Space Travel : A Symposium

Introduction

BY COLONEL PAUL A. CAMPBELL, USAF (MC), Chairman

Many of us here today are of the opinion extra-atmospheric flight. Possibly that will that extra atmospheric flight--space flight, insoluble, and if they can--within the frame- if you please--is now entering the realm work of security--make predictions. of the feasible. We have on our program I am certain one of these problems will be Percent 130,000 99.7 120,000 99.5/8 110,000 99.1/4 100,000 190,000 90,000 '31,235 98.5 60,000 ,0,49 r 96 7,6 70,000 / 93 3/4 60,000 ,,I,~ ~,0'~6 --50,445 50,000 87 I/2 40,000 . ,4E,,0 75 30,000 f J 20,000; /20p,0 50 lO,OOO 0 J' I f 1905 1910 1915 1920 1925 1930 1935 1946 1945 1950 1955 1960 1965

Fig. 1. Graph showing man's altitude achievements plotted chronologically by years and the percentage of atmosphere penetrated. The broken line represents un- confirmed records reported in the press. today a group of experts representing vari- to attain agreement as to what constitutes ous disciplines. Their contributions toward be answered today. our goal can be questioned by no one. They To start off, I would like to show two have been asked to discuss the present state diagrams (Figs. 1 and 2) showing evidence of the art in their line of endeavor, prob- of man's approach toward space. The first lems which are soluble and those which are is the time-worn graph of altitude achieve- ment plotted chronologically. Note the This symposium was presented on May 8, 1957 at the 28th annual meeting of the Aero break-through produced by the advent of Medical Association, Denver, Colorado. rocket propulsion. The dotted lines repre- Dr. Campbell is special assistant for med- sent that portion of the achievements which ical research to the commander, Air Force Office of Scientific Research, Washington, have been reported at times in various news D.C. media but have never been confirmed. OCTOBER, 1957 479 SPA.CE TRAVEL---CAMPBELL

The second diagram represents the same American Aviation, Los Angeles, will set us chronological graph of altitude achieve- straight on some of the quite serious human ments but plotted in terms of per cent of problems. mass of atmosphere penetrated. Note the Commander George W. Hoover, USN, Percent loo I jp." -? 90 jl v 00 ~ r 70 / 00 5O / 40

20

10

0 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 Fig. 2. The penetration of the atmosphere plotted according to year of achievement. The broken line represents unconfirmed records reported in the press. smooth asymptotic progress, and also that Office of Naval Research, Washington, D. tile sudden break tel)resented by advent of C., has chosen the subject, "What Instru- rocket propulsion has ironed out. Note, mentation Will Be Required." please, that the most rapid progress if one A. M. Mayo, chief equipment and safety uses this parameter took place in the early research engineer of the Douglas Aircraft days of aviation. That is a little defla- Company, El Segundo, California, will cover tionary. However, we shall hear many of survival aspects of space travel. the answers today from the members of Dr. J~ohn P. Hagen, Naval Research Lab- our symposium. oratory, Washington, D. C., will describe Konrad K. Dannenberg, director, Tech- the space travel implication of the Vanguard nical Liaison Group, Army Ballistic Mis- project.* siles Agency, will tell us how the "Pro- As a fitting conclusion of this series of pulsion Engineer Views Space Travel." discussions, Dr. Hubertus Strughold of the Professor Walter Orr Roberts, High Al- School of Aviation Medicine, Randolph Air titude Observatory, of the University of Force Base, Texas, will discuss the question, Colorado, will discuss "The Astronomer's "What are the Possibilities of an Inhabitable Views." Extra-Terrestrial Environment Reachable Dr. Heinz Haber of the University of from the Earth?" California, Los Angeles, will comment on "The Astrophysicist's Views." *Dr. Hagen was not present to read the Scott Crossfleld, test pilot for North report included in this symposium--E~IToR. 480 ~VIATION ~V~EDICINE The Propulsion Engineer's Views

BY KONRAD K. DANNENBERG

The purpose of this presentation is to that air molecules at the 250 mile peak al- analyze the status of existing-propulsion titude of the Wac Corporal are so rare that systems and their usefulness for extra-at- there was less air than is present in the best mospheric flight. First, a definition of the vacuum tubes. Today's knowledge can pro- extra-atmospheric portion of flight would vide marl with the transportation to venture be in place. Ninety-nine per cent of the into space right now. total air is contained within a 50-mile shell, and this coincides with the upper border of STATE OF THE ART the stratosphere. However, there is still Calculations have shown that conven- noticeable air resistance at this altitude tional power plants can do the job. New especially on high speed bodies, such as power sources should presently be viewed meteors and rocket ships. Not until 120 as possible improvements but are not a miles are exceeded is the atmosphere so thin necessity. Today's designs for solar and that it no longer offers detectable resistance nuclear power generators are very heavy to a traveling object, thus defining the mini- and, therefore, inefficient. It is generally mum altitude of manned space flight for expected that a 21-pound satellite will take short-lived satellites. to its orbit in late 1957 or early 1958. Im- The region beyond 120 miles is called the proved designs will permit several hundred exosphere. It has been demonstrated that pounds to be thrown into the orbit and rockets can move through it at great speeds. should follow shortly. In the early 1960s The lower border of the exosphere was we should be able to accelerate several reached by high altitude firings of single- thousand pounds to a velocity which would stage V-2 rockets in Germany in 1944 and permit any desired orbit, the altitudes of in the United States in 1948. More recently which will be determined by the satellite's a Viking rocket rose to approximately 160 specific mission. miles. A Wac Corporal launched as a For example, as an assembly point for second-stage from a V-2, reached a peak al- manned space ships, Dr. yon Braun pro- titude of 250 miles in 1949, thus traveling poses a celestial route 1,075 miles above the well within the exosphere. Newspapers late earth. Such a satellite would complete a trip in 1956 reported another flight of a multi- around the earth every two hours, which is stage rocket. Unconfirmed reports claimed desirable for observational purposes. It a peak altitude of about 600 miles which would orbit well beyond the atmosphere, and would then extend well into the upper re- would provide an excellent stepping stone gions of the exosphere. The precise borders for further progress into space. Vehicles of this outer atmospheric layer are un- taking off from such a satellite to go to the known at present. It simply "thins out" moon and to neighboring planets would need until there are no nitrogen or oxygen mole- only small power plants because the weight cules left. It is believed by many to extend of the ship does not need to be lifted off up to 700 or 800 miles. the earth's surface. Thrust ratings lower Propulsion units, for all practical pur- than the ship's weight are normal. It can, poses, encounter physical conditions of ex- therefore, be said that once propulsion prob- tra-atmospheric fl igh t when traveling lems of manned spaceships to extra-atmos- through the exosphere. It should be noted pheric orbits have been solved, there should be no major obstacle hindering the propul- Mr. Dannenberg is director of the tech- sion engineer to step into lunar space, or nical liaison group of the U. S. Army Bal- listic Missile Agency, Redstone Arsenal, even into the adjacent interplanetary space Alabama. of our two neighboring planets. OCTOBr.R, 1957 481 PROPULSION ENGINEER'S VIEWS--DANNENBERG

ENERGY PROBLEMS quate, if one is willing to limit travel to the adjacent interplanetary space. The vast difference in energy level be- tween the earth's surface and space creates SPECIFIC IMPULSE the primary problem. To leave the gravity The "specific impulse" tells us how much field of the earth permanently with an thrust is obtained while consuming one escape velocity of 7 miles per second pound of propellant per second. A high would require 14.9 Kcal/g, whereas to orbit specific impulse is, therefore, desirable be- at an altitude of 140 miles at a circular cause it results in a smaller rocket having velocity of almost 5 miles per second only the same operational capabilities. However, 7.6 Kcal/g. would be required. Energy the specific impulse is not the only criteria levels presently of interest are in this span, for the desirability of a propellant. High We have a number of fuels which yield the density, for instance, permits one to carry desired amounff of energy; however, they the same amount of energy in a smaller have to be used with oxygen or another propellant and tank package. Very dense- oxidizer. This in turn cuts approximately in propellants may even result in decreased half the yield per gram of mass. Further- dimensions and weight of the rocket en- more, we must package our propellants in gines. Therefore, the product of specific containers, and must add instrumentation impulse "Isp" and the bulk density "d" of and a pilot's compartment. This requires hoth propellants is often used for com- additional fuel quantities to fulfill the parison. The "ideal" fuel, hydrogen, looks energy needs. Such a problem could be very poor when judged from this point of solved by the "staging" of our ships. The view; whereas, combinations containing total chemical energy of the first stage fluorine and fluorine compounds perform could thus be converted into stored kinetic excellently. energy, and from this mass with an original- Here are a few comparative figures ly higher energy level, we could start our quoted for a 300 psi chamber pressure with second stage. This in turn will add by its 1 arm nozzle exit pressure: combustion of propellants to the energy level of the remaining mass. Because this lsp d Isp.d V-2 Propellants:LOX--75% Alcohol 234 0.98 230 process can be repeated as often as neces- IRBM Propellants:LOX--Kerosene 249 1,02 254 "Ideal" Propellants:LOX--Hydrogen 345 0.23 79 sary available chemical propulsion units are Proposed Prot~ellants:*RF Nitric Acid- able to meet our energy requirements, Hydrazine 242 1.25 302 Possible Propellant s :*Fluorine-I'Iydra- zine 300 1.07 321 For travel to the outer planets, energy re- quirements cannot be met by chemical pro- *Hypergolical propellant combination. pellants. Expected improvements will not In any case, the final choice can be made change the situation much. Obtainable com- from a great variety of propellant com- bustion chamber temperatures offer difficul- binations, some having extensive test and ties at about 3000 ~ C. (5400 ~ F.) at 500 psi operational experience, others possessing chamber pressure. A limit is presently an- outstanding performance but with unknown ticipated around 4000 ~ C. (7200 ~ F.) and characteristics of operational behavior. Dr. 1,000 psi chamber pressure due to heat yon Braun for logistic reasons favors nitric transfer and material strength problems. acid and hydrazine as the most promising Use of atomic reactors to heat working propellant for a large satellite project which fluids does not improve this situation. The could be implemented today. desired propulsion system for outer space and interstellar flight is therefore an atomic LOGISTICS rocket which will convert energy directly Propellant logistics pose the greatest in- into thrust, yielding a million times the dividual problem. Continuously ferrying amount obtained with present fluids or pro- supply rockets will devour huge quantities pellants. of propellants; the storage depot at the However, as stated before, today's con- space station must be stocked, and a sizeable ventional propellant combinations are ade- amount must be used during pre-flight test-

