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Home , Mariner program, Orbit of Venus

Deep Space Chronicle: Foreword Foreword

From the 1950s to the present, to some and , have been visited. We have Americans, space has represented prestige placed in around our Moon and a positive image for the United States on and the , , and Jupiter; we the world stage. To others, it has signified have landed on Venus, Mars, and our Moon. the quest for national security. Some view it NASA’s stunning missions to explore the as a place to station telecommunications outer have yielded a treasure of satellites and little else. To still others, space knowledge about our universe, how it origi- is, or should be, about gaining greater knowl- nated, and how it works. NASA’s exploration edge of the universe. It represents, for them, of Mars—coupled with the efforts of the pure science and the exploration of the Soviet Union/Russia—has powerfully shown unknown. Even so, the history of space sci- the prospect of past life on the Red . ence and technology is one of the largely neg- Missions to Venus (including some that lected aspects in the history of the space landed on it) and have increased our program. This important monograph by Asif understanding of the inner planets. Lunar A. Siddiqi chronicles the many space probes exploration has exponentially advanced that have been sent from to explore human knowledge about the origins and evo- other bodies of the solar system. It provides lution of the solar system. Most importantly, a chronological discussion of all space we have learned that, like Goldilocks and the probes, both those developed by the United three bears, Earth is a place in which every- States and those developed by the Soviet thing necessary to sustain life is “just right,” Union/Russia and other nations; basic data while all the other planets of our system about them; their findings; and their status seem exceptionally hostile. over time. As such, this monograph is a handy reference work that will provide fun- Planetary exploration has not taken place by damental data for all missions undertaken magic. It required visionary leadership, during the twentieth century. strong-willed management, and persevering execution. Like NASA and other aspects of Since the first flights discussed here, every the space program, it began as a race planet of the solar system has been explored between the United States and the Soviet in a modest way at least once (save Pluto), Union to see who would be the first to get and several of the moons of planetary bodies some sort of spacecraft near the Moon. It (including our own), as well as some comets expanded in the 1960s when space science

Foreword 3 first became a major field of study. During more since astronomers realized that it was that decade, both the United States and the shrouded in a mysterious cloak of clouds per- Soviet Union began an impressive effort to manently hiding the surface from view. As a gather information on the planets of the solar further attraction, it was also the closest system using ground-, air-, and space-based planet to Earth and a near twin to this planet equipment. Especially important was the cre- in terms of size, mass, and gravitation. ation of two types of spacecraft, one a probe that was sent toward a heavenly body, and After ground-based efforts in 1961 to view the second an Earth-orbiting observatory the planet using radar, which could see that could gain the clearest resolution avail- through the clouds, and after learning, able in telescopes because it did not have to among other things, that Venus rotated in a contend with the . retrograde motion opposite from the direction of orbital motion, both the Soviet Union and The studies resulting from this new data the United States began a race to the planet have revolutionized humanity’s under- with several . The United standing of Earth’s immediate planetary States claimed the first success in planetary neighbors. These studies of the planets, per- exploration during the summer of 1962, when haps as much even as Project , cap- and were launched tured the imagination of people from all toward Venus. Although Mariner 1 was lost backgrounds and perspectives. Photographs during a launch failure, Mariner 2 flew by of the planets and theories about the origins Venus on 14 December 1962 at a distance of of the solar system appealed to a very broad 34,827 kilometers. It probed the clouds, esti- cross section of the public. As a result, NASA mated planetary temperatures, measured the had little difficulty in capturing and holding charged particle environment, and looked for a widespread interest in this aspect of the a magnetic field similar to Earth’s magnetos- space science program. phere (but found none). After this encounter, Mariner 2 sped inside the and Exploration of the Terrestrial (Inner) eventually ceased operations on 3 January Planets 1963, when it overheated. In 1967, the United States sent to Venus to investigate During the 1960s, NASA space science the atmosphere. Both spacecraft demon- focused much of its efforts on lunar missions strated that Venus was a very inhospitable with projects Ranger, Surveyor, and Lunar place for life to exist and determined that the Orbiter. Even so, a centerpiece of NASA’s entire planet’s surface was a fairly uniform planetary exploration effort in that era was 425 degrees Celsius. This discovery refuted the , originated by NASA in the probability that life—at least as humans the early part of the decade to investigate the understood it—existed on Venus. nearby planets. Built by Jet Propulsion Laboratory (JPL) scientists and technicians, The most significant mission to Venus began satellites of this program proved enormously in 1989 when the spacecraft set out productive in visiting both Mars and Venus. for Venus to map the surface from orbit with imaging radar. This mission followed the Mariner made a huge impact in the early Pioneer Venus 1 spacecraft that had been 1960s as part of a race between the United orbiting the planet for more than a decade States and the Soviet Union to see who would and had completed a low-resolution radar be the first to reach Venus. This goal was topographic map, and Pioneer Venus 2, which more than just an to beat the had dispatched heat-resisting probes to pene- rival in the Cold War; scientists in both the trate the atmosphere and communicate infor- United States and the Soviet Union recog- mation about the surface, Venus’s dense nized the attraction of Venus for the further- clouds, and the 425°C temperature. It also ance of planetary studies. Both the evening built on the work of the Soviet Union, which and the morning star, Venus had long had compiled radar images of the northern enchanted humans, and it has done so all the part of Venus and had deployed balloons into

