missions before the end of this century. The in the mid-1990s. The budget timeline also level of funding for specific programs is pri- specifically includes MO&DA funds for the marily based on NASA projections for each Space Station activity, in recognition of the of the programs, where such exist, and on high cost likely to be involved in operating informal consultation between the Commit- such facilities. tee and officials at NASA centers (princi- The solar and space physics programs in pally Goddard Space Flight Center, Mar- Figure 4 are currently managed by several shall Space Flight Center, and Jet divisions within NASA, including Astrophys- Propulsion Laboratory) for those programs ics, Earth Science and Applications, Shuttle where such funding levels have not as yet Payload Engineering, and Solar System Ex- been formalized. ploration. The Committee has specifically The funding timeline incorporates those excluded from these budget projections the programs already approved in FY 85, antici- significant funds that need to be allocated pates implementation of Phase 1 of the ISTP for experiment payloads on planetary program in FY 86, and foresees utilizing Ex- spacecraft that are recommended for studies plorer program funding for solar and space of the magnetospheres and upper atmos- physics following the completion of the cur- pheres of the planets. These funds have tra- rent set of payloads by FY 88. The incorpo- ditionally been included as part of the over- ration of the Explorer program into the fund- all budget of the specific planetary ing timeline is in accordance with the missions. The budget also does not include recent SSB report. A Strategy for the Ex- specific funds to accommodate possible plorer Program tor Solar and Space Physics flights of opportunity that are not currently (NAP, 1984). identified, such as programs of other federal In the area of Space Shuttle instrumenta- agencies (DOD, NOAA, etc.) or programs tion, the currently approved program [Space- arising from international initiatives. A re- lab (SL) 1 and 2, Space Plasma Lab (SPL), cent example of such a worthwhile opportu- Earth Observation Missions (EOM), and Sun- nity was U.S. instrumentation on the Giotto lab] stays at a constant funding level spacecraft that was accommodated by the launched by the year 2000. overall flexibility of the OSSA budget. In the area of Space Shuttle instrumenta- tion, the currently approved program (Spa- The Committee feels that the program en- celab (SL) 1 and 2, Space Plasma Lab (SPL), visioned in this report is scientifically chal- Earth Observation Missions (EOM), and Sun- lenging, technologically achievable, and re- lab) stays at a constant funding level flects the maturity of a field that was the through the early 1990s. In the late 1980s, space research program when the nation in- facility-class instruments will be developed, itially ventured into space. The implementa- which have been studied previously as part tion plan outlined in Figure 4, by attempting of the Solar Terrestrial Observatory (STO) to achieve a constant yearly funding level and the Advanced Solar Observatory (ASO). and distributing the new starts over a num- The instruments will eventually be assem- ber of years, makes it possible for NASA to bled onto science platforms, which are in- strive once again for leadership in solar and tended to become part of the Space Station space physics research.

13 5 SUMMARY OF RECOMMENDED PROGRAMS

Introduction pling energy to the solar wind; and to moni- tor solar luminosity. (It may ultimately be- In this Chapter we briefly summarize the come necessary in the decades following scientific objectives that were discussed in the 1980s to monitor the effects of solar vari- detail in Chapter 3. These objectives are to ability on luminosity over several solar be achieved through a sequence of research cycles.) programs in solar and space physics. We also summarize the descriptions of these Terrestrial Magnetospheric Physics programs that are discussed in more detail in Chapters 7, 8, and 9. The primary meas- To advance quantitative understanding of urement objectives to be addressed between the time-dependent exchange of energy and now and 2000 include the following: plasma between the solar wind and magne- tosphere requires measurements of physical Solar Heliosphere Physics processes in at least six regions simultane- ously: (1) deep in the Earth's magnetic tail, • High-resolution observations are needed (2) in the solar wind upstream of Earth, (3) to advance understanding of active regions near the mid-magnetosphere equatorial and the small-scale velocity and magnetic plane, (4) at high altitudes above one polar fields important to chromospheric and co- cap, (5) from the ground, and (6) at low alti- ronal energy balance, as well as solar tude in polar orbit. (Measurement of this flares. These require space-borne instru- last area is needed to indicate the dynami- ments that achieve 0.1 arcsec resolution in cal and chemical response of the atmos- the spectral range from the infrared to H phere to magnetospheric variability.) Lyman alpha and less than 0.5 arcsec reso- This global research program should be lution from the extreme ultraviolet to hard X supplemented with an increased level of rays. support of theory and computer modeling • Remote sensing and in situ measure- efforts directed toward understanding mag- ments are needed to provide qualitatively netic reconnection, boundary layer phenom- new information critical to understanding ena, and other related problems in magne- coronal plasma processes and solar-wind tospheric physics. In addition, active generation. These require optical instru- experiments should be flown that can in- ments that can make spectroscopic meas- crease our knowledge of magnetospheric urements out to 5 or more solar radii and a and plasma processes. solar flyby or probe that penetrates as close to the sun as possible (4 solar radii seems technically feasible). In addition, measure- Terrestrial Upper-Atmospheric Physics ments of the heliosphere at high helio- graphic latitudes are required. A series of space observations is needed to • Space observations lasting a significant advance understanding of the interacting portion of the next solar cycle are needed to dynamical, chemical, and radiative proc- infer solar interior dynamics from large- esses in the stratosphere, mesosphere, and scale motions and oscillations at the Sun's thermosphere. The first in this series is the surface; to study transient events; to study UARS spacecraft which will provide an al- (through observations, theory, and model- most global data set on the chemistry, dy- ing) such fundamental problems as mag- namics, and energy input of the middle at- netic reconnection, particle acceleration, mosphere to understand basic atmospheric and magnetohydrodynamic (MHD) turbu- properties and processes. Thereafter solar- lence; to observe the large-scale magnetic terrestrial processes should be addressed by and plasma structures instrumental in cou- remote sensing of the chemical, dynamical,

14 and thermal response of the mesosphere space physics research. Moreover, theory and lower thermosphere to solar and mag- and quantitative modeling can guide the netospheric perturbations. Continuing up- entire information chain (data acquisition, per-atmospheric observations throughout reduction, dissemination, correlation, stor- the 1990s are needed to provide good solar- age, and retrieval) to a higher level of so- cycle coverage. Complementary high-resolu- phistication, so that data can be made tion studies should be made using Shuttle available in a form compatible with the facilities. needs of scientific interpretation.

Evolution of Shuttle Science Coordinated Research

It is essential to maintain a strong program Coordinated research is an essential feature for the development and flight of Shuttle- of solar and space physics, which is con- class instruments in solar, atmospheric, and cerned with time-variable phenomena span- magnetospheric physics. Continued prog- ning several regions of space and relying ress in solar-terrestrial physics requires in- on several scientific disciplines for interpre- novative new measurements. The Shuttle tation. provides an excellent platform for the flight The research programs proposed above of many types of solar-terrestrial instru- are justifiable on their individual merits. ments and acquisition of short duration (up Coordinating them through the ISTP can to a week or more) measurements of specific greatly increase our understanding of the phenomena. Shuttle experiments can in- solar-terrestrial interaction. Examples of clude both in situ and remote observations such coordinated research include the fol- of natural phenomena and diagnostics of lowing. active perturbations of the plasma medium (a) Detailed examination of the three-di- with chemicals, waves and electron or ener- mensional structure of the Sun's large-scale getic plasma beams. magnetic field is made possible by in-eclip- Ultimately Shuttle instruments can be tic coronal observations that are simultane- used on the Space Station, which combines ous with those from the International Solar the greatest advantages of the Shuttle and Polar Mission (ISPM) spacecraft. smaller spacecraft, namely high resolution (b) Simultaneous in-ecliptic and ISPM and long duration. measurements of the solar wind and cosmic rays can provide important information about the large-scale structure of solar-wind Theory, Computer Modeling, and disturbances. These in-ecliptic measure- Information Handling ments can be provided by the interplanetary element (WIND spacecraft) of the global The ultimate goals of the solar and space magnetospheric study proposed above. physics scientific missions are the resolu- (c) As we noted earlier, simultaneous tion of outstanding scientific questions and measurements in the polar upper atmos- the creation of reliable predictive models of phere and the magnetosphere can provide the solar-terrestrial environment. Critical to new quantitative insight into how solar- achieving these goals is conversion of the wind perturbations couple to upper-atmos- observations into scientific understanding pheric winds and chemistry. through a strong theoretical and computer The NASA research proposed here pro- modeling program. This process leads to the vides a foundation for coordination of re- resolution of outstanding questions and the search sponsored by other agencies of the formulation of new ones, which in their turn United States government and possibly for- lead to the formulation of new missions; it eign nations. For example, coordination also leads to the gradual building of relia- with other agencies is critical to provide the ble, predictive, cause and effect models of ground-based observations recommended the solar-terrestrial environment. A strong above. We urge that NASA play a prominent theoretical and computer modeling program role in developing and coordinating a joint is a cornerstone for successful solar and program as rapidly as possible.

15 Planetary Research goal is to explore the solar atmosphere where the solar wind becomes supersonic. Since we do not understand other planets as The mission should carry a complement of well as Earth, studies of each individual particle and field instruments to measure planet must continue to be important for the density, velocity, and composition of the foreseeable future. Nonetheless, to increase thermal solar wind plasma, as well as the the impact on space physics we should seek magnetic fields, plasma waves, and ener- comparative understanding of the interac- getic particles present in this unexplored re- tion of the Sun and solar wind with planets gion of the heliosphere. and comets. Comparative studies highlight Solar Polar Orbiter the physics pertinent to each planet and put that of Earth in a broad scientific context. The study of the three-dimensional proper- Since many members of the space physics ties of the heliosphere will require observa- community also work actively in planetary tions more detailed than those that will be research, advances in one area are rapidly obtained by the ISPM, the first exploratory communicated and applied to the other, so mission to high solar latitudes. A Solar Po- that comparative studies will naturally lar Orbiter (SPO) in near circular orbit about emerge provided that planning and data the solar poles, at heliocentric distance less analysis in each are coordinated. Therefore, than or equal to 1 AU, will be able to distin- measurements of plasmas, fields, and ener- guish latitude from radial variations and, getic particles must remain integral parts of since it will make several polar passes, to each planetary mission. distinguish spatial from temporal effects. SPO should carry a full complement of plasma, energetic particle, magnetic field, Major Missions and radio wave instruments, similar to those flown on ISPM, and should have Solar and Heliosphere Physics pointing capability for detailed solar and coronal observations. The mission will re- The Solar Optical Telescope quire the development of low-thrust, contin- uous acceleration propulsion. Mission de- The first approved facility-class instrument sign for SPO should be undertaken in the under development in the Spacelab program mid-1990s, following a thorough analysis of is the Solar Optical Telescope (SOT). SOT the results of ISPM; launch should occur by consists of a 1.25-m aperture telescope with the year 2000. 0.1-arcsec resolution, which will provide sufficient resolution to observe levels in the Plasma Physics solar atmosphere ranging from the photos- phere through the transition region. The International Solar-Terrestrial Physics critical problems to be studied include Program plasma-magnetic field interactions related The International Solar-Terrestrial Physics to the solar dynamo and studies of energy Program (ISTP) is being planned together by transport in the solar atmosphere. the U.S. NASA, the Japanese Institute of SOT will be flown as an attached Shuttle Space and Astronautical Science (ISAS), and payload at intervals of 1 to 2 years starting the European Space Agency (ESA) as a co- in 1990. The program is expected to evolve operative effort with launches beginning in with the addition of increasingly versatile 1989 and with operations continuing into the focal-plane instrumentation and other com- mid-1990s. The overall scientific objectives plementary experiments. Eventually, SOT of ISTP are to develop a comprehensive, would form the basis for an advanced solar global understanding of the generation and observatory on a space station platform. flow of energy from the Sun, through the interplanetary medium and into the Earth's Solar Probe space environment (geospace), and to define The Solar Probe is a mission to study the the cause-and-effect relationships between unexplored region between about 4 and 60 the physical processes that link different re- solar radii from the Sun. The basic scientific gions of this dynamic environment.

16 ISTP will provide complementary meas- the global flow of energy from the solar urements for several other spacecraft, Shut- wind through the magnetosphere to the ion- tle/Spacelab missions, sub-orbital and osphere and into the atmosphere. The proc- ground-based investigations that are being esses by which different parts of the geos- conducted in the same time interval. Plans pace environment interact are highly include coordinated operations and data in- variable with time, often changing in re- terpretation with at least the ISPM, the Jap- sponse to fluctuations in the characteristics anese Exospheric Satellite-D (EXOS-D), the of the solar wind on the time scale of tens of Upper Atmosphere Research Satellite minutes. Thus, the key to success for GGS (UARS), Shuttle/Space Plasma Lab, and is in making simultaneous measurements in Shuttle/Sunlab. the four regions in which these four space- Six spacecraft missions are being planned craft orbit. for ISTP; spacecraft characteristics are de- The two ESA spacecraft systems (CLUS- scribed as follows: TER and SOHO) are planned for launch in WIND, provided by NASA, will have seven in- 1992-1993. Each system makes a unique con- struments to measure the solar wind magnetic tribution to the overall science program. field, plasma, plasma wave, and energetic parti- CLUSTER consists of four spacecraft with cle characteristics; the orbit is a double lunar adjustable separations designed to make swingby with excursions of 250 Rr into the up- cross-correlative measurements of plasma stream solar wind. characteristics and processes within the vol- GEOTAIL, provided by ISAS, will have seven in- ume defined by the four spacecraft set. struments to measure the magnetic and electric These measurements provide information on fields, the plasma energy and composition, and the plasma waves in various regions of the geo- the nature of the microscopic plasma proc- tail; the orbit initially is to be a double lunar esses that occur near boundary layers in the swingby out to 250 RE in the geotail, to decrease magnetosphere. The use of 4 spacecraft will to 8 RE × 20 Rr in the equatorial plane. enable the separation of spatial and tem- POLAR, provided by NASA, will have eleven in- poral effects. When in the solar wind, the struments to make comprehensive in situ meas- spatial resolution made possible by the four urements of the plasma, fields, energy, composi- spacecraft will significantly enhance stud- tion, and waves with the added capability to ies of MHD turbulence. image the Earth at x-ray, ultraviolet and visible SOHO performs three types of measure- wavelengths from a polar orbit of 1.5 RE × 8.5 RE. ments: observations of global oscillations to EQUATOR, provided by NASA, will carry nine deduce information about the solar interior, instruments to fully characterize the plasma, fields, energy, composition, and waves in the the solar corona including both long-term equatorial region at an orbit of 2 RE × 12 RE. variations and transient features of the so- SOHO, provided by ESA with nine telescopic in- lar corona through both imagery and spec- struments to measure the solar surface and solar troscopy, and in situ solar wind characteris- corona over a wide range of wavelengths and tics. SOHO provides the relation between five solar wind instruments to measure fields, solar variations and resulting phenomena in plasma characteristics, and plasma wave emis- the solar wind and observed in the magne- sions, will be stationed at the L_ Lagrangian tosphere with the GGS spacecraft. point and will be three-axis stabilized. An essential element of the ISTP program CLUSTER, provided by ESA, will include four Ex- is a coordinated data analysis and archival plorer-class spacecraft, each with about six in- system that will facilitate effective interac- strurnents to carry out spatially separated (100 krn - 20,000 kin) measurements of magnetic tion by the participating community of in- fields, plasma waves, energetic and thermal par- vestigators who will interpret the ISTP and ticle distributions, and plasma composition in an associated data bases. effort to explore turbulent boundary-layer phe- The collaborative ISTP Program will bring nomena in the magnetosphere and magnetohy- a broad international science community to- drodynarnic turbulence in the solar wind. The gether with enhanced opportunities for sci- orbit is polar, 3 Re × 20 RE. entific accomplishments through an inte- The first four spacecraft make up the ele- grated attack on the problems of solar- ments of the first ISTP phase with launches terrestrial relations, magnetospheric phys- planned for 1989-1991 called the Global ics, space plasma physics, and solar phys- Geospace Study (GGS). GGS will focus on ics.

17 Upper-Atmosphere Physics address focused problems in a timely man- ner. The highest priority in observatory-class 2. Scientific opportunities for solar and missions for the 1980's has been UARS, now space physics research merit an average of a new start in FY 85. UARS is the spacecraft approximately one Explorer satellite oppor- recommended in the Kennel report and will tunity a year in the future. If an average of provide for the first time an almost global one launch per year is not feasible with data set on the chemistry, dynamics, and current funding, the Explorer budget should energy inputs of the 10-70 km region of the be augmented. atmosphere, i.e., the stratosphere and lower 3. An Announcement of Opportunity (AO) mesosphere. The goals of the UARS pro- mechanism and selection process should be gram are to understand the mechanisms used to identify approximately twice the controlling middle atmospheric structure number of solar and space physics Explor- and processes and to understand the re- ers that can be expected to be flown in the sponse of the upper atmosphere to natural time interval between AOs. Further, the se- and human perturbations. The UARS data lection process should be conducted in two will be critical elements in evaluating the stages in order to reduce the amount of time extent of ozone depletion caused by human and effort expended by the science commu- activities and the role of upper atmosphere nity. The first stage would be a selection for processes in climate change. The instru- definition studies, the second stage a selec- ment payload has been carefully selected to tion for development. meet the goal of coordinated and comple- These recommendations have been incor- mentary global measurements of ozone, porated in the funding timeline shown in temperature, pressure, energy input, winds, Figure 4, with a flight frequency of about and chemical trace species by remote sens- one launch per year, to be shared as appro- ing. The UARS program includes theoretical priate by solar/heliospheric, magnetos- studies and model analysis as an integral pheric, and upper atmosphere missions. part of the program to complement the measurements and data analysis. Spacelab/Space Station Payload Evolution

Explorers Initial utilization of the Space Shuttle in Explorers have played a crucial role in the 1982-1985 for solar and space plasma phys- development of solar and space physics re- ics investigations is through the OSS-I, Spa- search, and we see their role continuing in celab-1, and Spacelab-2 missions. Missions to follow in the 1986-1990 interval include the future. The primary role of Explorer mis- sions is to attack well-defined scientific Sunlab, Space Plasma Lab, Tether, and problems of high current interest in a timely SOT. Instruments and investigation tech- fashion. Explorers may also be used produc- niques developed for these Shuttle missions tively in conjunction with the global pro- form the basis for two solar and space phys- grams required by solar and space physics ics facilities on the Space Station--the Ad- research, as identified in "Major Missions" vanced Solar Observatory (ASO) and the So- above. lar-Terrestrial Observatory (STO). The basic strategy for use of the Explorer The early Shuttle/Spacelab missions will program in solar and space physics is con- carry solar instruments to measure the total tained in a recent NAS report (A Strategy/or solar irradiance variation on short and long the Explorer Program for Solar and Space time scales and instruments to measure the Physics, NAS, 1984). The recommendations emission spectra, the magnetic field config- of that report are as follows: uration, and the spatial patterns of solar 1. The size, complexity, and management active regions. These and additional instru- of future Explorer missions should return to ments are to be re-flown in a series of Sun- the originally perceived philosophy of the lab missions. Derivatives of these instru- Explorer program (i.e., relatively small, sim- ments will be developed to become part of ple satellites) and should be designed to the ASO. 18 Theearly Shuttle/Spacelabspaceplasma energetic electrons accelerated in solar missionshaveemphasizedactive space flares and other transient phenomena can plasma experiments utilizing electron beam be imaged on the sub-arcsec scale and so and energetic plasma sources. These that the solar corona can be imaged and sources perturb the plasma in the immedi- analyzed over a wide wavelength range. ate vicinity of the orbiter as well as along Eventually, instruments can be added to the magnetic field lines leading to optical emis- ASO to measure the variability in solar irra- sions, energetic particles, and electrostatic diance, solar energetic particles, and waves. The perturbations are observed re- gamma ray emissions. motely with optical telescopes, spectrome- ters, and wave receivers as well as in situ Suborbital Program through plasma diagnostics packages. These plasma perturbation and diagnostics Suborbital programs employing balloons, instruments will become part of the Space rockets, and aircraft provide an important Plasma Lab instrumentation which will and, in some cases, unique platform for cer- have, in addition, a VLF and HF wave gen- tain scientific investigations. For example, eration system. In the Space Station time the effects of solar cosmic rays on atmos- frame, the Space Plasma Lab instruments pheric composition represent a form of so- should become part of the STO for the con- lar-terrestrial coupling that can be most di- duct of active experiments and for monitor- rectly observed in situ using rockets and ing the Space Station plasma environment. balloons. Such observations would include The STO is also to include instruments for simultaneous in situ measurements of the viewing the Sun and the Earth's atmosphere high energy particle and bremsstrahlung to provide cause-and-effect measurements spectra of NOx, 03, and other related minor of the Sun-Earth interactions as well as constituents. Similarly, determination of the measurements of the chemistry, dynamics, ion composition of the ionosphere below and energies of the middle and upper at- about 120 km can probably be most effec- mosphere. tively performed with in situ instruments. In 1987 the Tether Satellite System (TSS) Suborbital platforms are also valuable in will be initiated to tether a diagnostic satel- the development and testing of future lite 20 km above the Shuttle. With a con- spacecraft instrumentation in a relatively ducting tether, the system can be utilized to inexpensive and timely fashion, can serve excite long-wavelength, low-frequency to provide "ground truth" for atmospheric re- waves, create controlled plasma wakes and mote sensing measurements, and often can alter the electrodynamics of the ionospheric provide data on much finer spatial and tem- medium. With a non-conducting downward poral scales than those presently achieva- tether, it becomes possible to drag an at- ble by remote sensors. mospheric satellite at 130 km altitude--a re- Rocketborne payloads also offer frequent gion previously inaccessible on a global and flexible flight opportunities for the in- scale. The TSS will be implemented on the creased quantities of "active experiments" Space Station to extend the investigation in atmospheric science. Experiments that re- periods. quire waiting for appropriate geophysical SOT is designed to measure 0.1-arcsec conditions cannot be easily accommodated scale features of the solar surface in the using Spartan- or Shuttle-type orbiting pay- visible light range to investigate small loads. An additional aspect of the suborbi- scale convective patterns. After the maiden tal program is the important opportunities it flight in about 1990, the SOT will be outfit- offers to graduate training by providing ted with co-observing instruments in the x- complete formulation to data analysis expe- ray and extreme ultraviolet wavelength rience in space science programs. ranges to examine the range of processes on the 0.1-arcsec spatial scale. The SOT and its co-observing instruments will become Theory and Computer Modeling the core of the ASO on the Space Station. Also, a Pinhole Occulter Facility (POF) will The disciplines in solar and space physics be added so that hard x rays produced by are seeking quantitative understanding of