482 .~VIATTON ~{EDICINE PROPULSION ENGINEER'S VIEWS--DANNENBERG ing, training and test flights with crew and flown and which has undergone only rudi- relief personnel. Thus, propellant needs will mentary testing. The engines of these be tremendous. The problem should not vehicles will be swiveled for programmed only be analyzed from the desire for a flight controh They will be mounted in minimum sized rocket, but also from the such a maturer that missile roll can be com- overall economy of the venture wbich may pensated. The high ratio between the com- be an overriding viewpoint. bustion chamber pressure and the ambient The problem can possibly be reduced by condition of zero pressure will permit low the use of nuclear power at the launching combustion chamber pressures and thereby site to provide, among other things, energy light-weight engines, which still would for the manufacture of propellants. The yield excellent specific impulses. The ex- fuel and oxidizer may therefore be chosen haust nozzles will be designed for high ex- on grounds that they can be manufactured pansion ratios. No severe cooling problems at the site from air and from water. This are expected because the expanding gases may determine preference even over pro- will cool down to such an extent that use pellants of higher energy output. Such a of uncooled nozzle ends is intended. combination would be nitric acid-hydrazine; Highest emphasis will be placed on re- propellants like fluorine would be at a dis- liability. Thorough testing of all com- advantage. To team atomic energy and ponents, of the engine sub-assembly, and of rocket propulsion in this fashion appears the assembled missile will be scheduled. presently much more realistic than the Most tests do not necessarily have to be direct use of nuclear p~wer plants in the made at the launching site, but may be per- vehicle, especially for first stages. formed at the contractor's manufacturing plant or at a proving ground at home. A HARDWARE captive firing at the launching site just The powerplants of passenger-carrying prior to take-of may be desired and could space ships can be much smaller in thrust be arranged. It can be of short duration, output than the commuting ferry rockets as but the used propellant portion should be outlined earlier. Therefore, no great diffi- replenished before take-off. Existing meth- culties in design, construction and operation ods of .in-line and test-site inspection will of chemical space ships are expected after have to be improved greatly. In fact, exist- the much larger units for the flight to and ing difficulties in rocket systems occur es- from the space station have been accom- sentially in the smaller components, which plished. "Staging" of alI ships to the space do not always get the same attention as the station will be required. Engine throttling large items; thus, we now have more diffi- permits limitation of acceleration values to culties with heat exchangers, pipe lines, con- tolerable loads. If desired for economy, re- trol valves and pressure regulators than we covery of the exhausted portions of the have with other often less understood and lower stages can be accomplished. Much more compl.icated systems such as turbo experience will be accumulated from further pumps, combustion chambers, and injectors. perfection of existing automatic and manned It will be the mission of American industry vehicles for high altitude flight. This in to overcome these difficulties by better and turn will lead to further advances and more efficient inspection and by improved eventually to the manned orbiter. methods of production and product evalua- Published design proposals normally pro- tion. This mission will be complicated by vide a large number of smaller engines to the need for redesign of propulsion sys- meet the requirements for a high total tems, as well as of the guidance and con- thrust. This does not necessarily decrease trol systems, for full automation. The the system reliability. In fact, I would at pilots will not have the necessary time and any time prefer to fly with a large number capability to fulfill these functions and will of well proven, and extensively tested have to depend upon mechanized automatic IRBM engines rather than with a newly control for the entire ship during the pro- developed single engine which has never pelled flight. The human response time is OCTOBER, 1957 483 ASTRONOMER'S VIEWS--ROBERTS too long to perform the necessary maneuvers see no difficulties of a magnitude which with the required precision and accuracy. would prevent the initiation of a venture Furthermore, acceleration and the events of into space immediately with good assurance the flight put man under such physical and of success. Forthcoming results of existing mental stresses that he cannot be relied upon. missile and satellite programs will yield in- The handicaps are just too great. We are, valuable information towards the final solu- consequently, back again to space flight's tion. We've come a long way, and I am worst bottleneck--man himself. convinced that once men unite their knowl- edge and combine their efforts toward the As a plain and earth-bound propulsion progress of science and technology, nothing engineer and not as a co-pilot of the ship, I can permanently stand against them.

The Astronomer's Views

BY WALTER ORR ROBERTS, PH.D.

Our symposium today signalizes that an fell me in the meanwhile. And even within age old dream of the astronomer nears the solar system where the time for travel reality. The science of rocketry has, at last, is relatively short, and the over-all pros- brought the realistic prospect of exploring pects brighter, the problems are many and far into space with telescopes, photoelectric look difficult to surmount. In short, I'm devices, and other measuring instruments frankly pessimistic about space travel for that will telemeter their findings back to humans. earth. The chance to probe directly into the Here is where my pessimism ends, how- hidden facts of nearby space is exciting fare ever. Important mysteries of space can be for the astrophysicist. solved with the rockets and satellites on to- My view of the prospects for space day's blueprints if we plan imaginatively. travel by living persons is less sanguine. I The wealth of rocket data already available see only an outside possibility of some about the upper atmosphere, cosmic rays, limited flights into the first few hundreds of the aurora, and the ionosphere is but a taste miles of space for perhaps a few hardy of what we can learn. Pointing the way are souls. Except for this I doubt that human the brilliant researches of groups like the space travel is for our generation, however Naval Research Laboratory teams headed fascinating it may be in science fiction. Nor by Tousey, Newell, and Friedman and do I think this will be much loss. I, for Chubb, or the work of Van Allen and his one, wouldn't want to spend forty years of colleagues at State University of Iowa, to my life getting to a nearby star where there name but a few of the many. We are in- is perhaps one chance in a million of finding deed at the threshold of an era of space a planet like earth. If I did make it, and physics. there were a suitable planet, it would prob- The years ahead will see us breaching the ably be a dusty, windy desert, like Mars, or protective shield of the ozone layer and a steaming jungle, rather than just the right penetrating regularly into the D, E, and F blend of temperate climate. regions of the ionosphere some 50, 65, and Even if I could travel at the improbably 1.50 miles overhead. There we shall find, I fast speed of 50 million miles an hour-- believe, clues to the true atmospheric chem- round the world in about one second--it istry and physics of the layers we rely on would still take me forty years or so to for long distance radio communications. Go- reach the nearest star if no worse fate be- ing beyond, we shall find, possibly, new facts of the primary cosmic rays unaffected by Dr. Roberts is director of the High Alti- atmospheric collisions, data on spatial mag- tude Observatory, University of Colorado, Boulder, Colorado. netic fields, and measures of the tempera- 484 AVIATION MEDICINE ASTRONOMER'S VIEWS--ROBERTS tures of the tenuous but highly significant prime constituent, hydrogen, to helium and gaseous layers, in and above the ionosphere. thus to the energy ultimately radiated as Indeed, we are very likely to get the first sunlight. This visible solar light is given off realistic census of the true space density at such a constant rate that despite deter- of meteors, the .debris of space on which mined efforts no significant variations have

Fig.1. A large solar flare that rose to maximum in five min- utes. Such a sudden brightening on the surface of the sun is often accompanied by an immediate fadeout of short wave radio communication on the sunlit half of the earth. This flare was photographed in the light of hydrogen at the Sacramento Peak Observatory on February 29, 1956. may conceivably depend such things as ever been observed. We know that varia- worldwide tendencies in rainfall. tions, if they exist, are a small part of But to a solar astronomer the greatest 1 per cent. challenge of all is the prospect of looking In contrast to this steady emission, the at the sun with a freedom impossible for sun probably sends out a multitude of the earth-bound. To understand this chal- radiations in non-visible wave lengths, many lenge, let's look for a moment at the basic of them highly variable both in intensity and facts about the sun. The sun is a gaseous duration. Because of the opacity of the sphere about 864,000 miles in diameter. The earth's atmosphere to these radiations, our weight of the successive layers of gas knowledge of them is almost entirely in- compress the central gases to a density ten direct. From 100 A to 900 A, for example, times that of steel. To support this weight we do not even have reliable guesses of the central temperature rises to tens of mil- what the solar emission looks like. Those in lions of degrees. Deep in this core thermo- the wave lengths from 1 to 1500 A are of nuclear processes slowly transform the sun's particular interest because of their suspected OCTOBER, 1957 485 AS'I'I{ONfJMI:.R'S VI E\VS--ROBERTS influence on the earth's atmosphere. All sorts. For example, the flares are thought of these short wave emissions must origin- to emit powerful x-rays and ultraviolet ate in sources far from thermodynamic emanations that change the ionization of the equilibrium. Their behavior makes the lower ionospheric regions, and produce solar atmosphere a fascinating laboratory abrupt radio fadeouts. Other regions of the sun, far less well defined, are suspected of ejecting electrified particles that travel in a day or two from sun to earth with a speed of about a thousand miles a second. Some particle streams appear in a steady continu- ous flow; others arrive in irregular spurts. There is evidence that these particles pro- duce the auror a and the magnetic storms. But this is still hypothetical. Even more speculative is the possibility that some of these solar emissions are responsible for upper atmopherie heating that may have far reaching effects on the location of the jet stream and on world-wide weather pat- Fig. 2. A large eruptive prominence seen terns. But there are intriguing suggestions at the edge of the solar disk showing mater- that this is so! ial being ejected into space at high velocity. Photographed in the light of hydrogen al Another interesting possibility is that the the Climax observing station of the High earth moves in the outer reaches of the Altitude Observatory of the University of sun's very tenuous atmosphere and that Colorado on March 5, 1953. there is actually heating of the earth's own outer atmosphere through thermal conduc- for study of the physics of hot gases at tlon resulting from the million degree low pressures, high velocities of ionized corona of the sun. We now know also that gases in magnetic fields, and non-equilibrim the sun emits radio waves from several radiation physics. meters to a few millimeters wave length, At the surface of the sun, also, are found that vary greatly from day to day, hour challenging astrophysical problems. Dark to hour, and even second to second. It sunspots form like vortices, cooler areas in does not seem probable that research efforts the warmer surrounding surface. Associated now underway may reveal terrestrial effects to one degree or another with the sunspots from these radio waves. But solar-ter- are the many other phenomena of the sun's restrial research is full of surprises. changeable atmosphere, the prominences, Space exploration offers us the chance to corona, chromosphere, faculae, plages, flares, study all the emanations from the sun be- filaments, spicules, granulation. And each fore their energy is spent in modifying the of these varies with its own characteristic earth's atmosphere. I will regard the earth- time and size scale. satellite program a success if just once it At one end of the time scale are the ex- brings us a life history of the x-ray and plosive solar flares, sudden brightenings on ultraviolet emanations from the sun at the the sun's face, that rise in seconds or time of a solar flare. The techniques are minutes to multimillion square mile regions all available today, and it seems that even a of dense hot gases with temperatures that light load-carrying satellite could carry the may reach 5 x 10~ degrees (Fig. 1). At the necessary photocells, amplifiers, and telemet- other end of the time scale are the brilliant ering equipment. Great ingenuity and ex- quiescent prominences, suspended clouds of pense is still needed, and it will be easy to the solar atmosphere, sometimes visible for become impatient. But rewarding goals months (Fig. 2). beckon and the techniques lie within our With many of these solar features there grasp. are believed to be emissions of different Lifetimes of research into sun-earth rel- 4~ AVIATION MEDICINE ASTROPHYSICIST'S VIEWS--HABER ationships lie ahead. Solar effects on earth the sun is a star, and that other astronomi- physics are being found in meteorology, cal bodies may also affect the earth, we ionospheric physics, geomagnetism, airglow, have labelled our new program "astro-geo- auroral physics, upper atmospheric physics. physics." The astro-geophysical potentiali- and ~_n many other fields of geophysics. So ties of space flight with unmanned vehicles promising is this field that we have recently carrying scientific instruments represent one created at the University of Colorado a new of the great research opportunities of our program of graduate study. Mindful that century.

The Astrophysicist's Views

By HEINZ HABER, PH.D.