4 Deep Space Chronicle the Venusian atmosphere. Magellan arrived 4,000 kilometers long and 5.6 kilometers at Venus in September 1990 and mapped 99 deep. As the dust settled, meandering “rivers” percent of the surface at high resolution, parts appeared, indicating that, at some time in the of it in . The amount of digital imaging past, fluid flowed on Mars. Suddenly, Mars data the spacecraft returned was more than fascinated scientists, reporters, and the twice the sum of all returns from previous public. missions. This data provided some surprises, among them the discovery that plate tectonics Project Viking represented the culmination of was at work on Venus and that lava flows a series of missions to explore Mars that had clearly showed the evidence of volcanic begun in 1964. The Viking mission used two activity. In 1993, at the end of the mission, identical spacecraft, each consisting of a NASA’s Jet Propulsion Laboratory shut down lander and an orbiter. Launched on 20 August the major functions of the Magellan space- 1975 from the (KSC), craft and scientists turned their attention to a Florida, spent nearly a year cruising detailed analysis of its data. to Mars, placed an orbiter in operation around the planet, and landed on 20 July 1976 on the Mars has attracted significant attention from Chryse Planitia (Golden Plains). was the beginning of the space age. An attraction launched on 9 September 1975 and landed on yet to be relinquished by most planetary sci- 3 September 1976. The primary mission of the entists, Mars prompted many missions. In Viking project ended on 15 November 1976, July 1965, flew by Mars and took eleven days before Mars’s superior conjunc- 21 close-up pictures. Mariners 6 and 7, tion (its passage behind the Sun), although launched in February and 1969, the Viking spacecraft continued to operate for respectively, each passed Mars in August six years after first reaching Mars. The last 1969, studying its atmosphere and surface to transmission from the planet reached Earth lay the groundwork for an eventual landing on 11 November 1982. on the planet. Their pictures verified the Moon-like appearance of Mars and gave no Since the Viking landings, there have been hint that Mars had ever been able to support several missions to Mars seeking to further life. Among other discoveries, these probes unlock its mysteries. These were energized in found that much of Mars was cratered almost 1996 when a team of NASA and Stanford like the Moon, that volcanoes had once been University scientists announced that a Mars active on the planet, that the frost observed meteorite found in Antarctica contained pos- seasonally on the poles was made of carbon sible evidence of ancient Martian life. When dioxide, and that huge plates indicated con- the 1.9-kilogram, potato-sized rock, labeled siderable tectonic activity. , sched- ALH84001, was formed as an igneous rock uled to enter Martian orbit in November about 4.5 billion years ago, Mars was much 1971, detected a chilling dust storm warmer and probably contained oceans hos- spreading across Mars; by mid-October dust pitable to life. Then, about 15 million years obscured almost all of Mars. Mariner 9’s first ago, a large hit the Red Planet and pictures showed a featureless disk, marred jettisoned the rock into space, where it only by a group of black spots in a region remained until it crashed into Antarctica known as Nix Olympia (Snows of Olympus). around 11,000 B.C.E. The scientists presented As the dust storm subsided, the four spots three compelling, but not conclusive, pieces of emerged out of the dust cloud to become the evidence that suggest that fossil-like remains remains of giant extinct volcanoes dwarfing of Martian micro-organisms that date back anything on Earth. Olympus Mons, the 3.6 billion years are present in ALH84001. largest of the four, was 483 kilometers across These findings electrified the scientific world, at the base with a 72-kilometer-wide crater in but they excited the public just as fully and the top. Rising 32 kilometers from the sur- added support for an aggressive set of mis- rounding plane, Olympus Mons was three sions to Mars by the year 2000 to help dis- times the height of Mt. Everest. Later pic- cover the truth of these theories. tures showed a canyon, ,