19 the relevant physical processes. The inter- solar and space physics can be addressed play between theory and experiment, cou- with currently available computers, many pled with the tool of computer simulations, problems (especially related to solar dynam- is proving invaluable in advancing this un- ics, MHD turbulence, and ISTP related is- derstanding. Theory provides the mecha- sues) will require availability of supercom- nisms for unifying laboratory, space, and puters, supported by high data rate astrophysical plasma physics. telephone or microwave links to research- The Colgate report (Space Plasma Physics: ers, as well as enhancements of local com- The Study of Solar System Plasmas, NAS, puter processing facilities. A firm NASA 1978) identified the need for adequate theo- commitment to advanced computer facilities retical studies in solar and space plasma dedicated to atmospheric and plasma phys- physics. In response, NASA established in ics modeling is of critical importance. We 1980 the Solar Terrestrial Theory Program concur with the recommendation in the (STTP) to fund "critical mass" theoretical Physics Survey Report for a National Com- groups in the major discipline areas and to putational Program that proposes a large- provide stable career opportunities to scale theoretical modeling and simulation younger theoreticians. The STTP has been effort for basic plasma physics, space phys- highly successful; groups have been estab- ics, and astrophysics. lished that are providing major new insights into critical problems such as reconnection, collisionless shock structure, particle accel- Mission Operations and Data eration, and radio emission processes. The Analysis STTP is now contributing to basic laboratory plasma physics and to a better understand- The MO&DA program is vitally important to ing and interpretation of numerous space NASA's space research mission. It is data sets. A summary of much of this re- through this program that the scientific re- search is described in Solar-Terrestrial Phys- turn from space experiments is finally real- ics-Present and Future, ed. D. Butler and ized; MO&DA funding supports the experi- K. Papadopoulos, 1984, which also includes ment operations, provides (sometimes) for descriptions of theoretical research spon- extended missions, and is responsible for sored by NSF and NASA under other pro- the processing and analysis of the data. grams. Currently operating spacecraft are a na- Funding for STTP is currently at $3.3 mil- tional resource and frequently provide lion in FY 85. Substantial increases in this unique opportunities for gathering scientific program would provide growth opportuni- information. For example, Interplanetary ties for established groups and allow for Monitoring Platform-8 (IMP-8) is the only new entries. A level of about $6 million (in spacecraft that can provide information on FY 85 dollars) to be achieved by FY 90 will solar wind parameters at the present time. provide the appropriate balance between The Pioneer Venus Orbiter has been provid- theory and the experimental program. ing unique and invaluable information on NASA has also recognized the need for the solar wind-ionosphere-atmosphere inter- theoretical groups to participate in a princi- action processes; its continuously rising per- pal investigator (PI) role in NASA missions. iapsis is allowing measurements to be This offers the possibility of establishing made in new and unexplored regions of the closer quantitative links between mission Venus plasma environment. The Interna- planning, data analysis, and theoretical tional Comet Explorer (ICE) mission will ex- and computational modeling than has here- plore a comet tail for the first time in Sep- tofore been possible. DE, UARS, ISTP, and tember, 1985, and provide essential Combined Release and Radiation Effects measurements of solar wind parameters up- Satellite (CRRES) are examples with theoret- stream from Halley during its perihelion ical PI participation. We recommend that passage in 1986. Furthermore, the deep the policy of theoretical PI team participa- space missions of Pioneers 10 and 11 and tion be continued in solar and space phys- Voyagers 1 and 2 provide the only means of ics and in planetary investigations. studying the global properties of the helios- Although many theoretical problems in phere at large distances from the Sun. Thus,

20 it is important for NASA to continue MO&DA and we recommend areas within the R&A funding for existing spacecraft and for program where increased funding is re- "cruise mode" measurements by planetary quired. spacecraft. Historically, NASA has not adequately Technology Requirements and funded its MO&DA needs. Since MO&DA is Instrument Development a critical element of all NASA's science pro- grams, care must be taken to ensure that it All of the missions recommended for the not be neglected as large programs occupy 1980s and most of the missions recom- increasing attention and funding commit- mended for the 1990s can be implemented ments. with existing spacecraft technology. The ex- In Chapters 7, 8, and 9 of this report, ex- ceptions are the requirement for a low-abla- amples of MO&DA needs are specified and tion heat shield for the Solar Probe and ad- recommendations for increased funding are vanced propulsion (probably solar-electric made. powered ion thrusters) for the SPO. If it were available in time, advanced propul- Research and Analysis sion could also be used to enhance the So- lar Probe mission by achieving a shorter A strong research and analysis program is period solar orbit. We recommend that the essential foundation for the entire sci- NASA proceed with these developments to ence program. Its vital elements include the meet the planned new start dates of 1991 following: and 1997 for the Solar Probe and the SPO, 1. the theory and analysis essential for respectively. assessing the state of the field, for combin- The development of scientific instruments ing and interpreting the results of the var- is now and should continue to be a high- ious flight projects into a self-consistent priority effort. Major emphasis should be body of physical knowledge, for transfer of placed on the development of (1) PI-class new results to and from the fields of labora- and facility instruments for solar observa- tory plasmas and astrophysics, and for tions, leading ultimately to the ASO; (2) im- planning future research; aging instruments to remotely sense the hot 2. development of instruments for future plasma processes in the magnetosphere; flight projects; and (3) post-UARS instruments for detection 3. correlative observations that enhance of a greater number of chemical species in the scientific return from the space flight the upper atmosphere, particularly impor- projects; and tant free radicals such as OH and HO2 4. supporting or complementary research along with ozone, solar irradiance, and tem- performed in laboratories or with suborbital perature. For all the missions later in our flight programs. implementation plan, many instruments Another important function of the R&A should be enhanced by taking advantage of program is to provide the long-term stability new technologies such as better detector ar- required to maintain the scientific capabil- rays, cryogenic systems for sensor cooling, ity of research groups through the lean microprocessors, data storage devices, and years between major flight projects. software to process and compress data on In Chapters 7, 8, and 9 of this report, we board the spacecraft. Chapters 7, 8, and 9 review the R&A programs in each of the specify the technology requirements for main disciplines of solar and space physics, each of our main disciplines.

21 6 SCIENCE HIGHLIGHTS AND ACCOMPLISHMENTS

This Chapter is a brief review of some of ciated with large flares is carried away the most significant scientific accomplish- from the Sun by coronal mass ejections-- ments of several past research programs. observations that led to improved knowl- We include it in this report to demonstrate edge of the energetics of flares and the rela- the important contributions to our under- tionships between the diverse phenomena standing of the Earth's environment and the observed during flares; basic physical processes of the universe • discovery of nearly random spatial dis- that have resulted from research activity in tribution of coronal x-ray bright points iden- this area. tified with small magnetic bipoles and the discovery of rapid temporal variations in the emission from these features, providing in- Skylab sights concerning the emergence of mag- netic flux from below the surface and the Skylab, with its battery of solar telescopes role of magnetic field dissipation in heating in the Apollo Telescope Mount, was the coronal plasma; and launched in May 1973 and was operated by • discovery of rapid, large amplitude fluc- three crews until February 1974. Eight in- tuations in solar extreme ultraviolet (EUV) struments, including two x-ray telescopes, flux, but without evidence for an expected an EUV spectroheliograph, a uv spectrohe- periodic component, providing evidence that Iiometer, a uv spectrograph, a visible-light the corona is not heated by periodic waves coronagraph, and H-alpha telescopes, stud- as predicted in some theoretical models. ied the Sun over the wavelength range 2- 7000 A. Principal scientific results included the following: P78-1 • recognition of the highly inhomogenous structure of the corona and the close corre- The P78-I spacecraft is part of the DOD lation between coronal radiation and mag- Space Test Program and was launched by netic field structure, finding that over most the Air Force on 24 February 1979. The satel- of the surface the elemental structures are lite was built with assistance from NASA, magnetic arches or loops connecting regions which provided the stabilization and solar of opposite magnetic polarity (This along pointing control systems and other flight with the Skylab observations of coronal space components from NASA's seventh Or- holes revolutionized our concepts about the biting Solar ObservatOry (OSO). Solar in- structure of stellar coronae.); strumentation includes a white-light corona- • confirmation that coronal holes are graph, soft x-ray Bragg crystal sources of recurrent high-speed solar wind spectrometers, and hard x-ray proportional streams, resolving a long-standing problem counters. Some scientific results are as fol- on the solar origin of these streams and lows: leading to major revisions in models of the • first observation of earth-directed co- solar wind at its coronal source; ronal transients, i.e., "halo" transients, • discovery of transient mass ejections demonstrating that at least some transients from the corona at an unexpected high rate are bubble, rather loop-like, in shape; and an unexpected large scale, significantly • the accumulation of a data base for revising concepts about the role of transient outer coronal activity that extends from 1979 phenomena in the energetics and evolution until September 1985, producing many sta- of the corona; tistical results, e.g., on average two coronal • discovery of hot, x-ray emitting mag- mass ejections occurred per day during the netic loops associated with flares and the years 1979-1981 near sunspot maximum; discovery that a substantial fraction (often • the discovery that greater than 75 per- greater than 50 percent) of the energy asso- cent of the interplanetary shocks observed

22 by the Helios spacecraft originated with co- • discovery of large-scale circulation pat- ronal mass ejections; terns in the chromosphere and low corona • the discovery of four sungrazing comets, in active regions, suggesting a solution of none of which were seen after perhelion, mass conservation dilemmas indicated by implying either destruction by the solar at- earlier observations. mosphere, or actual impact into the photos- phere; Orbiting Solar Observatory-8 • the first accurate determination of the temperature of the bulk of the soft x-ray The Orbiting Solar Observatory-8 (OSO-8) emitting thermal flare plasma; was launched in June 1975, as the last of a • the discovery that 300-500 km s -_ upflows series of satellites intended to study the Sun at temperatures of about 15 x 10_ K are a through a solar cycle and to map the entire common occurrence during the rise phase of sky in ultra violet, x-ray, and gamma-ray large solar flares; radiation. Some important results include • the first systematic study of the time be- the following: havior of random mass motions in soft x-ray • demonstration that the energy flux in flare plasmas; and sound waves at the top of the chromosphere • the discovery of high density (-_ 10_2cm -3) is too low to explain coronal heating and coronal plasma (_ 2 x 106 K) of very small • verification of widespread down-flow in volume (-_ 109 kin3), produced coincident the chromosphere-corona transition region. with the hard x-ray flare impulsive compo- nent. Heiiosphere Missions

Solar Maximum Mission Several missions have been valuable in ex- ploring the heliosphere. The Solar Maximum Mission (SMM) was • Pioneer 10 and 11, the first experiments launched in February 1980 and repaired on- to the outer solar system (launched in March orbit in 1984. It is dedicated to coordinated 1972 and April 1973, respectively), performed observations of specific solar activity and flybys of Jupiter and Saturn and conducted solar flare problems. The payload contains studies of planetary and interplanetary seven instruments, including an Active Cav- magnetic fields, solar wind parameters, ity Irradiance Monitor, a coronagraph, and cosmic rays, transition region of the helios- several imagers and/or spectrometers cover- phere, neutral hydrogen abundance, and ing the spectrum from uv to gamma rays. properties of dust particles. Some of the most significant results include • Voyager 1 and 2, launched in September the following: 1977 and August 1977, respectively, studied • accurately measured changes in solar ir- Jupiter and Saturn as well as the interplane- radiance associated with solar activity, sug- tary medium. gesting the probability of transient energy • The Interplanetary Monitoring Platforms storage inside the Sun; (IMP) series of missions carried out studies • discovery of near temporal coincidence of interplanetary space and the Earth's mag- of gamma rays produced by energetic ions netosphere. The last of the series, IMP-8, and of hard x rays produced by energetic was launched in September 1972. electrons at times of solar flares, providing • Helios, developed by the FRG in cooper- constraints on the energy release mecha- ation with NASA, was a two-spacecraft mis- nisms in flares; sion, launched in December 1974 and Janu- ° discovery of frequent occurrence of ary 1976. The purpose of the mission was to small flares producing hard x-ray and EUV study the interplanetary medium between radiation, indicating powerful energy re- 0.3 and 1 AU. leases on scales smaller than previously Some scientific results include the follow- known; ing: • discovery of hard x-ray and EUV sources • discovery that the interplanetary sector at the foot points of coronal loops, providing structure is the ecliptic plane projection of a strong evidence for the thick-target model of three-dimensional heliospheric current sheet x-ray production; and (Pioneer 11);

23 • tracking of type III solar radio bursts to • extension of ion composition measure- Earth orbit [Simultaneous measurements of ments to high altitudes, demonstrating both plasma waves, radio waves, and energetic ionospheric and solar wind plasma sources electrons (IMP 6) provided a global view of (ISEE- 1,2); the three-dimensional structure of the inter- • electric field measurements throughout planetary magnetic field.]; terrestrial magnetosphere and environs • studies of three-dimensional MHD turbu- (ISEE-1,2) (Since electric fields are the lence in the solar wind beyond 1 AU using causal agents of particle acceleration and magnetic field and three-dimensional they effect plasma transfer, the successful plasma data (Voyagers 1 and 2) --first deter- measurement of electric fields represents an mination of the three global invariants of important advance in observational tech- incompressible, three-dimensional MHD tur- niques.); bulence; and • improved observations of reconnection • discovery that coronal holes are the in magnetotail, including detailed structure source of high-speed solar wind streams of plasma sheet (ISEE-1,2,3) (Reconnection (Helios, Skylab). processes appear to be very important both for the quiet time structure of the plasma sheet and for the temporal evolution of the International Sun-Earth Explorer magnetotail structure during substorms.); • demonstration of the importance of sin- The International Sun-Earth Explorer (ISEE) gle particle motion within boundary regions was a three-spacecraft mission, with of the plasma sheet (ISEE-1,2); launches in October 1977 (ISEE-1 and -2) and • continuous monitoring of solar wind in- August 1978 (ISEE-3), to investigate solar-ter- put functions from upstream libration point restrial relationships near the boundaries of providing critical information about the so- the Earth's magnetosphere, the solar wind lar wind electromagnetic fields that "drive" near the Earth's bow shock, cosmic rays, geomagnetic activity (ISEE-3); and solar flares in the interplanetary region • first detailed survey of distant tail show- near 1 AU. IS_-3 was moved, in June 1982, ing the structure, evolution, and dynamics from its halo orbit in the solar wind to make of the region beyond the lunar orbit (ISEE-3); several excursions into the far magnetotail • confirmation of plasmoid formation and (1983) and was then directed into a trajec- escape from magnetotail during substorms tory that will intercept the tail of comet Gia- (ISEE-3) (Such plasmoids carry away very cobini-Zinner in September 1985. The signifi- large amounts of mass and energy from the cant results to date include the following: near-Earth tail and represent a major form • mapping the structure and fundamental of dissipation as the magnetosphere returns physics of the Earth's bow shock and up- toward a "ground-state" after substorms.); stream region (ISEE-1,2); and • demonstration of steady-state reconnec- • first high-resolution measurements of tion at dayside magnetopause, thus show- the isotopic composition of solar flare and ing the operation of a physical process that galactic cosmic ray nuclei, thus advancing had long been predicted theoretically and our understanding of cosmic-ray accelera- inferred from global magnetospheric obser- tion and propagation processes (ISEE-3). vations (ISEE-1,2); • discovery and characterization of tran- Dynamics Explorer sient reconnection (flux transfer events) at dayside magnetopause (ISEE-1,2), showing Dynamics Explorer (DE), launched in August the dynamical importance of a more 1981, was a two-spacecraft mission de- "patchy" kind of energy transfer between signed to study the strong interactive proc- the solar wind and magnetosphere; esses coupling the Earth's magnetosphere • measurement of magnetopause wave and ionosphere. The spacecraft were placed structure and motions (ISEE-1,2), showing in polar orbits to permit simultaneous meas- that the magnetopause is a highly complex urements at high and low altitudes on the and dynamic region as opposed to the sim- same field lines. Significant results to date ple laminar region often pictured in models; include the following:

24 • first global images of auroral oval and particle energization and generation of in- polar cap showing substorm evolution; tense electrostatic waves. • strong coupling between convectively • In most cases, the onset of plasma ener- driven ions and the neutral atmosphere, im- gization and anomalous ionization limited plying an important form of energy and mo- charging to below 100V. In one case, kV mentum coupling at ionospheric altitudes; charging was detected. The preliminary ex- • a new relationship between the convec- planation for this is inaccessibility of the tion electric field and field-aligned currents conducting areas to the plasma energized and interpretation of this in terms of the by the beam injection. mechanism for driving the magnetospheric- • Discovery of the "Shuttle Glow" and its ionospheric coupling currents; correlation with electrostatic wave and par- • first observation of postulated non-ther- ticle energization phenomena caused by col- mal line profiles of oxygen in the nighttime lective plasma interactions may support a thermosphere; plasma hypothesis for this phenomena. • neutral winds of very high speed (ap- • Major enhancement in ionization when proximately 1500 km/hr)---over twice maxi N2 was released in the "ram" direction from mum speed observed during the Atmos- the Shuttle, may be similar to "Critical Ioni- pheric Explorer (AE) mission--implying zation" although the speed of the release great variability of the upper atmospheric was subcritical. wind system; • polar wind at high latitudes, which, pre- dicted theoretically, demonstrates that the Planetary Magnetosphere/ polar ionosphere is an extensive source of Atmosphere Missions magnetospheric plasma during magnetic storms; The Pioneer and Voyager missions were de- • nitrogen ions in the magnetospheric scribed in the section on Heliosphere Mis- plasma, clearly of low ionospheric origin sions. The significant results of their inves- and previously unobserved; tigations of the magnetospheres and • correlated magnetic and electric field atmospheres of Jupiter and Saturn include variations that provide remote sensing of the following. ionospheric current and conductivity, which • Jupiter is the dominant source of 1-40 determine, in significant measure, the lev- MeV cosmic-ray electrons in the helios- els of energy dissipation in the ionosphere; phere. • first global scale mapping of thermos- • Jupiter's magnetosphere is the largest pheric winds and temperatures that showed object in the solar system, 10 solar diame- neutral atmospheric circulation patterns (In ters in width, with an identifiable tail that particular, the mission confirmed that ion extends at least beyond the orbit of Saturn drag is a dominant force on high latitude (Pioneer 10 and 11 and Voyager 1 and 2). neutral atmosphere in polar regions.); • Jupiter's moon, Io, serves as a source of • first measurement of height of auroral heavy ions that form a torus surrounding hiss emission region; and Io's orbit in the inner magnetosphere. Ions • frequent occurrence of extremely high from the toms are accelerated to relatively densities of field-aligned currents, suggest- high energies (tens of keV) and are found ing a "clumping" and localization of current throughout the magnetosphere (Voyager 1 patterns rather than broad, uniform distribu- and 2) at extremely high temperatures tion over large polar regions. (about 3 x 108K). Because of Io's plasma to- ms, radio emissions from Jupiter's iono- sphere and magnetosphere reveal a com- Shuttle/Spacelab--Space Plasma plex pattern in frequency and space Physics unanticipated from ground-based observa- tions (Voyager 1 and 2). • Electron beam and plasma emitters suc- • Saturn's magnetosphere is intermediate cessfully operated on the Shuttle without in structure between Earth's and Jupiter's, any significant charging. There is evidence both in scale and in importance of centrifu- for strong beam-plasma interactions with gal distortion. Internal plasma sources in-