The interest of the astrophysicist in space body on the one side, and the radiation flight is twofold. First, he is justified in sources contained in a solid angle of 360 ~ expecting that observations of cosmic fac- on the other. Since the body is assumed tors outside the contaminating blanket of to be in a vacuum no medium is present the earth's atmosphere will result in im- that would transfer heat to or from the portant new data of great benefit to the body. Under these conditions the body's advance of astrophysics. Second, he can temperature will approach asymptotically put his specialty at the service of space a certain value T'e at which temperature technology by supplying data to engineers the amount of radiative energy received and space surgeons for the design of space by the body equals the amount radiated vehicles and protective devices. away by the body. This state is called This is not the place to discuss possible "radiation equilibrium," and the temperature research projects in the field of astrophysics Te itself is designated by "equilibrium temp- which couht be initiated as soon as un- erature." manned or manned space vehicles become It follows that the equilibrium tempera- operational. It appears more important at ture of the body will be determined by tile this time to consider those areas of astro- law of Boltzmann. Referring to a body in physics that can and will contribute toward extraterrestrial space, two major radiation the successful design and operation of such sources must be considered, namely, the sun vehicles. Perhaps the most important con- and the earth, while the background of space tribution of astrophysics will result from including the other celestial bodies is con- an analysis of the field of radiation existing sidered as a radiation sink with the temp- in the proximity of the earth and how this erature of O ~ Kelvin. Furthermore, the field of radiation relates to the surface body is assumed to have a temperature temperature of a body exposed to it. This comparable to or only slightly greater than paper confines itself to a discussion of this that of the earth, while the temperature problem and to its possible solution by of the sun's surface is taken as 6,000 ~ laboratory experimentation. Kelvin. Under these conditions it 4ollows from the laws of black-body radiation that RADIATION TEMPERATURE EQUILIBRIUM the body and the earth radiate preponder- ately at wavelengths greater than 3~, while If a body is exposed to a field of radia- the bulk of solar radiation (more than 99 tion in a complete vacuum, its temperature per cent) lies in the wavelength region will be .determined solely by the exchange smaller than 3g. o.f radiation between the surface of the On the basis of the above assumptions Buettner~ has derived an equation which Dr. I-Iaber is a member of the faculty of the Institute of Transportation and Traffic permits the calculation of equilibrium Engineering, University of California, Los temperatures of various surface materials Angeles, California. and configurations of bodies in space under OCTOBER, 1957 487 ASTROPHYSICIST'S VIEWS--HABER idealized conditions. Using his equation may sometimes not be reached if the heat Buettner 2 has calculated the equilibrium capacity per unit area of the body's surface temperatures of a plane body of infinite is large in relation to the time of exposure dimensions which was assumed to be per- to "day" or "night." Even though Buettner's fectly insulated thermally from the rear. results can be taken only as an approxima- tion of equilibrium temperatures to be ex- pected for actual space vehicles, they seem TABLE 1. EQUILIBRIUM TEMPERATURES to point out that untreated metal surfaces (IN DEGREES C.) OF A PLANE BODY OF will probably be unsuited as surface cov- 1NFINITE DIMENSIONS INSULATED erlngs because of their extremely high sur- THERMALLY FROM THE REAR face temperatures T,. The outer metal skin Plate faces of the artificial satellite (project Vanguard) Surface ] Sun I will receive a special treatment in order EarthS'unllt DarkEarth ' ~-~- " to maintain moderate operational tempera- White -- 13 --29 Black ] 122 [ 68 -- 29 tures in its orbit. The coating will consist Aluminum I 428 ] 295 -- 29 of this multi-layer metal and metal oxide sandwich: a 0.00005 inch thick gold plating applied to the actual metal shell; upon Assuming a black (lampblack), a white the gold plate is vacuum evaporated a (magnesium oxide), and a polished alumi- layer of chromium ; on this layer of chromi- num surface, Buettner obtained equili.brium um will be deposited a thin layer of silicon temperatures for the plate tracing perpendi- monoxide which in turn will bear a thin cularly the sun, the sunlit earth, and the aluminum coating. On the aluminum will dark side of the earth, respectively. His be deposited a silicon monoxide layer of results, in Table I, show that aluminum such a thickness so as to give the desired surfaces attain extremely high equilibrium radiative emissivity. It is hoped that this temperatures as soon as solar radiation is surface treatment will result in an opera- involved, either directly or reflected from tional temperature of the satellite compatible the earth. The same holds for other with its transistor instrumentation inside. metal surfaces with steel assuming some- what lower, and nickel somewhat higher. CASES OF RADIATION EQUILIBRIA temperatures than aluminum. These high equilibrium temperatures occur because In the denser layers of the atmosphere metals are very poor radiators in the long the surface temperature of a vehicle is wavelength band comprising the maximum chiefly determined by the exchange of heat of the Planck curve for moderate tempera- between its hull and the ambient air. With tures. Even though highly polished metal increased altitudes the heat transfer between surfaces may reflect as much as 90 to 95 the vehicle and the atmosphere decreases per cent of the incoming solar radiation, and fnMly ceases. Owing to adiabatic and their emissivity at lower temperatures is so friction heating, the process of heat ex- low that equilibrium temperature is reached change between the outer hull of the ve- only at higher values. This particular prop- hicle and the air is dependent on the ve- erty of metals is exemplified by the high hicle's velocity. For a body at rest in temperatures assumed by chromium parts relation to the ambient air the condi- of cars parked in the sun. A white surface, tions of pure radiation equilibrium are however, assumes fairly low equilibrium practically 1fulfilled at an altitude of about temperatures. thirty miles. With increasing velocities of A rocket missile or a satellite will be the body these conditions will be fulfilled exposed to changing periods o~f exposure to only at increasingly greater altitudes. For full sunlight as it enters or leaves the the maximum operational speeds anticipated earth's shadow. Buettner I has also given (i.e., orbital velocity of about five miles equations that describe the asymptotic ap- per second) conditions of radiation equi- proach of the temperature towards the final librium are found at altitudes in excess equilibrium temperature Te which, however, of about 150 miles. This range lies in the

488 AVIATION ~V]'EDICINE ASTROPHYSICIST'S VIEWS--HABER presumable operational area of intercon- illuminated by the sun, at least for the tinental missiles and satellite vehicles. An duration of several weeks. Special radiation intercontinental missile will enter the criti- conditions will prevail for missiles and cal .range above 150 miles only after it satellites if additional solar radiation is re- has been heated by aerodynamic stagnation ceived through specular reflection from

Fig. 1. Vacuum chamber deveolped by Litton Industries capable of simulating altitude of 150 miles. and friction prevalent during the powered broad areas of ocean surface. From these ascent. Its temperature will then seek its conditions the following practical cases of equilibrium level which will depend upon radiation equilibria can be compiled: the position of the sun, the duration of its ICB1V[ ascending into day free flight, its spin and wobbling movements, ICBM ascending into night ICBM non-rotating if any, the nature of its Surface, and its IC:BM rotating and/or wobbling thermal capacity per unit area. ]CBlY[ under soeCular reflection Satellite in eclipsing orbit A satellite vehicle generally will be sub- Satellite in terminator orbit Satellite non-rotating jected to repeated exposures to sunlight and Satellite rotating to the earth's shadow. Each "day" and Satellite under specular reflection "night" of a satellite operating within the All these cases, of course, must .be per- altitude range between 200 and 800 miles mutated with different geometrical con- will last approximately forty-five to forty- figurations, surface materials, and thermal eight minutes. During each revolution, parts capacities. of the satellite will face the sun, the sunlit earth, the dark earth, and free spac.e Ro- SIMULATION OF SPACE CONDITIONS tation of the satellite will introduce a fur- ther parameter. If the satellite Orbit is Theoretical treatment of the problem of arranged so as to coincide with the plane equilibrium temperatures in space is rend- of the earth's terminator (the great circle ered difficult and involved because of the dividing the earth into its sunlit and its large number of parameters entering the dark hemisphere), the vehicle will be always problem. For these reasons an experimental OCTOBER, 1957 489 ASTROPHYSICIST'S VIEWS--HABER study in the laboratory appears highly de- The pumps are specified to evacuate the sirable. To do this a properly equipped chamber to a minimum pressure of the facility must be available for simulating order of 10.6 mm. Hg. The chamber is the various conditions and properties of designed to admit a human operator space. The following factors must be simu- equipped with a pressure suit. (Fig. 2) The suit which was designed by Hansen and his associate of Litton Industries, is equipped with leads for oxygen pressure, water, humidity, and temperature control. The gloves of the suit are so designed that the operator is able to execute fairly delicate manual tasks. Litton Industries plans the construction of a larger chamber equipped with an air. lock through which the pressure-suited operator can enter aml leave without the necessity of recompressing the main chamber. The Litton facility more than adequately fulfils the conditions of vacuum for experimentation in the field of radiation equilibria. In addition it has the advantage of the presence of a human operator who can monitor and modify the experimentation.

Solar Radiation.--The spectral distribu- tion of solar radiation closely approximates that of a black body having a temperature of 6,000 ~ K.~ The peak of the continuous spectrum of the sun lies around the wave length of 470 m~.. Specifically, for three arbitrarily subdivided regions of the solar spectrum--ultraviolet, visible, and infrared-- the distribution of solar energy is as foI- lows: UV (0--400 m~) : V (400-- 740 Fig. 2. Pressure suit with vapor cover, m~) : IR ( ~ 740 m~) ~ 9 : 45 : 46. developed by Litton Industries, designed for Because of the absorption of ultraviolet use in experimental vacuum chamber. radiation by atmospheric ozone and oxygen, the percentages at sea level are changed lated: (1) a vacuum; (2) solar radiation; to the following approximate ratio: UV : (3) radiation of the sunlit earth; (4) radi- V : IR :----- 7 : 45 : 46. Because the ation of the dark earth; and (5) radiation region critical for radiation equilibria lies characteristics of free space. above the actual atmosphere, the extra-ter- restrial values ,have to be used. The ab- Vacuum. TO simulate the vacuum condi- sorption of solar radiation caused by iono- tions of space a large evacuated chamber spheric layers that lie above the operation- representing the air density conditions equi- al region of missiles and satellites is con- valent to an altitude of 150' miles is neces- fined to the extreme short-wave ultraviolet, sary. A chamber meeting these specifica- and comprises less than 0.1 per cent of tions has recently been developed and built solar radiation under conditions cff normal by Litton Industries,a Beverly Hills, Cali- solar activity. fornia. The present facility consists o,f a A first good approximation of solar en- cylindrical steel shell, 12 feet long oll the ergy can be obtained from the ,radiation inside with a diameter of 8 feet. (Fig. 1) emitted by a carbon arc which includes 490 AVIATION MEDICINE ASTRO'I'HYSICIST'S VI E\.VS--HABER the radiation from both the plasma and constant. This energy flux then corresponds the solid ends of the positive crater. The to the radiation emitted by the sunlit earth peak temperature of a normal carbon arc covering a solid angle of 180 ~ as is always is 4,470 ~ C., i.e., the vaporization tempera- the case for operational altitudes of mis- ture of pure carbon. This temperature, of siles and satellites. Any excess light from course, is lower than that of the sun's artificial or natural light sources represent- photosphere with the result that the above ing solar and terrestrial radiation (sunlit ratio is shifted in favor of infrared radia- earth) must be allowed to fall into a baffled tion and an appreciable depletion of ultra- black radiation sink. Specular reflection violet radiation. However, the spectral ab- from the oceans raises the influx o,f radia- sorptivity of most metals in the visible and tion energy upon the test object by an the near ultraviolet is rather flat, so that amount of up to I0 per cent. Even though an ordinary carbon arc of sufficient energy the spectral distribution of sunlight reflected can be expected to produce a fairly equiva- by the ocean surface differs slightly from lent effect on test bodies so far as spectral that of original sunlight, specular reflection distribution is concerned. Application of can be simulated without introducing an water cell filters will probably be sufficient appreciable error by adding 10 per cent to to approach the spectral distribution of the flux from the carbon arc (or sunlight) solar radiation. representing the radiation from the sunlit Even though atmospheric absorption fal- earth. sifies the spectral distribution of solar radia- tion, the sun can be considered as a radia- Radiation from the Dark Earth.--In or- tion source for the experiments. In this der to simulate the long-wave heat radiation case a beam of sunlight, made stationary emitted by the dark earth the test object by means of a coelostat, can be focused must be located in the center of a blackened on the test object. A proper convergence hemisperical dish having a sufficienly large of the beam can be chosen to correct for radius. The surface of the dish must be the loss of solar energy in passing the kept at such a temperature that the bolo- optical system consisting of mirrors and metrically measured radiation flux received filters so that the energy flux recevied by by the test object is equal to about 15 the test object is equal to one solar constant per cent of one solar constant. (2 gcal per cm z and minute).