Foreword 5 The United States has undertaken several entists compared those features to those left missions since then, including the hugely by flash floods on Earth. popular . After launch in December 1996, it sped to Mars and landed Everyone agreed that the presence of liquid on 4 July 1997. There, a small, 10.4-kilogram water on Mars would have profound implica- robotic rover named departed from tions for the question of . NASA’s the main lander and began to record weather Associate Administrator for Space Science, patterns, atmospheric opacity, and the chem- Ed Weiler, commented, “If life ever did ical composition of rocks washed down into develop there, and if it survives to the present the Ares Vallis flood plain, an ancient outflow time, then these landforms would be great channel in Mars’s northern hemisphere. places to look.” The gullies observed in the Pathfinder returned more than 1.2 gigabits images were on cliffs—usually in crater or (1.2 billion bits) of data and over 10,000 tan- valley walls—and showed a deep channel talizing pictures of the Martian landscape. with a collapsed region at its upper end and The images from both craft were posted to at the other end an area of accumulated the Internet, and individuals retrieved infor- debris that appeared to have been trans- mation about the mission more than 500 mil- ported down the slope. Relative to the rest of lion times through the end of July 1997. the Martian surface, the gullies appeared to be extremely young, meaning they may have Another mission reached Mars on 11 formed in the recent past. It is possible, sci- September 1997, when the Mars Global entists said, that water could be about 90 Surveyor, launched in December 1996, meters to 400 meters below the surface of entered orbit. That spacecraft’s magneto- Mars. Some scientists have been skeptical of meter soon detected the existence of a plane- these claims, but all agree that the only way tary magnetic field. This held important to find out what is truly present is to send implications for the geological history of additional missions to Mars. Mars and for the possible development and continued existence of life there. Planets like Exploration of the Jovian (Outer) Earth, Jupiter, and Saturn generate their Planets magnetic fields by means of a dynamo made up of moving molten metal at the core. A As the heady projects of the molten interior suggests the existence of 1960s—culminating in the lunar exploration internal heat sources that could give rise to effort—suffered from more constrained volcanoes and a flowing crust responsible for budgets in the 1970s, NASA’s most ambitious moving continents over geologic time periods. planetary science expedition was hatched amongst its leadership. Once every 176 years, These missions, coupled with others, began to the giant planets on the outer reaches of the create a new portrait of the Martian environ- solar system gather on one side of the Sun, ment through the analysis of data relating to and such a configuration was due to occur in weather patterns, atmospheric opacity, and the late 1970s. This geometric line-up made the chemical composition of rocks washed possible close-up observation of all the down into the Ares Vallis flood plain. Despite planets in the outer solar system (with the significant setbacks to the Mars exploration exception of Pluto) in a single flight, the so- program with the failure of two missions in called “Grand Tour.” The of each planet 1999, scientific returns from the Mars Global would bend the spacecraft’s flight path and Surveyor reenergized interest in the planet. increase its velocity enough to deliver it to In what may prove a landmark discovery, sci- the next destination. This would occur entists announced on 22 June 2000 that fea- through a complicated process known as tures observed on the planet suggested that “gravity-assist,” something like a slingshot there may be sources of liquid water at or effect, whereby the flight time to near the surface. The new images showed the could be reduced from thirty to twelve years. smallest features ever observed from Martian orbit—the size of an SUV. NASA sci-

6 Deep Space Chronicle In 1964, to prepare the way for the “Grand were funded to conduct intensive flyby studies Tour,” NASA conceived Pioneers 10 and 11 as only of Jupiter and Saturn, in effect repeating outer-solar-system probes. Although severe on a more elaborate scale the flights of the budget constraints prevented the commence- two Pioneers. Even so, the spacecraft builders ment of the project until the fall of 1968 and designed as much longevity into the two forced a somewhat less ambitious effort, Voyagers as possible with the $865-million was launched on 3 March 1972. It budget available. NASA launched these from arrived at Jupiter on the night of 3 December Cape Canaveral, Florida; lifted off 1973, and while many were concerned that on 20 August 1977, and entered the spacecraft might fall prey to intense radi- space on a faster, shorter trajectory on 5 ation discovered in Jupiter’s orbital plane, September 1977. the spacecraft survived, transmitted data about the planet, and continued on its way As the mission progressed, with the suc- out of the solar system, away from the center cessful achievement of all its objectives at of the Milky Way galaxy. By May 1991, it was Jupiter and Saturn, additional flybys of the about 52 astronomical units (AU) from Earth, two outermost giant planets, and roughly twice the distance from Jupiter to Neptune, proved possible—and irresistible— the Sun, and still transmitting data. to mission scientists. Accordingly, as the spacecraft flew across the solar system, In 1973, NASA launched , pro- remote-control reprogramming was used to viding scientists with their closest view of prepare the Voyagers for the greater mission. Jupiter, from 42,800 kilometers above the Eventually, between them, Voyager 1 and cloud tops in December 1974. The close Voyager 2 explored all the giant outer approach and the spacecraft’s speed of planets, forty-eight of their moons, and the 172,800 kph, by far the fastest ever reached unique systems of rings and magnetic fields by an object from Earth, hurled the Pioneer those planets possess. 11 spacecraft 2.4 billion kilometers across the solar system. In 1979, Pioneer 11 encountered The two spacecraft returned information to Saturn, closing to within 20,900 kilometers of Earth that revolutionized solar system sci- the planet, where it discovered two new moon- ence, helped to resolve some key questions, lets and a new ring and charted the magne- and raised intriguing new ones about the tosphere, its magnetic field, its climate and origin and evolution of the planets. The two temperatures, and the general structure of Voyagers took well over 100,000 images of Saturn’s interior. In 1990, it officially the outer planets, rings, and satellites, as departed the solar system by passing beyond well as millions of magnetic, chemical Pluto and headed into interstellar space spectra, and radiation measurements. They toward the center of the Milky Way galaxy. discovered rings around Jupiter, volcanoes on Both Pioneers 10 and 11 were remarkable Io, shepherded satellites in Saturn’s rings, space probes; they stretched a thirty-month new moons around Uranus and Neptune, and design life cycle into a mission of more than geysers on Triton. The last sequence of twenty years and returned useful data, not images was Voyager 1’s portrait of most of the only about the other Jovian planets of the solar system, showing Earth and six other solar system, but also about some of the mys- planets as sparks in a dark sky lit by a single teries of the interstellar universe. bright star, the Sun.