25 clude the atmosphere, moons, and rings, measurements of the daytime photoelectron which serve as sources of both protons and spectra, electron spectra in the high latitude heavy ions (Pioneer 11, Voyager 1 and 2). ionosphere and quiet dayside cusp that pro- • Radio emissions from Saturn define a vided accurate electron impact emission stable rotational period, but the intrinsic rates of auroral and airglow features that magnetic field is symmetric about the rota- are diagnostic of energy input to the ther- tion axis, so the cause of the modulated mosphere; emissions is not established (Voyager 1 and • measurements of solar wind plasma in- 2). jection in the dayside cusp, of convection in • Elongated radial features ("spokes") are dayside auroral arcs, of polar cap electron found in the B-ring near the orbit synchro- acceleration regions and substorm effects nous with planetary rotation, and are best on the auroral plasma that provided impor- understood by invoking charged dust grains tant data to understand magnetosphere-ion- electrostatically coupled to local plasmas osphere coupling; and (Voyager 1 and 2). • detailed in-situ measurements of plasma • Saturn's atmospheric structure is similar bubbles and irregularities in the equatorial to Jupiter's, but equatorial wind speeds up ionosphere, which are important signatures to 1500 km/hr are four to five times faster of plasma instabilities in the F region. than those on Jupiter (Voyager 1 and 2). • Titan's exosphere generates strong EUV emission by magnetospheric interactions Nimbus-7 (Voyager 1 and 2). This interaction is impor- tant in the evolution of Titan's atmosphere. The Nimbus-7 Satellite, which is the last in the Nimbus series, was launched October 24, 1978, for the purpose of sounding the Atmosphere Explorers oceans, Earth radiation budget, and the middle atmosphere. Four experiments were The Atmosphere Explorer (AE) series of dedicated to study of the middle atmos- spacecraft were designed to study the phere, three of which were limb sounders Earth's upper atmosphere. The last of the (LIMS, SAMS, and SAM II) and the fourth, series was launched in November 1975. The the SBUV experiment, used nadir backscat- principal results include the following: tered ultraviolet radiation. A collective sum- • comprehensive measurements and un- mary of middle atmosphere scientific results derstanding of the ion and neutral photo- is as follows: chemistry of the thermosphere and inference • Provided first global distributions of of various reaction rate coefficients, which H20, NO2, HNO3, N20, and CH4 showing lati- led to the solution of outstanding photo- tudinal gradients, significant variability, chemical problems of the thermosphere; seasonal changes, and important new chal- • detailed measurements of the diurnal, lenges to theory. Concurrent observations of latitudinal, longitudinal, and seasonal vari- CH4 and H20 provide a unique opportunity ation of the neutral constituent concentra- to study the production of H20 through the tions in the thermosphere, which indicate tropical tropopause. the importance of solar and geomagnetic • Produced first experimental evidence of activity on the thermosphere; downward transport of NOx from high alti- • in-situ measurements of vertical veloci- tudes to the mesosphere and upper strato- ties, kinetic temperature, and interhemis- sphere in high latitude winter providing de- phere transport induced by neutral meri- tailed observations for comparison with dional winds that provided a firm basis for theoretical results, for study of impact on understanding compositional changes in the the NOx budget in the stratosphere, and for thermosphere; analysis of photochemical time constants, • direct measurements of the winter he- vertical velocity, and lower mesosphere lium and hydrogen bulges, demonstrating wave activity. the importance of transport by interhemis- • Provided detailed observations of rapid pheric wind systems; NO2 decreases with latitude at high winter • high resolution, low energy particle latitudes in the stratosphere (the NO2 "cliff")

26 and showed importance of including inter- Solar Mesosphere Explorer action between dynamics and chemistry to explain the phenomenon. The Solar Mesosphere Explorer (SME) satel- • Demonstrated strong correlations be- lite was launched in October 1981. Its pur- tween potential vorticity and temperature, pose was to investigate some of the factors 03, HNO3, and H20 fields, illustrating the influencing the ozone balance of the mesos- utility of potential vorticity for tracer stud- phere and upper stratosphere, thus adding ies. Observations give evidence of species to our knowledge of the behavior of this transport associated with breaking plane- very important atmospheric constituent. tary waves. Some of the most significant discoveries • Confirmed NO2 diurnal change theory noted to date include the following. and provided latitude cross sections of the • Systematic observation revealed the day/night ratio (Observations provided of ozone distribution at about 50-70 km by two diurnal change in lower mesospheric techniques and 50-95 km by one technique. ozone). These results provide important data • Observations of water vapor in the up- for in situ tests of photochemical theory. per stratosphere are now also being ob- • Provided detailed observations of con- tained and their relationship to ozone is un- stituents and temperature distributions dur- der study. ing the major stratospheric warming event • It was discovered that day-to-day ozone of the winter of 1979. This provides data for variations at mesospheric heights are prin- analyses of the warming period through cal- cipally driven by temperature variations. culation of derived dynamical quantities • It is indicated that solar flux variability (e.g., winds, heat, momentum, and Elias- significantly influences ozone distributions sen-Palm fluxes) and by study of the global near the stratopause over the time scale of morphology and variability of constituent a solar rotation. and temperature patterns. • Observation was made of the distribu- • Discovered the presence and measured tion and variability of stratospheric NO2, a the variability of polar stratospheric clouds species which catalytically destroys ozone in both the northern and southern winter in the stratosphere. The sharp decreases in polar regions. These clouds, observed glob- wintertime NO2 at high latitudes (the "NO2 ally for the first time, have important impli- cliff") were confirmed. cations for the water budget and heteroge- • Detailed observations of the response of neous chemistry. mesospheric ozone to solar proton events • Measured optical depths of aerosols in showed very good agreement with photo- polar regions that had been transported chemical theory, confirming that the cata- from much lower latitudes after an eruption lytic destruction of ozone by hydrogen radi- of the E1 Chichon volcano on the Yucatan cals (OH, HO2) proceeds as expected. peninsula, providing information on hori- • Large seasonal variations have been de- zontal transport times for use in model stud- tected in ozone near the 80 km level. Present ies. study suggests that these changes are due • Developed six-year climatology of polar to the influence of breaking small-scale stratospheric aerosols for use in climate im- gravity waves. pact studies. This is significant because of the suggestion that polar aerosols may have Pioneer Venus an important effect on climate. Pioneer Venus (launched in May 1978) was a • Detected SO2 in the stratosphere directly (from the E1 Chichon eruption) for the first two-spacecraft mission, with 4 entry probes, time. This gas is a precursor to sulfuric acid designed to conduct a comprehensive study of Venus' atmosphere. The most significant formation which is the main component of the stratospheric sulfate layer. results include the following. • Lack of an intrinsic planetary magnetic • Confirmed the effect of solar particles on field was established. stratospheric ozone during a solar proton event and found strong correlations of ozone • Shape of the bow shock and the volume variations at the 3 mb level with 27-day of the solar wind interaction with the planet solar flux changes. were clarified.

27 • Intensemagneticflux ropes were ob- netosphere have been obtained computa- served deep in the ionosphere. tionally; features such as the bow shock, • Ionospheric composition and tempera- magnetopause, cusp, tail lobes, and neutral tures were established. points are all evident. • Nighttime auroral precipitation and • Two- and three-dimensional simulations emissions were observed. of magnetotail reconnection have shown • The extent of the nighttime ionosphere many of the features predicted by fluid dy- was established showing that it is main- namics and seen in magnetospheric plasma tained by a combination of transport from observations. the day side and electron precipitation. • Analysis and simulations illustrated • An extended gas envelope, consisting of many important processes operating in the hot oxygen and hydrogen atoms, was 0b- auroral zones and responsible for key obser- served, confirming the loss of hydrogen and vational features. Lower hybrid and ion cy- oxygen from Venus by solar wind scaveng- clotron waves effectively heat and acceler- ing. ate heavy ions; double layers and resistivity • Extremely low (about 100 IO nighttime caused by spiky turbulence drive the elec- thermospheric temperatures were observed. tric fields necessary to produce auroral • Lightning was detected by wave obser- beams; and the electron cyclotron maser in- vations. stability causes the terrestrial kilometric ra- • At least four distinct cloud layers Were diation. found. • Major advances in our understanding of • Haze layers contain small aerosol parti- both fluid and MHD turbulence have been cles, possibly droplets of sulfuric acid. achieved. In the ionosphere, key features of • Atmosphere circulation is dominated by the natural and artificial spread F have large planetary-scale systems. been reproduced in simulations. In the solar • A collar of polar clouds discovered, wind, magnetic data have been used to con- which may be part of a large atmospheric struct the three rugged MHD invariants and polar vortex. led to the suggestion that the solar wind is a strongly turbulent medium. ° Major progress in the theoretical under- Theory Program standing of beam plasma interactions re- sulted in the resolution of several outstand- The following are representative of a host of ing issues. In the interplanetary medium it recent achievements in the areas of theory led to the most sophisticated modeling of and computer simulations. type III bursts; in the ionosphere to the un- • Quasi-perpendicular bow shocks have derstanding of the extremely short energy been simulated at a new level of sophistica- deposition lengths associated with artificial tion and have produced results in remarka- beam injection. ble agreement with high resolution ISEE ob- • Compressible convection studies of the servations. solar convection zone have shown that en- • Acceleration by self-generated, convect- ergy transport occurs on the space scale of ing, hydromagnetic waves has explained giant cells and have demonstrated the exist- many properties of energetic diffuse ion ence of convective overshoot. populations observed upstream of both • Global thermospheric and ionospheric Earth's bow shock and traveling interplane- models have been developed and show that tary shocks. magnetospheric influences have an unex- • First generation, two- and three-dimen- pectedly great importance, e.g., by inducing sional, global MHI) models of Earth's mag- convection.

28 7 DETAILED MISSION PLANS--SOLAR AND HELIOSPHERIC PHYSICS

Introduction data bases to be provided by the WIND in- struments. The strategy for advancing solar and helios- Further discussion of WIND will be found pheric physics combines in-situ measure- in the section on ISTP in Chapter 8. ments of the heliosphere with remote obser- vations of the Sun from low-Earth orbit SOHO (LEO). Below we first describe the several SOHO is a mission aimed at three distinct, pieces of the program and then, in Section yet interrelated plasma regimes, the solar C, discuss their relative priorities. interior, the corona, and the solar wind. Ex- periments on SOHO will use the methods of Program Descriptions solar seismology, spectroscopic plasma di- agnostics, and in-situ measurements to de- rive the physical state, chemical composi- Free-Flyers for Solar and Heliospheric tion, and the internal and bulk motions of Physics the plasma structures that make up the Sun and heliosphere. The objects of the study WIND will range from the dense matter hidden in- The WIND spacecraft is one of a network of side the Sun, in the thermonuclear furnace spacecraft proposed as part of the Interna- and in the radiation and convection zones; tional Solar Terrestrial Physics Program through the tenuous corona, where matter is (ISTP). The overall goal of the ISTP is to held together and possibly heated and ac- develop a comprehensive and global under- celerated by magnetic fields; far out into the standing of the physical mechanisms by interplanetary medium, where the solar which energy generated at the Sun flows mass loss manifests itself as the solar wind. through the interplanetary medium and fi- The detailed data acquired by SOHO, com- nally enters the Earth's magnetosphere and bined with sophisticated, well-developed upper atmosphere. Understanding the cou- methods of interpretation, will allow tests of pling between solar and interplanetary the numerous models of plasma structures. processes and the Earth's magnetosphere, Examples of such structures are the solar ionosphere, and atmosphere requires de- convection zone, coronal magnetic loops, tailed knowledge of the source function. and the sharp boundary layers between low This can be obtained only through in situ and high speed solar wind streams. measurements in the solar wind. The primary objectives of SOHO are as The WIND spacecraft has a central role in follows. ISTP, for without detailed knowledge of the • Use solar oscillations to probe the solar behavior of the solar wind upstream of its interior structure from the core to the solar interaction with the Earth's magnetosphere, "surface", or photosphere. no comprehensive understanding of the ef- • Determine the angular rotation profile of fects of this interaction is possible. WIND the solar interior and measure the solar will measure the properties of the helios- gravitational quadrupole moment. phere at 1 astronomical unit (AU) in the • Measure variations in solar irradiance ecliptic plane while the International Solar from minutes and days to weeks and years Polar Mission (ISPM) acquires similar data to ascertain effects of solar activity on solar far from the ecliptic. Study of magnetohy- luminosity. drodynamic turbulence, important for under- • Study the generation of the solar wind standing both the formation and evolution through measurements of plasma velocities, of the solar wind and the behavior of labo- temperatures and densities out to 5 solar ratory plasma devices, requires the nearly radii. continuous data coverage and the extensive • Locate sources of low speed solar wind.

29 • Determine how coronal transients propa- radii. In situ measurements should clarify gate through the corona and how and where this issue. they are accelerated. The location of the critical point and the • Obtain high resolution temperature, plasma properties (speed and temperature) density, velocity, and magnetic measure- of the supersonic wind will depend greatly ments in an effort to determine the origin of on the physical processes that heat the cor- coronal heating. ona. Theoretical studies suggest that the SOHO is a three-axis stabilized spacecraft proton temperature profile is very sensitive that is to be placed in a halo orbit around to these heating processes. It is not clear the L_ Lagrangian point at 1.5 × 10Gkm from whether the corona contains an extended Earth. The spacecraft is to be built by the region of heating (out to as far as 20 solar ESA with experiments provided by both Eu- radii) or undergoes adiabatic expansion be- ropean and U.S. scientists. yond the solar surface. Plasma temperature data and observations of the wave types and amplitudes should lead to the identifi- Solar Probe cation of the important heating and acceler- The general problem of the origin of the ation mechanisms. solar wind has been a focus of observa- Many other important problems can be tional and theoretical activity since the orig- studied with Solar Probe, including a de- inal theoretical work of E.N. Parker. Direct tailed characterization of coronal streamers, measurements of the solar wind plasma, the the place of origin and the boundaries of interplanetary magnetic field, the energetic high speed and low speed flows close to the particle population, and associated wave- Sun, the extent of heavy element fractiona- particle interactions are available, but only tion and elemental abundance variations, at distances greater than the 0.3 AU perihe- and the scale sizes of inhomogeneities and lion distances of Helios 1 and 2. From the the development of the magnetohydrodyn- solar surface out to a distance of about 60 amic turbulence that characterizes the solar solar radii, we must rely on indirect obser- wind near 1 AU and beyond. The Solar vations and theoretical extrapolations. We Probe mission can also study the solar spin recommend a Solar Probe mission whose down rate through measurements of solar primary objective is to carry out the first in wind angular momentum flux. situ observations of the solar wind plasma Further study needs to be carried out to and fields (electric and magnetic) near the determine the best method of designing de- source of the wind in the solar atmosphere. tectors that are required to look in the direc- Included will be a detailed study of ener- tion of the Sun. getic particles which will yield important In previous studies on the concept of a diagnostic data on particle acceleration solar probe (Starprobe: Scientific Rationale, processes and coronal structure. J.W. Underwood and J.E. Randolph, JPL The spacecraft must be placed in an orbit Publ. 82-49, 1982), several other investiga- that will bring it as close to the Sun as tions were also included in the potential possible and still survive to provide useful payload, e.g., imaging, a drag-free experi- data near closest approach. We anticipate a ment for studying relativistic effects, and perihelion distance of 4 solar radii, where measurement of the solar gravitational we expect the local wind speed to be about quadrupole moment*. While these investiga- 50 km/s, the electron and ion plasma tem- tions undoubtedly have important scientific peratures to be about 106 K, and the plasma objectives, the primary objective of the mis- density and magnetic field strength to be sion is the study of the solar wind accelera- less than 106 electrons/cm 3 and 105 gamma, tion region. In order to fit this mission into respectively. our implementation plan (Figure 4), cost Theories of solar wind origin place the considerations have forced us to define the transition region from subsonic plasma flow mission to address the prime objective only. to supersonic flow somewhere between 1

and 10 solar radii. Radio scattering experi- " Much progress can be made in measuring the solar ments on Viking during superior conjunction gravitational quadrupole moment from solar oscillation suggest a critical point closer to 10 solar studies.

30 With additional funds, these other worth- addition, SPO should have pointing capabil- while objectives could also be addressed. ity, through the use of a despun platform on a spinning spacecraft, or as a three-axis stabilized spacecraft, for detailed solar ob- Solar Polar Orbiter servations using a coronagraph, x-ray tele- The heliosphere is known to have a compli- scope, and similar photon observing instru- cated three-dimensional structure. The mag- ments. netic field is a tight spiral near the solar Mission design for SPO should be under- equatorial plane, but is expected to be es- taken in the mid-1990s, following a thorough sentially radial over the solar poles. Co- analysis of the results from ISPM. Launch ronal holes, one of the sources of high should occur in the late 1990s. speed solar wind, are expected to produce The principal technical development re- quasi-steady high speed flows over the so- quired for SPO is solar-electric propulsion lar poles during much of the solar cycle, system, or its equivalent, for low-thrust, whereas at low latitudes interacting high continuous acceleration. In the cost projec- and low speed flows predominate. tions for SPO it is assumed that such devel- To understand heliospheric conditions at opment will not be charged against the mis- low solar latitudes has required numerous sion costs, because the need is common to missions, e.g., Explorers, Pioneers, Mari- several proposed programs. Also, studies ners, and Voyagers. To understand helios- need to be conducted on the impact of a pheric conditions at high latitudes will simi- continuous propulsion system on particle, larly require repeated missions. In 1986, field, and photon instrumentation, and on NASA and ESA will fly the first exploratory the measurements these instruments make. mission over the solar poles, the ISPM. However, as with most exploratory mis- sions, ISPM will probably uncover more Solar-Heliospheric Research with the Shuttle questions than it will answer, and follow-on missions will be required. Remote observations of the sun and corona The objective of the Solar Polar Orbiter will be made with Shuttle-borne instruments (SPO) would be to provide a detailed, re- ranging in size from small Spartan experi- peated study of conditions at all helio- ments to moderate Spacelab/Sunlab instru- graphic latitudes. In circular orbit, SPO will ments to large facility-class instruments. Af- observe the heliosphere at constant radius ter Shuttle experience is obtained, we and thus will distinguish latitude from ra- envision that appropriate facilities and dial effects. With a circular orbit at less moderate instruments will evolve into a than or equal to 1 AU, and thus an orbital Space Station-based Advanced Solar Ob- period less than or equal to 1 year, SPO servatory (ASO) as the primary means for should be able to make several passes over remote sensing in the next decade. Develop- the solar poles in a nominal mission life- ment of new instrumental techniques and time, and thus distinguish spatial from tem- exploration of some solar phenomena do not poral effects. require large facilities. These problems can No detailed study of an SPO mission has be addressed using smaller experiments of been done in recent years. However, the re- the PI class, suitable for Shuttle, free-flyers, quired orbit should be achievable through sounding rockets, and balloons. Shuttle- the use of a low-thrust, continuous accelera- based observations include measurements tion propulsion system such as solar-electric of propulsion. For example, it may be possible to launch SPO in the direction of the Earth's • energy and mass flux irom the photos- orbit, and use solar electric propulsion to phere through the corona; tilt the orbital plane in heliographic lati- • magnetic and velocity fields and their tude. evolution and interactions; The SPO spacecraft should carry a full • temperature and density structure of the complement of plasma, energetic particle, solar atmosphere; magnetic field, and radio wave instruments, • changes in solar radiative flux; and similar to what is to be flown on ISPM. In • some coronal processes that may govern

31 the generation, structure and variability of The Solar Optical Telescope the solar wind. The purpose of SOT is to study physical We have identified three Shuttle programs processes on the Sun with an instrumental that are critical for solar-heliospheric phys- angular resolution of 0.1 arcsec. This corre- ics. sponds to 70 km and is about half an atmos- 1. Spartan. The Spartan program, which pheric density scale height. We know that is a successor to the sounding rocket pro- much of the fine structure and energy trans- gram, can fly innovative, relatively small port in the solar atmosphere are closely as- and inexpensive instruments prepared on a sociated with the strong magnetic field con- rapid time scale. The Spartan carrier will centrations associated with sunspots and contain a pointing system, power supply, smaller flux tubes in the chromosphere and and tape recorder. When placed into orbit corona. by the Shuttle, the Spartan will be a free- SOT will study (by remote sensing) the flyer for one to two days before being solar atmosphere from the photosphere, recovered by the Shuttle. To continue ade- where the gas pressure plays a major role quately research currently done with sound- in containing the magnetic fields, to the up- ing rockets, Spartan flights with solar-he- per chromosphere and lower transition re- liospheric experiments should be flown at gion, where magnetic forces are dominant. least three times per year. This requires spectral coverage extending 2. Spacelab/Sunlab. This program pro- from the near infrared to the far ultraviolet. vides opportunities to fly moderate sized in- Two specific scientific problems can be struments in complementary groups described that illustrate some of the capa- mounted on the Instrument Pointing System bilities of this facility. (developed by the ESA). The experiments will be attached to a pallet fixed in the Shuttle bay. Interactive control of the exper- 1. In the solar atmosphere, the magnetic iments by payload specialists is an impor- fields and fluid motions interact in such a tant part of this program. Flight opportuni- way that at the solar surface the fields are ties should be roughly every two years to highly inhomogeneous. A large fraction of provide for orderly instrumental evolution the magnetic flux is clumped into very in- from Spartan to more advanced programs. tense flux tubes. Field strengths of 1500 3. Facility Class Instruments. To attain gauss contained within flux tubes of a few the highest spatial, spectral, or temporal hundred kilometers in diameter are common resolution requires experiments that take even outside of sunspots. SOT will help an- full advantage of the Shuttle's electrical swer questions of how this clumping arises power, large payload capacity, and data and how the magnetic flux ultimately disap- handling capabilities. Instruments in the pears after reaching the surface. Both proc- Facility Class include telescopes, spectrom- esses may be an essential part of the dy- eters, filters, photometers, polarimeters, and narno mechanism of solar magnetic field imaging detectors covering most of the elec- generation that is believed to be responsi- tromagnetic spectrum. Facility development ble for the solar magnetic field and cycle. begins with the Solar Optical Telescope (SOT), designed to measure physical phe- 2. It has become increasingly clear that nomena from the photosphere through the the solar magnetic fields play a key role in transition region, followed by the Pinhole the heating of both the chromosphere and Occulter Facility (POF), designed to image the corona. Skylab data showed that co- high energy events in the corona and to ronal forms are tied to magnetic field geom- measure dynamical phenomena of the cor- etry while OSO-8 data showed that acoustic ona. Three additional facilities have been shock waves are not sufficiently strong to identified: a soft x-ray facility, a high en- carry the necessary energy into the corona. ergy facility, and an extreme ultraviolet tel- SOT is expected to provide quantitative escope (EUVT). These facilities should be measures of the coupling between photos- developed as soon as possible to comple- pheric magnetic field stresses and chromos- ment SOT and POF. pheric and coronal heating.

