The Planetary Report

A Publication of THEPLANE~ SOCIETV o o o. o-8;--e- o o

Board of Directors FROIVI THE CARL SAGAN BRUCE MURRAY EDITOR President Vice President Director. Laboratory for Planetary Professor of Planetary Studies, Cornefl University Science, California Institute of Technology LOUIS FRIEDMAN Executive Director JOSEPH RYAN O'Me/veny & Myers MICHAEL COLLINS Apollo 11 astronaut STEVEN SPI ELBERG director and producer THOMAS O. PAINE former Administrator. NASA HENRY J. TANNER Chairman, National financial consultant Commission on Space Board of Advisors rover from Earth has landed on A Mission to the Pluto-Charon DIANE ACKERMAN JOHN M. LOGSDON A Mars! In this issue of The Planetmy System-Many of you have asked us: poet and author Director, Space Policy Institute, George Washington University ISAAC ASIMOV Report, we reveal for the first time in "What about a mission to Pluto? How author HANS MARK Chancellor, print that the Soviet Union landed a rov­ soon can we complete our reconnaissance RICHARD BERENDZEN University of Texas System educator and astrophysicist ing vehicle on Mars during their 1971 of the solar system?" From Mercury out JAMES MICHENER JACOUES BLAMONT author Mars 3 mission. (A sister craft, Mars 2, to Neptune, our spacecraft have visited Chief Scientist, Centre National d'Eludes Spatiafes. MARVI N MINSKY crash-landed on the planet.) This news is every planet but Pluto, and now missions France Toshiba Professor of Media Arts and Sciences, Massachusetts exciting, because for many years Mars to this distant world are on the drawing RAY BRADBURY Institute of Technology poet and author rovers have been on the wish-lists of plan­ boards. This article enumerates the ques­ ARTHUR C. CLARKE PH ILIP MORRISON Institute Professor. Massachusetts etary scientists. Both the Soviet Union tions Pluto poses to us and describes a author Institute of Technology COR ~I ELIS DE JAGER and the United States hilVe been studying possible mission to answer them. Professor of Space Research, PAUL NEWMAN The Astronomies/Institute at actor such missions for the late 1990s or early Page 24-World Watch-Momentum Utrecht, The Netherlands JUN NISHIMURA 2000s. Until now no one outside of the toward Mars is building in the Soviet FRANK DRAKE Director-General, Institute of Space Professor of Astronomy and and Astronautical Sciences, Japan Soviet Union knew that a rover was al­ Union and in the American administra­ Astrophysics. UniverSity of California al Santa Cruz BERNARD M. OLIVER ready on Mars. For this exclusive story, tion, but progress is not equal on every Chief, SET! Program, LEE A. DUBRIDGE_ NASNAmes Research Center turn to page 4. front. In this column we report on a few former presidential science advisor SALLY RIDE Director, California Space Institute, Page 3-Members' Dialogue-In our steps forward and one step back. JOHN GARDNER Unwersity of California, San Diego founder. Common Cause and former astronaul March/April issue, a member suggested Page 2S-Society Notes- We 've trun­ MARC GARNEAU ROALD Z. SAGDEEV that Mars exploration can wait until we cated this edition of "Society Notes" to Canadian aslronaut former Director. Institute for Space Research, solve difficult problems facing humanity bring you more news in "World Watch," GEORGIY GOLITSYN Academy of Sciences of the USSR Institute of Atmospheric Physics, here on Earth. This suggestion triggered a but check out this column for announce­ Academy of Sciences of the USSR HARR ISON H. SCHMITT former US Senator, NM flurry of letters; we print here two repre­ ments of some exciting and fast-ap­ THEODORE M. HESBURGH and Apollo 17 astronaut President Emeritus, sentative responses. The Search for Ex­ proaching events. University of Notre Dame S. ROSS TAYLOR SH IR LEY M. HUFSTEDLER Professorial Fellow, Australian traterrestrial Intelligence and a correction Page 26-Spark Matsunaga, 1916- National University, Canberra educator and jurist to a photo caption round out this column. 1990-We don't often run obituaries in GARRY E. HUNT LEWIS THOMAS space scientist, Chancellor. Memorial Sloan Page 4-From the Moon Rover to the The Planetary Report, but when someone United Kingdom Kettering Cancer Center SERGEI KAPITSA JAMES VAN ALLEN Mars Rover-The Soviet Union has been dies who has played a major role in the Institute for Physical Problems, Professor of Physics. Academy of Sciences of the USSR Unwersity of Iowa building planetary rovers since the late exploration of our solar system, we feel it 1960s and continues a vigorous program fitting to remember him or her. Spark The Planetary Report (ISSN 0736-3680) is published six times yearly at that may well lead to another Mars rover Matsunaga was a politician, not an aero­ the editorial offices of The Planetary Society, 65 North Catalina Avenue. Pasadena. CA 91106. (818) 793-5100. It is available to members of The mission by the end of the century. Author space engineer or a planetary scientist, yet Planetary Society. Annual dues in the US or Canada are $25 US dollars or $30 Canadian. Dues outside the US or Canada are $30 (US). Alexander Kermurjian has worked in the his contributions to international coopera­ Editor. CHARLENE M. ANOERSON Soviet rover program since its inception. tion in space were crucial. Technical Editor. JAMES D. BURKE Assistant Editor, DONNA STEVENS Here he shares reminiscences of the Page 27- News & Reviews-Titan is Copy Editor. MARY ELIZABETH WILLIAMS Art Director. BARBARA SMITH Lunokhod programs and describes designs tantalizing us again with radar echoes that Viewpoints expressed in colu mns or editorials are those of the authors and for the Marsokhods yet to be launched. seem to contradict theories that scientists g~ ;g~i. ~;~:s~a~~9C,eg~ef~~t ~~~i~~~~ Sfo~~:t:'lanetary Society. its officers Page 12-The Family Gallery-After have been building over the past fe w In Canada, Second Class Mail Regislration Number 9567 taking humanity on an astounding journey years about this large moon of Saturn. COVER: From this early portrait of Earth and its to Jupiter, Saturn, Uranus and Neptune, Pluto as well is posing questions we can Moon together; to thousands of images of the outer the Voyager project undertook one last answer only with spacecraft investiga­ planets, their rings and satellites; to the family challenge: to image our family of planets tions. gallery of Sun and planets that closed out its imag­ arrayed about the Sun. No other space­ Page 28 - Q & A-And what have you ing mission, Voyager has done more than any other spacecraft to show us our place in the solar system. craft now flying could have accomplished been wondering about lately? Hot spots in Voyager 1 took this image on September 18, 1977, this mission; no spacecraft now planned the solar system? Ways to die in space? 13 days after it was launched. Nearly 13 years later, will be able to do it in the future. Here are The dangers of meteorite impacts on the on February 14, 1990, it looked back toward Earth again, and returned a series of images of the plan- the images and the story behind them. moon? Find the answers in this column. ets that we feature in this issue. Image: JPUNASA Page 18-Pushing Back the Frontier: -Charlene M. Anderson, Editor NEWS BRIEFS