Clmracteristics o,f Free Space.--The ra- Radiation from the Sunlit Earth.--Ac- diation sink representing free space will cording to Fritz 4 the radiation emitted by pose a few problems. Previous discussions the sunlit earth has the following spectral with Hansen have resulted in the follow- distribution (see above for arbitrary divi- ing suggestion: The sink might best be sions): UV : V IR = 4.5 : 39.0 : 12.6. constructed by a system of staggered radi- Since about 91 per cent of the .radiation ation baffles consisting of thin copper plates reflected by the sunlit earth is reflected covered with a layer of dull lampblack. and scattered by clouds and the free at- The baffles themselves bear a system of mosphere, the color temperature of the copper tubing soldered to them which con- reflected light is higher than that of original duct a flow of liquid air. In the absence sunlight. Accordingly, the infrared part of of air and, consequently, humidity inside the reflected sunlight is sharply depleted the chamber such a radiation sink appears in favor of the visible part. In order to to be entirely feasible; no condensation will simulate this spectral distribution, radia- occur on the plates and tubing destroying tion from a carbon arc or from the sun their radiative properties of a black body must be filtered by water cells and color at very low temperatures. The radiation sink filters. If a parallel beam of radiation is will cover the second half of the =full solid directed at the test object, its energy flux angle around the test object which is not must be adjusted to correspond to 35 per covered by the hemispherical dish represent- cent (albedo of the earth) of one solar ing the earth. Ocro~ER, 1957 491 TEST PILOT'S VIEW POINT--CROSSFIELD

PARAMETERS OF EXPERIMENTATION A facility of the kind described above can be operated similar to wind tunnel From the foregoing a set of parameters operations. A proper permutation of all and their logical permutations for conduct- important experimental parameters will ing individual experiments can be derived. provide a set of extremely valuable data They fall into the following categories: on the problem of radiation equilibrium GEOMETRY temperatures. It would be an important Circular disk Square and rectangular plate contribution of astrophysics to intercon- Cylinder tinental missiles, flight at highest altitudes, Cone and unmanned and manned satellites. Sphere Wire ACKNOWLEDGMENT SURFACE Metals antl alloys of different textures : high polish, The author wishes to express his grati- smooth, rough, heat-treated tude to Mr. Siegfried Hansen and Mr. Paints Richard Roche of Litton Industries for Dull Black many valuable discussions and suggestions. Sandwiches Ceramics REFERENCES Non-uniform Abraded (mlcro-meteorite effects) 1. BUETTNER, K.: Thermal aspects of HEAT CAPACITY travel in the aeropause-problems of Thickness of hull thermal radiation. In Physics and Materials of different specific Medicine of the Upper Atmosphere, heat ed. by C. S. White and O. O. Ben- Test bodies of different size son, Jr. Albuquerque, N. M.: Uni- Evacuated bodies versity of New Mexico Press, 1952. Air-filled bodies 2. BUETTNER, K. : Bioclimatology of MOTION manned rocket flight. In Space Stationary Medicine, ed. by J. P. Marbarger. Rotating at varying ~eriods and Urbana, Ill.: University of Illinois axial positions Press, 1951. 3. First Quarterly Report for Phase Two: INITIAL TEMPERATURE High Vacuum Research Laboratory. Aerodynamic heating Beverly Hills, California: Litton In- Long-term exposures to space dustries of California, July 9, 1956. conditions 4. FRITZ, S.: The albedo of the planet TIMJF_, Earth and of clouds. J. Meteorol., Exposures equivalent to: 6:277, 1949. ICBM ascending into day 5. HABER, H. : The Physical Environment ICBM ascending into night of the Flyer. Randolph Field, Texas: Satellite in eclipsing orbit USAF School of Aviation Medicine. Satellite in terminator orbit 1954, p. 51.

A Test Pilot's Viewpoint

BY A. SCOTT CROSSFIELD, M.S.

The test pilot in his business permits no atmospheric flight. "To test" requires a flights of fancy, but is personally directly specific purpose in mind and in design and, and vitally concerned with all the subjects therefore, to escape the meandering of lack discussed at this meeting wherein they apply of definition, let me select a case to discuss. to aviation. The word "test" here implies The following observations, while not neces- early or developmental efforts toward extra- sarily original, are a personal responsibility. Let's assume a virgin engineering effort to Mr. Crossfiel.d is engineering test pilot for North American Aviation, Los Angeles, construct a chemically powered rocket ship California. to attain, orbital velocity at altitudes of se- 492 AVIATION MEDICINE TEST PILOT'S VIEW POINT--CROSSV[ELD

veral hundreds of miles and be repeatedly afore-mentioned performance requirements, recoverable. First considerations then ap- designs itself. Referring to Figure 1, with pear to be: some function of fuel-to-weight ratio as the

AREAOF / ~Zl/7~ ~ MAXATTAINABLE ~pR~EgITICcAALTIDoEN~GN__~_/ ....~~ SPECIFICIMPULSE

AIRFRAMELIMITS ~ ~/- PRMIO~ULSIONSYSTEM

f (THRUST)

Fig. 1. Orbital vehicle design practicality.

1. What is the requirement . . . that is, ordinate and some function of thrust as what are we seeking to establish . . . the abscissa, several basic things need to be and why. Satisfying that this venture has a purpose, then: satisfied. By analysis of the design, mater- 2. It certainly involves consideration of ials, and fabrication capabilities, we can de- economy of time, manpower, money, fine an airframe practicality boundary some- resources, and perhaps defense re- what as shown, which is a function of size, quirements as influencing factors upon loads, temperatures, et cetera. The engines the degree of the effort. and fuel systems are affected by the same 3. Are reliability considerations or risk acceptance in the required mechanisms considerations, and a practical propulsion involved in the proposal to help to system boundary may appear as shown. A further determine the extent of the requirement for power recovery upon return effort ? to earth would lower both of these curves 4. The elimination of exotic approaches relative to the level permitted by aerody- that have little subsequent use for practical and useful development. namic recovery alone. Like the airframe and propulsion system, The above four considerations almost the pilot has load limits. A physiologic tol- necessarily define a manned vehicle. Also, erance to accelerations of thrust, lift, and thoughtful analysis of the four considera- drag will define a boundary perhaps as tions reveals one very important absolutism: shown. These three curves bound an area Tyrannical authority of .design decision and with the ~xes within which the subject responsibility must be vested in one source vehicle can be successfully constructed. to attain uncluttered objective results in However, as shown, maximum attainable this venture. specific impulse will rule out a lower The subject case, intended to be powered bounded area that moves down and to the by a chemical rocket engine and with the left as specifics are increased. A design and OCTOBER, 1957 493 TEST PILOT'S VIEW POINT--CROSSFIELD manufacturing capability to build this vehi- the maintenance of fuel and pump suppres- cle exists only when the four boundaries sion pressures and alternative controls if enclose a point or define an area within getting out of the orbit is deemed desirable. which the physical characteristics of the Probably, in the propulsion section, should machine lie. Therefore, there seems to be be included the pilot concern for internal little question that our ability timewise to exchange in heat for man and equipment solve such a problem as this rests with our environmental control, and, if necessary, determination of the degree of simplicity the managing and allotment of stored heat of approach that we can accept consider- sources. ation three above. What does all this mean to the pilot ? One NAVIGATION AND COMMUNICATION fact becomes outstanding if it is urgent to Here the pilot's first concern is accurate construct such a-machine at the earliest pos- knowledge and prediction of the vehicle's sible time: Use of the pilot to close out the path in space with reference to some datum. control loop of the internal mechanisms, Will the ship be beclouded with a visually as well as the mission, in lieu of gross au- and electronically opaque ionized exhaust lomaticity, becomes mandatory. What then product atmosp'here which permits no out- i.,: the concern of the pilot? Let's look at side contact? Can he see or hear electroni- some observations by area; possibly--or cally through the ionosphere? If not, will probably--they are controversial. reliance solely upon inertial guidance be re- PHYSIOLOGIC CONSIDERATIONS quired and, if so, what are alternative methods? In this discussion, continual re- Basic and measurable are' accelerations, ference to alternatives stems from the temperatures, pressures, breathing require- notion that a pilot is always in control until ments, moisture control requirements, and he runs out of alternatives or . . . into the waste disposal requirements. All of these ground. yield to engineering solutions at hand. Subtle and unmeasurable, or at least un- INSTRUMENTATION predictable, are effects of radiation, zero G, There is a fashionable concept that is in visual and orientation disturbances. Meteo- grave error. This is the treatment of pilot rite collision might be included here as a presentation and instrumentation in a broad physiologic hazard. No conclusive evidence sense. It is felt very strongly that pilot in- yet exists that any of these are real pro- strumentation, like the proper parts of any blems in a limiting sense. mechanical assembly of thoughtful design, PROPULSION is uniquely determined by the vehicle, its mission, time allowables, internal mechanics, We know that we will require extreme and pilot experience. performance engines, exotic fuels, high There is another and related fashionable specifics, high chamber pressures, and very concept that is open to question. This is high thrusts, at least in the early exit the idea of not giving the pilot quantitative, phases. To the pilot, this means critical en- real physical information. The red light- gine control requirements and fuel handling, green light idiot's delight may well prove and allotment. Furthermore, he requires ade- the undoing of any advanced performance quate information from engine and fuel endeavor. system instrumentation for alternative ac- tion should it be necessary. The pilot is SURVIVAL also concerned with recognition of, and al- ternative action to be taken for, problems Two philosophies (a word used here to such as those arising from main and auxi- cover a lack of systematized factual in- liary engine exhaust attenuation at zero formation) are about at a standoff here. nozzle back-pressures. These may give rise One approach devotes major attention to to radiation and local vehicle environmental analysis of the occurrence and prevention problems. There is vital pilot concern over of danger, and to airframe recoverability 494 AVIATION MEDICINE INSTRUMENTATION FOR SPACE FLIGHT--HOOVER to restricted escapable regions in case a plan, a planned change in plan, alternative danger does arise. The other approach de- control capability, and analysis of known votes major attention to the "abandon ship information; and (3) a control method immediately" idea. Of course, as in all which may be pilot-mechanical, electro- black and white arguments, the gray area in hydro-mechanical, or push-button-mechani- the middle probably is the more defensible cal which includes the wide area of gross and probably more acceptable to ~ large automaticity probably correctly termed pilot- number of pilots. l~ush-button- electronic - electro - hydro-mech- In the subject orbital vehicle, there are anical. two serious doubts. First, that accidents re- Practice and experience demand that all quiring abandonment can occur at extreme electrical, hydraulic, and pneumatic control or even moderate altitudes because of the functions of a primary nature require absence of fire and explosion hazard and complete duality, with the associated priority lack of structural loads, and, second, that and "fail-safe" characteristics, for reli- the pilot is any better off in a life boat than ability, Therefore, in an early effort such he was in the original vehicle because if as proposed here, wherever reasonable, the latter has failed the former must be a pilot-mechanical methods are highly attrac- better spaceship, and the question is raised live. Thus, still following the original that perhaps he should have taken the life thesis, this then allows the pilot to assume boat in the first place. One opinion is that the major role in closing the control loop the basic uncompromised integrity of the and to retain control over his fate. basic uncompromised vehicle is the predom- The degree of acceptability of the fore- inant source of safety and survival. going observations is subject to one very important operational concept. If the mis- STABILITY AND CONTROL sion can be made reversible, that is, if the pilot can change his plans at any time and As with all other airships, this beginner's abort a planned mission and return to earth spaceship will succeed or fail upon its to try again, then much greater latitude is stability and control characteristics during afforded. launching, exit, orbiting, re-entry, recovery, The thing that appears to precipitate from al,d landing. Of all of the problem areas, all of this is that the pilot's problems are this one of stability and control of the craft not those of capability, environment, or and its internal mechanisms is the most dif- physiological stress, but as usual, are as- ficult to solve. The pilot is vitally con- sessed to be in the area of system and sub- cerned with the inherent stability of all that system reliability and control. Therefore, he controls, but is directly and immediately based upon the original thesis of an early concerned with his control situation. For virgin effort, one pilot would prefer a control, he requires: (1) information based sound, severely objective design with which upon a plan, instruments, and ground refer- to establish the ground rules for the ela- ence monitoring; (2) decisions based upon borate developments to follow.