32 The Pinhole Occulter Facility coupled with the high resolution studies us- ing SOT, will provide essential knowledge The Pinhole Occulter Facility (POF) is de- of the spatial and temporal relationships signed to image hard x-ray sources with un- between the energy releases in electromag- precedented angular resolution. The goal is netic radiation over the range of a few eV to to study the production of solar energetic over 100 keV. electrons, which constitute the bulk of the initial energy release in solar flares. Stud- ies by POF of the sites and phase relation- The Soft X-Ray Telescope ships of particle acceleration relative to the The primary purpose of the Soft X-Ray Tele- magnetic field and fluid dynamics will pro- scope (SXRT) is to study the thermodynamic vide insight into the physical mechanisms and hydrodynamic structure of the corona in operating. POF will provide more than an relation to its magnetic field patterns. High order of magnitude improvement in spatial to moderate resolution spectrographs pro- resolution. vide plasma diagnostics in the temperature A second major area of study is the mas- range from approximately 106K to 108K. This sive acceleration of large volumes of co- soft x-ray spectral data, arising mainly from ronal plasma in the form of coronal tran- the thermal plasma, is complementary to sients. These mass ejections have been the hard x-ray data from the POF, arising studied in the outer corona at low resolution mainly from non-thermal electron streams. by Skylab, SMM, and the P-78 satellites. Be- Past experience has shown that the soft x- cause of its 50-m length and larger tele- ray region from approxmately 300 A to 1.75 scopes, POF will be able to improve signifi- A (40 eV to 7.1 keV) is the richest spectral cantly the angular resolution of previous region for studies of the corona. The ab- studies, to obtain clean observations of both sence of strong background radiation from the middle and outer corona and to perform the photosphere and chromosphere in this detailed spectroscopy of the coronal spectral region allows the corona to be ob- plasma. Two specific objectives of POF us- served against the disk of the Sun. This has ing these instruments are described below the triple advantage over limb observations in more detail. of greatly simplifying the effects of line-of- 1. Coronagraphs. These instruments will sight integration, of showing the lateral provide new data on some of the processes structure of the corona in two dimensions, by which energy and momentum are depos- and of showing the locations of coronal ited in both the expanding open field re- structures relative to magnetic field patterns gions and in the more slowly evolving in the photosphere. closed magnetic field regions of the corona. Soft x-ray data obtained with Skylab and It is not currently known whether the heat other space experiments have radically al- input to the corona is evenly distributed or tered our concepts of the corona, particu- localized; nor is it known whether the heat- larly with respect to the importance of mag- ing occurs continuously or sporadically. The netic fields in both heating and shaping the coronal structure. However, it is clear from spectral diagnostics of the coronal plasma these same observations that the true co- together with observations of its dynamical ronal structure is unresolved at 2 arcsec, properties at high spatial resolution are ex- pected to provide answers to these ques- which is the best resolution yet attained for tions. a sustained period of time. The SXRT has a design goal of 0.5-arcsec 2. Solar X Rays. Imaging hard solar x spatial resolution. The collecting area of rays will aid in understanding the mecha- 1140 cm 2 is approximately twice the collect- nisms by which electrons are accelerated to ing area of the High Energy Astronomical high energies during the impulsive phases Observatory(HEAO)-2 telescope and 27 times of solar flares. It is currently thought that that of the experiment on Skylab. As such it hard x rays are produced by the impact of will offer major advances in both spatial these electrons on the denser regions of the resolution and sensitivity. lower atmosphere. Observations using POF, Two examples selected to illustrate the

33 objectives of the SXRT are (1) study of the portant components of the energy transport. heating of coronal plasma and (2) investiga- Two objectives for the EUVT are (1) to un- tion of the thermal properties of flares and derstand the mechanisms giving rise to the the conversion of stored magnetic energy fluid motions in the transition region and into thermal energy during the flare main upper chromosphere and (2) to understand phase. Coronal heating is known to fluc- the multifaceted energy transport within tuate spatially on scales down to 1 arcsec or and through these layers. How are the up- less and temporally on scales of minutes. flows and downflows related? Are the driv- The spatial resolution of 0.5 arcsec provided ing forces hydrodynamic or are magnetic by the SXRT should be sufficient to isolate forces essential? How does the solar wind regions in which the heating fluctuations emerge from these more massive flows? and fluid motions are relatively coherent. By These questions are typical of those that combining the SXRT with the SOT, the fluc- can be addressed by the EUVT, particularly tuations in coronal heating and fluid motion when used in concert with the SOT, the can be correlated with related fluctuations XUVT, and the SXRT. in the chromosphere and with photospheric magnetic field fluctuations. High Energy Facility Major flares typically heat the thermal plasma in the corona to temperatures in ex- cess of 107 K over volumes that are large The primary purpose of the High Energy Fa- compared to those in which the non-thermal cility is to study acceleration of ions. Obser- electrons are concentrated. Just how the vations acquired during the last solar maxi- thermal flare plasma relates to the preced- mum demonstrated that gamma-ray ing impulsive non-thermal flare events is measurements open up a new window for unclear. The SXRT, in combination with the studying particle acceleration on the Sun, POF and the SOT, will provide the type of the most powerful natural particle accelera- data needed to answer such questions. tor in the solar system. Gamma-ray lines from many different elements (C, H, O, Fe, The EUV Telescope Mg, Sc, N and Ne) have been detected in solar plasmas. SMM observations indicate The primary purpose of the EUV Telescope that ion acceleration to about 10 MeV is a (EUVT) is to study the upper chromosphere common phenomena in solar flares. In addi- and the chromosphere-corona transition re- tion, energetic neutrons (50-500 MeV) have gion with high spatial resolution (<_ 0.5 arc- been detected. Because of these results, sec). Within these regions the temperature there is strong interest in new observations rises from below 104 K to over 106 K in a with instrumentation of high sensitivity, as short distance. The principal radiation from could be provided by a high energy facility. these reaions lies in the EUV and XUV at The High Energy Facility, together with wavelengths below 1600 A. The exceedingly other solar facilities such as POF and SOT, high temperature gradients lead to a major provides a powerful tool for addressing the flow of energy from the corona back down to fundamental processes of particle accelera- the chromosphere by thermal conduction. tion. Additionally, there are strong vertical fluid currents with average mass fluxes exceed- ing those in the solar wind by about two Explorers for Solar and Heliospheric Physics orders of magnitude. The upper chromos- Studies phere and transition region are the least understood regions of the solar atmosphere. The active utilization of the Explorer Pro- The temperature gradients are so steep that gram would be a great benefit to solar and electrons in the high energy tail of the ther- heliospheric physics. Rather than endorse mal velocity distribution penetrate into re- any particular mission, however, we recom- gions of much different temperature giving mend that the selection be the result of a rise to non-Maxwellian distributions and a competitive process that encourages innova- breakdown of classical thermal conduction. tion, in accord with the recent recommenda- Moreover, the vertical fluid currents are im- tion of this committee contained in A Strat-

34 egy for the Explorer Program for Solar and low the solar altitude accessible to the Solar Space Physics, NAP 1984. We briefly present Probe. This lower region of acceleration of two examples of such missions that are dis- the solar wind can be probed with radio cussed in greater detail in that report. techniques (time delay, spectral line broad- ening, scintillation, and Faraday rotation) Advanced Solar-Wind Composition by placing a spacecraft carrying a radio Explorers beacon (at several frequencies) on the far side of the Sun from the Earth. Orbits could A complete chemical and isotopic analysis be picked so the ray path would either of the solar wind would provide information slowly circle around the solar disk or move on some, and probably all of the following along a solar radius vector. topics: improved knowledge of solar-wind mass/charge fractionations which, in turn, would shed light on the solar-wind acceler- Long-Term Solar and Heliospheric ation process and refined solar system Measurements abundances; tests of the fundamental as- sumption that the Sun and planets formed Solar and heliospheric phenomena vary from a common reservoir; limits on inte- over a great range of time scales. Well-es- grated solar surface nuclear processes; and tablished, cyclic phenomena occur at the 11- constraints on solar structure and evolution. year and 22-year sunspot and magnetic Instrumentation to be flown on ISPM and cycle periods. Careful study of the long-term WIND will allow determination of the ele- time dependences of selected solar and he- mental and ionic-charge compositions of all liospheric parameters will provide valuable major solar-wind ions from H through Fe. insight into fundamental solar and helios- Advanced instrumentation is required for pheric processes that is not available in any studies of the rarer elements and isotopic other way. abundances. Two different, complementary approaches appear to be possible within the Solar Constant budgetary constraints of the Explorer pro- Variations in the solar radiative output not gram. In one approach an advanced ener- only have impact on the Earth's ionosphere getic ion mass spectrometer would be and atmosphere, but also provide funda- placed on a spacecraft that spends a signifi- mental knowledge about the Sun and its cant amount of time beyond the Earth's bow internal structure and dynamics. For our un- shock. Direct samples of coronal material derstanding of deviations of the Sun from its can also be provided by energetic solar par- equilibrium steady state to progress, long- ticle measurements spanning the energy term satellite monitoring of the total solar range from about 10 keV/nucleon to 100 energy output and its distribution over MeV/nucleon which would significantly en- wavelength should take place. Unfortu- hance the interpretation of the solar wind nately, there is no one agency dedicated to measurements by providing data for many the support of long-term monitoring of this additional elemental and isotopic species. type, and no one agency has devoted suffi- Because this set of instrumentation would cient resources or interest in this area to do probably be quite massive, there might be it properly. Long-term, synoptic observa- few, if any, other instruments on board. Al- tions are often the only means of discover- ternatively, it is possible to perform a solar- ing linkages in the behavior of elements of wind sample return mission in which high- the system, despite the absence of clear purity collector material is exposed to the cause-and-effect relationships. solar wind for about 2 years, and is then retrieved for performance of chemical and Long-Term Monitoring of Interplanetary isotopic analyses in terrestrial laboratories. Particles and Fields

The study and elucidation of solar and ter- Coronal Radio Probe Explorer restrial interactions that are mediated by The objectives of this mission would be to the solar wind or by solar energetic parti- obtain new data on the coronal plasma be- cles requires a commitment to long-term

35 and continuousmonitoringof the interpla- phere and, at present, provide the only pos- netary plasma, magnetic field, and cosmic sible means of detecting the boundary rays. For example, further study of sus- between the solar system and the interstel- pected 22-year effects in the intensity of lar medium. cosmic rays may lead to better understand- Finally, IMP-8 is, at present, the only ing of the solar magnetic cycle and the tur- means of studying the solar wind and its bulent dynamo that is the source of the so- effects on the terrestrial environment. lar magnetic field. Studies of magnetohydrodynamic turbulence are seri- ously hampered by discontinuous data rec- Research and Analysis ords caused by incomplete satellite track- ing. The early stages of instrument development (preflight through testing with sounding rockets) are supported by the R&A program. Theory and Modeling Several such developments are crucial to the success of the flight programs described Magnetic field reconnection should form one in the paragraphs above. Examples are a important aspect of theoretical studies sup- multilayer mirror for imaging solar x rays, a ported by ISTP, as should the study of large- space qualified instrument for mapping so- scale plasma flows within the magnetos- lar oscillations with the SOHO spacecraft, phere and ionosphere. In the Plasma Turbu- and advanced solar-wind and energetic-par- lence Explorer Study report, the need for a ticle composition analyzers. multi-spacecraft analysis of interplanetary Another component of the solar and he- fields and fluid velocity data coupled with liospheric R&A program is obtaining and theoretical studies was proposed as one analyzing correlative data from many types means of progressing in understanding of of ground-based observatories. The value of magnetohydrodynamic turbulence. Such a solar observations from SMM, the SOHO study, which might include three-dimen- spacecraft of ISTP, the Shuttle, and the sional modeling of MHD turbulence using space station/platform can be greatly en- Cray-class computers, might lend itself to a hanced by simultaneous observations of ad- "non-hardware" mission because the man- ditional facets of the phenomena under power and computer resources required ex- study. Examples include coronagraphic and ceed the nominal magnitude of awards un- magnetographic observations from ground- der the STTP. Preliminary work in this area based solar observatories, maps of solar ra- has been supported by R&A funding, guest dio emission obtained with the Very Large investigator grants under the ISEE program, Array and other facilities, and the observa- and other institutional support provided by tion of scintillation of radio sources caused NASA. by coronal and interplanetary disturbances. Finally, there are several types of labora- Mission Operations and Data Analysis tory and suborbital research that comple- ment and enhance the rest of NASA's solar An example of an extended mission requir- and heliospheric physics program and ing MO&DA support may be provided by should therefore be supported by NASA as ISPM. The prime mission phase allows for a well as by other agencies (e.g., NSF, DOD). pole-to-pole passage during solar maximum This research includes laboratory simula- conditions. If as expected, ISPM survives tions of solar plasma processes, such as beyond the second polar pass, an extended magnetic reconnection in solar flares, and mission could provide invaluable data on the measurement of cross sections required solar and heliospheric conditions at high so- to interpret solar data. Long duration bal- lar latitudes during other portions of the so- loon flights may prove to be a very cost lar cycle. effective and valuable technique for obtain- A second example is the complement of ing data on hard x rays and gamma rays deep-space planetary missions, Pioneer 10 emitted during solar flares. and 11 and Voyager 1 and 2. These contrib- The four principal components of the R&A ute unique information about the helios- program--theory and analysis, instrument

36 development, correlative observations, and Mission by decreasing the period of the ec- complementary research--are listed here in centric solar orbit to allow more than one approximate priority order. The scientific re- close solar passage within the useful life- turn from the R&A program is high, and we time of the spacecraft. Advanced propulsion recommend an increase in its level of fund- is also under consideration by the planetary ing starting in 1990, after the peak spending community for a multiple asteroid rendez- years for UARS and ISTP. vous mission. Thus, we recommend that NASA either accelerate its development of this technology or join forces with some Technology Development other agency working on advanced propul- sion. The new technology requirements of the so- lar and heliospheric physics program can be conveniently divided into components, Priorities instruments, and spacecraft capabilities. Many different instrument and facility de- We assume that the following missions are velopment requirements have been dis- approved and will be flown: International cussed in the paragraphs above. Except for Solar Polar Mission, solar instruments on the components listed immediately above, Spacelab 2 and Spartan 2, and the Solar development of these instruments/facilities Optical Telescope Facility. For new mis- requires the normal sequence of detailed sions for solar-heliospheric physics, we design and hardware development, but lit- have identified the first and second priori- tle or no new technology. Thus, although ties. the developments require significant fund- • WIND and SOHO components of ISTP ing for the design and test of space-quali- • Pinhole Occulter Facility fied hardware, the risks of significant In addition, we have prioritized other pro- schedule slips or cost growth are not high. grams in the following categories: All the approved solar and heliospheric • Major Free-Flying Missions physics missions, ISTP, and the solar instru- -- Solar Probe ments/facilities planned for the Shuttle or -- Solar Polar Orbiter space station/platform can be implemented • Explorer Missions with existing spacecraft technology; i.e., no -- Solar-heliospheric Explorer missions enabling technology development is re- at the rate of one per two or three quired for those missions. New technology years is needed for the Solar Probe and SPO, how- • Shuttle Missions ever. The concept of obtaining data with a -- Additional moderate-sized solar in- spacecraft located 3 solar radii from the so- struments beyond the Spacelab-2 ex- lar surface is predicated on the develop- periments ment of a heat shield that keeps the instru- -- Spartan missions to succeed the ments and spacecraft within operating sounding rocket program temperature range, without ablation of -- Additional flights of the SOT with co- enough material to prevent the observation observing instruments and enhanced of the ambient coronal plasma. NASA has focal plane instruments already started the development of such a -- Additional solar facilities: Soft X-ray heat shield and we recommend that this de- Telescope, High Energy Facility, and velopment be continued at a pace consistent EUV Telescope Facility with a new start for the Solar Probe in 1991. • Space Station Missions Advanced propulsion is required for the -- Deployment of Solar Optical Tele- SPO. Our proposed time line of mission se- scope and other facility class and ap- quences is based on the assumption that propriate instruments as the start of such a capability, probably based on solar the Advanced Solar Observatory powered ion thrusters, will be available by There are several important activities that 1997. If it were available, a low-thrust pro- are not specifically mission related. These pulsion system could also be used to en- include the Theory and Modeling Program hance the scientific return of the Solar Probe and Research and Analysis. Both of these

37 SOLARANDHELIOSPHERICPHYSICSPROGRAM

YEARS 851 1 I.1.1.i,,1°1,31.1 [ 1,,I.I. POLARCROSSING ISPM

WIND ISTP

CLUSTER_ _SOHO SOULRPROBE SOLARPROBE /

SOLARPOLARORBITER EXPLORERS EXPLORER

SPACELABtSUNLAB SL-A SL-B SL-C SL-D SL-E I_

SOLAR SOT[ FACILITYDEVELOPMENT

SOUNDINGROCKET]SPARTAN

RESEARCHANDANALYSIS [

MO ANDDA

FIGURE5

activities are prerequisites for a healthy situ measurements of the evolution of the program in solar-heliospheric physics. heliosphere at one solar longitude. Another Within the Research and Analysis program example is a Heliosphere Boundary Probe we assign priorities in the following order: intended to locate and explore the helio- (1) theory and analysis, (2) instrument devel- pause and to explore the particle, field, and opment, (3) correlative observations, and (4) plasma environment of interstellar space. complementary research. Funding constraints also caused us to re- The time line shown in Figure 5 for the duce the capabilities of several proposed solar and heliospher/c physics program re- missions. For example, an early study of the sulted from considerations of scientific Solar Probe (Starprobe: Scientific Rationale, priorities, funding constraints, technological J.H. Underwood and J.E. Randolph, JPL Publ. readiness, and the phase of the solar activ- 82-49, 1982) with an experiment payload that ity cycle. included imaging, drag-free experiments, The program of solar-heliospheric physics and a maser clock was estimated to cost discussed here is constrained by funding. approximately $1 billion. The mission rec- As a result we excluded a number of excit- ommended here, however, addresses only ing missions that might be reconsidered in our highest priority objective, i.e., the inves- the twent¥-Iirst century. For example, a he- tigation of the sources ot the solar wind. liostationary orbiter, whose period equals More comprehensive missions should be the rotation period of the Sun, would permit considered for implementation early in the continuous observations of the evolution twenty-first century. and decay of solar activity and unique in

38 8 DETAILED MISSION PLANS--PLASMA PHYSICS

Introduction Major Programs

The critical scientific objectives of space International Solar-Terrestrial Physics plasma physics are to Program • trace the transport of energy, momen- The International Solar-Terrestrial Physics tum, and matter from the Sun, through the Program (ISTP) is being planned by NASA, interplanetary medium, across the magne- ISAS0 and ESA in order to develop a com- tospheric boundaries, through the magne- prehensive global understanding of the pro- tospheres and ionospheres into and out of duction and flow of energy within the Sun, the upper atmospheres; the heliosphere, and Earth's magnetosphere • understand the physical processes that and ionosphere. As of the summer of 1984, control the entry, transport, storage and re- the ISTP program is planned to begin devel- lease of plasma and of energy and momen- opment in 1986 and will continue operations tum in magnetospheric systems, with spe- through the 1990s. The program will define cial emphasis on understanding basic the complex relationships that exist within physical processes not readily accessible to the solar-terrestrial system. Here we de- laboratory investigation; scribe each of the six spacecraft compo- • investigate the processes that couple nents of ISTP. distinct parts of the system including the solar wind, magnetospheres, ionospheres, WIND. WIND is proposed to be built and and upper atmospheres; and launched by NASA (1989) as the first of this • describe and understand fully the series. It will utilize lunar swing-bys to sources and sinks of magnetospheric plas- maintain its apogee on the day side of Earth mas. and thus to survey the upstream region out These objectives are implicitly included in to distances of 250 RE during perhaps the the report, Solar-System Space Physics in first two years after launch. After that time, the 1980"s: A Research Strategy prepared by plans include the possibility of placing the Committee on Solar and Space Physics WIND into a halo orbit about the L_ libration in 1980. Mission planning must recognize point. WIND will make correlative measure- the requirement to perform measurements ments with the rest of the network of space- directed toward these objectives. Integration craft in the ISTP program (SOHO, POLAR, of theoretical activities in support of mission EQUATOR, GEOTAIL, and CLUSTER). WIND design and development and in analysis of will measurements will accelerate progress in • investigate sources, acceleration mecha- understanding the complex magnetospheric nisms, and propagation processes of ener- system. getic and solar wind particles in correlation with SOHO; • provide the complete solar wind plasma, energetic particle and magnetic field inputs Program Descriptions for magnetospheric and ionospheric studies to support POLAR, EQUATOR, GEOTAIL, In this section a mix of major, moderate, and CLUSTER; and small programs with associated • determine the magnetospheric output MO&DA and R&A resource requirements is (particles, beams, and waves reflected from discussed. The near-term program through the bowshock and the magnetopause) in the the early 1990s and a longer-term program upstream region; that utilizes the Shuttle/Space Station/Plat- • investigate basic plasma processes oc- form systems beyond 1992 are described. curring in the solar wind near Earth; and