On June 27 NASA engineers reported a As administrators of a membership organization, The Planetary Society's Directors and major flaw in the main light-gathering staff care about and are influenced by our members' opinions, suggestions and ideas about mirrors of the Hubble Space Telescope. the future of the space program and of our Society. We encourage members to write us and The flaw is likely to cripple its ability to create a dialogue on topics such as the space station, the lunar outpost, the exploration of see the depths of the universe for several Mars and the search for extraterrestrial life. years. Send your letters to: Members' Dialogue, The Planetary Society, 65 N. Catalina Avenue, The engineers stated at a news confer­ Pasadena, CA 91106. ence that there was a distortion in one of the two mirrors used to focus light. Jean Olivier, deputy project manager said, Regarding the letter by Margaret S. Hunt in the March/April Planetary Report: The only "We don't know if it's on the primary or means now available for finding extraterrestrial civilizations involves searching for artifi­ cially produced radio signals. Any society that cannot produce radio signals, however inter­ secondary mirror yet, but it looks like a esting they may be, will simply "fall through the holes in our net." Thus, the methods avail­ textbook-perfect aberration that is per­ able to us limit the kinds of societies we might contact to those that have at least minimal fectly symmetrical." The distortion, technology. This is why many people believe we will share at least some mathematics and called a spherical aberration, prevents some science with any society we contact. the telescope from finely focusing the I have co-authored a paper with Dr. R. T. Oehrle of the Department of Linguistics where light it gathers. Because of this, the in­ we constructed a language with which we might communicate with an alien society. We strument loses the ability to separate very considered many possible approaches, but we soon found that since we and our contactees close objects or to see very faint ones, share only the physical universe, our language had to be based on our respective precise they said. descriptions of this universe; i.e., our respective sciences and their associated mathematics. Some of the instruments on the space­ -CARL L. DeVITO, Department of Mathematics, University of Arizona, Tucson craft will be unaffected by the problem. But the wide-field planetary camera that The caption accompanying the cover photo of the March/April 1990 Planetary Report is was to perform 40 percent of the scientif­ not entirely correct. The launch of Apollo 17 was the last piloted Saturn 5, but not the actual ic work will be unusable [until fixed, last launch of that class of launch vehicle. That distinction belongs to the April 14, 1973 which some scientists think possible with crew less launch by a Saturn 5 of the Sky lab Orbital Workshop. correcting optics brought up from Earth]. -ARTHUR 1. STOPPE, Moorestown, New Jersey Also, the camera for making extremely precise images of faint objects won't I cannot resist commenting on Bruce Woollatt's letter in the March/April issue of The Plane­ work as designers planned. tary Report. While his charitable sentiment is admirable [before we attempt a Mars mission Although there may be ways for we should take care of the basic needs of everyone on Earth], he makes two seriously wrong ground controllers to compensate for assumptions: First, that the problems he describes would be ameliorated or solved more some of the problems caused by the quickly if the resources spent on space exploration were diverted to their solutions. Their distortion, a permanent correction will solutions are not in throwing more money or talent at them, but in attacking them properly. probably have to wait two or three years Second, he apparently assumes that space exploration is simply frivolous self-gratifica­ for astronauts to visit the craft and re­ tion. Much of what we have gained from space exploration, such as improved weather fore­ place some parts, NASA said. Ed Weiler, casting, global communication, life-support systems and the lessons of comparative plane­ a principal NASA program scientist for tology, have already had a direct impact on worldly problems of hunger, education, water Hubble, said, "We can still do important quality and disaster preparation. and unique science" until the problems Carrying his reasoning to its logical conclusion, we should not hold the Olympic Games are solved. "We are deferring some of again until we've found cures for all forms of paralysis or debilitation, or grant college the science. We are not losing science." degrees until we have cures for all forms of mental retardation. -from Warren E. Leary Rather than advancing the stragglers by holding back the leaders, our brightest hope is in in The New York Times the advance of the vanguard of ability and knowledge. One can see the direction we ought to go simply by juxtaposing his letter and the article on the very next page after it, on The Planetary Society'S participation in Earth Day celebrations. -W. VAN SNYDER, La Crescenta, California Japan's space scientists have lost track of Hagoromo, their miniature Moon satellite Some people seem to have forgotten (or have never heard) that the first human expedition [[fed into lunar orbit on March 19 of this to Mars has already been postponed for about 30 years! NASA originally proposed a lunar year. Contact with the probe was lost, it base for 1979, a human landing on Mars before 1985 and a semi-permanent Mars base seems, because of a broken transistor in before 1990! All of this was scrapped, including plans for a space station and a fully the radio. Japanl~unched the mother ship, reusable space shuttle. Billions of dollars have been saved by squeezing the life out of the Muses-A, on Jamiary-24' (see News Briefs space program for two decades. Has a single cent saved from the space program been used for March/April 1990). The ship was then to feed the hungry of the world? Rather, hasn't the effect been a dampening of the spirit of renamed Hiten, or Spaceflyer, in orbit. the United States, endangering its leading role in technology, weakening its ability to Kuninori Uesugi, chief scientist at effectively assist poorer nations? Japan's Institute of Space and Astronauti­ A healthy, strong nation has to be active in all worthwhile areas- including the fight cal Science, said the Muses-A project met against hunger and a vigorous space program. Waiting until all problems on Earth have its main goal of giving Japanese engineers been solved before we go to Mars is a naive and unrealistic proposal which only leads to experience in targeting the flight of a stagnation and doesn't help solve anything. spacecraft to a distant solar system body. -JOHANNES KOCH, Hong Kong, China -from Space Today 3 his spring The Planetary Society hosted Drs. Alexander Kennurjian and Valery Gromov of the Soviet Union's Industrial Transport Insti­ tute of the Ministry of Defense Industries during their visit to Pasadena, the home of the California Institute of Technology (Caltech), the Jet Propulsion Laboratory (JPL) and The Planetary Society. Al­ though the name of their institute scarcely betrays it, these two men are instrumental in the Soviet Union's planetary rover program. We invited them to the United States to meet their counterparts in the American Mars rover program. Dr. Kennurjian is the Chief Designer of the In­ dustrial Transport Institute. In that position, he is in charge of building the mobility systems for roving vehicles that the Soviet Union is planning to send the to Mars, perhaps before the end of this century. Dr. Kennurjian has worked in the space program since 1963, when his institute was assigned the task of building the chassis for the Lunokhods, the robotic rovers that explored the Moon during the early 1970s. Moon These extraordinary robots traversed the lunar ter­ rain perfonning many experiments, and their success is rivaled only by the Lunas that returned samples from the Moon. Dr. Kennurjian's group was in charge of the parts that provided motion-the wheels, motors, transmissions and steering. The Lavochkin Association oversaw the entire design, Rover while the Institute for Space Research supplied most of the scientific experiments. Dr. Gromov has spent 25 years in the space pro­ gram, specializing in the physical and mechanical properties of soil. His experiments began with the Luna 13 mission in 1966 and continued with the Lunokhods. He studied Venus ' soil through data re­ to the turned by the Venera and Vega landers, and was an experimenter on the Phobos mission that unfortu­ nately failed before it could place a lander on that martian moon. While visiting Planetary Society headquarters in Pasadena, Dr. Kennurjian submitted the accompany­ Mars ing paper to The Planetary Report and revealed to us exclusively that the Soviet Union has already landed small rovers on Mars--during the Mars 2 and 3 mis­ sions of 1971. Both landers failed before the rovers were deployed; nevertheless, they were the first rovers to reach the surface of the Red Planet-a task both the United States and the Soviet Union are now Rover working on. Drs. Kennurjian and Gromov also presented a seminar at Caltech and showed a video of their ex­ perimental vehicles. They toured JPL to meet their American colleagues and to see the equipment de­ veloped so far. The American team is concentrating on artificial intelligence to enable a rover to take by Alexander Kermurjian care of itself on Mars, while the Soviets have con­ centrated on building a vehicle able to overcome obstacles likely to lie in its path. The two approaches are complementary, and if the two leading spacefar­ ing nations were to pool their resources and work together, the timetable for putting roving robots on Mars could be reduced by several years. -Charlene M. Anderson, Director of Publications 4 n 1990 the Lunokhod or Moon The Lunokhod's total mass was Rover is 20 years old. This paper 750 kilograms [1,650 pounds], with commemorates its anniversary. the undercarriage weighing 105 kilo­ [Lunokhod 1 landed on the Moon grams [230 pounds]. Its speed was November 17, 1970; its mission 0.8 to 2 kilometers per hour [0.5 to lasted 11 months.] 1.2 miles per hour] . . The Lunokhod was made up of an As part of the undercarriage, the air-tight compartment containing Lunokhod (Figure 1) carried the equipment and a self-propelled un­ PROP (a Russian acronym for Surface dercarriage. It had a temperature­ Evaluation mstrument). Although it control system with an isotope heat was a scientific instrument, the PROP source, a radio and television trans­ (Figure 2) was also used as part of mitter, a command receiver, a power the safety system to determine the de­ plant with solar and back-up storage gree of wheel slippage and to forecast batteries, a remote control, a small- further motion [in response to com-

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angle of the surface slope made it possible to determine the characteris­ tics of the soil along Lunokhod's route. The penetrometer had a conical pressure-tool. During a measurement, the tool was implanted in the soil and turned 180 degrees. At the same time, the forces needed to penetrate the sur­ face and to tum the instrument were measured. Lunokhod 2 landed on the Moon on January 16, 1973. The two Luno­ frame television, panoramic telepho­ mands]. The PROP system consisted khods operated for a total of 414 tometers [facsimile cameras, which of a free-rolling wheel (the "ninth days, logged about 50 kilometers [30 compile an image by scanning back wheel") and a penetrometer. miles], took several hundred panora­ and forth] and a complex of scientific The ninth wheel had spikes on its mas and over 100,000 photographs instruments. rim so that it could roll without slip­ of the Moon using the small-frame The self-propelled undercarriage ping. The number of its revolutions television. gave mobility to this planetary rover. provided information on the distance The special equipment on the self­ This undercarriage consisted of traveled. This wheel was attached to a propelled undercarriage, which itself wheels, electric motors, suspension, lever so it could move up and down acted as an independent scientific in­ automatic motion-control, a complex freely. Its vertical movement provided strument, provided scientific and en­ of onboard sensors to monitor the as­ information on the unevenness of the gineering data. For example, it has semblies and systems, and a device to terrain that the Lunokhod covered. helped determine: transfer data to the telemetry system. Comparing the number of revolu­ -The temperature of the Moon's The undercarriage had eight rigid tions of the ninth wheel and the drive surface and how it varied in relation drive-wheels with perforated, cleated wheels (which were also counted) to the Sun, as well as the temperature rims. The wheels did not swivel, so made it possible to calculate how of the [wheel-driving] electromechan­ the rover was turned by imparting much the rover slipped. Measuring si­ ical transmission; different velocities to the left or right multaneously the slippage, the forces -The topography and crater distribu­ side. acting on the wheels and the average tion along the Lunokhods' route; 5 Figure 5: "Hopper" carried by Phobos 2 spacecraft