Instrumentation for Space Flight

BY COMMANDER GEORGE W. HOOVER, USN

The success or failure of flight into space, only on the performance of the engine and either manned or unmanned, will depend not the vehicle itself, but equally upon the in- strumentation. The success of the instru- mentation will only be assured, not by Commander Hoover is weapons systems manager, air branch, Office of Naval Re- modifying present aircraft instrumentation, search, Washington, D. C. but rather by treating the problem as a OcTot*m~, 1957 495 INSTRUMENTATION FOR SPACE FLIGHT--HOOVER completely new art. The general require- errors in the total system and place the ments for space instrumentation are that all satellite into many different orbits. components must be absolutely reliable, ex- It is conceivable that with the proper in- tremely simple and lightweight, completely formation being telemetered back to earth it will be possible to construct large ob- ORIENTATION OF THRUST AXIS servation satellites by placing the necessary components into the same orbit, one at a POSITION OF time, and then guide them by ground con- VEHICLE / .--- EARTH trol to connect with each other, thus form- J "HOW GOES ~T" [ ing much more effective stations. In order RING to do this however, an integrated instrument display must be developed which will in a sense put the controller's eye into the nose of each component. Such a system will be the test bed and operational flight trainer ~ ORBIT for the more sophisticated manned vehicle. The unmanned observatories will not only give us an early space platform for observ- Fig. 1. Drawing showing how position ing the the earth and for gathering astrono- of space ship might be displayed as part of mical data, but will tell us what we will the total situation. need in order to control and maneuver a manned space ship. automatic and, in the case of the manned Although the space ship will be inherently vehicle, provide presentation capable of be- automatic, the pilot being a human being ing interpreted with no possibility for error. must be made aware of the total situation at Space instrumentation can be divided into all times. It will be necessary to provide in- two general categories: research instrumen- formation concerning time, orientation, velo- tation, and control "instrumentation." Both city, altitude, flight path, power, fuel mana- types will eventually be needed in all vehi- gement, and ship condition. cles, whether manned or unmanned. Let us Time will be of extreme importance to talk first about unmanned vehicles and then the pilot and will include local time, for de- proceed to the manned ships. termining the boundary time limits between The first satellites will of necessity prim- take-off and landing. Sidereal time will be arily contain research instrumentation. Here necessary for determining the position of the successful gathering of data is de- the orbit. Orbital time will be required to pendent upon the reliability of the informa- determine perigee and apogee, "how goes it" tion gathering sensors and the telemetering information, and for rendezvous in the or- transmitters. Failure of any of these com- bit. Elapsed time will be necessary in order ponents will render the flight useless except to calculate flight duration and fuel man- for data which can be gained only from agement. visual tracking. Because of the critical One way of displaying orbital time might limits in weight, every ounce must be be to show "how goes it" information by a shaved off the instrumentation in order to ring around the ship's position in order to obtain the maximum amount of experimen- show actual position relative to intended tal data. position (Fig. 1). The instrumentation re- As the satellite grows larger with the de- quired for orientation must include an an- velopment of better rockets, more and more swer to the question, "Which way is Up", instruments can be employed but weight and and with respect to what? Orbiting the reliability will still be at a premium because earth will require knowing a vertical radi- the need for remote guidance will become ally from the earth, and azimuth as a func- necessary, at least until the satellite has tion of the initial orbit. A change in axis reached its orbit. Such data will permit the orientation will be required to change the ground controller to make corrections due to orbit. 496 AvxATxoN MzvzcxNE INSTRUMENTATION FOR SPACE FLIGHT--HOOVER

Changes in thrust when tangential to the will be shown relative to the earth, altitude, orbit will increase or decrease the radius of or orbit. the orbit. However, any change in eleva- Altitude, measurements and display will tion will change the size and shape of the be interesting but difficult to solve (Fig. 3)

ACTUAL RATE OF DESCENT (RATE INPUTS LIKE "ZERO READER"I

Fig. 2 Drawing showing the result of applying thrust in the space ship traveling in an orbit around the earth. orbit, and any change in azimuth Will cause a geographical ch,'mge in the orbit. So it can be seen (Fig. 2) that accurate orienta- t:.on of the thrust axis will be mandatory. In addition to orientation, the problem of posi- ~'~-CONTROL. TO CHANGE tion will be most important to the space SCALE IN WINDOWS FROM FEET, THOUSANO$ pilot A continuous check on orbital posi- OF F~ET, MILl'S lion and transition into and out of the orbit will be required. Maintaining position in the Fig. 3 Schema of instrumentation for displaying velocity of space ship. orbit will be relatively simple, requiring an application of thrust or negative thrust along with orientation of the thrust axis. The problem will consist of determining Determining position during interplanetary how to measure altitude, how to indicate it, operation, however, will be a much more and altitude with respect to what. T'hen complex problem because of shifting from ascending or descending the measurement orbit to orbit. Celestial fixes and inertial will probably be in feet and thousands of systems will probably provide data to the feet. When orbiting, altitude will probably computers to solve the orbital technique re- be measured in miles from the object about quired. which the ship is orbiting. When actually A great deal of effort has gone into re- shifting orbits, altitude will become distance search to determine the proper display for and thus will resolve into a function of orientatiort as well as other data for ordin- navigation in three dimensions. ary aircraft. Final decisions have not been Power and fuel management (Fig. 4) reached as to how this information will be will be fairly simple to handle but will re- displayed. The problem of velocity is really quire positive indication because rate of fuel three-fold, namely: how to measure it, how consumption will be critical. Fuel remaining to indicate it, and how to use it. A new and fuel flow will be necessary but the real method of measurement or perhaps several requirements will be for fuel available tak- will be required when operating in space. ing into account all possible losses as well Celestial references, ionization, Doppler, and as fuel consumption. Power could be mea- inertial references are all possibilities. The sured as thrust and indicated as per cent of displays will undoubtedly be a function of power available. each mode of flight and will be shown as Ship condition divides into several pro- actual velocity relative to a desirable veloc- blems: temperature, pressurization, meteo- ity. Numerical values may be used but more rite hits, radioactivity, and engine condition. likely velocity will be shown as per cent Means must be provided to measure the orbital ,ate of ascent or descent, and re- skin temperature of the vehicle accurately entry velocity. At any rate, all velocities both during the flight, where solar radia- OCTOBER, 1957 497 SURVIVAL ASPECTS OF SPACE TRAVEL--MAYO tion o1 lack of same will be a problem, space suit. Radioactivity of the ship will and during re-entry where the rise will occur have to be indicated because it appears cer- from skin friction. In addition, a tempera- tain that the vehicle will be under constant ture rise due to impact of solid particles bombardment of cosmic rays and other forms of radiation. In the unmanned satel- lites, instrumentation for this problem will FULL be a research tool but in the manned ship they will definiteIy be required for control. ~ACTUAL FUEL Meteorite hits will be a part of the temp- CONSUMPTION erature problem as well as of those related to pressurization and damage control. En- NALW gine conditions will need instrumentation to keep a constant check on the operation of I"-"OPTI#/AJM RATE OF the power source and will require displays FUEL CONSUMPTION not only of the condition but command dis- ETURN plays to indicate the action required to pre- vent damage or loss of power source. The development of instrumentation for Fig. 4. Schema of instrumentation for displaying fuel management data of space space ships must be considered just as im- ship. portant as the engine, the control, and the ship itself. All space flights will be instru- in space will complicate the problem. ment flights, and the success of these flights Pressurization will be constantly under will be directly proportional to the ability surveillance and will require, not only in- of the crew to read and interpret the neces- dications of the condition of each compart- sary information. An interesting observa- ment, but an automatic damage control. tion about space flight is that in an airplane Some type of trend irLdication will be a a pilot is always worried to a degree about must in order to permit the occupants spinning in. In the space ship he'll be more either to vacate the damaged area or don a worried about "spinning out"

Some Survival Aspects of Space Travel BY ALFRED M. MAYO

In a space craft as in aircraft the over- reaching the sister planets in our own solar all objectives must command first attention. system. Survival problems resulting ~from space The design of crew compartments will environment will be so severe however, that be dictated by the requirements of human a larger percentage of total space craft operators not significantly different in basic design time is likely to be spent in their ptlysical and mental capabilities from those solution than in airborne craft. Aside from of the pilots of present aircraft. The need short flights around the moon or nearby for information to be gathered from very space excursions, it seems likely that the great distance to provide time for a human trips even to planets in our own solar crew member to think and act is emphasized system would involve a substantial period in Figure 1. It is evident from the dis- of time. A ~rip around the sun in fact has tance involved that survival will depend been a commonly proposed method of increasingly on the reliability and accuracy of high speed automatic control systems. Mr. Mayo is chief equipment and safety research eengineer, Douglas Aircraft Com- Automatic controls will be needed as great- pany, El Segundo, California. ly for actuation ~i safety equipment and 4~ AVIATION MEI)X~NE SURVIVAL ASPECTS OF SPACE TRAVEL--MANO environmental control of the crew quarters and less uncertainty with respect to health as in control of the cra, ft and its propul- problems of living algae or other plants, sion and power systems. A major problem might grow out of intensified research in will be that of suitably linking the human the area of synthetic photosynthesis. The