39 • provide baseline observations in the • help determine the role of internal mag- ecliptic plane to be used in correlation with netospheric substorm trigger mechanisms observations made at high heliospheric lati- and separation of such effects from external tudes by the ISPM spacecraft. trigger mechanisms through correlations with SOHO and WIND; POLAR. POLAR is one of the three magne- • provide direct observations of the inter- tospheric components of ISTP. It would be actions between geomagnetic tail and iono- built and launched by NASA (1991) into an spheric plasmas in the equatorial magne- eccentric polar orbit having perigee at ap- tosphere; proximately 2 RE and apogee at about 8.5 • measure the transport, energization, and RE. It will make correlative measurements of storage of ionospheric and tail plasmas in plasma, energetic particles, and electric the near-Earth plasma sheet and ring cur- and magnetic fields in conjunction with rent, correlating data with those from GEO- WIND, EQUATOR, GEOTAIL, and CLUSTER. TAIL and POLAR; and POLAR will have the following magnetos- • measure the coupling between the solar pheric and ionospheric plasma physics ob- wind and the magnetosphere at the sub- jectives: solar magnetopause, correlating data with • determine the role of the ionosphere in those from WIND and SOHO. substorm development and in the overall magnetospheric energy balance, correlating GEOTAIL. GEOTAJL is the third magnetos- data with those from EQUATOR and GEO- pheric component of ISTP. It would be built TAIL; by Japan and launched by NASA (1991) into • measure plasma energy input through a lunar swing-by orbit in order to maintain the dayside cusp region, correlating data an apogee in the distant (80-250 RE) magne- with those from WIND and SOHO; totail for a period of about 1 year. After this • determine characteristics of ionospheric time, a propulsion system will place GEO- plasma outflow and energized plasma in- TAIL into an equatorial orbit of 8 RE by 20 Re flow to the atmosphere, in support of the for making detailed measurements of sub- UARS mission; storm processes in that region. GEOTAIL • study the characteristics of the regions will have the following important magnetos- wherein auroral plasma is accelerated, cor- pheric objectives: relating data with those from CLUSTER; • determine the overall plasma and field • provide global, multispectral auroral im- properties in the distant geomagnetic tail ages of the footprint of magnetospheric en- region; ergy deposition into the ionosphere and up- • determine the relative roles of the dis- per atmosphere at high latitudes; and tant and near geomagnetic tail in substorm • measure magnetic field signatures of processes, and in the overall magnetos- field-aligned currents. pheric energy balance correlating data with those from EQUATOR, POLAR, and WIND; EQUATOR. EQUATOR is another of the • study the initiation of reconnection proc- _hree magnetospheric components of the esses in the geomagnetic tail and observe ISTP Program. It would also be built and the microscopic properties of the energy launched by NASA (1991) into an equatorial conversion mechanisms in this reconnection orbit with perigee at about 2 RE and apogee region, correlating data with those from near 12.4 RE. It will make correlative meas- EQUATOR, CLUSTER, and POLAR; urements of plasmas, energetic particle • separate the relative contributions of the populations, and of electric and magnetic ionosphere and solar wind to the geomag- fields in conjunction with POLAR, GEOTAIL, netic tail plasma; and and CLUSTER. EQUATOR will have the fol- • study the entry, energization and trans- lowing magnetospheric objectives: port of plasma in interaction regions such • determine overall magnetospheric en- as the inner edge of the plasma sheet, mag- ergy balance and the effects of substorms in netopause and bow shock. populating the ring current and inner mag- netosphere, correlating data with those from CLUSTER. CLUSTER consists of one main POLAR and GEOTAIL; and three companion spacecraft, each hav-

4O ing on-orbit propulsion capability to adjust the following objectives that are important inter-satellite separations from 100 km to up to the magnetospheric plasma physics in- to several Earth radii. The CLUSTER would volved in the overall ISTP program: be an ESA program designed for launch • study the solar wind plasma, collision- either by an Ariane IV booster or by a Space less shocks in the solar wind and other ir- Shuttle flight. Data from CLUSTER will be regularity structures, correlating data with correlated with those from other ISTP space- those from WIND; and craft as part of the overall international pro- • provide information on solar wind input gram. The proposed mission plan is to place functions for use in interpreting data from the CLUSTER spacecraft into a polar orbit 20 WIND, POLAR, EQUATOR, GEOTAIL, and RE x 3 RE. CLUSTER will perform correlative CLUSTER. multipoint measurements at known separa- tions of its four individual spacecraft, and will Explorers for Magnetospheric Plasma • explore the boundary regions of the Physics magnetosphere as a readily accessible ex- ample of the sharp interface between two While many of the important global aspects cosmical plasmas and thereby to investi- of magnetospheric plasma physics will be gate the detailed processes by which mass, addressed by the comprehensive ISTP mis- momentum, and energy are transported sions involving WIND, EQUATOR, POLAR, across boundaries such as the magneto- GEOTAIL, and CLUSTER, there are specific pause; scientific objectives and measurements that • study the magnetic reconnection proc- are more limited and can only be addressed esses and the small scale MHD structure by Explorer-class missions of low-to-moder- and plasma acceleration associated with re- ate cost. Recent examples include the Dy- connection regions; namics Explorers (DE) spacecraft, measure- • study MHD turbulence, vortex formation, ments from which have significantly and eddy diffusion, especially in the polar advanced our understanding of magnetos- cusp and boundary regions; phere-ionosphere coupling processes; and • investigate the structure and properties the Active Magnetosphere Particle Tracer of collisionless shocks, including the bow Explorers (AMPTE), which investigated shock, and the associated wave generation plasma entry into the magnetosphere via and particle acceleration; tracer ion releases in the solar wind. These • determine the small scale properties of and previous Explorer missions have been the solar wind flow around the Earth; and the mainstay of research in space plasma • utilize the four-spacecraft configuration physics and their availability in the future to determine unambigously the three-dimen- is crucial to the development of this disci- sional shape and dynamics of magnetic pline. structure with scale sizes from 0.1 RE to 10 Explorer missions in space plasma phys- Rr (four-point measurements can determine ics generally require orbits that are high the curl of a vector field, i.e., the spatial (greater than 1 RE) altitude and are intended current density). to provide measurements over extended pe- riods of time (greater than 1 year), i.e., not SOHO. The SOHO spacecraft is proposed to compatible with Shuttle or Space Station or- be three-axis stabilized to allow a variety of bits. Potential missions have been studied optical instruments to view the solar surface by NASA in the past (e.g., Plasma Turbu- and corona from an L_ libration point orbit. lence Explorer) but have not been carried SOHO is proposed to be an ESA program, out because of budget limitations. Other il- and will be designed to be launched by lustrative mission concepts are given in the either an Ariane IV booster or from the report A Strategy for the Explorer Program Space Shuttle (1993). Although its primary /or Solar and Space Physics, NAP, 1984. objectives are to observe solar phenomena Among these missions are spacecraft to (see Chapter 7), it is planned to carry study plasma instrumentation for in-situ measure- • acceleration at heliospheric shocks, ments of the solar wind. SOHO will have • magnetopause structure and dynamics,

41 • activeplasmainjection(seeding)experi- in the southwestern United States, as well ments,and as by aircraft-borne instrumentation. • ionosphericinstabilitiesandturbulence. The CRRES payload will include the fol- Thesemissionconceptsrepresentonly a lowing: fewexamples,and a solicitationof thesci- • tracer experiments in which releases of entific communitythroughtheAO process foreign elements can be used to trace geo- will undoubtedlyproducea varietyof mis- magnetic field lines, assess natural electric sionideasaddressingfirst-classscientific fields and potential structures, and measure problems.It shouldbe notedthatthe instru- winds; mentationandspacecrafttechnologyfor the • modification experiments involving mas- few illustrative missionsgivenaboveis all sive releases that can significantly perturb within currentstate-of-the-art,and no new the ambient ionosphere; and developmentsare necessary. • simulation experiments in which re- leases are used to simulate plasma physical phenomena not amenable to laboratory ex- Active Experiments perimentation. Once the CRRES is transferred to a geos- Active experiments, where the environment tationary transfer orbit, several high alti- can be perturbed with injections of parti- tude releases will occur. These releases are cles, beams, or waves and then studied to primarily for tracing magnetic field lines determine its responses, are a unique op- and for modifying the immediate region at portunity to perform laboratory-style experi- low latitudes just at the plasmapause. ments in space. Such experiments are ex- tremely valuable in aiding our Tethered Satellite System understanding of basic plasma processes because the experimenter has a great deal The Tethered Satellite System (TSS) is a of control of the experiment and can there- joint project for NASA and Italy's National fore address sharply focused questions. Ex- Research Council. NASA is responsible for periments in this category include the fol- producing the Shuttle-borne deployment lowing: mechanism and tether, while the Italian Na- tional Research Council is to furnish a sat- Combined Release and Radiation Effects ellite system to carry scientific experiments Satellite attached to the tether. The tether may be Combined Release and Radiation Effects either a conductor or insulator, depending Satellite (CRRES) is a free-flying spacecraft on the type of scientific mission. It can be mission undertaken jointly by DOD and utilized to study electrodynamic processes NASA. The NASA portion of the mission in- in the ionosphere or atmospheric phenom- volves chemical release experiments solic- ena in regions down to 130 km where few measurements have been made and are dif- ited by an AO, evaluated by a peer review committee, and selected by NASA/OSSA. ficult to achieve by other means (rockets or This chemical release program is designed satellites). Here we discuss only the con- to replace partially the cancelled Chemical ducting tether missions and refer to Chapter Release Module program, and has research 9 for discussion of atmospheric tether mis- sions. goals consistent with those in the Kennel report. Two electrodynamic tether missions are CRRES is a two-part mission. The space- planned, TSS-1 and TSS-3. TSS-2 is to be an craft will be launched initially into a low- atmospheric mission (see Chapter 9). TSS-1 Earth-orbit (LEO) where it will remain for a is planned for a mid-1987 Shuttle launch, period of 45 to 90 days. During LEO, se- TSS-3 to fly about mid 1990. These missions lected chemical releases will be carried out will be in a nominal 28 ° inclination orbit at at specific locations designed to be observa- 300-400 km altitude. On TSS-1, the conduct- ble from suitable ground-based diagnostics ing tether and its attached satellite will be facilities such as the Arecibo and Jicamarca deployed upward to a distance 20 km above Observatories or high-altitude ground sites the Shuttle. The tether will be attached to

42 the conducting surface of the satellite, and forms similar to the STO. Such equipment through an electron gun to the orbiter's as that used to inject large amounts of elec- ground plane, to return electron current to tromagnetic wave energy into the iono- the ionospheric plasma. The entire duration sphere and magnetosphere, or inject power- of the TSS-I test will be 36 hours. Scientific ful electron or ion beams into those regions, experiments will be limited on TSS-1, which can benefit greatly from on-orbit residence is an engineering test of the TSS, while times much greater than the 7 to 9 days TSS-3 is planned to carry a more sophisti- available on Shuttle missions, but an or- cated scientific payload. derly program of preliminary developmental The objectives of TSS-1 and TSS-3 are the flights on the Shuttle would allow final de- following: velopment of a flight-qualified inventory of • determine the current/voltage character- such equipment for use in plasma physical, istics of the system at high voltages; magnetospheric, and ionospheric research • study management of electrical charge on a station or platform of several months to on the orbiter; a year mission duration. The effects of these • produce Alfven waves in the ionosphere active experiments can be diagnosed with using the tether current source; near-by probes and through the constella- • produce LF (< 1 kHz) waves by modula- tion of magnetospheric free-flying satellites tions of the tether current and study their from programs such as ISTP and the Explor- propagation; ers. • study nonlinear plasma physical proc- Spacelab-2 esses in the dynamic sheath around the sat- ellite; and Spacelab-2 (SL-2) is a multidisciplinary mis- • utilize the conducting tether as an effi- sion carrying 12 PI-class experiments on a cient antenna for transmitting diagnostic nominal 7-day mission planned for launch VLF waves to distant receivers. in April 1985 into a 50° inclined orbit. Three SL-2 experiments are plasma physical or ionospheric in nature. The VCAP experiment Shuttle/Spacelab Programs involves an electron gun capable of pulsed operation up to 500 kHz at peak currents of The Shuttle/Spacelab capabilities are espe- 0.1 A at 1 kV. It also has diagnostics, in- cially suited to accommodate active experi- cluding a capacitive probe to measure orbi- ments, since they are massive and have en- ter charge states, and can carry out orbiter ergy, power, and heat rejection charge management experiments. A free- requirements that exceed the usual capabil- flying Recoverable Plasma Diagnostics ities of unmanned free-flyers. Of particular Package (RPDP) will measure electromag- interest is the use of this carrier to perform netic interference levels in and around the active experiments in which electromag- orbiter cargo bay, diagnose effects of the netic wave energy, energetic charged parti- VCAP electron beam (waves and particles), cle beams, plasmas, and neutral gases, and and perform wake and sheath measure- controlled releases of various chemical spe- ments near the orbiter (up to 1 km separa- cies are effected during 7- to 9-day mis- tion). A third experiment uses dedicated en- sions. In addition, these instruments can be gine bums of the Shuttle's Orbital reflown on subsequent Shuttle missions in Maneuvering Subsystem (OMS) in a series either their original form, or refurbished or of active experiments for plasma depletion upgraded as results from previous flights studies in ionospheric and radioastronomi- may dictate. cal areas. The primary diagnostics employ An attractive use of such Shuttle/Spacelab ground-based radars and optical imaging missions is also apparent: active experi- systems. ment instrumentation can be developed in an evolutionary fashion, using the Shuttle/ Spacelab Reflight Missions Spacelab flights as test beds for develop- ment of instruments in a form for later use A series of reflight opportunities utilizing in the Space Station and/or associated plat- existing Spacelab instruments can be ex-

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Y plotted. An example is the EOM-1 mission, • perform high-current, high-voltage elec- on which it is planned to carry the Japanese tron beam experiments and study the beam- SEPAC instrument and the diagnostic AEPI plasma discharge and artificial auroral dis- instrument to support it, both flown on SL-1. plays; These instruments will carry out electron • perform field-line tracing and electrical beam injections and observations associ- potential structures diagnostics using the ated with geomagnetic field line tracing, electron beam from SEPAC; and electrical potential structures, beam-plasma • perform Shuttle wake and sheath meas- discharge phenomena, artificial auroral dis- urements, antenna radiation efficiency esti- plays and neutral or plasma gas injections. mates, electron beam evolution, and OMS Other reflights-of-opportunity should be thrusher firings diagnostics using the RPDP, planned or identified. AEPI, and ground-based instrumentation.

Space Plasma Lab Program Space Station/Platform Programs Space Plasma Lab-1 (SPL-1) is planned for a launch on a near-polar (77°) orbit at about The Space Station/Platform capability pro- 350-500 km in December of either 1988 or vides an ideal vehicle for missions involv- 1989, depending upon budget constraints ing the active experiments using energetic and development schedules. It is to carry a particle beams, wave energy injections, and wave injection instrument with capability to chemical releases. The capability to re- radiate VLF from 1 to 30 kHz with up to 1 kW cover, service, and change out scientific ex- power input to a dipole antenna of length periments on-orbit opens new possibilities between 100 and 300 m. A Canadian-fur- for experimentation using these heavy, nished HF transmitter and receiver will power consuming experiments that can ben- transmit and receive sounding signals be- efit from extended mission durations in low- tween 100 kHz and 30 MHz. The SEPAC in- Earth orbits. strument from SL-1 Will perform electron It is desirable that such active instrumen- beam injections, with the AEPI instrument to tation be developed in an evolutionary man- support it with optical observations and a ner using earlier Shuttle/Spacelab flight op- set of newly developed plasma diagnostics portunities for test-bedding and check-out. (TEBPP). To support the active experiments Since the Space Station architecture (in- by making in situ measurements at prede- cluding the question of inclusion of one or termined distances along magnetic field more science platforms) remains to be deter- lines connecting to the orbiter, a RPDP will mined, only general statements can be be flown. made. One can suggest missions up to 6- The scientific objectives of SPL are to months duration on platforms that provide • test the ability of a dipole antenna in up to perhaps 25 kW of power, with energy the ionospheric plasma to radiate VLF wave storage units capable of furnishing high- energy; peak-powers for pulsed operation of active • study the nonlinear plasma physical experiments. Platforms in near-polar orbit phenomena around the high-voltage dipole would be ideal for wave and beam injec- antenna; tion, while lower inclinations may be useful • study wave-particle interactions in the for missions involving the TSS. A compre- trapped electron population produced by hensive study of possible missions and pay- VLF signals from an antenna above the F- loads can be found in the final report of the layer maximum; science study group: Solar-Terrestrial Ob- • perform VLF propagation studies for all servatory, October 1981, and in Solar-Terres- paths possible out to 100 km from the orbiter trial Observatory: Conceptual Design and and including radiation to ground stations; Analysis Study, April 1982, both NASA Mar- • perform bistatic HF sounding measure- shall Space Flight Center documents. ments with orbiter and RPDP receivers to The objectives of an STO-like Space Sta- study ionospheric irregularities, travelling tion Platform are to increase the under- ionospheric disturbances, and coupling to standing of wave-particle processes; magne- gravity waves; tospheric-ionospheric mass transport; the

44 globalelectriccircuit; ionosphere irregular- ments at relatively low cost and low risk. ity structure, travelling ionospheric disturb- Developmental testing of spaceflight hard- ances, and their coupling to atmospheric ware can be accomplished readily on rocket gravity waves; electrodynamic tether inter- flights. Furthermore, many auroral studies actions including Alfven, magnetosonic, and active experiments (e.g., beam experi- and plasma wave production; non-linear ments, chemical releases) can be accom- plasma physics; beam-plasma interactions; plished most cheaply and most readily and plasma physics experiments in micro- through rocket campaigns. gravity and without walls. Finally, aircraft facilities can also be a The latter area is of special interest, and valuable asset. Aircraft are utilized to meas- should be examined carefully. There are ure electric fields associated with weather laboratory plasma experiments that can be systems, for example. Also, testing of opti- defined ideally but not carried out on Earth cal systems in safe and inexpensive ways is because of the presence of chamber walls. possible. Such testing can be most helpful Some of these are related to the fusion en- in preparation for full spaceflight develop- ergy program. For example, storage rings ment work. Rapid deployment capability is could be formed taking advantage of zero- also an attractive feature of aircraft facili- gravity to eliminate support structures that ties. represent plasma sinks or contribute un- In summary, we recommend the mainte- wanted impurities into the experimental nance of a strong suborbital program where plasma. A set of plasma physics experi- it makes scientific, technical, and financial ments should be identified and examined sense. Those programs that can use Shuttle for possible performance in a Space Station capabilities effectively should be encour- facility. aged to use the Spartan and Hitchhiker sys- tems, for example, but where scientific ob- jectives can be achieved effectively, Suborbital Programs expeditiously, and at lower cost by use of balloons, rockets, or aircraft, these alterna- The suborbital programs have traditionally tives should be provided. included balloon, rocket, and aircraft sys- At present there is a funding level of ap- tems. For some types of measurements proximately $3M for rocket and balloon pay- these programs are appropriately being load in the space plasma physics budget. supplanted by Shuttle and Space Station As illustrated in our budget timeline, we programs. However, there are measure- recommend that this level be increased ments of the stratosphere, middle atmos- modestly (to about $4M) through FY 88 and phere, and ionosphere for which the mainte- then be decreased. We recommend that the nance of vigorous suborbital capabilities is Spartan program be funded at the $2M level desirable and, indeed, imperative for the in FY 85 (in part with funds otherwise allo- unique capabilities not achievable with Shuttle or satellites. cated to the rocket program). We then sug- gest that by FY 87 there be a constant level Balloon payloads can measure atmos- of funding, at about $4M/yr, through the mid pheric electric fields and atmospheric poten- 1990s in the Spartan program and an equiv- tials. Payloads for magnetosphere studies alent amount for the Hitchhiker program. can include bremsstrahlung X-ray sensors, photometers, and even neutron (or other) sensor systems. Balloons also provide an in- Planetary Magnetospheres expensive way to test new instrument con- cepts. Furthermore, a relatively long dura- Studies of the plasma environments of other tion set of measurements can be made in a planets can yield data relevant not only to nearly constant location in latitude, longi- planetary science but also to understanding tude, and altitude. Correlations with ground Earth's environment in broad scientific radar and with spacecraft measurements in terms. this way have proven very efficacious. Magnetospheric structure and dynamics Similarly, rockets provide unique advan- depend upon many aspects of the interac- tages in terms of specific local measure- tion between an object and its environment.