Figure 4: Prototype for a caterpillar-type rover

-The physical and mechanical on the Moon was about 200 grams This showed that the soil on the sur­ properties of the soil, such as the [about half a pound]. face is sufficiently firm to support a bearing strength and rotational spacecraft. The first panoramas made shearing strength (Lunokhod 1 took Creating the Lunokhod it possible for the soil structure and measurements at 500 points); In creating the Lunokhod, many diffi­ the distribution of small stones to be -The specific power losses for soil cult scientific and technological prob­ evaluated. deformation as a function of tractive lems had to be overcome. They must Special instruments on Luna 13 force; also be dealt with in developing the (a soil penetrometer and a radiation -The existence of a thin dust layer Marsokhod, or Mars Rover. densimeter) measured the bearing on the Moon's surface. The trace of There was no reliable information strength and density of the lunar soil. the ninth wheel, as seen in Figure 3, about the lunar surface until the Sovi­ After that, designing the Lunokhod is between 10 and 15 millimeters et Luna 9 made the first soft landing took a surer course and lunar-soil 6 deep [about half an inch]. Its weight on the Moon on February 3, 1966. models were used for tests on Earth. First Rover on Mars-Soviets Did It in 1971 For the Marsokhod the problem differs. The martian surface is Wo robotic rovers reached the sur­ blown over by the fierce martian wind. known to have rock outcrops and face of Mars in 1971 during the So­ Mars 2 was launched May 19, 1971 soft sands. T viet Mars 2 and 3 missions, Dr. Alexan­ and reached the Red Planet on Novem­ Gravity substantially affects the der Kermurjian has revealed exclusively ber 27. Mars 3 followed a few days later, rover's cross-country capability to The Planetary Report. Neither vehicle launching on May 28 and landing on De­ and the stability and lubrication of completed its mission: Mars 2 crash­ cember 2. The orbiters continued their its parts. This creates a problem in landed on the planet and Mars 3 ceased work until August 1972, when the Sovi­ testing equipment on Earth since it transmissions 20 seconds after landing. ets declared the missions completed. is necessary to preserve the rela­ The presence of mobile vehicles on The United States' Mariner 9 space­ tionship between the mass and these missions had not been revealed for craft had taken advantage of the same weight of the planetary rover. [On nearly 20 years. Previous descriptions of launch window (when the relative posi­ the Moon, a rover weighs only Mars 2 and 3 omitted mention of the tions of Earth and Mars allow the quick­ one-sixth as much as on Earth; on small vehicles that were attached to the est route between them). It launched on Mars it weighs a bit more than main landers by tethers. Their range was May 30 and entered orbit about Mars on one-third.] to be 15 meters from the lander. November 14. Since its mission was In tests, terrains were chosen The rovers moved by using skis set on strictly an orbital one, Mariner 9 was that mimicked the surfaces of the either side (see photograph). The two able to wait out the dust storm. When Moon and Mars. The equipment thin bars at the front of the lander (if you the dust cleared, it discovered the great was built to allow simulation of look closely at the photograph, you'll volcanos of Tharsis, the layered polar the gravity of various planets and see the division between them) are sen­ terrain, ancient river valleys, the nature celestial bodies. sors to detect obstacles in the rover's of seasonal change, and Valles Mariner­ Closely associated with the path. The vehicle could determine on is, the mighty canyon complex now problems of soil and gravity is the which side the obstacle lay, step back, named for its robotic discoverer. problem of choosing a means of change direction and try to go around it. With Lunokhod 1 in 1970, the Soviet locomotion. Experience in operat­ This rudimentary artificial intelligence Union had become the first nation to ing the Lunokhods, as well as dif­ was necessary for these martian rovers; land a rover on another world. In 1971 ferences in the conditions among signals from Earth to Mars can take be­ they almost succeeded in repeating their the planets and their satellites, tween 4 and 20 minutes to reach their triumph with Mars 3. The distinction of necessitated a search for better destination (see box, page 9) ~ too long successfully operating the first rover on means of motion. for a walking robot to wait for com­ Mars is still to be won. The changing re­ The searches proceeded in the mands from Earth. By the time an obsta­ lationships among the spacefaring na­ direction of improving the wheels cle had been recognized by mission con­ tions of the world make it possible that (their shapes, dimensions, tread trollers and commands transmitted from that prize will not be won by any single patterns and rigidity), trying a Earth, a rover could have already fallen country. It may well be that the first caterpillar-type mover (Figure 4) to its demise. spacecraft to "walk" on the surface of and trying other configurations. The Soviet rovers each carried two Mars will be built and operated by the For [the martian moon] Phobos, scientific instruments: a dynamic pen­ Soviet Union, the United States and oth­ because of its ultralow gravity etrometer and a densitometer. They were er nations working together to explore (one two-thousandth that of Earth), to measure the bearing strength and den­ the Red Planet. ~CMA hopping was found the be the best sity of the soil. means of movement. Figure 5 Although the Mars 2 shows the PROP-F (the Russian and 3 landers failed, acronym for Mobile Robot for their accompanying or­ Evaluation of the Surface of Pho­ biters both successfully bos) robotic spacecraft designed to completed their mis­ travel over Phobos' surface. This sions and returned use­ "hopper" was installed on the ful data to Earth. Mars Phobos 2 spacecraft. 2, although it crashed, The spacecraft mass was 40 holds the distinction of kilograms [90 pounds]. It was being the first human­ completely self-sufficient with its made object to reach the own power supply, radio transmit­ surface of Mars. The ter and receiver, event programmer landers had the misfor­ [a timer that turns components on tune to arrive during and off] , and an array of scientific one of the greatest mar­ instruments. tian dust storms in The spacecraft was to move by recorded history. A hops 10 to 40 meters long. After prevalent explanation •••• each hop it would roll over into its for the sudden loss of .. . .~. . operating position and perform its contact with Mars 3 is experiments. Data were to be that the lander was transmitted to the Phobos 2 space- • craft for return to Earth. Unfortunately, creating a walking rover for Mars. Fig­ crash-landed on the planet on Novem­ the PROP-F hopper was not destined to ure 6 shows one of the mockups of a ber 27, 1971. On December 2, Mars 3 operate on Phobos. [Contact with Pho­ robot that walks. was successfully deployed on the sur­ bos 2 was lost March 27, 1989 after it An apparatus that was to walk using face, but after 20 seconds of communi­ had reached the neighborhood of Pho­ skis (Figure 7, previous page) has been cations, transmissions ceased.] bos but before it had deployed the on the surface of Mars since 1971. This Installed on these walkers were PROP-F. Phobos 1 had failed en route small rover was delivered to Mars by dynamic penetrometers and radiation to Mars.] The search continues toward the Mars 2 and 3 spacecraft. [Mars 2 densimeters. They were to communi­ cate via cable with the landing station. The walk­ ers' distance traveled was intended to be 15 meters. They carried sensors and an automatic control sys­ tem to enable them to move around objects. For the conditions on Mars, the "wheel-walking" mode of motion provides the best cross-country capa­ bility. A distinguishing fea­ ture of this mode is that the wheel can both roll and walk at the same time. Figure 8 shows the first mock-up of a wheel-walk~ ing robot. This vehicle is capable of going up a fri­ able soil slope of 30 to 32 degrees, which would be in­ accessible for a wheeled or tracked vehicle. When mov­ ing along a hillside, this ve­ hicle will not slip as much · as other types. A Mars rover of this three seconds [the round-trip light control the Lunokhods from Earth] design is also capable of changing the time between Earth and the Moon, see had to acquire new habits. The position of its body to accommodate box below] in transmitting commands Lunokhod crew was carefully trained the relief of the terrain (Figure 9). and receiving a response, in addition in simulated conditions, which took Control is one of the main problems to the complexity of determining the account of the psychological and in creating a MarsokhiJd. sizes of surface features and distances physiological characteristics of every The problem of remote control also to them, required nonstandard modes member. As a result, the crew was existed for the Lunokhods. A delay of of driving. The "crew" [that was to able to remotely control the Luno-

Light-Time and Robots: Communication Across the Solar System

unar rovers can be and have been driven by remote during its 687-day year and Earth circles faster, going Lcontrol from Earth. Why then do we conclude that such around in only 365 days, the distance between the planets driving is completely out of the question for Mars? The an­ varies widely. During the flight of Mars Observer, Earth swer is that Mars is far away and even at the speed of light, and Mars will come within 102,000,000 kilometers of each our radio commands and the responses to them are de­ other when both are on the same side of the Sun, and the layed. distance will stretch to 367,500,000 kilometers when we Here are the relevant numbers: Light and radio waves and Mars are on opposite sides of the Sun. Dividing these travel at nearly 300,000 kilometers per second in the vacu­ figures by lightspeed, 300,000 kID/s, we find the one-way um of space. The Moon is about 400,000 kilometers from light times to vary from 5 minutes and 40 seconds to 20 Earth. Thus what we call the one-way light time to the minutes and 25 seconds. Moon is about 1 1/3 seconds. As the driver commands the Obviously nobody wants to leave a dumb rover to its rover he can never observe its response any sooner than 2 own devices for nearly 41 minutes! It could drive right off 2/3 seconds later. Many Earth-based experiments and the an unseen cliff. No, the martian rover absolutely has to be actual Lunokhod experience show that, though demanding smart. If it were not, its progress would be glacial, and of good on-board vision and hazard sensing, operator skill, even with considerable on-board intelligence it does not and patience, such driving is indeed practical- so long as dare go faster than a human walking pace. The compro­ the rover travels so slowly that the driver's delayed reac­ mise among high mobility and hazard tolerance, travel tions can keep up with it. speed, quality of vision and other on-board sensing, and Now how about a rover on Mars? As an example of the human control demands is one of the most interesting chal­ numbers in that situation we can examine the light times lenges facing the engineers who are now preparing for the for a typical martian mission, the Mars Observer to be mobile robotic exploration of Mars. launched in 1992. As Mars makes its way around the Sun -James D. Burke, Technical Editor range and dimensional fidelity.] The robot also has an information and con­ trol complex built around a two-pro­ cessor computer, a course-indication system and a displacement meter [odometer]. In motion tests, the robot traveled from a start point to a finish point. Motion was planned by process­ ing the information from the LTVS to determine a possible path. The shortest paths were chosen. The control problem is closely relat­ ed to that of the cross-country capabili­ ty. A large safety margin in the rover's cross-country capability enhances the reliability of motion in severe condi­ tions. This may decrease the number of maneuvers while reducing demands on the required resolution of the technical vision. Important to the efficient control of the rover's motion is its ability to ma­ neuver. A possible configuration for a self-propelled undercarriage is one in which all wheels tum together at a specified angle. In this case, the rover may move transversely at an angle to its initial course without changing its body orientation. khods, and they avoided accidents. It carries a laser-rangefinder technical­ There are other problems, such as For Mars, this problem of delay be­ vision system (LTVS). [Technical vi­ the wind, temperature, composition of tween sending commands and receiv­ sion produces an image that includes the atmosphere and its low density. ing responses greatly increases. A sig­ nal can take 5 to 40 minutes to travel to and from Mars. [Distances between Earth and Mars change as the planets travel their different orbits about the Sun.] So it is not possible to control a Mars rover in the same manner that the Moon rovers were controlled. A Mars rover must be more independent. Controlling a robotic Mars rover pre­ sents difficulties, the principal one be­ ing limited or nonexistent information on the rover's situation. In this connection, the capabilities of the Marsokhod's information system are increasingly important. It must also be able to determine distance and to sense its surroundings by "touch." It is probable that the Marsokhod will be capable of independent motion and also of being remotely controlled from Earth by specifying a path over a certain time and distance. The naviga­ tion system has to be able to hold a heading to a finish point. Obviously, the Marsokhod must have a sufficiently developed onboard "brain" for data processing, decision making and command transfer in ac­ cordance with specific programs. To test these abilities an experimen­ tal prototype of a planetary roving 10 robot has been developed and tested. Modern Concept of the as the inevitable re­ Table A Specifications for Prototype Marsokhod Marsokhod strictions [size, mass, The greatest cross-country capability power] on their Mass 360 to 450 kilograms [800 to 1.,000 pounds] Wheel diameter 500 millimeters [20 inches] can be ensured if the rover is a wheel­ placement on an Maximum height of walker with a three-part configuration interplanetary space­ obstacle to be overcome 1 meter and a hinged frame. Such a rover has craft suggest that it is Maximum angle of practically no road clearance. This is expedient to create soil slope to be ascended 33 to 35 degrees achieved by using conical wheels (Fig­ small mobile appara­ ure 10) that provide a continuous sup­ tuses (SMA). Such porting surface for the rover, thus en­ apparatuses may be suring a cross-country capability for used for the study of Table B Specifications for a Small Mobile Apparatus terrains full of obstacles and ruling out planetary surfaces Mass 70 kilograms [150 pounds] the rover's getting stuck on a high cen­ with scientific instru­ Wheel diameter 350 millimeters [14 inches] ter obstacle. The hinged frame and a ments and for recon­ Maximum hei.ght of special drive for folding or raising the naissance of landing obstacle to be overcome 750 millimeters [30 inches) sections enable it to overcome obsta­ sites. An SMA could Maximum angle of soil slope to be ascended 33 to 35 degrees cles whose height is twice the wheels' also be used as a mo­ diameter. bile radio beacon for For overcoming small crevasses, the landing the principal sections can clamp together to form a descent capsule and rigid frame. The sections can move al­ for exploration of hard-to-reach spots, ble specifications. ternately to enable the wheel-walker to where it could sample the soil and de­ Human thought cannot stop. creep up friable soil slopes with angles liver the samples to a rocket for return New thoughts, new ideas arise. of 33 to 35 degrees. Such a Mars rover to Earth. Therefore, it would be no surprise if might have the specifications listed in As an example, Figure 11 shows a the Mars rover that ultimately appears Table A. full-scale mock-up created from the bears little resemblance to what is The many problems that might be concepts for the planetary rover de­ presented in this paper. But today, we solved using automated rovers as well scribed above. Table B gives its possi- see it this way. 0 Tlie Family