Fig. 1. Relation of speed of space ship to time required for pilot response. operator to his "automatic" systems. As in need to provide reliable automatic controls every man-machine system decision malting with suitable standby systems can hardly control must be retained for the human be overemphasized. brain. An intermediate computer can un- The reconversion ,of liquid and food waste doubtedly be used to link sensed information products to useful nutrients that are psy- to both "automatic" systems and display chologieally satisfactory might also be ap- for the operator. proached by the use of secondary living Hermetically sealed crew quarters to organisms in the same manner as in nature. provide a livable earth environment in The desire for a system subject to more space will be a prime survival requirement. positive control and greater overall relia- The time of flight will tend to be suffi- bility might well dictate the expenditure ciently great that total regenerative air, of great effort to provide a .regenerative water and food cycles are likely to be the chemical cycle not dependent on the art only practical answer to this survival prob- of keeping biological specimens healthy, hap- lena. Suitable control of air pressure and py and productive. composition might be approached by a The evident need to protect against loss combination of stored materials possibly in of vital materials through a leak or from a solid chemical state together with a sys- structural damage will undoubtedly dictate tem which can reconvert water and other the considerations of extensive compart- excreted body gases to their original state. mentation and automatically controlled air The immediate possibility of utilizing sun- locks as a means of isolating damaged light and the action of chlorophyll in green compartments. Pressure-suited emergency plant life has occurred to many people. crew members may be able to make repairs Another, in which more precise control and return damaged compartments to use, OCTOBER, 1957 499 SURVIVAL ASPECTS OF SPACE TRAVEL--MAYO after a minimum loss of vital gases. The boundaries of the atmosphere with a high need for such compartmentation and re- enough surface temperature to allow these pair facilities might be emphasized by con- very large amounts of energy to be dis- siderations of the possible effects of meteor sipated entirely by radiation and molecular showers. rebound. Newer estimates indicate an increase A substantial amount of data with respecl over past data in the probable numbers Io human tolerance to acceleration as ;L of meteor particles of potentially dangerous function of time and acceleration (Fig. 2) size. In addition to eompartmentation, it is and an increasing understanding of the' also likely that added emphasis in the de- effects of rate of change of acceleration sign of the structure and skin will be on the human body are available. It should needed to provide penetration resistance to then be possible to configure a space crafl meteors of a larger size than previously so that the accelerations encountered under considered statistically important. The controlled take off conditions need not be large amount of kinetic energy per unit a serious survival problem. mass of meteor particles indicates that an The relative lack of knowledge as 1~ explosive type of impact with a surface the exact psychologic and resulting physio- is likely. Accordingly Whipple has sug- logic problems of the gravity free or weight- gested a relatively thin outer or buffer skin less state of free space flight probably to effect that explosion. The smaller par- should not cause excessive concern. The tides could then be absorbed by a larger engineer should be able to provide nearly mass of primary material. Self-sealing sub- any specified value of artificial weight by stances on the inner skin surface might rotating the craft about its own center of also help to reduce the importance of the gravity. The configuration of course would smaller penetrating meteors. A rapidly ap- need to be such that the resulting cabin plicable mechanical seal might also be spaces would be oriented in a usable direc- needed to seal larger holes quickly. tion with respect to such rotation. Con- Temperature control will undoubtedly re- siderable inconveniences might be expected quire specialized attention. For free space if the normal ceiling of the compartment flight it is likely that large heat radiating were to be oriented such that it were usable surfaces will be needed. Waste heat from only as a floor. powered equipment could be transferred The problems of surviving the effects of to these surfaces by an intermediate fluid. a wide variety of solar and cosmic radia- The resulting radiant refrigeration system tion are still not thoroughly defined. Physi- would then be roughly comparable in inter- cists and biologists are confident that shield- mediate stages to some present low tempera- ing against the lower energy solar radia- ture refrigeration systems. Similar su,rfaees tions will not be too difficult. No practical could be used to collect solar heat and by approach utilizing a reasonable weight of reverse cycle operation provide energy to shielding or deflecting material has yet been the chemical and mechanized systems during advanced to protect against the effects of periods when large amounts of power are very high energy cosmic particles. With the not being dissipated within the craft. The ionizing paths of such particles still in- orientation of the radiation surfaces with creasing after penetrating a foot of solid respect to the sun would determine whether lead, mass shielding does not appear prac- they added or removed heat from the sys- tical. tem. For free space travel there is then a rather direct though complex engineering Proposed methods of generating a suffi- approach to the problem of temperature ciently extensive and powerful electromag- control. During re-entry in a craft not netic force field indicate an even less utilizing retro-thrust or contained fuel to promising approach. Practical methods of dissipate its high kinetic and potential en- utilizing the reduced secondary emission ergy, much aerodynamic and thermodynamic effect of low atomic weight materials in study will be needed. The craft would need shielding still remain to be advanced. This to operate long enough in the thin outer avenue may prove interesting. The inherent 500 AVIATION MEDICINE SURVIVAL ASPECTS OF SPACE TRAVEL--MAYO capability of a complex biological organism landing involving re-entry through an at- to tolerate and/or repair damage along mosphere. the patlns of penetration of individual cos- Du.ring the initial part of the take-off mic particles on a statistical basis appears phase, failure o.f the control system or a

Fig. 2. Human tolerance to acceleration as a function of time and acceleration. to be the only present practical reason major power plant malfunction could im- for hope. Available physical and biological pose escape requirements not too radically data are not extensive enough for categoric different ~from those of a high perform- statements that tolerance to the cosmic ance aircraft. The requirement to separate radiations, existing in space is practical cleanly a suitably stabilized section and to for extended times. On the other hand, provide controlled deceleration to solve the competent physicists and biologists are primary G time tolerance of the crew would showing considerable optimism on the basis not materially differ from that of a very of the data available. high performance aircraft. A separate crew Careful consideration must be given 1o section of high structural and environmental a proper balance of the fundamental moral, integrity might also aid in the solution of morale and economic factors to provide problems pertaining to. fire, power plant escape equipment justifiably on the basis malfunction and structural failure during oF the total purpose of the craft involved. the take-off phase. Such a device if prop- Certain of the space craft escape require- erly isolated might even be useful in cer- ments are merely extensions of those which tain types of explosions where the build- need to be met in aircraft. Others are up of pressure might be slow and the initial unique and a function of space itself. In violence limited. A number cff different order to outline some of the problems in- types of acceleration control devices vary- volved, it migbt be well to consider three ing from a winged escape vehicle to para- phases of space flight. These are: (1) Take- chute decelerated systems or combinations off through an atmosphere and against of both suggest possible solutions to this gravity; (2) free space flight; and (3) portion of the problem. OCTOBER, 1957 501 SURVIVAL ASPECTS OF SPACE TRAVEL--MAYO

As the craft moves into free space and given to the need for adequate emergency power is no longer needed to maintain vel- communication, locating and rescue proced- locity, a new set of problems and require- ures. ments present themselves. Many of these During the re-entry and landing phases

10/300 SL MACH= I00 76300 MPH ,~176176I /- ALTITUDE SL MACH=IO MILES '~176 Z610 MPH

.01 i 0 15 30 45 60 75 90 APPROACH ANGLE- DEGREES

Fig. 3. Tolerable .deceleration distance vs. approach angle. problems are concerned with providing an of flight, the hazards of possible instability adequate human environment and are just and induced accelerations from air drag as real a safety consideration during nor- would be .added to the environmental prob- mal flight as in a properly configured lem. Additionally if it were necessary to escape section. Since .both the mother craft re-enter an atmosphere without retro-thrust and any escape device will continue to travel equipment, the escape craft must have suit- indefinitely at constant velocity in space, able aerodynamic and heat resisting char- it is evident that the average time :for acteristics. Both the extreme kinetic energy rescue after separation must. be assumed of high velocity and the high potential to be relatively large. Additionally the prob- energy of gravitational attraction must be lem ot~ sending distress and rescue mes- dissipated as radiant heat or molecular re- sages, and that of providing directions to bound. This presents a problem of allow- rescue =forces would not only be of para- ing a very high surface temperature for a mount importance, but in all probability will relatively prolonged period o,f time. It present a problem not easily solved. The further requires an aerodynamic and drag basic unf,riendliness of the free space en- configuration capable of precisely controlling vironment coupled with the probable sub- a craft within the fringes of a relatively stantial times of waiting for rescue dictate thin atmosphere until sufficient slow down the need for adequate air, water and food is effected and energy dissipated. The de- provisions. These problems in themselves celeration problem is further emphasized might well determine a minimum practical by Figure 3 which shows minimum dis- size for the free space escape vehicle. The tances versus speed and angles that are case of a crew successfully separating it- required for survival as a function of avail- self from a dangerously damaged mother able deceleration and time data. For ex- craft only to be lost in space to starve or ample if a man were traveling at Mach 1 die from exhaustion of environmental con- in a 90 ~ sea level dive, his physical toler- trol facilities would be a not unlikely situa- ance to acceleration for the required time tion if very careful consideration is not would make it necessary to utilize ap- 502 AVIATION MEDICINE VANGUARD PROJECT--HAGEN proximately .12 miles of distance to stow temperature aerodynamic and acceleration him down without killing him. Similarly problems of re-entry indicate that the size if he were travelling toward the earth of any useful separable portion of a large at Mach 100, or approximately 70,000 miles space craft would need to be sufficiently per hour, a distance of the order of magni- large to store the provisions necessary for tude of 10,00t3 miles would be required to survival. slow him down within his acceleration tol- Many difficult problems in nearly every erance limit. branch of science remain to be solved if a reasonable survival potential is to be In order to achieve satisfactory perform- generated for man in space flight. The anee and economic compromise without boundless curiosity of men of science has sacrificing the escape potential, it appears already provided paths toward the solution evident that major use must be made of to some of these problems and new data portions of normal crew stations in order are being gathered and organized to provide that excessive penalty to the overall craft solution to others. So much remains to be will not make impractical the provisions dcme that much time will he required ml- of escape capability. The requirements for less a substantial increase in the amount of extended times of survival coupled with the effort is provided.

The Vanguard Project

BY JOHN P. HAGEN, ProD.

Tile earth satellite program, while de- if a 21.5 pounds, 20-inch sphere in a satel- signed as a scientific experiment in the II1- lite orbit approaches closer than 300 miles ternational Geophysical Year, may serve also to the earth's surface, the lifetime may be as man's first venture into space travel. As you now know, space vehicles will travel in orbits about the earth, moon, a planet

or the stm. The least difficult of these to ASCENT effect is the trip around the earth, or the TRAJECTORY earth satellite. I say the least difficult be- cause even this first step is not easy with present day techniques. Let me first describe the Vanguard launching vehicle, its trajec- tory and the planned orbit for the earth satellite program. The first consideration in choosing limits placed upon the orbit is that of atmospheric drag. Even in the sparse outer regions of our atmosphere the low density gases will Fig. I. Plan view os orbit with 200 mile remove energy from the rap.idly moving perigee and 1400 mile apogee. satellite, causing the orbit eventually to col- less than two weeks. At the other extreme lapse. Since the density increases exponen- it is desired to have the satellite get no fur- tially as height decreases, the rate of losing ther away than about 1500 miles. The energy increases and hence the rate of decay actual orbit (Fig. 1) will be an ellipse with of the orbit. Based on our rocket-gained the earth's center at one focus. The launch- knowledge of the atmosphere, it is felt that ing will be so designed that if successful the closest approach of the satellite will be Dr. Hagen is director, Project Vanguard. 200 miles and the greatest separation 1500 U. S. Naval Research Laboratory, Wash- ington, D. C. miles. To put a satellite in such an orbit re- OCTOBER, 1957 503 VANGUARD t'ROJ ECT--HAGEN quires a launching vehicle that can lift it pounds. The first-stage, far the largest of against the gravitational attraction of the the three, is powered by a General Electric earth some 300 miles, and then accelerate it engine having a thrust of 27,000 pounds. to a velocity of about 25,000 feet per se- The engine is on gimbals and it is by engine

@ _t Fig. 2. Schema of the Vanguard launching vehicle.