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s The planet or other central body (we include tion rate, and internal plasma source, Io, is moons embedded in corotating planetary radially distorted into a disc-like configura- plasmas) may be unmagnetized (Venus, pos- tion modulated at the 10-hour rotation pe- sibly Mars, major moons) or magnetized riod. Indeed, the 10-hour modulation and (Mercury, Jupiter, Saturn, possibly Mars control by Io of radio frequency emission and/or Io); may lack an atmosphere (Mer- probability were first noted by Earth-based cury, Ganymede, Europa, Callisto) or have observers. Those observations were con- an atmosphere (Venus, Mars, Jupiter, Sat- firmed in situ and features of the Jovian urn, Io, Titan); may be embedded in sub- environment (magnetic field magnitude and Alfvenic flows (Io), near-Alfvenic flows (Ti- direction, existence of field-aligned cur- tan), or super-Alfvenic flows (all others). rents) inferred from remote observations There may or may not be secondary plasma proved remarkably accurate. The Galileo sources such as Io's volcanoes or Saturn's mission, to reach Jupiter in 1988, will permit rings within the magnetosphere. Rotation an orbiting spacecraft to monitor the tem- may be slow enough to be ignorable (e.g., poral variability of Jupiter's giant magnetos- Mercury) or may dominate dynamical be- phere. In addition, Galileo will traverse the havior (e.g., Jupiter). For each combination regions in which the Galilean moons form of parameters, the relative importance of secondary magnetospheres within the rotat- different physical processes changes, and ing Jovian plasma, thus extending studies spacecraft measurements can provide of comparative magnetospheres. unique insights. Saturn has a magnetosphere much like Mercury's magnetosphere is small, even that of Earth, but modified by embedded on the scale of the planetary radius, be- moons and rings. Radio frequency emis- cause its magnetic field can barely stand off sions from Saturn are modulated at the pla- the solar wind. Yet there is evidence that netary rotation period, but there is no evi- substorms and particle acceleration occur at dence for asymmetries needed to explain Mercury much as at Earth. Data from two the modulation. flybys raise questions (e.g., what is the na- Insights gained from studies of magnetos- ture of hydromagnetic flow in a magnetos- pheres of other planets are of great impor- phere so small that an ion Larmor radius is tance to our evolving understanding of not negligible?) but do not give answers. space plasmas. The next steps in planetary Venus missions have illuminated the way exploration should include the following: in which solar wind plasmas interact with • a Mars orbiter instrumented for fields dense ionospheres. The solar wind mag- and particles investigations, with orbits op- netic field drapes around the ionosphere, timized for magnetospheric measurements; and some magnetized plasma convects into • a Saturn orbiter with trajectory selected the ionosphere, producing spatially con- to allow high latitude measurements from fined regions of large, twisted magnetic which field asymmetries and radio sources fields (flux ropes) deep inside the iono- can be investigated; sphere. Magnetic flux tubes couple iono- • a spacecraft placed in orbit about Mer- spheric plasma to the solar wind and pro- cury, the only known magnetized planet vide direct paths for particle losses from the without an atmosphere, to illuminate the ionosphere. role of atmospheres in substorms and other Past missions to Mars have not yet com- magnetospheric processes; and bined appropriate fields and particle instru- • exploration and intensive study of the mentation and spacecraft trajectories for inner Jovian system--density, composition, studies of the magnetosphere. Thus, it re- and energy of the magnetospheric particles; mains uncertain whether Mars has an in- large-scale structure and rotation, time-de- trinsic magnetic field or not. Some think pendent phenomena and relation to Io, that Mars represents an important "interme- other satellites, and orbiting gas and diate" case, standing off the solar wind plasma; auroral activity on Jupiter; and partly with a magnetic field (like Mercury) electromagnetic emissions. [This objective, and partly with an ionosphere (like Venus). from the Space Science Board's Committee Jupiter's large magnetic field, rapid rota- on Planetary and Lunar Exploration report,

46 A Strategy for Exploration of the Outer Solar • It will be possible to study the evolution System (in preparation), is endorsed by the of the comet-solar wind interaction as a CSSP]. function of the level of cometary activity. • It will be possible to map the major close-to-the-nucleus features of the comet- Comets solar wind interaction in order to under- stand the major ionospheric processes such The exploration of comets is a step into a as ionization, acceleration, and heating of new regime of space plasma physics in the plasma, which ultimately forms the tail. which a flowing magnetized plasma inter- • It will be possible to determine the acts with a dilute neutral gas in the pres- abundances and velocity distribution func- ence of a source of ionizing radiation. tions of the minor as well as the major ion Ground-based observations and satellite- species in the inner coma where the local based remote sensing of cometary plasma chemical composition is determined by ion- still have many unanswered questions neutral reactions. Measurement of the elec- about tron temperature is also vital to understand- • the range of physical mechanisms re- ing the inner-coma chemistry. sponsible for the rapid ionization of the In view of the important and essential gases released from the nucleus; plasma physics that can be learned on a • the mechanism(s) responsible for the comet rendezvous mission, such a mission pick up of newly ionized material by the should include instruments for the measure- solar wind (i.e., acceleration and thermali- ment of plasma parameters--at a minimum, zation of the cometary ions and the deceler- an ion mass-velocity spectrometer, an elec- ation and heating of the solar wind); tron spectrometer, a magnetometer, and a • the details of the mechanisms responsi- plasma wave analyzer. ble for acceleration of plasma into the ion tail; Theory and Modeling • the magnetohydrodynamic topology of the interaction region (e.g., Is there a thin or NASA's Solar-Terrestrial Theory Program a thick ionopause? Are there flux ropes? Is (STTP), initiated in response to the Colgate there a shock internal to the ionopause?); and Report, has been one reason why solar sys- tem plasma research has reached a new • the interaction between plasma and dust. level of precision, whereby it is strongly contributing to both general plasma physics A series of cometary exploration missions and to the interpretation of space data. have recently been initiated. Although this program has resulted in • The International Cometary Explorer substantial progress toward the goal of as- will fly through the tail of comet Giacobini- similating our accumulated knowledge into Zinner in September 1985. comprehensive theories, several important • A series of five spacecraft will pass sun- problem areas remain. The level of support ward of the nucleus of comet Halley in of particle acceleration as a generic topic March 1986. One of these spacecraft, ESA's with application to almost every area of Giotto, is planned to pass close enough to space physics research is incommensurate the nucleus to penetrate the ionopause (if with its prominence and the available theo- such an identifiable structure exists) and retical knowledge and tools. The same is very briefly sample the cometary iono- true for particle confinement and transport. spheric plasma. It is worth noting that while over 50 active • A mission to rendezvous with a short- beam injection experiments from rockets period comet is currently under study by and the Shuttle have been performed, the NASA's Solar System Exploration Division. theoretical effort to interpret these results The comet rendezvous mission offers the has only just begun. As a result, the subject possibility of obtaining qualitatively differ- of controlled beam experiments is scientifi- ent types of measurements than those that cally behind, despite the enormous progress can be obtained with the flyby missions. in the understanding of natural beam and

47 radioemission physics. A newly emerging Because of the wealth of scientific data area that needs attention deals with neutral provided by space physics missions and be- gas plasma interactions including the ef- cause of the inherent need for correlative fects of large structures. Research on these analyses, the space physics community has topics is a must in the era of cometary ex- been a leader in improved data analysis ploration and of space station research. A techniques. In fact, the Space Physics Anal- major increase in funding is immediately ysis Network (SPAN) system has grown out necessary for these high-leveraged scientific of the need in the space plasma community investigations. to merge, correlate, and intercompare very Specific theoretical problems may be diverse data sets. SPAN arose from a "grass identified that are too complex to be ad- roots" effort among space physicists and dressed with current funding levels and now is leading virtually all NASA disci- whose solution within a specified time pe- plines in scientific data interchange and in riod is judged important. A concerted theo- the associated development and implemen- retical attack on such problems should be tation of networking, graphics standardiza- approached through the use of an AO or a tion, and data formatting techniques. "Dear Colleague" letter, by which one or Based upon the direct "hands on" experi- more groups should be chosen and funded. ence provided by the SPAN system, pro- Computer time should be made available to grams such as ISTP and UARS are develop- these groups on national computer facili- ing data facilities around well-tested ties, and support provided for their addi- concepts of data handling and data process- tional manpower needs. The subject of ener- ing. Superior, cost-effective scientific return getic beam injection in space is a potential will result within these new programs. Ex- example: by collecting the many experimen- isting and future programs of other types tal results produced over the years and uti- will benefit from this continuing experience. lizing the computational theoretical tools We recommend that increased MO&DA available, the scientific return to the tens of funding be provided to allow data archiving millions of dollars spent on experimental in- and cataloging, improved networking, and vestigations over the years can be substan- enhanced analysis capability in a discipline tially increased at a total cost of less than with proven experience, capability, and net- $1M/yr. working infrastructure.

Mission Operations and Data Analysis Research and Analysis

The scientific value of space missions Funds associated with individual space comes, quite obviously, from the data that missions increase and decrease on rela- are returned and processed through ground tively short time scales whereas the train- systems. Hence, a primary consideration of ing, assembling, and maintenance of scien- space programs has to be the proper plan- tific teams is, and should be, a much longer ning of data systems from the earliest term activity. The expertise and capability stages. Equally important is the recognition of a scientific staff must be continued and that scientists--the true users of the data-- nurtured in order to allow progress in basic should be involved in all phases of the research. The kind of long-term stability in planning and implementation of data sys- funding that leads to real success in the tems. space sciences comes about from the R&A Many space plasma missions have contin- funding program. ued to operate well beyond the primary mis- Analyses have shown an alarming de- sion phase. Funding in the MO&DA pro- crease in the R&A funding in space plasma gram must therefore be provided with the physics. In terms of constant FY 84 dollars, recognition that the data from the extended this decrease has amounted to $4M from mission period are an extremely important $15M to $11M between FY 78 and FY 84. In scientific asset. These data provide the ba- order to restore an appropriate level of fund- sis for testing the hypotheses developed ing R&A, and in order to establish a more during the primary mission phase. proper balance of R&A among the space sci-

48

r ences disciplines, we recommend an in- Long-Term Studies crease from $11.5M in FY 85 to $16M in FY 86. From _/87 forward we strongly recom- Mission objectives are typically restricted to mend a level of about $20M in space plasma those attainable within a few years, yet in R&A funding. studies of solar cycle variations and other An area requiring particular attention in long-term changes of magnetospheric prop- space plasma physics is advanced instru- erties, it is crucial to monitor key regions of ment development. If one relies solely on the magnetosphere over long periods of funding associated with new missions to time. For this purpose, geostationary satel- provide instrumental design improvement lites are particularly well suited; it is essen- (and innovation), then hardware progress tial that scientific instrumentation be pro- will be unacceptably inadequate. We rec- vided on geostationary satellites or Space ommend that NASA provide a vigorous pro- Station Platforms for continued monitoring gram of R&A support explicitly earmarked of fields, particle fluxes, and plasma com- for instrument development including new position over many solar cycles. detection techniques, improved onboard processing capabilities, higher spatial and temporal resolution, and other instrument Priorities improvements. The highest priority for magnetospheric plasma physics is clearly the ISTP program. Technology Requirements/Instrument The other recommended missions of the Development space plasma physics program are a healthy and diverse mix of free-flyer space- It is evident from the description of the rec- craft and active experiments. The elements ommended missions that current spacecraft of the program are dictated by the overall technology is adequate in all cases to carry discipline funding profile and integration out the program. Recent advances in micro- with the phasing of Shuttle, Space Station, processor systems and custom-made VLSI and other capabilities. chips suggest that onboard data processing The rededication of a vigorous Explorer techniques may well result in acquisition program is imperative to perform small-to- and evaluation of much larger volumes of moderate cost, specialized missions in solar data than previously thought possible, with- and space physics that complement the ma- out a consequent increase in data rates jor rnagnetospheric plasma physics mis- transmitted to the ground. Incorporation of sions represented by ISTP spacecraft. reliable data storage devices aboard space- On a comparable level are missions to craft will minimize requirements for continu- carry out the programs that will lead to evo- ous tracking coverage by the Deep Space lutionary production of active experiments Network (DSN) [for spacecraft in orbits that for use in the Space Station era. These are cannot use Tracking and Data Relay Satel- the Shuttle/Spacelab and Tethered Satellite lite System (TDRSS)], thereby decreasing System programs, including SPL, SL ref- costs in manpower and facilities for data lights such as EOM-1, and the TSS-1 and -3 acquisition. missions. Science instrument development, on the Strong MO&DA and R&A programs and other hand, is an ongoing process. Funding mission-directed theory and modeling ef- for such development is included in the rec- forts must be inseparable components of the ommended R&A program, except in those above flight missions. These programs must cases where major, facility-class instru- be supplemented by stable programs sup- ments are required to carry out any of the porting more general R&A and space missions recommended for space plasma plasma physics theory and modeling. physics. Nevertheless, science from mis- Space Station/Platform missions are long- sions later in the tirneline is likely to be term but have a priority set by their time- enhanced by the development of more ad- line. Development of the active experimen- vanced instruments and techniques, as they tal instrumentation should proceed so that it become available. can be easily retrofitted to Space Station use.

49 MAGNETOSPHERICIPLASMAPHYSICS

YEARS o

ISTP l _ A A A A _ I EMOI I

SPL-1,2

CRRES

EXPLORERS I _'. I /"* '_ " _ ' I

TETHER

STOFACILITYINSTRUMENTDEVELOPMENT z _ A r,. I STOISPACESTATION SHUTrLFJSPACESTATIONEXPERIMENTS

SOUNDINGROCKETStSPARTAN (_, 5-8 FLIGHTS/YEAR)

RESEARCHANDANALYSIS

MO ANDDA

ST THEORYPROGRAM

FIGURE6

Suborbital programs have not been priori- and tested by a larger segment of the com- tized here. It is assumed that a steady level munity at rather low cost. of funding will be provided by which these Figure 6 shows the timeline for the pro- small programs-of-opportunity can be sup- gram in space plasma physics. There are ported as they are identified and defined. several programs that we consider scientifi- CRRES and SL-2 are not prioritized because cally important but could not include in our they are approved programs. timeline because of the funding constraints New opportunities to provide frequent that we have imposed on this implementa- flight opportunities at relatively low cost are tion plan. Most important among these are developing on the Shuttle through the Spar- missions to study the magnetospheres of tan and Hitchhiker programs. These pro- other planets (Mars, Saturn, Mercury), a grams should be encouraged and managed comet rendezvous mission, and a helios- in the same manner as the sub-orbital pro- phere boundary probe. gram. New research ideas can be developed

50 9 DETAILED MISSION PLANS--UPPER ATMOSPHERIC PHYSICS

Introduction incentive for coordination of individual pro- grams in solar physics, magnetospheric/ The upper atmosphere is defined here as space plasma physics, and upper atmos- the region above the tropopause (about 12 pheric physics to achieve a better under- kin) and includes the stratosphere, mesos- standing of the effects of solar cycle, solar phere, thermosphere (and ionosphere), and activity, and solar-wind disturbances upon exosphere. The program is constructed on the Earth's atmosphere from the thermos- the premise that this entire region should be phere down through the troposphere. investigated as one dynamic, radiating, and chemically active fluid. Historically, the up- Program Descriptions per atmosphere was investigated by remote observations of limited regions or layers. The satellite era led to intensive study of Major Missions the Earth's thermosphere by in situ meas- urements. Complementary observations The highest priority in observatory-class were obtained with sounding rockets and missions for the 1980s has been the Upper- ground-based incoherent backscatter ra- Atmosphere Research Satellite (UARS), now dars. a new start in FY 85. It will provide, for the In-situ measurements of the stratosphere first time, an almost global data set on the have been made by balloon-, rocket-, and chemistry, dynamics, and radiative inputs airplane-based instruments whose flight du- of the 10 to 70-kin region of the atmosphere, rations are short, and the resulting data are i.e., the stratosphere and lower mesosphere, restricted in geographic coverage as defined although some instruments are capable of by their trajectories or launch locations. useful measurements to an altitude of ap- Rockets, for example, have provided limited proximately 200 km (Figure 7). The goals of knowledge of vertical structure in composi- the UARS program are to understand the tion and temperature at isolated locations. mechanisms controlling middle atmospheric Recently, ground-based capability to probe structure and processes, to understand the these regions have been demonstrated by response of the upper atmosphere to natural MST radars and lidar, but again at only a and human perturbations, and to define the few locations. role of the upper atmosphere in climate and To gain a global perspective of the upper climate variability. To accomplish these atmosphere in both horizontal and vertical goals, several areas of scientific study will coverage and investigate the upper atmos- be fostered by the mission, including energy phere as one interactive fluid, comprehen- input and loss, global photochemistry, dy- sive remote sensing measurements from namics, coupling among processes, and space platforms are the major directions for coupling between the upper and lower at- the future. Thus, the upper atmospheric mosphere. The UARS data will be critical in physics program was designed around the evaluating the extent of ozone depletion Upper-Atmosphere Research Satellite caused by human activities and the impact (UARS) spacecraft--one of the principal rec- of upper atmosphere processes on climate ommendations of the Kennel report. change. Another area of upper atmospheric study The instrument payload has been care- is solar-terrestrial coupling, which is con- fully selected to meet the goal of coordi- cerned with the response of the Earth's mag- nated and complementary global measure- netosphere, ionosphere, and atmosphere to ments of ozone, temperature, pressure, solar inputs and their variability. Studies of energy input, winds, and chemical trace solar-terrestrial phenomena are of consider- species by remote sensing. A broad comple- able practical importance and provide an ment of stratospheric constituents will be

51 UPPERATMOSPHERICPHYSICSPROGRAM

YEARS

UARS NEWSTART LAUNCH EXTENDEDDATAANALYSIS MLSSION INSTRUMENTDEVELOPMENTPROGRAM FORSHUTrLE/$PACESTATION(FARIR RADIOMETRY,IRtNTERFEROMETRYAND t __ STO/SPACESTATION GASFILTERTECHNIQUES,GASFILTER ) CORRELATIONTECHN1OUES, MICROWAVETECHNIQUES,ETC. EXTENDEDUARSWITHNEWIN- STRUMENTSORSPACESTATION/STO UARSRELAUNCHRETRIEVALANDLI ATMOSPHERICEXPERIMENTS ORSTOLAUNCH LOWERTHERMOSPHERE/MESOSPHERE t A I CONTINUEWITH EXPLORER STOISPACESTATION TETHEREDSATELLITEPAYLOADS I A A z_d TS_I TSS2 TS_3 CRRES LAUNCHLAUNCH LAUNCH SL2 8 3 SPL-1 SPL-2 SHUTTLESCIENCE IA A Z_] ATMOSPHERICANDPLASMASCIENCE

SI_JTrLEREFLIGHT EOM-1EOM-2 UPPERATMOSPHERERESEARCHAND ANALYSIS(EXCEPTTROPOSPHERICAIR QUALITY)INCLUDESINSTRUMENTSFOR SUBORBITALPROGRAMS MOANDDA

FIGURE 7

measured as part of the UARS payload. principal investigators as an integral part of Many of the important free radical species the program to complement the measure- (C10, NO2) will be measured simultane- ments and data analyses. Through this co- ously, as well as ozone densities. Further, ordinated program in measurements, data most of the long-lived species (e.g., CH4, and model analyses, and theoretical investi- N20, CF2C12) that are the source of these gation, it is anticipated that substantial radicals will also be observed. progress will be made in solving the out- It is well known that stratospheric ozone standing physical and chemical problems and other stratospheric trace gases are de- above the tropopause. pendent not only on photochemistry, but UARS will be launched in the fall of 1989 also on atmospheric dynamics. Perhaps the using the Shuttle, which will deliver it di- most important aspect of the UARS mission rectly to the operational circular orbit at 600 is that direct measurements of atmospheric km and inclined 57 ° to the Equator. At this winds will be made simultaneously along altitude and inclination the remote sensors with the photochemical observations, so looking 90° to the spacecraft velocity vector that the interactions between photochemis- can see to 80 ° latitude, providing nearly try and dynamics can be examined better global coverage. The inclination of the orbit than from previous satellite missions where plane also produces a precession of the only temperature was measured. plane to allow all local solar times to be The UARS program includes theoretical sampled in about 33 days, which should studies and model analyses with theoretical give resolution of diurnal atmospheric el-

52 fects in a period that is short relative to of their energy. These energy inputs cause seasonal effects. significant perturbations to the chemistry, The UARS spacecraft can be retrieved by dynamics, and thermal structure of the the Shuttle and is designed to be refur- lower thermosphere and can also propagate bished, thus allowing for an extended UARS to the other regions of the atmosphere. For mission. For an extended mission, new re- example, as discussed in the Kennel and mote sensing instruments developed under Explorer reports, it is known that nitric ox- the instrument development program (dis- ide (NO) can be produced in the lower ther- cussed below) to investigate the same and/ mosphere by aurorae and solar proton or another region of the atmosphere could events and subsequently be transported replace the existing instruments. Since the down into the mesosphere, and possibly selection of the UARS instruments, technol- into the stratosphere where it can affect ogy has advanced sufficiently that it is now stratospheric ozone concentrations. Another possible to remotely sense key radicals result of energy deposition is thermospheric (e.g., HO_) that play a critical role in the heating during geomagnetic storms that photochemistry of the middle atmosphere. drives an upward expansion of the neutral These measurements should have high atmosphere, increasing satellite drag and priority on an extended UARS mission. causing global ionospheric perturbations The UARS objectives include the need for via chemical and dynamical processes that coverage of seasonal phenomena, probably are still poorly understood. requiring at least 3 years of observation. Because neither UARS nor ISTP missions The planned first mission of 18 months will will directly address these scientific ques- not fulfill this requirement, and an extended tions, we suggest a mesosphere-lower ther- mission is therefore highly desirable. mosphere explorer (MELTER) to remotely UARS also could be inserted in a high sense the chemical, dynamical, and thermal inclination (polar) orbit for its extended mis- response of the 70- to 150-km region to solar sion and accomplish the global coverage as and magnetospheric perturbations. This re- originally proposed for the second space- gion has been called the "ignorosphere" be- craft of the UARS mission. High latitude cause of the great difficulty in measuring its phenomena are of particular importance in properties. It is desirable that the MELTER improving our understanding of global dy- mission occur simultaneously with the namics, chemistry, and particle inputs. UARS and ISTP missions to acquire a com- Alternatively, in this time frame (FY 94), prehensive solar-terrestrial data base. Sub- the Space Station and/or STO may prove to stantial cost savings are possible in this sit- be a better platform for remote sensing in- uation as critical instruments on UARS and struments. Current plans allow for consider- ISTP would not have to be duplicated on able flexibility in selecting the best platform MELTER. Although the complexity of the in- for remote sensing of the atmosphere in the strument payload will have to be limited, late 1990s. Based on current projected UARS preliminary studies suggest that such a mis- mission costs, an extended UARS mission sion can be successfully accommodated would cost about $270M in FY 95 dollars, within the guidelines for the Explorer Pro- assuming $80M for new instruments. gram as specified in our earlier report. To study the dynamics and photochemis- try of the mesosphere-lower thermosphere, Explorers measurements of the following geophysical quantities are important: winds, tempera- The Explorer Satellite program has been es- tures, concentrations of NO, 03, O, and odd- sential to the development of upper atmos- hydrogen radicals, electric fields, particle pheric physics, as evidenced by the impor- precipitation, and tracers such as H20 and tant contributions from AE, SME, and DE CO. Since all of these quantities cannot be (Chapter 6). In the solar-terrestrial context, measured by a single Explorer satellite, a perhaps the most important region of the selection of quantities from this list must be atmosphere is the mesosphere and lower made. thermosphere where electric fields and par- Another Explorer-class spacecraft is the ticles from the magnetosphere deposit most Combined Release and Radiation Effects