ome. Family. This will be Voyager's endur­ Looking from its Pasadena home on Earth's northern ing legacy: It has changed forever the feel­ hemisphere, the spacecraft now appears to be coast­ ings raised by those words. Through its ing above our solar system. -- robotic eyes we have learned to see the solar system Voyager 1 was chosen to take the family portrait as our home. Through its portraits of the planets we because fewer instruments might be damaged by know that they are part of our family. looking back toward the Sun. And, to Voyager 2, Apollo astronauts showed us a tiny Earth alone in now beyond Neptune and traveling much closer to the blackness of space. Now, with these images, the ecliptic, Jupiter was too close to the Sun to be Voyager has shown us that Earth is not really alone. picked up by the spacecraft's cameras. Around our parent Sun orbit sibling worlds, com­ So on February 14--Valentine's Day 1990- panions as we travel through the Galaxy. Voyager 1 aimed its cameras at a string of small These family portraits of the Sun and planets were colored dots clustered just to the right of the constel­ Voyager's final photographic assignment. Planetary lation Orion-the Hunter. The spacecraft was then Society President and Voyager Imaging Team mem­ 32 degrees above the ecliptic and nearly 6 billion ber Carl Sagan worked for a decade to get these pic­ kilometers (3.7 billion miles) from the Sun. It took tures taken. Between the two Voyager spacecraft, 39 wide-angle views and 21 narrow-angle images. they returned some 67,000 images of the four outer The narrow-angle camera, with a lens resembling a planets and their 56 known moons. Voyager 1 had telephoto, took three consecutive images through the slightly easier assignment: It encountered Jupiter colored filters of seven of the nine planets. This en­ in March 1979 and swung by Saturn in November abled image processors at the Jet Propulsion Labora­ 1980. Then it headed out in search of the heliopause, tory to construct the colored portraits of the planets the edge of our Sun's sphere of magnetic influence, seen on pages 16 and 17. The Multi-Mission Image and where the solar wind gives way to the wind Processing Laboratory then pasted together the from the stars. In August 1989 Voyager 2 flew by wide-angle images into the mosaic on the next page. Neptune, completing its reconnaissance mission, Voyager had produced the first portrait ever of our having visited Jupiter in 1979, Saturn in 1981 and Sun and planets together. Uranus in 1986. After passing Neptune, Voyager 2 But like shy family members at a holiday gather­ joined its twin on the way to interstellar space. ing, the smallest planets avoided having their pic­ The Voyagers had been launched in 1977 to take tures taken. Mars and Mercury were lost in the glare advantage of a planetary alignment that occurs only of the Sun. The outermost planet, Pluto, was too tiny once every 176 years. The outer planets were lined and far away. So this family portrait is incomplete. up so that a spacecraft could swing from one to an­ The next generation of spacecraft will be unable to other, threading its way past the 4 gas giants in only take another family portrait. Magellan and Galileo, 12 years. Mission planners at the Jet Propulsion and the planned missions, such as the Soviets' Mars Laboratory could select their paths from among '94 and NASA's Mars Observer and Comet Ren­ many possible trajectories and targets. dezvous/Asteroid Flyby, plus the joint NASA/Euro­ For Voyager 1, they chose to send the spacecraft pean Space Agency Cassini mission, will all be close by Titan's south pole to obtain close-up data locked in orbit about their target planets. None of on Saturn's largest moon. Titan's thick nitrogen at­ these will ever gain a perspective from which they mosphere proved to be heavy with complex, carbon­ could see the solar system as Voyager did. rich organic molecules, and its surface is possibly Voyager alone could look homeward and capture dotted with lakes of liquid hydrocarbons. For car­ our family of planets as they looked on February 14, bon-based lifeforms living in a primarily nitrogen 1990. Voyager alone could so graphically show us atmosphere-such as ourselves-a world like Titan how Earth and the planets are inextricably linked to is well worth a close look. our parent Sun. But to fly close to Titan, the project team had to Home is now a corner of space brightened by a sacrifice Voyager l's encounters with Uranus and small yellow star. Family is now a company of plan­ Neptune or a close-up look at Pluto. Its path around ets circling that star together. Our home and family Saturn swung the spacecraft up and out of the eclip­ now encompass an entire solar system. 12 tic, the plane defined by Earth's orbit about the Sun. Thank you, Voyager. -Charlene M. Anderson Gallery Center Spread:

e've taken the liherty of arraying Voy­ paths. ager's last color images of the planets in­ Venus shines with an opalescent glow from the W to the family gallery on the following sulfuric acid clouds that enshroud it. A crushing­ pages. The Sun and planets' positions are plotted ly thick carhon-dioxide atmosphere has raised relative to each other as Voyager saw them from surface temperatures to some 480 degrees Cel­ the outskirts of our solar system. Even at this sius (900 degrees Fahrenheit) through a run­ great distance, the memhers of our solar system away greenhouse effect. On Earth liquid water family display distinct personalities. makes life possihle; any liquid water that Venus Venus is the hrightest planet visihle in may once have had has long since vanished. The Earth's sky, hut here it shows its true standing sister worlds have grown to he different as heav­ among the other planets , filling only 0.11 pixel en and hell. But at Voyager's distance, it is im­ in a frame in Voyager's narrow-angle camera. possihle to tell them apart. Venus orhits the Sun closest to Earth and is Earth, the only life-hearing planet we know, ahout the same size as our planet; for these rea­ is a tiny hlue dot only 0.12 pixel across in this sons they are often called sister worlds. But they image. In ;ust the last three decades, we have 14 have followed entirely different evolutionary gotten used to images of our home planet taken with multiple reflections off the op,tics. The rays are a diffraction pattern off a calibration lamp mounted in fron~of Voyager's wide~angle lens. Particles stream out from the SUn at supersonic, speeds, forming a "wind" Jupiter managed to fill four pixels in that blows out to the edge of the magne~ . Voyager's camera. Its distinctive orange color reg~ tosphere. There it slows to subsonic isters clearly, but the banded atmosphere, includ~ speeds and, at some point, it gives way ing the Great Red Spot that could swallow three to a wind from the stars. Sometime be~ Earths, is impossible to see at this distance. tween 2000 and 20 I 0, one of the two ,upiter's was the first planetary system visited Voyagers will probably become the first by Voyager, and here the spacecraft made some human~built object to cross that boun~ of its most startling discoveries: the tenuous ring ary fntii interstellar space. around ,upiter; the erupting volcanoes of 10; the smooth, icy surface of Europa that may conceal an underground ocean; the tectonically active surface of Ganymede; and the ancient, cratered face of Callisto. Saturn with its rings was the loveliest planet that Voyager saw, and even at this distance, its slightly oblong shape suggests an enigmatic per~ sonality. Voyager discovered that the great, classical rings are really made of thousands of tiny ringlets, with "spokes" of charged particles rotat~ ing around them. Saturn is orbited by Titan, a world wrapped in hydrocarbon haze, with a thick nitrogen atmosphere colored orange by an assort~ ment of organic molecules. Uranus was a bland blue ball to Voyager 2's cameras as it flew through the system in 1986. In this image (and in that of Neptune), the planet appears as a smear because the spacecraft was moving during the long 15~second exposure. At Uranus Voyager found a corkscrewing mag~ netic field tilted nearly 60 degrees from the plan~ et's axis, which is itself tipped 98 degrees from its plane of revolution about the Sun. The planet is circled by narrow, coal~black rings that contrast starkly with Saturn's bright ice rings. The star of the show turned out to be the tiny moon, Miran~ da, only 480 kilometers (300 miles) across. What it lacked in size, it made up in strangeness, dis~ playing the most varied terrain seen by Voyager. Neptune was Voyager's last planetary en~ counter, and it is still fresh in our minds. Its cool blue disk displayed a Great Dark Spot remark~ from space. The blue nitrogen~oxygen atmosphere ably similar to ,upiter's Great Red Spot. The per~ tinged with white water clouds; the bright, famil~ plexing ring arcs detected from Earth turned out iar continental landforms; the dark, world~girdling to be thicker segments of complete rings. Voyager ocean-all these have long since shrunk to in~ thus discovered that all of the giant outer planets significance in Voyager's cameras. are surrounded by ring systems. Neptune's largest Of all the worlds imaged by the Voyagers, only moon, Triton, provided a last planetary surprise Earth seems to have managed to produce a multi~ when Voyager caught geysers erupting from its plying, changing, thriving veneer of living matter. icy surface. Sitting on Earth, surrounded as we are bg a warm, nurturing atmosphere, friends and other Many members of the Voyager team played parts living things, it's hard to conceive of how tiny, in the conception of these images. Among those rare and fragile our world actually is. As Dr. contributing their ideas and energy were: Candice Sagan envisioned, the preeminent value of an im~ Hansen, Charles Kohlhase, William Kosmann, age like this is that it can take us out of ourselves Steve Matousek, Carolyn Porco, Carl Sagan and and show us a truer perspective of our place in the Brad Smith. universe. 15