THIRD STAGE

SECONDSTAGE BURNOUT

RANGE 15DOMILES IRST STAGE BURNOUT TINE IO NIN. AFTER t r AND SEPARATION LAUNCHING

Fig. 3. Planned trajectory of the Vanguard launching vehicle. cond, or 4.6 miles per second. At the same deflection that the rocket is steered in its time the controls of attitude of the rocket course. The second-stage, made by Aerojet must be precise so that the launching will General Corporation, is initially attached to be nearly parallel to the earth. the nose of the first, and also is Ix)wered by All this requires a finely designed vehicle a gimballed rocket-motor burning liquid and, with present day fuels, one with three propellants. Buried in the nose of the se- stages (Fig. 2). The Vanguard launching cond-stage and protected by a disposable vehicle is being constructed for the Navy nose cone is the third-stage. This is the under prime contract with the Martin smallest of the three and burns a solid pro- Company. It is 72 feet long, four feet in pellant. Mounted on the nose of the third- diameter at its base and weighs 22,000 stage is the satellite pay load. After the end 504 AVIATION MEDICINE VANGUARD PROJECT--HAGEN of burning of the last stage the satellite will is spun up and ignited it will "shoot" out of be separated from the empty casing. the second-stage casing much like a shell out The rocket will be launched at the Air of a rifle. At the end of third-stage burn- Force Missile Test Center in Florida. The ing, if all works well, the third-stage casing

SUNLIGHT : E

- Js~Je I ds

HOT SIDE COLD SIDE E.a +ERa*J e "E = Js = ~GT 4 je.E = js = ~o-T 4

.'.T = f(~) .'. m IS INDEPENDENT OF o & ( E, E R,SUNLIGHT TERMS Je,Js~LOW TEMP RADIATION TERMS-] SUNLIGHT ABSORPTANCE E ~ LOW TEMR EMITTANCE | ~ OF SATELLITE OF SATELLITE _.J

Fig. 4. Diagram showing the flow of heat in and out of the satellite. azimuth of launch will be somewhat south and the satellite will have a velocity some- of east so that the plane of the orbit will be what in excess of 4.6 miles per second. If inclined to the equator some 35 ~. The this occurs and the direction is proper, the planned trajectory is shown in Figure 3. satellite will be in a stable orbit and space After ignition of the first-stage motor the flight will have been achieved. rocket will rise vertically and then be pro- One of the early experiments to be car- grammed over toward the south east. As ried out in the earth satellite is designed to it rises through the atmosphere it will tilt measure the environmental factors in the more and more toward the horizontal. After satellite itself and in the space through first-stage burnout, the empty casing of the which the satellite moves. It is the results first-stage will be discarded and the second- of these measurements which can aid in the stage ignited. After second-stage burnout design of future space vehicles. Once the the velocity will be up to 50 per cent of vehicle is beyond the protective atmosphere final velocity and the second-third-stage of the earth it will be exposed to high combination, having discarded the nose energy radiation and to collisions with cone, will coast for several minutes. During meteoric particles from which we are nor- the coasting period the rocket will gain al- mally protected by absorption in the at- titude to 300 miles when it is about 900 mosphere. The vehicle for long periods, miles out from the launching point. The will be in full sun-absorbing heat. The complete guidance mechanism is in the only means for keeping temperatures in the second-stage and during this period it will vehicle within bounds is to control the in- control the attitude of the second-stage and frared emission of the outer surface because point it in a direction parallel to the surface the vehicle can lose heat only through of the earth so that when the third-stage radiation. OCTOUER, 1957 505 VANGUARD PROJECT--HAGEN

The environmental experiments include erosion. A thin metallic coating on a glass thermistors attached to the shell and to the plate will be used to measure this effect inner structure to measure the temperature through the change in resistance of the strip at these points, thus determining (1) the as it wears away. Another way to detect

100[. , I ' I I i I ~ I ' I J

,,, 80~

w POLISHED Mg ALLOY / --COATED WITH A 1.3/.1. n.- LAYER OF STRONGLY OXIDIZED Si 0

20 VISIBLE INFRA-RED

. i i i I i I 06 0.8 IO 2 6 I0 14 WAVELENGTH M ICRONS Fig. 5. Reflectance of coating material as a function of wave length. distribution of heat within the satellite, (2) collisions with mierometeorites is being the effectiveness of the measures taken to used. Small, sensitive microphones are at- insulate the electronics, and (3) the effec- tached to the inner surface of the shell and tiveness of the surface coatings in radiat- will record the "ping" as each particle ing away heat. The flow of heat in and out strikes the surface. For the more rare oc- of the satellite is shown in Figure 4. Here casions when a larger particle is encountered it is clear that the controlling factor in the and penetration of the skin may occur, temperature of the satellite will be in- pressure zones are attached to the skin and frared emission. In recognition of this, the can register the occasion where they are surface of the satellite will be highly polish- first punctured. Optical and radar measure- ed aluminum coated with silicon monoxide ments of meteors are not sufficiently sensi- (SiO). This material (Fig. 5) has the pro- tive to detect the smaller particles which perty of being transparent in the visible and yet may have sufficient energy to puncture opaque in the infrared, thus permitting con- the satellite skin. Extrapolation from counts trol of the infrared emissivity through con- of the larger particles show that the 20-1nch trol of the coating. satellite has a probability of puncture of Another environmental experiment is that once every couple of weeks. of measuring the rate of erosion of ex- The scientific experiment to be carried posed surface. The vehicle will be moving in the first satellite attempt will measure the at a high velocity of 4.6 miles per second, intensity of solar ultraviolet in the region and will have numerous collisions with of Lyman. Knowledge of this intensity has meteoric material, much of it finely divided great significance for our interpretation of particles. The surface will also be bom- the nature of our outer atmosphere. It will barded by ionized molecules of the at- also be of importance to future space flight mosphere. Both of these actions can cause because the solar ultraviolet will be the most 506 AVIATION MEDICINE INHABITABLE ENVIRONMENT--STRUGHOLI)

intense high energy radiation to which percentage of the heavier nuclei. These material will be subjected in space. particles due to their greater mass are much The most penetrating of all radiation that more capable of producing ionization and will be encountered will be that of the hence can be more damaging, to the human primary cosmic rays. There is a scientific body. Project Vanguard can contribute to experiment, designed by the State Univer- future space flight by taking the first step sity of Iowa, planned for an early satellite in placing a vehicle in space and by determ- attempt to measure cosmic ray intensity. ining the ambient conditions in which a The primary cosmic rays contain a small space vehicle must operate.

The Possibilities of an Inhabitable Extraterrestrial Environment Reachable from the Earth

BY HUBERTUS STRUGHOLD, M.D., P~I.D.

The problem of 1Ke on other worlds is from the standpoint of human physiology a subject which captivates the imagination and of general terrestrial biology, against of mankind tremendously. Not until it was the physical planetary data offered in the recognized by Copernicus in 1543 that the astronomical literature. earth is not the center of the universe but Such a study can be called planetary rather only one of the members of the ecology. For the science which particularly planetary family of the solar system, could studies the possibility of indigenous life on such thoughts arise in the human mind. the planets the terms "astrobiology" and There are two technical events that have "astrobotany" are in use. With regard to had a catalytic effect upon man's occupation this latter problem this discussion will with this question: the invention of the consider only the kind of life known to telescope some 350 years ago, which has us, based on carbon as the structure atom brought the celestial bodies closer to us and on oxygen as the energy liberation optically, and recently, the successful de- atom. velopment of the rocket which possesses Table I shows a list o4 certain ecological the potentialities of bringing us closer to factors indispensable for the existence of them physically. Not only has the older life such as: the presence of an atmosphere question of the existence of indigenous life and a hydrosphere, or water in its liquid on other planets come anew into the focus state, a biologically suitable temperature, of scientific and general public interest, carbon dioxide which is, in addition to but in addition, with the development of water, the raw material for photosynthesis space operations, this question is posed: in green vegetation, and finally, oxygen, the Are there planets in the solar system that key element in the biological energy libera- offer an environment of such kind that an tion. The table further shows, by use of astronaut from the earth--the species homo the marks ~- and -- whether or not these sapiens terrestris--could land there and stay ecological factors are found on the planets there for some time at least? of our solar system. By screening the We get an answer to both of these planets in this way, only Mars and Venus points very quickly by projecting the spe- remain as bioplanets or conceivable bio- dfications of the environment required, planets. And these planets are found in neighboring orbits near the sun only. The Dr. Strughold is research adviser to the decisive factor :responsible for this zona- commandant, U. S. Air Force School of Aviation Medicine, Randolph Air Force tion ef the planets with life-favoring condi- Base, Texas. tions is the intensity of solar radiation OCTOBER, 1957 507 INHAI{ITABLE ENVIRONMENT--STRUGHOLI ) which decreases with the inverse square of of heat energy, is apparently effective in tile distance from the sun. The difference providing biologically acceptabIe tempera- in the radiation intensities to which the tares .on planets only in the range from planets are exposed, and have been ex- Venus to Mars, which justifies our speak-

TABLE I. THE PLANETS AND SOME OF THE ECOLOGICAL NECESSITIES FOR LIFE

Planets Atmosphere Hydrosphere Bio- Carbon Oxygen Temperature Dioxide Mercury Venus Earth + + Mars (+) (+) Jupiter (-) Saturn (-) Uranus (-) Neptune (-) Pluto (-)

-b present, (+) probably present in small amounts. -- not present, (--) present in frozen state. posed since their protoplanetary stage, are ing of a "biotemperature belt" in the plane- therefore tremendous. tary system. The occurrence of water in We get a dramatic picture o:f this by this same zone represents a kind of "liquid considering the size of the sun as seen water belt" in the planetary system.5 at the distances of the various planetary Finally a zonal distribution is evidenced orbits (Fig. 1). To an observer on Mercury in the chemical composition of the plane- the diameter of the solar disk would appear tavy atmospheres. On the inner planets we more than twice the size it does to us on find atmospheres containing oxygen, and earth. As seen from Mars, the sun would such oxygen compound as carbon dioxoide, have a considerably smaller apparent di- while the atmospheres of the outer planets mension than our moon. At the distance of contain hydrogen and such hydrogen com- Jupiter the sun's diameter is only one-fifth pounds as methane and ammonia. Originally as large as seen from the earth, and at the about two and one-half billion years ago, distance of Pluto the sun would appear no the atmospheres of all the planets were larger than the evening star Venus appears basically hydrogen and reduced atmospheres. to us on earth. This means that in the T.his protoatmospheric composition domin- more remote portions of otlr planetary ated by hydrogen has been transformed in system, the role of the sun, as dominating the course of many millions of years into source of light and heat energy, fades into one of oxygen and oxidized compounds by that of a common star. If there were tile effect of ultraviolet of solar radiation', people on Pluto, these Plutonians would not but only on the planets relatively near the even know the concept of a sun. This con- sun, namely on Venus, earth and Mars. sideration makes it quite clear why life- These planets, therefore, form a kind o,E supporting planets are conceivable only in atmospheric "oxygen belt" in the planetary a certain zone within the planetary system. system. The atmospheres of the outer More in detail, the visible section of the planets, moving beyond the effective reach solar radiation spectrum presents a narrow of ultraviolet solar radiation, are still pro- zone of physiologically desirable planetary toatmospheres preserved in a f,rozen state. illumination, a kind of "euphotic belt" sur- They form a "hydrogen belt" of the pri- rounded by dysphotie (hyperphotic and hy- mordial brand in the planetary system. But pophotic) regions. With this we have added Jupiter, nearest to the sun in this outer belt, a new ecological factor not mentioned in shows some indication of photo-chemical Table I, namely, light. The infrared por- reactions in the upper atmospheric regions, tion of solar radiation, as the main carrier manifested in green and reddish coloratioDs,