53 Satellite (CRRES). This NASA/DOD joint ef- The STO Science Study Group discussed fort will perform experiments in the solar- eight representative solar-terrestrial scien- terrestrial system by means of active prob- tific objectives that benefit from the platform ing with injections of matter and energy. approach and a program of measurements The research goals of CRRES are to provide for each. These objectives are to understand a better understanding of the solar-terres- • solar variability, trial environment and also to study physical • wave-particle processes, processes in the magnetosphere, iono- • magnetosphere-ionosphere mass trans- sphere, and upper atmosphere. The scien- port, tific objectives, programmatic details, and • the global electric circuit, recommendations regarding this mission • upper atmospheric dynamics, are outlined in Chapter 8. • upper atmospheric chemistry and ener- Additional Explorer missions will be pro- getics, posed by the upper atmospheric physics • lower atmospheric turbidity, and community to investigate important scien- • planetary atmospheric waves. tific problems. One of the goals of the Ex- A two-stage approach to a multidiscipli- plorer program is a quick-reaction capabil- nary payload is proposed: an initial STO ity to respond to mission targets of that uses a single platform in a low-Earth- opportunity; therefore, we should not now orbit and an advanced STO that uses two attempt to predict what will be the most platforms in differing orbits. Coordination of important scientific opportunities in the mid STO with an interplanetary companion, to late 1990s. such as WIND or SOHO, would be highly desirable. In addition, properly planned and Space Station/Solar Terrestrial Observatory implemented operations, data handling, data analysis, and theoretical modeling Requirements for the Space Station Program must be treated as an inseparable part of are only now being defined, so it is difficult the STO mission. With the characteristics to present definitive plans for a scientific outlined above, the Solar Terrestrial Ob- program. Nonetheless, the STO, which was servatory can make a unique and valuable recommended by the Kennel Report and contribution to NASA's Space Station pro- studied in some depth by NASA, is compati- gram for solar-terrestrial physics and inte- ble with the Space Station Platform from the grate the subdisciplines of solar and space perspective of upper atmospheric physics. physics into a true terrestrial program. The STO is a problem-oriented instrument payload based on a platform approach, i.e., Spacelab/Shuttle Science the payload is located on a space platform and is set in orbit, serviced, and retrieved Scientific observations from the Shuttle by the Space Shuttle. The central scientific have just barely begun. More frequent use goal of the STO is to understand the physi- of this platform for passive and active ex- cal processes that couple the major regions periments is an absolute requirement. In the of solar-terrestrial space. This goal encom- time line of Table 7 are indicated the passes the solar atmosphere, the interplane- launches of Spacelab 2 and 3, Space tary medium, the Earth's magnetosphere Plasma Laboratory 1 and 2, along with Shut- and ionosphere, and the entire neutral at- tle reflights as part of the Environmental mosphere of the Earth. Observation Missions (EOM). Important at- The platform approach offers a unique mospheric observations will be made during combination of capabilities, different from these missions even though atmospheric those of both conventional free-flyers and physics is not the primary driver for SL and Shuttle/Spacelab. The characteristics that SPL flights. These missions are discussed in are important for the STO are more detail in the magnetospheric/plasma • large Shuttle-class instrumentation, physics section (Chapter 8). • long duration in orbit, The payload for the first EOM uses five • high power generation, proven instruments from Spacelab 1, 2, and • regular in-orbit servicing, and 3 missions in a continuing effort to monitor • multidirectional pointing. variations in the total solar irradiance and

54 thesolarspectrumwith state-of-the-artpre- tended. Current Shuttle instrument develop- cisionand to characterizesomeof theat- ment should be compatible with providing mosphericresponsesto changesin the inci- an eventual continuous presence in space of dentsolarenergy.A seriesof flights is Shuttle-class instrumentation for solar-ter- plannedsothat similar measurementscan restrial research. NASA should consider use be madeovera complete11-yearsolar of existing low-cost payloads, with prime cycle. candidates being engineering models left TheTetheredSatelliteSystem(TSS)will over from SAGE and Nimbus 7 (e.g., SBUV, providean importantnewfacility for con- SAGE, SAMS, LIMS). These could be flown ductingspaceexperimentsin regionsre- on Shuttle missions or, more preferably, on motefromtheSpaceShuttleOrbiter.Pay- a longer term platform such as the Euro- loadsof 200to 500kg can be deployedto pean Shuttle-launched spacecraft (EURECA). distancesof 100km andheld in fixed posi- tion with respectto theorbiterby meansof Theory and Modeling a closed-loopcontrolsystemactingupona Theory and computer modeling play a fun- tether.Datahandling and commandcapa- damental role in upper atmospheric and so- bilities will permit activeexperimentinter- lar-terrestrial research. They are crucial in pretationandcontrolby orbiterandPayload the identification of key observations that OperationsControlCenter(POCC)ground must be made to establish a correct under- personnel. standing of the processes at work. Com- TheTSSis expectedto opentheway to puter models are useful for simulating large severalentirelynew areasof long-termsci- systems, for testing the importance of com- entific experimentationnotheretoforepossi- peting coupling processes on a global scale, ble. Forupperatmosphericphysicsthese and for providing a framework within which areasinclude large amounts of data may be analyzed. • direct observationof magnetospheric- In upper atmospheric physics, the ulti- ionospheric-atmosphericcouplingprocesses mate objective is a quantitative model that in the 125-to 150-kmregionof thelower predicts the upper atmosphere's response to thermosphereand internal and external perturbations and de- • thein situ observationof importantat- scribes how changes in it influence the mosphericprocessesoccurringwithin the lower atmosphere and the plasmasphere. lowerthermosphere. Comprehensive models must take into ac- Werecommendcontinueddevelopmentof count chemistry, energetics, and dynamics, theTSSfor useon the Space Station/Plat- because they are tightly coupled. In some form missions. Multiple tethered satellite areas, such as the non-LTE radiation budget deployments would allow simultaneous of the upper mesosphere, current models measurements of the ionosphere and atmos- are primitive and a substantial effort will be phere at several altitudes and controlled required. In others, where more complete electrodynamic perturbations of the iono- understanding of composition, radiation, sphere. and dynamics currently exists, continuing Achievement of polar orbital capability interaction between model development and and long-duration use of Shuttle instru- observation is the primary need. ments are related goals toward which Shut- The Solar-Terrestrial Theory Program tle operations should evolve in the 1980s. (STTP) can contribute towards attaining Many important magnetospheric and atmos- these goals but additional effort and funds pheric processes can only be studied from will be needed in the future for specifically polar orbits; they are necessary to provide upper atmospheric physics to complement complete geographical coverage of the at- the present modeling emphasis on the mag- mosphere and are excellent vantage points netosphere as well as our recommended ex- from which to view the Sun. Lack of polar perimental program. orbital capability would therefore seriously weaken the impact of the Shuttle on solar- Mission Operations and Data Analysis terrestrial physics. We also recommend that the time on orbit As the Friedman-Intrilligator report, Solar- of Shuttle-class instrumentation be ex- Terrestrial Research for the 1980"s, pointed

55

I out, unprecedented amounts of scientific universities, national laboratories, and pri- data have accumulated from past space vate industry, which provide the scientific missions. Data handling and management expertise and leadership to carry out the have become a problem due to a variety of more ambitious efforts outlined in this re- factors: e.g., scattered location, incompati- port. ble formats, obsolete technology (see Solar- Terrestrial Data Access Distribution and Ar- Technology Requirements/Instrument chiving, NAP, 1984). Planning efforts for sev- Development Program/Suborbital Programs eral recent missions (e.g., AE and DE) and future missions (UARS and ISTP) have given The upper atmosphere cannot be studied in careful consideration to the difficulties, and isolation. The source molecules of critical the trend is toward requiring experimenters importance to stratosphere chemistry (N20, to meet specified data-management condi- CH4) are produced in the troposphere by tions designed to speed up the data reduc- complex biological processes, some of tion time, to use common physical units and which are certainly subject to anthropogenic data formats, and to render the data base perturbations (e.g., use of nitrogen fertili- available to the scientific community rap- zers). Thus, effective study of the strato- idly and in a "user-friendly" form. Objec- sphere must involve analysis of (a) ex- tives to be met include the provision of im- change processes with the troposphere and mediate and remote access to data by (b) further study of biosphere-ocean-atmos- principal investigators and their teams dur- phere interactions. To some degree, these ing a mission, similar remote access by the can best be performed in the near term from scientific community at-large as soon as aircraft and balloons with the development proprietary requirements have been ful- of instrumentation to measure gas abun- filled, and timely and automatic acquisition dances and fluxes. A global perspective of the data by the National Space Science will, however, require remote sensing from Data Center in order to satisfy all archiving an appropriate space platform with ad- requirements and the future needs of the vanced instruments. entire scientific community. A high priority should be given to funding Currently, in years following the end of advanced instrumentation development for Explorer and observatory-class missions, upper atmospheric studies because the vi- funding levels have not been adequate to tality of the field requires the continuous analyze and interpret much of the acquired development of "state-of-the-art" technology. data to its full potential. In order to meet Technological advances are anticipated in the above goals and ensure that the princi- detector arrays, electro-optical subsystem pal investigators and scientific community and component technology, onboard infor- at large have adequate resources to analyze mation processing, and cryogenic cooler de- their expensively acquired data, we recom- velopment using both active and passive mend a significant increase in MO&DA systems. These advances should impact the funds. We do note that NASA has made a next generation science requirements and start in this direction with their strato- instruments for STO, Space Station, and/or spheric data analysis program. the extended UARS Mission. Development and testing on sub-orbital platforms must be Research and Analysis an integral part of such instrumentation ad- vances. Exclusive of Shuttle launch and op- The health of upper atmospheric physics de- erations cost, a funding level of about $15M/ pends crucially on long-term support of indi- yr is estimated as required for development vidual scientists, research associates, and of the next generation of scientific instru- graduate students. The Research and Analy- ments through the demonstration test sis (R&A) funds provide the foundation of phase. the creative and innovative research base A strong rocket and balloon program is and graduate education that has made the needed to measure the ionic content, the United States preeminent in space science. concentrations of a number of minor spe- It is essential that sufficient funds are avail- cies, the electrical state, and other proper- able to maintain strong research groups at ties of the middle atmosphere that cannot

56 be observed remotely. Further, the unique flux as small as 0.1 percent. For our under- ability of rockets and balloons to measure standing of the influence of solar variability small-scale spatial and temporal variability on climate to progress beyond speculation, is essential to our understanding of middle- long-term satellite monitoring of the total atmospheric transport processes. Balloons solar radiant energy flux is an absolute ne- and rockets also provide in situ corrobora- cessity. Monitoring the solar spectral irradi- tion of remote-sensing spacecraft observa- ance is highly desirable, because the ultra- tions. In addition, only rockets can make in violet part of the spectrum below 1800 A is situ vertical profile measurements in the 40- known to vary significantly (> 20 percent) to 120-km altitude region. Active experi- with solar activity. ments in the thermosphere and lower iono- Long-term observations of solar spectral sphere are also most effectively conducted irradiance and solar-wind parameters are using rockets. prime examples where there has been inad- When the low cost, fast-turn-around Geta- equate past commitment of resources and way Specials ("GAS CAN"), "Hitchhikers", effort. Spectral irradiance monitoring has and Spartan experiments become a reality been recognized in the past as essential to on the Shuttle, we recommend a phase out ionospheric/magnetospheric research. How- of all non-in situ rocket experiments. We ever, these observations have been sup- recommend the development and perfection ported only in piecemeal fashion by various of long-duration (2-4 weeks) balloons to government agencies. No one agency is carry out in situ and long-duration remote dedicated to the support of long-term moni- sensing measurements. toring of this type, and no one agency has devoted sufficient resources or interest in Planetary Atmosphere Studies this area to do it properly. NASA is the suit- able agency to assume responsibility for A thorough understanding of the evolution these observations, and it is our recommen- and behavior of our own atmosphere re- dation that NASA assign high priority to quires that it be viewed in the broader con- suitable instruments on space platforms text of comparative planetary studies. We over the next 15 years to acquire these ex- heartily endorse the SSEC recommended tremely valuable data. core missions that contain atmospheric ex- Monitoring of Ozone ploration components: Mars Geoscience/Cli- Ozone is one of the most important atmos- matology Orbiter, Comet Rendezvous/Aster- pheric species because it is the only constit- oid Flyby, and Saturn Orbiter/Titan Probe Missions. We also recommend the prompt uent capable of effectively absorbing bio- implementation of the Mars Aeronomy Orbi- logically harmful ultraviolet radiation in the wavelength range from about 2500 to 3000 A. ter Mission after the completion of the ini- Since the ozone layer's absorption at these tial core program. These intensive studies of wavelengths effectively protects life at the other planetary atmospheres will comple- surface, the study of the stability of the ment our recommended program for the ozone layer is of prime concern. Earth's upper atmosphere. A detailed under- Our understanding of the ozone layer has standing of the photochemistry, dynamics, evolved considerably over the last decade. and energetics of these planetary atmos- In particular, refinement of our understand- pheres will provide a proper context to un- ing of stratospheric photochemistry has led derstand the complex interplay of chemical to substantial reductions in the estimated and physical processes in our atmosphere that sustain life. changes in ozone expected to result from chlorofluorocarbon releases. Current models predict maximum local changes near the 40- Long Term Programs km level, with much smaller changes be- low. The total column changes are likely to Solar Constant be strongly dependent on dynamical and ra- Radiative-balance climate models indicate diative feedbacks, because much of the to- that the Earth's surface temperature is sen- tal column resides at low altitudes (i.e., be- sitive to changes in the solar radiant energy low 20 km) where ozone is controlled by

57 dynamical processes. Model calculations in- Priorities considered when constructing this dicate that the long-term response of strato- time line were primarily funding constraints spheric ozone to increasing chlorine abun- and already-approved new starts that NASA dances may be closely coupled to radiative is committed to execute to completion. The feedbacks related to simultaneous increases FY 85 new start for UARS represents a major in CO2, N20, and other species. commitment of funds into the early 1990s. Therefore, it is important to monitor ozone Current NASA planning indicates that the both at the 40-kin level, where changes are Space Station will be available for scientific predicted to be greatest, and at altitudes of research in the middle 1990s. It is essential about 10-30 km, where most of the total col- that appropriate instruments be developed umn is located. The methods currently to fully exploit its capability. An FY 88 start being used for long-term monitoring of these is thus essential for the instrument develop- regions are substantially different. At the ment program to provide the needed 5 years 40-km level, observations are provided by for development through flight testing on ultraviolet sensors onboard satellites, which the Shuttle. An additional 2 to 3 years is offer complete coverage, reasonable altitude required to select from the successfully de- resolution, and good climatology. The low veloped instruments that should be built for altitudes (near 10-20 km) are not very acces- long-duration use on the Space Station. In sible to ultraviolet satellite technology and the event that the Space Station encounters are best addressed either by infrared remote difficulties similar to those that plagued the sensing or perhaps by a concerted balloon Shuttle program, we recommend the back- program using optical in-situ or perhaps up option of retrieving and refurbishing the chemiluminescent sampling. An important UARS spacecraft. Scientific progress can problem, however, remains--that of satellite thus be maintained. calibration. Since many of the available sat- The CRRES and Tethered Satellite pay- ellite measurements are subject to possible loads are approved missions along with SL- instrument drift, their accuracy may not be 2 and 3, SPL 1 and 2, and EOM 1, 2, and 3 sufficient to conclusively detect changes of Shuttle flights. Funding constraints limit the the magnitudes expected to be found in the new start of the MELTER mission in the Ex- 1990s. This highlights the need to develop plorer program to FY 88 at the earliest. It accurate in-situ instrumentation for use in would be highly desirable to launch this connecting satellite data. It is particularly Explorer within 6 months of the UARS important to improve current balloon instru- launch to obtain the maximum overlap in mentation so that reliable soundings can be data coverage. For reasons previously made at high altitudes. noted, the research and analysis program is Thus, a balloon program should represent of utmost importance for the continued an integral part of the future long-term pro- health of the field and therefore the mainte- gram, both because of the dominant role of nance of this budget item at the indicated the lower stratosphere in the global total levels is of the highest priority. ozone budgeL but also because of the need Although the detailed understanding of for calibration of satellite instruments. We planetary atmospheres complements terres- recommend that NASA continue its program trial atmospheric studies, we did not make in monitoring ozone and improve calibration specific recommendations in this area nor of future satellite data to meet accuracy re- include it in our budget time line because of quirements to detect predicted ozone programmatic reasons. Nevertheless, we changes in the 1990s. strongly recommend a continued and in- tense exploration of planetary atmospheres. Priorities

In Figure7 the time line for the upper at- mospheric physics program is presented.

58 10 PERSPECTIVES

Introduction rope, organized by the U.S. Space Science Board and the European Science Founda- Our intent in this chapter is to highlight tion's Space Science Committee, (An Inter- several items that are important to the gen- national Discussion on Research in Solar eral health and conduct of our discipline. and Space Physics, NAS-ESF, 1984), the con- They are organized into this chapter be- ferees recommended that an international cause they are applicable to all of the sub- program in solar and space physics be es- disciplines (solar, plasma, atmosphere), tablished to address the mutual scientific they do not necessarily involve specific pro- objectives of this discipline. grams, and they are not explicity included This conference was valuable not only in in our recommendations. They are nonethe- attempting to structure an integrated pro- less, extremely important to the future of gram of scientific activities directed at spe- solar and space physics and need to be con- cific goals, but also in enabling the two sidered in terms of the broad context of NA- communities to discuss, frankly, scientific, SA's role of conducting science in space. programmatic, and institutional issues. Such conferences are therefore important as Data Management forums for the exchange of views at the level of working scientists and should be expanded in the future to include other com- The management of space science data has munities interested in this area of research, not received the attention necessary to most most notably, Japan. effectively utilize this national resource. The The ISTP Program as currently planned is problems of past and present data manage- certainly responsive to the recommendation. ment systems and organizations were iden- tified in CODMAC - Volume 1. The recent We emphasize, however, that the science objectives are the essential goal to accom- NAS Report, Solar-Terrestrial Data Access, Distribution, and Archiving (NAS, 1984), plish---if, for any reason, the international made recommendations for improved data agreements for missions to address these objectives cannot be implemented, the pres- management for solar and space physics. In ent plans will have to be modified so that particular, that report identified access to the science objectives can be accomplished. data as the main problem in the discipline and developed plans including a Central Data Catalog and Data Access Network to Mission Costs alleviate the problem. The report also rec- The issues concerning costs of space sci- ommended a pilot program, to be initiated ence programs are particularly difficult for by NASA's Information Systems Office, that scientists to address because of their lim- would develop the detailed plans necessary for establishing the catalog and network. i.ted engineering, project management, and accounting expertise. Nonetheless, such is- NASA has not yet acted on this recommen- sues are important to scientists because dation. We believe that this pilot program is a necessary step for constructing the data high program costs or low budgets lead to situations where access to space becomes system for the ISTP, the highest priority new impossible. program in solar and space physics, and we Several of these issues, discussed in turn urge NASA to implement the pilot study as below, are soon as possible. • assessing program costs for planning International Cooperation purposes, • controlling mission costs, and At a recent meeting of scientific representa- • maintaining basic research capability tives of the United States and Western Eu- within a mission-oriented environment.