Pushing Back the Frontier: n AMission to the Pluto-Charon System

by Robert Farquhar and S. Alan Stern

n the past three decades humanity Pluto is distinctive in several re­ through this region-untraveled by has sent spacecraft to all the plan­ spects, and not a twin world to Titan other planets-the surfaces of Pluto Iets in our system except Pluto. In or Triton. The Pluto system has a and Charon may preserve the best the early 1970s, when mission plan­ unique tale to tell us about the forma­ record of the flux of comets through ners first began considering the epic tion of the outer solar system and the edge of our planetary system. Voyager reconnaissance, they investi­ about several physical processes yet gated sending the Voyager 1 space­ to be investigated by any planetary An Eccentric Planet craft on to Pluto. At that time, scien­ mission. Because of its orbital eccentricity, tists thought that Saturn's moon We've now learned just how differ­ Pluto experiences strongly varying Titan, Neptune's moon Triton and ent Pluto is. It is the smallest planet, solar heating during each 248-Earth­ Pluto--all small, organic-rich bodies only some 2,300 kilometers in diame­ year orbit. During its passes within traveling in the deep freeze of the ter; its single, large moon, Charon, Neptune's orbit (the current phase outer solar system-were very simi­ has a diameter of 1,200 kilometers. It lasting from 1979 to 1999), Pluto re­ lar worlds. To examine one or two follows the most distaHt and most ec­ ceives much more sunlighnhan it close up would be enough to under­ centric orbit of any known planet, does in the farthest reaches of its or­ stand their common nature. ranging from within 4.5 to over 7 bil­ bit. The changing heat reaching its Voyager 1 mission planners chose lion kilometers from the Sun. Pluto's surface causes Pluto to be the only to send the spacecraft in for a close orbit is tilted 17 degrees-far more planet with an atmosphere that forms look at Titan, which they knew from than any other planet's-from the and decays during each orbit. This at­ telescopic studies to have a thick, in­ ecliptic plane described by Earth's or­ mosphere is also more extended com­ , triguing atmosphere containing the bit about the Sun. And there is new pared to the planet's size than the at­

organic molecule methane (CH4). evidence that Pluto's orbit may vary mosphere of any other known world Voyager 2 would investigate Triton, chaotically over astronomical (in comparison, Earth's atmosphere is and Pluto would be left for another timescales. (See "The Solar System a thin, gaseous film). generation of spacecraft and explor­ in Chaos," in the May/June 1989 Pluto seems also to be the rockiest ers. Planetary Report.) planetary body in the outer solar sys­ But since the Voyagers were Many scientists believe that a pop­ tem; yet it contains a substantial sup­ launched, our knowledge about Pluto ulation of comets, called the Kuiper ply of volatile ices, including water has changed markedly. Indeed, even Disk, orbits the Sun between 30 and and methane. The fact that Pluto is so the existence ofPluto 's moon, 50 astronomical units (one AU equals much rockier than the giant planets or Charon, was unknown when Voyager the average distance between Earth the small, icy comets is telling us was launched. Discoveries reported and the Sun, about 150 million kilo­ something important about its forma­ 18 in the late 1980s have indicated that meters). Since its orbit carries Pluto tion. We think the Sun and planets Complete Traiectory to Pluto Edipt.ic. Plane View

.... . It's a long way out to Pluto, as you (an see in this trajectory plot of a possible mission to this far­ .. thest known planet in our solar system. Illustration: S. A. Smith

condensed from a swirling cloud of gas and dust called the solar nebula. Around the larger planets "subnebu­ lae" formed, from which their rock­ and-ice moons then condensed. Rock­ ier Pluto probably condensed on its own, and therefore it offers a better .' sample of the original solar nebula .. than do the outer planets' satellites. It has a unique tale to tell about the out­ er part of our parent nebula. Earth and its large, single Moon are • •• sometimes called a double-planet sys­ tem. However, with Charon, Pluto is a much more extreme double-planet system. The Pluto-Charon mass ratio is 6 to 1; for Earth and its Moon, the " ratio is 81 to 1. The strong gravita­ tional interactions between Pluto and Charon are unique, and probably pro­ duce strong tides in Pluto's outer at­ .mosphere. One particularly fascinat­ ing possibility is that Pluto's tenuous .outer atmosphere may even envelop Charon, leading to mass transfer be­ tween the two. (This would be analo­ gous to the physics of some binary FLYBY star systems where matter flows be­ JUNE 2015 tween the stars.) Like Uranus, Pluto is tipped on its side; Uranus is off 98 degrees, while Pluto tilts 108 degrees from the eclip­ tic. This orientation may be the result PLfJTO FLYBY STUDY SPACECRAFT FLIGHT CONFIGURATION

ABOVE: Pluto is the only planet in our solar system not yet visited by an ex­ PlASMA WAVE SPECTROMETER ploring spaceuaft. It's so far out that ANTENNA even the Hubble Space Telescope at its best would be unable ta pick out features on its surface. The reconnaissance of the nine primary planets in our solar system will remain incomplete until a spaceuaft studies Pluto and (haron. Painting: JPL/NASA ~,T.... --LAUNCH ADAPTER INTERFACE RIGHT: This is a possible configuration for a Pluto-exploring vehicle. Mission de­ 1C:'..IiL-~_- LOW-GAIN ANTENNA MEDIUM-GAIN signers at the Jet Propulsion Laboratory ANTENNA are working on spacecraft that can be VECTOR ELECTRON THRUSTER CLUSTER SPECTROMETER built inexpensively yet carry a powerful (1 OF 4) array of scientific instruments. (1 OF 2 SENSOR CLUSTERS) 20 Illustration: JPL/ NASA of an ancient giant impact. The cur­ rently leading theory for the forma­ The Pluto/Charon System tion of Earth and its satellite holds that a collision with a Mars-sized in­ truder splashed from Earth's mantle the debris that would become the Physical Properties Moon. If the same is true for Pluto and Charon, then they may constitute Pluto Charon an excellent analog to the formation of our own double planet. Radius 1,150 kilometers 600 kilometers Taken together, this abundance of peculiarities shows that the Pluto­ Visual color reddish gray Charon system offers us new perspec­ tives of planetary processes. And yet Rotation period (Earth days) 6.39 6.39 our present knowledge of them is comparable to what we knew of vol­ canic 10 and hydrocarbon-rich Titan Known surface ices Methane, no water Water, no methane before Voyager. Like 10 and Titan, Pluto appears Atmospheric composition Methane, other gases? none complex and enigmatic from afar. Given humankind's long history of Tilt of equator to Pluto's 122.5 degrees 122.5 degrees misconception and mistake about orbit about the Sun planets explored only from Earth, it is unlikely that we can understand Pluto without inspecting it close up. Fortu­ nately, NASA is now studying how it Orbit 01 Charon around Pluto might conduct a mission to fly through the Pluto-Charon system. Mean distance 19,500 kilometers (nearly circular)

Why Go Now? Tilt to Pluto sequator odegrees Interest in a Pluto mission has been growing since the recognition that Pluto might hold the answers to im­ Period 6.39 days portant questions about the history of our solar system. The spectacular Voyager images of Triton, a body Orbit 01 Pluto/Charon about 'he Sun roughly similar to Pluto and about the same distance from the Sun, further excited scientists by demonstrating Perihelion distance 29.6 astronomical units * how complex and active Pluto may (Closest point to the Sun) be. Most immediate, however, is our realization that Pluto mission oppor­ Perihelion date September 5, 1989 tunities with reasonable (11-14 year) flight times are infrequent. Aphelion distance 49.3 astronomical units Because of the energy needed to (Farthest point from the Sun) send a spacecraft to Pluto, gravitation­ al assists from Jupiter (see box, next page) are a required part of the trajec­ Mean distance 39.5 astronomical units tory design. Unfortunately, Jupiter­ Pluto transfers are only available ev­ Inclination 17.2 degrees ery 13 years. One such opportunity is (Tilt from ecliptic plane defined just ending. The next one will be be­ by Earths orbit about the Sun) tween 2001-2004, with the spacecraft arriving about 2015. After that, we must wait until 2014 to launch, and * One astronomical unit equals the mean disllInce between Emili and the Sun, about 150 million kilometers. that spacecraft would not arrive at . Pluto until 2028. If the project started now, by 2028 the taxpayers who fi­ nanced the mission, and the scientists and engineers who planned it, would be mostly gone. ble with a 2001-2004 launch, would a ceiling of $300 million, many guide­ More important though, as Pluto be an opportunity that cannot be re­ lines and constraints were applied. The recedes from the Sun and cools, its at­ peated until the 23rd century. most important was a directive to use a mosphere may collapse. This process In 1990, study of a low-cost Pluto relatively inexpensive (about $50 mil­ could be over by 2025. To watch a flyby mission began at the Jet Propul­ lion) Delta 2 rocket. Although its per­ planetary atmosphere collapse, possi- sion Laboratory. To keep the cost under formance is modest by planetary stan- 21 How Gravity Assist Works

We can change the trajectory of a spacecraft in orbit from the sphere of influence. about the Sun by sending it close by a planet. With such The spacecraft's direction has changed by an a planetary "gravitational assist," we can increase the amount called the bend angle. The bend angle will be energy of its solar, or heliocentric, orbit and change the larger if the planet is more massive, if the spacecraft orbit's size and direction. The diagram shows the trajec­ passes more closely or if it approaches more slowly. tory of a spacecraft near a planet. In deep space, the Since the spacecraft's speed has not changed, its orbital spacecraft follows an elliptical orbit about the Sun, and energy relative to the planet remains the same. the relatively weak gravity of the planets has little ef­ However, its orbital energy relative to the Sun has fect. But if the spacecraft passes close to a planet, to changed. The planet's velocity has been added to that of within a few dozen to a few hundred times its radius, the the spacecraft, and the spacecraft is now moving much effect of the planet's gravity increases. This happens be­ faster relative to the Sun. We've sent it into a larger orbit cause although the planet's mass is much less than the that will take it to much greater distances from the Sun. Sun's, it is much closer to the spacecraft and so exerts a By changing the aim point, and so the encounter greater force upon it. This region of dominant planetary geometry between the spacecraft, planet and the Sun, gravity is called the planet's gravitational sphere of in­ we can send our interplanetary explorers on myriad dif­ fluence. ferent orbits, even on to an additional gravitational assist Inside the sphere of influence, the spacecraft fol­ from another planet. Galileo is using this technique by lows a curved path around the planet, altered insignifi­ encountering Venus once and Earth twice on its way out cantly by the Sun's gravity. The spacecraft's velocity in­ to Jupiter. By using the most massive planet, Jupiter, to creases as it approaches the planet, then decreases as it slingshot our Pluto spacecraft on its way, we can reach moves away. Its speed is the same at entry to and exit the outermost planet in 11 to 14 years. -RF