508 AVIATION MEDICINE INHABITABLE ENVIRONMENT--STRUGHOLD which have recently been interpreted by during its protoplanet stage some two Rice 4 as caused by free radicals of methane billion ,years ago and which we still find and ammonia in a frozen state. today in the pores of the soil and other In summary, this general ecological con- poorly aerated spaces. However, the low

Fig. 1. Size of the sun as seen from the orbital distances of the various planets. sideration leads us to the assumption of temperature on the outer, so to speak, specific life ~favoring ecological belts in permafrost planets excludes the possibility the planetary system such as an euphoric of life in the hydrogen belt. The sun's belt, biotemperature belt, liquid water .belt, radiation in this region apparently has not and oxygen belt. Because all of these belts been sufficiently effective to change the at- are found in about the same region, they mospheric environment on these planets into are therefore parts of a "general life zone" a biologic climate. which we might call "ecosphere" in the solar For all of these reasons, it would be planetary system and which is confined to ecologically impracticable to extend space the orbital range from Venus to Mars. operations beyond the well irradiated eco- (Fig. 2) This is the zone on the planets sphere to the outer planets with their hydro- in which the kind of life now predominant gen, methane and ammonia saturated at- on earth is conceivable. On the planets in mospheres, and their arctic temperatures the hydrogen belt, micro-organisms such as and surrounding midnight sun light condi- hydrogen-, ammonia-, methane-, and iron- tions. But even the two ecologically ac- bacteria, are conceivable; these are the ceptable planets, Venus and Mars, pose kind which probably populated the earth considerable medical problems. Because of OCTOBER, 1957 509 INHABITABLE ENVIRONMENT--STRUGHOLD

lack of time, I will omit a discussion of an altitude of 55,000 feet in our atmosphere Venus, whose surface features are wrapped (Fig. 3). Barometrically, this altitude is in mystery by dense clouds of carbon the Mars equivalent level in our atmo- dioxide, and shall concentrate upon Mars. sphere. The oxygen pressure at ground

Fig. 2. Ecosphere or life zone of the planetary system comprising Venus, Earth, and Mars. Within this sphere lie the euphoric, biotemperature, liquid water and oxygen belts. All are essential to support life as we know it.

Of primary interest to the astronaut will level is probably lower than it is in our be tbe question of the kind of atmospheric stratosphere. environment he would find there from the Pilots flying at altitudes above 55,000 feet standpoint of human physiology, especially must wear pressure suits. The same would what protective measures he would have be required for an astronaut on Mars when to take concerning respiration. he leaves the sealed compartment of his Atmospheric entry will pose fewer aero- space ship. However, an air pressure of dynamic, aerothermodynamic and pertinent 70 mm. Hg. lies just within the critical physiological difficulties than are encount- border range in which a pressure suit, or ered in the terrestrial atmosphere because simple oxygen equipment with pressure of the lower air density. The most likely breathing, are a matter of dispute. Oxygen chemical composition according to de Vau- equipment with pressure breathing may be couleurs ~ is as follows: 98.5 per cent nitro- sufficient for shorter periods of time. Balke2 gen, 1.20 per cent argon, 0.25 per cent after spending six weeks at a height o[ carbon dioxide, and oxygen ~ 0.12 volume 14,800 feet at Morococca, Peru, ~or ac- per cent. The barometric pressure at ground climitization purposes, was able to with- level (there is, by the way no sea level stand an altitude of 58,000 feet in a low on Mars because of the absence of open pressure chamber for three minutes with bodies of water) is about 70 ram. Hg. or pressure breathing only. A certain altitude 95 millibar. This pressure corresponds to adapt~.tion of the astronaut can be expected 510 AVIATIOIq MV.OICI~r~ INHABITABLE ENVIRONMENT--STRUGHOLD

if the air pressure in the sealed cabin is logically desirable limits. The color of the kept at a pressure of half an atmosphere sky is probably whitish blue s due to scat- during the trip. Be that as it may, a tering of light by the various hazy cloud terrestrial explorer on Mars, wearing a layers. It might .be that under this umbrella pressure suit or pressure breathing device must always retreat, after an hour or hours depending on the efficiency of the equip- 85 ment, into the more convenient sealed com- KM partment of the ship, which should have MI its landing place in the lowlands because, ~. i u, ao with regard to the respiration equipment, ao i 8 every milimeter of Mercury of air pres- sure counts. Such a depressed area, for 2~ instance, is the Trivium Charontis, a dark 4 15 greenish patch several thousand 4eet below the level of the surrounding desert. 20 ~.BOdy fluid l~oils 37*C~ ,oS i11'- 2 In the event of a leak in the sealed compartment or in the pressure suit, the ~,, ...... ,o astronaut would encounter t.he same ,rapid decompression effects including anoxia and l~m b~eathing pure oxyoen aeroembolism as the pilots do in our at- IO mospheric region at about 50,000 to 55,000 feet. He would not, however, be endangered

by "ebullism" a new term s for the so-called 5 "boiling" of body fluids. This effect be- comes manifest on Mars at an altitude of 13,000 feet which corresponds to 63,000 feet 0 I00 200 300 400 SO0 600 700 in our atmosphere. These are the essential BAROMETRIC PRESSURE points which must be considered in insur- ( MM HG) ing physiological air and oxygen pressure for an .astronaut. A factor which, might Fig. 3. Mars equivalent altitudes within facilitate the oxygen requirement and the the earth atmosphere. The altitudes and air mobility of the astronaut is the relatively pressures of the martian atmosphere are projected onto those of the earth. The low gravity on Mars, which is 38 per cent curve shows points at which certain physio- of that on earth. logic effects of decreasing- air pressure are The temperature in summer during the observed. day in the equatorial regions may reach 25~ A, fter sundown when t.he tempera- of whitish haze the sun would be invisible. ture drops very quickly to ---45~ the Finally, an adaptation of the astronaut to space cabin must provide adequate protec- a different day-night cycle is not necessary tion. Harmful effects from solar ultra- because the day-night cycle on Mars is only violet rays can be disregarded. Even i~ thirty-four minutes longer than that on they were not sufficiently filtered out by earth. Such a're the climatic environmental the martian atmosphere, the skid of the conditions that a terrestrial explorer prob- astronaut is always protected from sunburn ably will find on Mars from the stand- by the respiratory equipment or by the point of human physiology or, in other cabin. Health hazards from primary cosmic words, with regard to himself. A strange rays are probably not to be expected be- "second earth"! cause of the atmosphere's absorbing power. Of particular interest for a terrestrial The same certainly would be true con- explorer on Mars will be the question: cerning meteorites. Does indigenous life exist on the planet "l~he intensity of day light on Mars is itself? With this we touch upon the much lower than on earth *,at still in physio- discussed dark green areas in the equatorial OcroBsR, 1957 511 INHABITABLE ENVIRONMENT--STRUGHOLD regions which show seasonal color changes tain desert in Central West Asia, or that and therefore have been interpreted as on the high plateau of Tibet. As previously vegetation. Will the astronaut find that mentioned, the air pressure conditions on this is correct or will he find instead vol- Mars correspond to those in the lower canic ash 3 or some hygroscopic inorganic region of our own stratosphere. So if we material 71 Recent spectroscopic studies combine the mieroclimate of the Pamir seem to support the martian vegetation plateau or Tibet with the macro-climatic theory. The physical conditions are extreme- air pressure milieu of the lower strato- ly severe with the exception of sufficient sphere, we have an approximation of the amounts of carbon dioxide and light. Such environment on Mars. It is more severe conditions, especially the extreme day-night than on the Panfir plateau but friendlier temperature variations, according to ter- to life than our stratosphere because of restrial standards could support only very its higher temperature during the day. hardy and cold resistant plants. We must, Such is the picture that can presently however, consider not only the climate as be drawn of an extraterrestrial environ- a whole but also the so-called microcllmate ment most probably reachable from the near, on, and below the ground qnfluenced earth. Whether or not this earthly concep- by surface and sub-surface features, snow tion corresponds to the martian reality, is coverings, hollows, and caves which usually a question that will probably remain open moderate the extremes of the macroclimate. until a successful space operation to the Then there is the enormous capacity of life green and red planet has been achieved. to adapt itself to abnormal climatic con- Until then, it will remain a common meet- ditions. With regard to the specific environ- ing place for discussion for astronomers, ment on Mars we should consider the pos- biologists, botanists and physiologists--in sibillty of specific structures and properties fact, for everybody. of the plants for storing water, carbon REFERENCES dioxide and photo-synthetically produced oxygen. Such phenomena are well known 1. ARRHENIUS, S. A. : VV*erde~ der V/elten. in terrestrial biology. Strong absorbing Leipzig: Akad Verlags Gesellschaft, 1908. power of the plant surfaces are infrared 2. KurpER, G. P. : The Atmosphere of the and reflecting power for blue could be Earth and Planets. Chicago: Univ. imagined as a means for temperature con- of Chicago Press, 1951. trol and protection against ultraviolet, re- 3. McLAUGHLm, P. : Interpretation of some martian features (in press). spectively, if the latter is necessary. The 4. RICE, F. O. : The chemistry of Jupiter. pronounced bluish tint of the green areas Scient. American, 194:119, 1956. on Mars might offer a hint in this respect. 5. SHAPLEY, H.: Climatic Change, Evi- Protection against frost might be possible dence, Causes and Effects. Cam- if the martian plants were able to develop bridge: Harvard Univ. Press. 1953. 6. TIKHOFF, G. A. : Astrobiology and some kind of antifreeze such as glycerol. Astrobatany. Moscow, 1953. We know that even terrestrial animal cells 7. VAUCOULEURS, DE, G. : Physics off the can survive temperatures as low as --70~ Planet Mars. London: Faber & when placed in glycerol solutions. Faber Ltd., 1953. 8. WARD, J. E.: The true nature of the 'The opinion has been expressed by Tik- boiling of body fluids in space. J. hoff s that a terrestrial climate which comes Av. Med., 27:429, 1956. nearest to that on Mars with regard to 9. WILKS, S., and BALI(E, B. : Increase in tolerance to pressure breathing by temperature, radiation and humidity is that altered breathing mechanics (in found on the Pamir plateau, a high moun- press).

512 Avi^~o~r MEDICINE