59 Planning Research Base

In establishing future program priorities Because NASA is a mission-oriented agency based upon cost and budget projections, where success is frequently measured in there is some risk that the projections are terms of flight programs, basic research ca- not completely accurate. Such is the case pability rarely receives high priority atten- for this report. While we have attempted to tion. If the funding in this area continues to obtain the best possible information on pro- erode, as it has in the past few years, the gram costs, we realize that they are, at ability to conduct missions in the future best, only estimates and are likely to may be dangerously compromised. It is im- change as project definition proceeds. Thus, portant that NASA our approach of establishing temporal prior- • establish adequate funding for R&A, ities is, we believe, still valid because the • protect these funds from development mission sequences and program emphasis demands, and are based on relative costs compared to a • regularly review the funding, and aug- reasonable budget allowance. ment it if necessary, in order to maintain the basic research capability. Controlling Costs The recent NASA Space and Earth Science Although the responsibility for controlling Advisory Committee report on Research & program costs belongs, rightly, to NASA Analysis in the Space and Earth Sciences managers, scientists are concerned about (July 1984) addressed the role and health of such matters because space research de- a continuing Resegrch and Analysis Pro- pends directly on funding allocations. Since gram in NASA and concluded that inade- the costs associated with space research are quate funding is the most pressing problem. inherently high, it is important to attempt We concur. experiments and to develop approaches aimed at reducing costs. Our Committee re- Facility Management and Operation cently identified a few ideas that we believe would prove useful in reducing costs of Ex- In several areas of space science, we can plorer missions (A Strategy for the Explorer foresee the need for long-lived, multi-instru- Program for Solar and Space Physics, NAS, mented space facilities. It is therefore im- 1984). These ideas included the following: portant that we now begin to consider how • reducing mission complexity by focusing these facilities will be managed and oper- on specific, sometimes limited, science ob- ated. Questions such as management ap- jectives; proach (principal investigators, guest ob- • providing budgets large enough to keep servers, science institutes), on-orbit development times reasonably short, maintenance requirements, and frequency thereby avoiding the cumulative effects of of instrument change-out will require care- inflation; ful study if we wish to make such facilities • more thoroughly preparing for high-risk available to a large segment of the scien- technological development; tific community and to control costs so as to • adjusting reliability and quality assur- ensure that they are affordable. ance controls to suit program objectives and to achieve realistic risk/cost tradeoffs; and • using more standardized or commer- Computer Facilities and Modeling cially available hardware. While these suggestions were made spe- Modem research in solar and space physics cifically for NASA's Explorer Program, we involves an interaction between experiment believe that they may well be more gener- and theory that is essential to continued ally applicable. We urge NASA to consider progress. In addition, the need for employ- these approaches and to work to develop ing a variety of diverse data sets to address others that will reduce the costs of space certain problems, the large volume of data missions and thereby make the whole enter- expected from some programs, the special prise of space research more effective. processing requirements for certain types of

6O data (e.g., imaging), and the need for large, • Evolutionary Approach. The four main multidimensional modeling studies will re- ASO elements, SOT, POF, SXRT, and EUV quire more emphasis on the availability of should be ultimately on the same platform. large computing facilities and of special- Each element, however, will be developed purpose facilities (i.e., array processors) for individually, beginning with SOT. Each ele- general use by the scientific community. ment would be flown initially as a Shuttle NASA should take the lead in making such facility and later integrated onto a perma- facilities available not only because the nent platform. In our time line (Chapter 7), agency is responsible for generating, ana- we show that when the third element, SXRT, lyzing, and interpreting much of this data, is completed it can join SOT and POF, and but also because NASA should be at the the instrument collection then becomes forefront of technological advances in space known as ASO. physics and should be supporting techno- This evolutionary approach should also logical innovation in the use of large com- be used for STO. The active experiment ele- puters. ments of STO should be set up with close manned involvement in the early experi- ments. Direct attachment to the manned sta- Space Station tion would permit early studies of the opera- tion of the equipment, i.e., beam injection In this report we have described several at various current levels and spacecraft areas where Spacelab instruments would neutralization, wave injection coupling to evolve toward use on the Space Station. the ionospheric plasma, and methods of Here we describe a possible scenario of how tracking chemical releases and dealing with solar instruments (ASO and STO), for exam- free-flying rnultiprobe and recoverable sub- ple, could do this. At present, it is possible satellites. Basic plasma studies could be only to take a preliminary look at the ac- conducted in the 28° inclination orbit and cornmodation of science instruments on the the equipment operation techniques con- Space Station. This is because we are only firmed. Following this period, the active ex- at a requirement-gathering stage of the periment package should be transferred to Space Station program. There will be a pe- the 90° inclination orbit and operated with riod of iterative matching of science require- the scientist involved from the manned sta- ments with engineering design that will tion or on the ground. take place over the next 2 years. In this discussion we will only sketch some of the • Orbital Mode. ASO and STO will likely requirements and raise some issues that utilize both 90° and 28° platforms---atrnos- will need to be dealt with in the Space Sta- pheric experiments on both, solar telescopes tion accommodations studies. (ASO) on either with a slight preference for • Manned Involvement. Scientific involve- 90°, the solar variability portion of STO on either platform, and the active experiments ment will be required in the acquisition of on a manned station or a 90° inclination data and operation of the instruments of platform, depending on their state of evolu- ASO or STO. Examples include control of tion. pointing of SOT or other telescopes at differ- ent solar features of interest, and adjust- ment of the instrument modes to match the Planetary Exploration study of the specific solar phenomenon in progress. Also, the initiation of an active In light of the evolving plans to implement experiment such as a chemical release or the recent SSEC report, our Committee re- an electron beam injection and the tracking viewed the future role of research in aeron- of the subsequent cloud or diagnosis of the omy and plasma physics in NASA's plane- plasma instabilities generated would re- tary program. Such research is an integral quire continuous scientist interaction. The part of the planetary program and accord- scientist involvement in the operation of ingly appropriate resources and portions of ASO could be on-orbit direct, on-orbit re- experiment payloads are to be allocated for mote, from the ground, or a combination of such investigations. However, a trend is de- all of the preceding options. veloping whereby aeronomy and plasma

61 physicsobjectives appear to be relegated to nally, the astrophysical implications of pla- low priorities in planned missions and little, netary exploration will rest in an important if any, spacecraft resources are being allo- way on the study of plasmas. cated for their implementation. We recommend that NASA continue its We feel that the manner in which the rec- past policy of planning an appropriate mix ommendations of the SSEC report are being of special purpose missions and/or missions implemented overlooks the essential contri- of more general objectives with sufficient butions made by aeronomy and plasma allocation of resources to permit broad in- physics to our understanding of planetary vestigations that include aeronomy and environments and planetary evolution. Fur- plasma physics. We also suggest that re- ther, investigations of planetary environ- sources within the planetary R&A budget ments have in the past and will certainly continue to be devoted to developing inves- continue to result in important contributions tigations in aeronomy and plasma physics to studies of the Earth's environment. Fi- for future planetary programs.

62 11 ORGANIZATIONAL STRUCTURE

A major intellectual thread linking several This unity is not realized in NASA's orga- recent NAS/NRC advisory committee reports nizational and management structure at has been the essential unity of the disci- present. The elements of the on-going solar plines comprising solar and space physics. and space physics program are managed by The study, Space Plasma Physics (Colgate several Office of Space Science and Appli- report), requested of the Space Science cations (OSSA) divisions: The Astrophysics Board by NASA, attested to the scientific Division is responsible for the scientific di- importance and intrinsic merit of the disci- rection of SOT and ISPM, as well as manag- plines of space plasma physics and solar ing the Explorer, sounding rocket, and bal- physics. The study committee, which was loon programs; the Solar System Exploration composed primarily of laboratory plasma Division is concerned with the atmospheres physicists and astrophysicists working in and magnetospheres of all solar-system ob- areas outside the disciplines examined, con- jects except the Sun and Earth; the Earth cluded that the research in solar and space Science and Applications Division manages physics is also important because it contrib- space plasma physics and upper atmos- utes to significant developments in other pheric research, including UARS; the Shuttle areas of science. This conclusion was re- Payload Engineering Division handles Spa- cently reiterated by the Physics Survey celab instrumentation. Committee. Coordinated research among the disci- Using the Colgate report as a basis, the plines that comprise solar and space phys- SSB Committee on Solar and Space Physics ics is an essential feature of our strategy. developed the scientific strategy for future Such coordination will not easily be space research in the field (Kennel report). achieved with management of the various This strategy is based on a high degree of pieces split among several organizations, coherence among the disciplines of solar each with its own set of goals and priori- and space physics. In addition, a Geophys- ties. The program we have proposed is sub- ics Research Board study (Friedman-Intrili- stantial in terms of both scientific content gator report) emphasized the unity of solar- and cost. We believe that NASA should con- terrestrial physics and recommended direc- sider whether its present management tions for solar-terrestrial research in the structure is appropriate for supporting this 1980s. program.

63

APPENDIX: LEVELS OF INVESTIGATION*

In Report on Space Science 1975, the Com- els of investigation. The first exploratory mittee on Planetary and Lunar Exploration uses of a given technique determine its fea- (COMPLEX) identified three stages of space sibility and identify research objectives. At investigations. Reconnaissance, the first the opposite extreme is its systematic use to penetration of a region of space by an in- produce basic physical information. In Fig- strumented spacecraft, has discovery as its ure A.1 we estimate the status of in situ objective. Reconnaissance is followed by ex- spacecraft investigations, in Figures A.2 ploration, whose aim is phenomenological and A.3 of remote sensing investigations identification of important processes. With and selected active experiments. phenomenology clear and physical proc- When research approaches its intensive esses identified, intensive study begins. study phase, one can judge its progress by Here, research focuses on quantitative eval- the quantitative understanding it has uation of physical mechanisms and the link- achieved. One way to do so is to evaluate age of one mechanism to another in compre- comprehensive models that link together hensive models. several interacting processes. Here we have These categorizations apply equally well defined four evolutionary phases. The first to in situ spacecraft investigations in solar is phenomenological identification of perti- and space physics. Slightly different ones nent physical processes and their interac- apply to remote-sensing studies. Detection tions. This done, it becomes feasible to con- and first preliminary surveys are followed struct preliminary quantitative models. by global surveys with sufficient coverage Whether they are correct or not, their exist- and resolution to identify basic physical ence signifies that moderate quantitative mechanisms. These are again followed by understanding has been achieved. They mo- intensive studies, usually requiring high tivate further observations and theory lead- space and time resolution, whose aim is ing to accurate quantitative models, suita- quantitative understanding of specific proc- ble for systematic comparison with esses. In addition, most of our major subdis- experiment. These then evolve into predic- ciplines can use or have made use of active tive models, at which point the threshold of experiments. Because of their diversity it is practical utility has been reached. Figure difficult to identify all but two extreme lev- A.4 contains our perception of the 1984 sta- tus of models of several problems in solar-

TThis Appendix is an update of the similar section of system space physics, selected for their il- the Kennel report. lustrative value.

PRECEDING PAGE BLANK NOT FILMED.

65 LEVELSOFIN SITU SPACECRAFTINVESTIGATION

PHYSICAL AWAITING INTENSIVE DISCIPLINE SUBJECT AREA RECONNAISSANCE EXPLORATION UNDER- RECONNAISSANCE STUDY STANDING

SOLAR PROBE STRUCTURE AND SUN, SOLAR CORONA J:::l k::] |:::1 I:::t I:i:t :::1 t::! I:.'.'-'.'11 DYNAMICS OFTHE HELIOSPHERE GENERATION OFSOLAR SOLAR PROBE IE;:I• l::;t 1::::1 L::,'J t::t WIND

HIGH-LATITUDE SOLAR ISPM SPO t.'_..1[:_-I I,::1I:::! WIND

IN-ECLIPTICSOLAR WIND BEYONDSATURN

INECLIPTIC SOLAR WIND BETWEEN MERCURY b' I JUPITER

HELIOPAUSE, INTERSTELLARMEDIUM

TERRESTRIAL MAGNETOSPHERE ISTP ;i3 f;:;! I MAGNETOSPHERE <6OR e PHYSICS EARTH MAGNETIC ISTP t:::! F):_ :::1 F:::I t:::| t:::j t-: TAIL. WAKE

SOLAR WIND ISTP ;-;-3 _ l INTERACTION

KEY: _'--'-']COMPLETEDIAPPROVED _RECOMMENDED

FIGUREA-1

66 LEVELSOF/N SITU SPACECRAFTINVESTIGATION (continued)

PHYSICAL AWAITING INTENSIVE DISCIPLINE SUBJECT AREA RECONNAISSANCE EXPLORATION UNDER- RECONNAISSANCE STUDY STANDING

TERRESTRIAL, THERMOSPHERE, ATMOSPHERIC IONOSPHERE > 150-KM / IONOSPHERIC 120-150-KM It.":1Y':] _.':'zl[.':] I._£| ,';..]L_ PHYSICS MESOSPHERE X ICE CRAF PLANETARY, COMETS I E_:i _TL. F:.,'I _ql ATMOSPHERIC SOLAR-WIND INTERAC- IONOSPHERIC J MAGNETOSPHERIC liON OF MARS MAO PHYSICS ATMOSPHERE OFMARS t.'74 E'4 L'_'4E,"] i'['_'4'."] [::] ['.':3F:.'4F::.l F,':: _-':.1_-'_-511

SULAR-ININO INTERAC- lION OF VENUS

MAGNETOSPHEREOF MERCURY

MAGNETOSPHEREOF GALILEO JUPITER

MAGNETOSPHEREOF SATURN

MAGNETOSPHEREOF VOYAGER URANUS, NEPTUNE UPPER ATMOSPHERE. IONOSPHEREOF JUPITER, SATURN, TITAN

KEY:_ COMt_ETED/APPROVIED_ RECOMMENDED

FIGUREA-1 (continued)

67 LEVELSOFREMOTE-SENSINGINVESTIGATIONS

PHYSICAL AWAITING PRELIMINARY GLOBAL ] INTENSIVE PRELIMINARY UNDER- DISCIPLINE SUBJECT AREA SURVEY SURVEY ] STUDY SURVEY STANDING

SOLARPHYSICS CORONALHOLES,LARGESCALE i I MAGNETICFIELDS

RADIOBURSTS ,I i

_ i GLOBALOSCILLATION • i

J FLARES • i SOHO I INTERNALSTRUCTUREb r::::::l I::::::: JL':::'J [:i;_:;! I;:;:;:] DYNAMICS - SOLARDYNAMO SOTIASO I SURFACEPLASMAMAGNETIC |::-:_;.1b':::::! b':-::i FIELDINTERACTION_ SOT[ASO I ENERGYSTORAGEAND RELEASE _:-._I_ SQT_ASO I ATMOSPHERICHEATING F::::::] I:;:_::d |:::::-I SOHO STRUCTUREAND DYNAMICSOF PorIASOI • L::::::I [_:::::_ l:::'::J I:::::::! t-::::l CORONAAND SOLARWIND

HELIOSPHEREPHYSICS INTERSTELLARNEUTRALS I

TERRESTRIAL, GLOBALAURORALMORPHOLOGY I:::::.':1 |.*;:;:;:! 1:.;;;;:;] ISTP 1 MAGNETOSPIERIC REMOTESENSINGOF PHYSICS MAGNETOSPHERICSTRUCTURE

TERRESTRIAL, L "ARs I ATMOSPHERIC MIDDLEATMOSPHERE IONOSPHERICPHYSICS MESOSPHERE]LOWER LEXPLORERStSTO THERMOSPHERE I:::::':] E_.'.::l I:]:_:]:1|:::::'J I::::::=J xeY:F-----lCOMeLmOIA_O__ReCO_DeO

FIGUREA-2

68 LEVELSOF INVESTIGATIONOFSELECTEDACTIVE EXPERIMENTALTECHNIQUES

PRELIMINARY SYSTEMATIC TECHNIQUE SUBJECTAREA NOTYETUSED USE USE

RADAR IONOSPHERIC,ATMOSPHERIC, ANDSOLARPHYSICS

ENERGETIC FROMROCKETSIN PARTICLE IONOSPHEREAND INJECTIONS MAGNETOSPHERE FROMSPACECRAFTIN SPL IONOSPHEREAND _:.':! f::!1 P::J I:::! _:_:] 1":::1I:::'11 MAGNETOSPHERE

WAVEINJECTIONS FROMGROUNDINTO I IONOSPHERE FROMSPACECRAFTINTO SPL,TETHER,STO L:!:_II::::1 ]:!:] E:-:1 E:-:] E:.::I [:_:] E:!:I E::'[I IONOSPHERE TETHER,STO CHEMICALRELEASES IONOSPHEREANDATMOSPHERE _;i;] ]_-'::l |:::l :::1 E:':] |i:il I:-:! CRRESSTO MAGNETOSPHERE i:::l E::1 L::'_ .':1 t:i:] t:::l I

SOLARWINDAND EXPLORERS k:::l E:4 t:::'l ::1 r:::! I:::J J MAGNETOSPHERE STO LIDAR ATMOSPHERE k::qI:::]_:-:1,::tE:-:]E:]I

KEY: E_ COMPLETIED/APPflOVEO_ RECOMMENDEO

FIGURE A-3

69 STATUSOFPHYSICALMODELS

SOME FIRST ACCURATE RUDIMENTARY PREDICTIVE D_CI_INE PROBLEM PHENOMENOLOGICAL QUANTITATIVE QUANTITATIVE UMDERSTANOING MODELS UNDERSTAmING MODELS MODELS

SOLARPHYSICS BASICFLAREMECHANISM

lARGE SCALEWEAK MAGNETIC C,:d I':'3 F:,;"]I:,: FIELD

NONRADIATIVE FEATING OF ATMOSPHERE

GLOBALOSCILLATIONS

THERMAL RARE PLASMA L:::J }:':] I:.:

TYPE i'llEMISSION

HELIOSPHERIC INTERPLANETARYACCELERATION i:i:] _::;:I _::: PHYSICS OFENERGETICPARTICLES

CORONALEXPANSION l:]::J L_:_3F:::

INTERPLANETARYMODULATION OF F:::I |::::I I:::: GALACTICCOSMIC RAYS

EVOLUTION OF SOLAR WIND L::;'I I::::I STRUCTURES

TERRESTRIAL, MAGNETOPAUSECOUPLING MAGNETOSPHERIC DYNAMICS OF GEOMAGNETICTAIL F.:;:I I::::1 |::: I;;::1 ];.':."1 PHYSICS PLASMA SOURCESAND SINKS I::::d F:::] I:.:i

GLOBAL MOOELS OF SOLAR WIND I:i:;:l F::::l I:::: [::i:J i::::l F:::] t::: I:.:::t k:::::l INTERACTION

AURORAL ARCS.PARTICLE [::::I F:,;,1F::: ACCELERATION

kEY: _ COMPLETED/APPROVED_ RECOMMENDED

FIGUREA4

7O STATUSOFPHYSICALMODELS (continued)

SOME FIRST ACCURATE RUOIMENTARY PREDICTIVE DISCIPLINE PROBLEM PHENOMENOLOGICA[ QUANTITATIVE OUANTITATIVE UNDERSTANDING MODELS UNOERSTANOING MODELS MODELS

TERRESTRIAL, COUPLINGTO IONOSPHERE |::i _::1 MAGNETOSPHERIC AND THERMOSPHERE E:)E:_-IE:-t PHYSICS (conlb_d] TRAPPED RADIATION BELTS

TERRESTRIAL AT MESOSPHERICCOUPLINGAN]) MOSPHERIC PHYSICS DYNAMOS

GENERATION OF THERMO- |::l l:.;J L;" SPHERIC WINOS EFFECTSOF PHOTONS AND ENERGETIC PARTICLES ON UPPER ATMOSPHERE STATIC UPPER ATMOSPHERE MOOELS

GENERALCIRCULATIONAL MODELS OF MIDDLE ;::J _;:_JI ATMOSPHERE

SUN-CUMATE ENTIRE AREA F:9 L":] _.'.:1F',::Ik::l t-:] WEATHER RELATIONS

PLANETARY MAGNETOSPHERESOF MARS, MAGNETOSPHERES, URANOS, NEPTUNE, AND IONOSPHERES.AND COMETS ATMOSPHERES MAGNETOSPHERESOF MER- CURY ANO SATURN STATIC MODELS OF PLANETARYATMOSPHERES

m: _ COMPI.ETEDIAPPROV[O_ RECOMMENDED

FIGURE A-4 (continued)

71 STATUSOFPHYSICALMODELS (continued)

FIRST RUDIMENTARY SOME ACCURATE PREDICTIVE DISCIPLINE PROBLEM QUANTITATIVE UNDERSTANDING PHENOMENOLOGICAL QUANTITATIVE MODELS MODELS UNDERSTANDING MODELS

MAGNETOSPHERES OF JUPITER AND I [:_:]I_:;]]:_:|i:--I _:! l VENUS

COMETS DYNAMIC MODEL t::_ _ t::Z I:::]

ACTIVE MAGNETOSPHERIC EXPERIMENTS t-:] 1_]:-4[:::J"_::J GASRELEASES

IONOSPHERICGAS RELEASES

ELECTRONBEAM RELEASES

WAVE INJECTIONS ]i:i:Jr::ilt:::] r::J _::J

FIGUREA-4 (continued)

72 GLOSSARY

AE Atmosphere Explorer AMPTE Active Magnetosphere Particle Tracer Explorer(s) AO Announcement of Opportunity ASO Advanced Solar Observatory AU astronomical unit COMPLEX Committee on Planetary and Lunar Exploration CRRES Combined Release and Radiation Effects Satellite CSSP Committee on Solar and Space Physics DE Dynamics Explorer DSN Deep Space Network EOM Environmental Observation Mission ESA European Space Agency EUV extreme ultraviolet EUVT EUV telescope GGS Global Geospace Study HEAO High Energy Astronomical Observatory ICE International Comet Explorer IMP Interplanetary Monitoring Platform ISAS Institute of Space and Astronautical Science, Japanese ISEE International Sun-Earth Explorer ISPM International Solar Polar Mission ISTP International Solar-Terrestrial Physics (program) LEO lower-Earth-orbit MELTER Mesosphere-Lower Thermosphere Explorer MHD magnetohydrodynamic MO&DA mission operations and data analysis OMS Orbital Maneuvering Subsystem OSO Orbiting Solar Observatory OSSA Office of Space Science and Applications PI principal investigator POCC Payload Operations Control Center POF Pinhole Occulter Facility R&A research and analysis RPDP Recoverable Plasma Diagnostics Package SL Spacelab SME Solar Mesosphere Explorer SMM Solar Maximum Mission SOT Solar Optical Telescope SPAN Space Physics Analysis Network SPL Space Plasma Lab SPO Solar Polar Orbiter STO Solar-Terrestrial Observatory STTP Solar-Terrestrial Theory Program SXRT soft x-ray telescope TDRSS Tracking and Data Relay Satellite System TSS Tethered Satellite System UARS Upper Atmospheric Research Satellite XUVT X-ray/Ultraviolet Telescope

73