dards, a Delta 2 can launch a 500 kilo­ 2001, the spacecraft travels a helio­ Hubble Space Telescope (HST) will gram (1,100 pound) spacecraft into the centric trajectory out about 3.2 Astro­ barely be able to tell how large Pluto's desired trajectory. JPL engineers suc­ nomical Units (AUs) from the Sun. polar caps are. It will see about as ceeded in designing a "mini-Voyager" Then, in January 2005, the spacecraft much detail as an amateur telescope that could do the job. swings back by Earth and slingshots can see on Mars. Detecting geologic This spacecraft would carry a mul­ out to Jupiter. There another gravity features or counting craters are be­ tispectral wide- and narrow-angle assist sends it on to Pluto by June yond the HST's capability. The mis­ imaging system similar to the one that 2015. sion we describe will be able to do will fly on the Comet Rendezvous/As­ that and more. And it can make mea­ teroid Flyby (CRAF) and the Cassini Building Up Benefits surements that are impossible by re­ mission to the Saturn system. The oth­ A benefit of this indirect trajectory is mote sensing, such as the composition er half of the payload might consist of that the spacecraft would fly by the of a planet's ionosphere or the an ultraviolet spectrometer to study asteroid 1442 Corvina on December strength of its magnetic field. Pluto's atmosphere and a plasma 14,2002. In addition to its scientific Some of the questions to be an­ physics package to investigate the in­ value, adding a closeup of another swered by a Pluto/Charon flyby in­ teractions of Pluto and Charon with in the zoo of small bodies orbiting clude: How varied are their surfaces? the solar wind of ionized particles between Mars and Jupiter, this en­ What atoms and molecules make up blowing out from the Sun. counter will be an excellent opportu­ the atmosphere? How does the vary­ Although this payload contains rel­ nity to calibrate the spacecraft's ing solar heat over each orbit affect atively few instruments, it strikes a imaging system. Plus, the Jupiter fly ­ the surfaces and atmosphere? How do balance between scientific complete­ by would be an opportunity to fol­ Pluto and Charon interact? Does the ness and cost. It can carry out a very low-up on Galileo's orbital mission, atmosphere evaporate and re-con­ exciting initial reconnaissance of the which will end sometime in 1997. dense every day or only seasonally? Is Pluto/Charon system. A major advantage of a planetary Pluto geologically active? What does You can follow the spacecraft's cir­ flyby over ground-based observations the cratering record tell us about cuitous path to Pluto in Figure 1 (see is its inherently finer imaging capabil­ comets in Pluto's neighborhood? 22 page 19). With a launch in November ity. Even at its best resolution, the What was the origin of this double- of measuring radiated heat from these .:' :-:.: ./:. t • • : l two worlds is clearly a technological Traiectory Arou~d a .Plqnet .. l{·;··,: . :.. ;;/; ~.. ::'; challenge because they are so cold.

, ':"';. ' ,~ " ". However, such an investigation could tell us much about their surfaces and atmospheres. To top off the scientific measure­ ments, the spacecraft's radio could help refine measurements of Pluto and Charon's mass and probe the atmo­ spheric and ionospheric structure. This payload, possible on a flyby mission of moderate cost, can answer a wide range of questions about the Plu­ to/Charon system that cannot be an­ . ,>-, swered from Earth or even from Earth orbit. Doubling the Return Because the upcoming Pluto mission opportunity is unique, we might con­ sider sending two spacecraft. If they are identical, the cost of the second spacecraft would be between 50 and 80 percent of the cost of the originaL If an . ' , international partner could launch the .. .' . :. second one, NASA's share of the cost . " would be modest. Candidates for a sec­ , .. ~ - .. , ~ ; ond launch are Japan's H-2, the Euro­ ." ' : • ~ -;: -:.. r ' .;.':' pean Ariane 4, and the Soviet Union's . . Proton . " JnusiraiI9l;s.

by Louis D. Friedman

MOSCOW-The Mars '94 mission re­ the 20th anniversary of Apollo. Now needed is congressional support to ceived final approval and full funding in This spring the White House directed define the program, develop precursor May 1990 from the Soviet government. that talks begin with European nations, missions, and study propulsion systems The Academy of Sciences had already Canada, Japan and the USSR to make the and technology for long-duration life received its funding, but until now engi­ initiative international. This step was a support. neering work and industry contracts had major change of policy in that it set inter­ been delayed. national involvement and included the LENINSK" USSR-A group of Ameri­ The Lavochkin Association is respon­ USSR before the program was even de­ can engineers visited several space facili­ sible for the development of the two fined. This administration policy, calling ties in the Soviet Union during a tour or­ spacecraft, which will be launched on for landing humans on Mars early in the ganized by The Planetary Society and the Proton boosters in October 1994. (The next century, is just what The Planetary USSR's Institute for Space Research. Soviets routinely send twin spacecraft on Society has been advocating since 1984. They returned with new insights into the planetary missions.) The Mars '94 mis­ USSR's human spaceflight program. The sion includes an orbiter, the Mars Bal­ engineers were members of the Space loon (with an instrument-carrying guide­ Systems Technical Committee of the rope designed by The Planetary Society), American Institute of Aeronautics and surface penetrators and small meteoro­ Astronautics. Several Planetary Society logical stations. members also participated in the meet­ A preliminary plan for missions to fol­ ings at the facilities in Moscow, Star City low Mars '94 was also approved, but it is and Baikonur (the main Soviet launch a plan with options, owing to an as-yet­ site, near the town of Leninsk in Kaza­ unresolved debate between the Institute khstan). We are now planning future for Space Research (IKI) and the Vemad­ tours for Planetary Society members. sky Institute of Geochemistry and Ana­ We learned that the Soviet space pro­ lytical Chemistry. IKI argues for a Mars gram is alive and healthy and that reports rover mission in 1998, followed by a of its death were premature. We saw two Mars sample-return mission in 200l. Energia heavy-lift launch vehicles and a Vernadsky wants to do a sample return Buran shuttle under construction. We al­ from the martian moon Phobos in 1996, so saw several modules for the Mir space using little new instrumentation and in­ station: Soyuz (for crew replacement), cluding a repeat of the partially failed Progress (for supplies), Kvant and · Phobos mission of 1988. The mission Kristall (science statioris). We were would be a step toward a Mars sample re­ shown a docking module for coupling the turn, which Vernadsky proposes for 1998. Buran and Mir, which means that a fully Another ambitious mission receiving developed space-station complex, built study-only approval is Tsiolkovsky, a so­ around the station already in orbit, could lar probe that would go first to Saturn be operational by the end of 1991. Soviet and drop off a small probe at Titan. officials also told us a Mir 2 is under de­ Several Soviet officials, both in the velopment for 1994 orbital insertion. science and engineering programs, reiter­ A flight of the Buran is planned for ated that lunar missions are receiving mid-1991, though it is uncertain whether very little attention in the USSR. the mission will carry humans or not. (The maiden flight of Buran, in late WASHINGTON-President Bush 1988, was unpiloted.) Tom Heinsheimer, called for Americans to set foot on Mars a member of the Planetary Society dele­ by 2019, the 50th anniversary of the gation, speculated that a mission in both first Apollo Moon landing. In a com­ modes would be logical: Buran 2 might mencement speech at Texas A & I Uni­ fly to Mir under automatic control and versity, he set the target date for the cul­ dock; the crew already in the space sta­ mination of the Space Exploration tion would board the shuttle and return to 24 Initiative first proposed in July 1989 on Earth. WASHINGTON-NASA has terminat­ instead on Mars '94. The Soviets per­ tion. It illuminates the low priority that ed its portion of a project with the French suaded the French to combine their in­ middle-level NASA management places space agency to develop an infrared map­ strument with the American one in an on international cooperation. ping spectrometer for the Mars '94 mis­ experiment to be called Omega-VIMS. The Planetary Society vigorously sion. The Centre National d'Etudes Spa­ Now that NASA has backed out, protested NASA's termination of tiales (CNES) was notified of NASA's CNES is faced with the task of develop­ Omega-VIMS development. One of our action in a letter from Lennard Fisk, As­ ing the instrument alone. This has left a primary goals is to see the nations of sociate Administrator for Space Science bitter taste among the French experi­ Earth explore the planets together, and and Applications to Jacques Breton, menters and Soviet mission planners. this cancellation strikes at the heart of CNES's science director. The situation was not helped when, in our program. Fortunately, our actions The move shocked those working on his letter, Fisk said that NASA might re­ have helped reopen the question. the international Mars' 94 mission, consider cooperating if the Soviets de­ NASA is now reconsidering the can­ which is being managed by the Soviet layed the Mars mission from 1994 to cellation and is exploring compromises. Institute for Space Research (IK!) and 1996. One possibility is that American elec­ includes participants from many coun­ Fisk cited proposed cuts to the fiscal tronic equipment- spare parts from an­ tries, including The Planetary Society. year 1991 budget, then before Congress, other planetary spacecraft-might be We are designing the SNAKE guide­ as the reason for the termination. The made available to the French if they de­ rope for the Mars Balloon being built by project would have required $20 million cide to continue building an infrared in­ CNES. (See the May/June 1989 Plane­ in 1991. strument for Mars '94. tary Report.) NASA's decision to back out of a co­ The French space agency, however, The spectrometer would have mapped operative program is inconsistent with faces its own budgetary problems, and the distribution of minerals on Mars. recent pronouncements from President may not be able to find the additional CNES had originally planned to build an Bush. On March 31, the White House is­ funds to continue the project. instrument, called Omega, alone. But sued a statement calling for greater co­ We will keep you informed as this sit­ when VIMS (Visible-Infrared Mapping operation among the spacefaring nations. uation develops. Spectrometer) was dropped from the The staff of the National Space Council, American Mars Observer spacecraft, which is studying space policy for the Louis D. Friedman is the Executive Di­ NASA suggested to IKI that VIMS fly President, was surprised by NASA's ac- rector o/The Planetary Society.

ety. This year the scientists will meet in Charlottesville, Virginia during the last full week in October. Call our in­ formation lines for more de­ tails.

This fall, The Planetary Soci­ ety, in cooperation with the (if-.V,lJ' r=l~-r ',1)1,'1:(='; 1_'J=l ',)=J:{0 I ;J;(jiEf:-(::r·,:1 - Ie) ','1_, :{, 'I, : (.:-.- National Air and Space Muse­ 1;)_, ' }=,; _ --; t; , ) = .- cl; I" ;(-.-' C:l '~I ~ of: J,' =: (' I - " !:, j 'I ~ \ I. ( um, is sponsoring a special Ryan Shepperd, winner of The On September 22, Louis Fried­ Carl Sagan will present a lec­ free showing of the new Plar:etary Society'S 1990 Mars man of The Planetary Society ture open to Planetary Society IMAX film "The Blue Planet." Institute Contest, delivered his and Frank Redd of Utah State members during the October NASA scientist Wes Huntress report at the Case for Mars IV University will report the meeting of the Division for will discuss our own Earth and conference, held this June in progress of the Mars Balloon Planetary Sciences of the its sister world, Venus, in an Boulder, Colorado. Team. The talk will be held at American Astronomical Soci- accompanying lecture. With his paper, "No Lunar Hansen Planetarium in Salt Detour,". the high-school stu­ Lake City. Our mailing address: dent from Fort Collins, Col­ In a Planetary Society-sup­ The Planetary Society, 65 N. Catalina Avenue orado beat an impressive field ported project, the team is de­ Pasadena, CA 91106 of contestants from around the signing an instrumented world. This year 's entrants guide-rope for the French bal­ CaU for an updated events calendar: were asked to consider the role loon probe that will fly on the (818) 793-4328 east of the Mississippi of the Moon in the human ex­ Soviet Union 's Mars '94 mis­ (818) 793-4294 west of the Mississippi ploration of Mars. sion. 25 Matsunaga served on none of the relevant committees for space. Nor was space cooperation a significant na­ Spark Matsunaga tional or local issue at the time. Why then did Matsunaga take up the issue of inter­ national space cooperation and pursue it tenaciously for the rest of his life? 1916 -1990 . Because that's the way Sparky was, and why it was such a pleasure to work for him. Cooperation on the space frontier fit into his own unique political paradigm. It offered a nonconfronta­ tional vision of the future. It required moral conviction. by Harvey Meyerson Its pursuit benefited most from imaginative ideas with universal appeal. It also drew on two of his favorite themes, science and poetry. As Chairman of the Senate's Energy R & When Senator Spark Matsunaga (D-Hl) died on April D subcommittee, he authored more renewable-energy 15,1990, The Planetary Society lost one of its friends. legislation than any other member of Congress. Visi­ On the floor of the United States Senate, he had cham­ tors to his office on any subject usually received lec­ pioned a human landing on Mars as an international tures on photovoltaics, ocean thermal energy, fuel endeavor whose challenge could pull the nations of cells-replete with such props as a solar-powered Earth toward their common destiny: Heforesaw an music box. He might wind up the lecture with a plug Earth-born humanity moving out into the solar system. for his 20-year campaign, ultimately successful, to In 1984 he introduced a resolution that renewed US­ establish a national poet laureate. When asked to con­ USSR cooperation in space. The next yea!; he intro­ tribute combat mementos to a World War II museum, duced another resolution calling for the joint explo­ Matsunaga sent copies of poems he wrote during the ration of Mars. These resolutions added political siege of Cassino. substance to Planetary Society proposals, and brought His distaste for confrontational debate was, I think, our vision of international space exploration much essentially aesthetic. He regarded it as a failure in com­ closer to accomplishment. We will miss him greatly. position, as if the harmonious tableau he was trying to - Charlene M. Anderson, Editor create had suddenly gone jagged. He knew the political process inside out- he even wrote a textbook on the park Matsunaga loved bringing people together. arcane procedures of the powerful House Rules Com­ In politics, relationships are as important as mittee, to which he once belonged. At the time of his Sarguments, he always said, because a winning death he was Vice-Chairman of the even more power­ argument has no enduring effect if the winner doesn 't ful and byzantine Senate Finance Committee-but he inspire respect and affection. Spark Matsunaga's efforts always kept his balance. toward space cooperation were a cumulative example In remarks on the Senate floor when introducing his of that axiom. When he and Roald Sagdeev met, they ISY resolution, Matsunaga said: "The unity of planet didn't shake hands. They embraced-and it was spon­ Earth so evident from space is undermined daily by taneous on both sides. human conflict, but it survives in our aspirations. The Matsunaga's successful two-year campaign to renew lingering memory of Apollo-Soyuz demonstrates its the US-Soviet space cooperation agreement was filled persistency and hints at an awaiting fulfillment. It with festive dinners and lunches for scientists, space probably won't happen in our lifetime. But what has officials and politicos from both countries. When he proved impossible on Earth will, I am convinced, even­ introduced the congressional resolution for an Interna­ tually prove necessary and unavoidable if humanity is tional Space Year (ISY), the astronauts and cosmonauts to realize its destiny in the cosmic immensity of the from the epoch-marking Apollo-Soyuz docking were in heavens. Meanwhile, governments have an obligation the Senate gallery, by special arrangemer:t. Afterward to respond to the deepest aspirations of their citizens in he brought them down to the floor to meet his Senate ways that do not conflict with national interest." colleagues. It's all there: an encompassing vision, compassion, Matsunaga was a combat veteran of World War II an obligation to aspirations, an appreciation of interests who attended Harvard Law School on the G. I. Bill of and above all a modest sense of contributing to a pro­ Rights. He was first elected to Congress in 1962, bare­ cess larger than himself. No, it didn't happen in his ly three years after Hawaii won statehood. He served lifetime. No, his contributions weren't recognized as continuously thereafter, gaining election to the Senate they might have been in his lifetime. But those weren't in 1976. the scales on which Matsunaga measured achievement. I remember first discussing space cooperation with If he could have chosen any words for his epitaph him in the spring of 1982. Congress was in recess. from the eulogies in the Senate that fill 15 pages of the We were sitting in his regional office in Honolulu. Congressional Record, I suspect they would be these, "This issue is important," Matsunaga said. "I want from James Exon of Nebraska: you to take all the time you need in pursuing it." "Spark Matsunaga was a truly loving and caring per­ The words are still vivid because, by prevailing son, the likes of which the US Senate may never have congressional standards, they made no sense. Senior seen before and may never see again." congressional staffers are rarely told to take all the time they need on anything. Rushing from topic to Harvey Meyerson was Spark Matsunaga's legislative 26 topic is a necessary way of life on the Hill. Moreover, counselor from 1980 to 1987. oyager taught us that planetary beauty is not a function of size. That small is beautiful--or fas­ V cinating-became clear from the first images of Ne Jupiter's moon 10 over a decade ago. Voyager gave us clear views of most of the moderately small objects in the outer solar system, setting aside for the moment the swarms of still smaller asteroids and comets that re­ main unexplored even in the inner solar system. Two intriguing worlds were not snared in Voyager's by Clark R. Chapman net: Titan and Pluto. Voyager 1 actually passed very near to Saturn's giant moon Titan, just 4,000 kilometers (2,500 miles) above its clouds. But Titan's smoggy haze totally hid its surface from view. All we really know about Titan concerns its atmosphere. But intri­ cate theories and speculations about that world include the notion that Titan's surface is a frigid laboratory for studying primordial processes that, on Earth, might A Small, Double Planet have led to life. In the June Scientific American, the Massachusetts In­ As for Pluto, when the original Grand Tour concept stitute of Technology's Richard Binzel treats the small­ was "descoped" in the early 1970s and a pared-down est and usually farthest out planet in our solar system. Voyager emerged, a Pluto flyby was one of the casual­ Astronomers have learned much about Pluto. As Binzel ties. From Earth, Pluto can be studied only with power­ chronicles, the 1978 discovery of Pluto's large moon, ful instruments and-soon-with the Earth-orbiting Charon, came just in time for the once-in-a-century Hubble Space Telescope. But ground-based astrono­ chance to study its "eclipses." These occultations and mers grow ever more resourceful. Recently they have transits of Charon behind and in front of Pluto began in made strides in studying both Titan and Pluto. early 1985 and have just ended. They have helped as­ tronomers map Pluto's smface with far greater clarity Penetrating Titan's Smog Layer than is possible by direct inspection of Pluto's tiny, The Cassini mission, now on NASA's drawing boards, fuzzy image in a ground-based telescope. Unfortunate­ would use radar to peer through Titan's hazes and map ly, the resulting map of Pluto's surface, still being re­ its hidden surface. Yet, just as for Venus (see the fined, is not shown in Binzel's article. September/October 1986 and 1989 issues of The Plan­ He does describe the relative sizes, masses, densities, etary Report), radar astronomers are doing what they colors, reflectivities and compositions of Pluto and can from Earth. Their radio-telescopes are much larger Charon. They are not at all alike, yet another manifes­ and more powerful than Cassini could ever caITY to­ tation of the wondrous complexity of our solar system. ward Titan. But the strength of radar echoes is excep­ Binzel thinks that Pluto is the "spittin' image" of tionally dependent on the target's distance-and Titan Neptune's Triton, recently unveiled by Voyager 2. is velY far away, much farther than Venus. While Triton orbits a planet and Charon orbits tiny Plu­ That didn't keep Duane Muhleman of the California to, the comparison seems otherwise apt. But just a Institute of Technology and his colleagues from trying, quarter century ago, Pluto was thought to be an Earth­ however. They transmitted radio waves with the Jet sized body, stuck in a faraway orbit. Size estimates for Propulsion Laboratory's Goldstone radar in the Califor­ Pluto dwindled so fast in the 1970s that some scientists nia desert, and then listened for echoes with the 27 tele­ joked that Pluto would vanish altogether before the end scopes of the Very Large Array in New Mexico. They of the century! Now Pluto's size seems secure, about succeeded not only in detecting Titan's surface, but in two-thirds that of our Moon. Charon is just half Pluto's scuttling some cherished theories. Naturally their his­ diameter, a bit bigger than the asteroid Ceres. toric data (reported in the May 25 issue of Science) are Binzel argues for a spacecraft mission to Pluto, a little "noisy" and there are some problems of inter­ which could "complete ... the preliminary reconnais­ pretation, but Titan's surface has been revealed. sance of all the major bodies in the solar system." How Titan's hazy atmosphere is thick with smog particles soon he forgets! With the large asteroids Ceres and made of such hydrocarbons as ethane (~H6) and acety­ Vesta, and the as-yet-undiscovered comets of the outer

lene (C2H2) . Theorists confidently predicted, from Voy­ solar system still ignored by NASA mission planners, ager's data on Titan's atmosphere, that the hydrocar- the arbitrariness of the word "major" seems stark. Just . bons should rain out onto Titan's icy surface, forming a a few paragraphs earlier, Binzel had lamented "precon­ frigid ethane ocean up to a kilometer deep. But Muhle­ ceptions" that Pluto might be "uninteresting." While man's J:adar echoes reveal Titan to be extremely reflec­ we await missions to the smaller and more distant bod­ tive at the radar's 3.5 centimeter wavelength. That is ies of our planetary system, we can rely on diligent as­ inconsistent with liquid and seems to require an icy tronomers, equipped with the latest instruments, to sUlface, with puddles of ethane at most. There are hints keep probing the mysteries of the heavens. in the data that Titan is geographically diverse, with the radar reflectivity varying widely from place to place. Clark R. Chapman is leading the Galileo Imaging Let's hope that Muhleman's team keeps tuned in on Ti­ Team's efforts to take pictures of Earth during its flyhy tan. this December. 27 Questions Answers

If a person stepped out of a space­ urn would allow gases that are normal­ trapped in body cavities, such as the craft on Mars wearing an oxygen ly dissolved in fluids (such as the oxy­ lungs, would expand, rupturing a lung mask and tank but no space suit, gen and nitrogen in blood) to come out or forcing gases into the circulatory what would kill him or her first? of solution, disrupting normal circula­ system. How long would it take? tion through small blood vessels. The A person can survive a decompres­ -Virginia Saucedo, San Gabriel, CA effects of tissue water vaporizing, sion to vacuum if he or she is brought which occurs at or below a pressure of back to higher pressures relatively This question addresses a serious con­ 47 millimeters of mercury (0.9 pounds rapidly-within 60 seconds or so. cern for practitioners of aerospace per square inch), would be even more Thus the dramatic scene in the film medicine because such hazards endan­ dramatic. (Normal atmospheric pres­ 2001: A Space Odyssey, where the as­ ger an astronaut working outside a sure is approximately 760 millimeters tronaut Dave Bowman, shut out of the protective spacecraft or space station of mercury). This process is called em­ pod by HAL, the insane computer, or, to a lesser degree, crew members of bolism and would cause tissues to comes in through an open airlock is high altitude aircraft that undergo a swell markedly. Circulation in the technically possible. rapid decompression. Sudden exposure large blood vessels would be blocked - DON STEWART, M.D., NASA to a near or total vacuum would quick­ by bubbles. The actual cause of death Aerospace Medicine Programs Office ly be fatal (probably 1-2 minutes), here would be asphyxiation. A person with the cause of death being multiple experiencing these conditions would After some thought on impact craters, physiologic disruptions. lose consciousness in 10 to 15 sec­ I was wondering about the safety of a That is, exposing a body to a vacu- onds. In addition to these effects, gases Moon base. What precautions are possible to prevent a meteor shower from destroying everything? -William H. Matzke, St. Paul, Min~ nesota

A meteor shower won't damage a lu­ nar habitat. The reason is that on the Moon living spaces will have to be buried to protect people, animals and plants from solar flare particles and cosmic rays, and the overburden (a meter or more of lunar soil) will easily stop the tiny particles that show as me­ teors in Earth's atmosphere. People and equipment out on the lunar sur­ face, on the other hand, are at some slight risk; however, data from Survey­ or, Apollo and other lunar missions show the meteorite danger to be negli­ gible in comparison to the other haz­ ards of such missions. Of course there is always the even more remote possibility of a large me­ A person exploring the surface of Mars would have about 60 seconds to make it back to the 28 safety of the base before a broken face mask became a fatal accident. Painting: Pam Lee teorite hit-as is the case on Earth. On This four-minute photo of Comet FACTINOS Austin was taken on April 28, 1990 while it was about 98 million kilome­ Scientists at the University of Arizona in ters (about 61 mil­ Tucson believe they've located the crater left lion miles) from by the lO-kilometer-wide (about 6 miles) Earth. The Planet­ Crossing Asteroid comet that hit Earth 65 million years ago. Survey (PCAS), led Many scientists believe that such an impact by Eleanor Helin, contributed to the demise of the dinosaurs. used the half-meter (18-inch) Schmidt Using seismic imaging, Alan R. Hilde­ telescope at the brand and William V. Boynton have identi­ Palomar Observato­ fied a 300-kilometer-wide (about 180 miles) ry to take this pic­ ture. Austin came undersea depression that may be the impact closest to Earth in site. The researchers reported in Science that late May at a dis­ tance of 35.2 million thick layers of mud and debris on Cuba and kilometers (22 mil­ Haiti indicate that a comet struck somewhere lion miles). The in the Colombian Basin of the Caribbean PCAS is partly sup­ ported by The Plan­ Sea, between North and South America. etary Society. Hildebrand and Boynton say they haven't yet proved that this crater is the impact site, Photo: Eleanor F. Helin, Brian P. Roman and Ken­ but they're confident that they've at least tar­ neth J. Lawrence assist­ ed by Wayne Johnson geted the region where the comet hit. "Now that we have a small part of the world to fo­ cus on, given five years we'll be able to map out the locations of other debris ejected by the impact and know where it [the impact] two separate occasions (1971 and cloud tops; on the night side it's about had to be," said Hildebrand. 1982) small meteorites crashed 270,000 kilometers out (170,000 -from Thomas Maugh IT through the roofs of houses in Weath­ miles). ersfield, Connecticut! A similar event Voyager team members had earlier in the Los Angeles Times on the Moon would trigger the clos­ found a relatively cold and dense ing of pressure-isolation doors in the plasma torus in the region of the base complex and the quick installa­ moons Rhea and Tethys. They Walter Munk of the Scripps Institution of tion of a patch at the damage· site. thought that perhaps the electrified Oceanography in La Jolla, California has -JAMES D. BURKE, fet Propul­ gases originated on the two moons. come up with what some call a "mad sion Laboratory Bombardment of the moons' icy sur­ scheme" to measure global wanning. Early faces by charged particles could be next year, a team of oceanographers plans to Is it true that Voyager 2 found gases stripping oxygen out of their water ice sail to a remote island in the Indian Ocean. near Saturn that were hundreds of and filling the region with energetic There they will lower a complex piece of times hotter than the Sun's corona? oxygen ions, which seem to be the equipment 150 meters (about 150 yards) be­ -Joe Bohnert, Festus, Missouri main ingredient of the cold torus. neath the sea and fire a "shot" that may be We haven't determined the compo­ heard halfway around the world-underwa­ Yes. Voyager 2 discovered a cloud of sition of the hot torus yet, but one ter. If the sound waves are detected off electrified gases around Saturn that is possibility is that the ionized gases are Bermuda and northern California, this test one of the hottest spots ever observed protons, or hydrogen ions, which will herald a decade-long attempt to measure . in the solar system-300 times hotter could also be byproducts of the solar global wanning in Earth's oceans. than the Sun's outer regions. Temper­ particle bombardments of the moons' The technique they will use, called atures in this area ranged from 300 to water ice. Interactions between the acoustic tomography (pioneered by Munk 600 million degrees Celsius. Voyager cold and hot torus could be producing and Carl Wunsch of the Massachusetts Insti­ 2 was able to take the heat because instabilities that are the mechanism tute of Technology), has been used to study the gases were tenuous, only 1,000 generating the extreme heat. local ocean regions, but this would be the particles per cubic meter (30 particles The data on the hot gases were col­ first test across five oceans at once. per cubic foot). This means that very lected by the low-energy charged par­ Measuring the speed of sound waves un­ few gas ions actually hit the space­ ticle instrument on Voyager 2 as it derwater can indicate global wanning be­ craft arid thus very little heat was flew through the saturnian system on cause sound travels faster in warm water transferred to it. August 26, 1981. Voyager 1 had than in cold water. So the speed of sound These hot gases orbit Saturn in a found evidence of the hot torus when waves traveling through the ocean can pro­ doughnut-shaped cloud, or torus, near it visited Saturn in November 1980, vide a temperature gauge. A lot of data on the planet's two icy moons, Rhea and but the temperatures were not as hot ocean temperatures already exists, but these Dione. The gases are made up of elec­ then, only as high as about 400 mil­ temperatures are notoriously tricky to mea­ trified ions and electrons; in such a lion degrees Celsius. Why there sure. Munk and his team hope that this initial form, scientists call them a plasma. would be such a difference is another test of tomography will provide the first reli­ On the day side of Saturn, the plasma aspect of the puzzle. able baseline-a baseline that could later be torus orbits about 700,000 kilometers -So M. KRIMIGIS, fohns Hopkins used to check temperature increases. (450,000 miles) from the planet'S University -from Ann Gibbons in Science 29 #328 SEDS Poster The Students for the Exploration and Exploring Earth Development of Space from Space (SEDS) present this by Jon Erickson. whimsical view of This basic, easy to under­ space exploration. stand book examines the Dimensions 18" x 24". many ways remote sensing Originally $6.00, now $4.00 devices are used to learn about Earth. 192 pages, soft cover. Originally $t4.00, now $11.00

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DAYTIME TELEPHONE NUMBER (__ ) ______Sales Tax: California residents add 6.25% Los Angeles County residents add o CHECK OR MONEY ORDER FOR $ ______(Sorry, no C.OD.'s) an addilional1/2% transit lax. Shipping and Handling: o VISA 0 Me .....:D:;.~A~M~E~X~P_.____,.:E~XP~I :::RA~T~IO~N~DA~T~E;.=:::;==;:=;:=r==r=~ All orders add 10% (maximum $10.00) Non-US add an additional $4.00 . COMPLETE ACCOUNT NO. LI-.J__ L-L-lL.L-.l __ L.L...L __ L-..L--L __ L-...L--'.---' for Air Mail, Call for Prices Officers of The Planetary Society contribute to the Society the royalties due them as authors of the books Total Order: SIGNATURE______advertised in these pages 1...______...1. ___...1 MAIL ORDER AND PAYMENT TO: THE PLANETARY SOCIETY, 65 N. CATALINA AVENUE, PASADENA, CA 91106 SATURN PROBE ENTRY-An atmospheric probe streaks down to penetrate Saturn's cloud-tops, on its way to investigate the composition and structure of this giant gas planet. Artist Ron Miller here imagines a mission not yet on the drawing boards of Earth's space agencies. However, the probe now being carried by Galileo will perform a similar mission when it arrives at Jupiter in 1995. Saturn's banded atmosphere is about 94 percent hydrogen and 6 percent helium, with cloud systems that persist for years. Ron Miller is a space artist and writer who lives and works in Fredericksburg, Virginia. He is currently working on In the Stream of Stars, a collection of US and Soviet art celebrating the international space artists' exchange partly funded by The Planetary Society. (See the Marchi April 1990 Planetary Report.) The book is due out this winter from Workman Publishing.

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