Meanwhile, NASA technicians prepared to It was nearly two decades after Voyager before launch what became known as Voyager. any spacecraft ventured to the outer solar Although the four-planet mission was known system again. In October 1989, NASA’s to be possible, it quickly became too expensive spacecraft began a gravity-assisted journey to to build a spacecraft that could go the dis- Jupiter and sent a probe into the atmosphere tance, carry the instruments needed, and last that observed the planet and its satellites for long enough to accomplish such an extended several years beginning in December 1995. mission. Thus, the two Voyager spacecraft Jupiter was of great interest to scientists

Foreword 7 because it appeared to contain material in its revealed that Europa may harbor “warm ice” or original state left over from the formation of even liquid water—a key element in life- the solar system, and the mission was sustaining environments. Many scientists and designed to investigate the chemical composi- science fiction writers have speculated that tion and physical state of Jupiter’s atmosphere Europa—in addition to Mars and Saturn’s and satellites. Because of a unique orbital moon —is one of the three planetary inclination that sent the probe around the Sun bodies in this solar system that might possess, and back on the way to Jupiter, Galileo came or may have possessed, an environment where back past both Venus and Earth, made the primitive life existed. Galileo’s photos of first close flyby of asteroid Gaspra in 1991, and Europa were taken during a flyby of provided scientific data on all. But the mission Ganymede some 154,500 kilometers away from was star-crossed. Soon after Galileo’s deploy- Europa. They revealed what appeared to be ice ment from the , NASA engineers floes similar to those seen on Earth’s polar learned that Galileo’s umbrella-like high-gain regions. The pictures also revealed giant cracks antenna could not be fully deployed. Without in Europa’s ice where warm-water “environ- this antenna, communication with the space- mental niches” may exist. In early 1997, craft was both more difficult and more time- Galileo discovered icebergs on Europa, a dis- consuming, and data transmission was greatly covery that lent credence to the possibility of hampered. The engineering team that worked hidden, subsurface oceans. These findings gen- on the project tried a series of cooling exercises erated new questions about the possibility of designed to shrink the antenna central tower life on Europa. While NASA scientists stressed and enable its deployment. that the data did not conclusively prove any- thing, they thought the images exciting, com- In mid-1995, Galileo deployed the probe that pelling, and suggestive. They called for a would parachute into Jupiter’s dense atmos- concerted effort to send a lander to Europa to phere. The two spacecraft then flew in forma- burrow through the ice to reach water beneath. tion the rest of the way to Jupiter, and while the probe began its descent into the atmos- NASA’s 2000–01 Near Earth Asteroid phere, the main spacecraft went into a trajec- Rendezvous (NEAR) mission to the asteroid tory that placed it in a near-circular orbit. On Eros achieved excellent results. NEAR was the 7 December 1995, the probe began its first spacecraft to orbit an asteroid. In one descent. Its instruments began relaying data year it met all of its scientific goals while back to the orbiter about chemical composi- orbiting the asteroid Eros, and then it under- tion; the nature of the cloud particles and took a controlled descent to the surface of the structure of the cloud layers; the atmos- asteroid on 12 February 2001. The chief goal of phere’s radiative heat balance, pressure, and the controlled descent was to gather close-up dynamics; and the ionosphere. The probe pictures of the boulder-strewn surface of 433 lasted for about 45 minutes, during which it Eros, more than 315.4 million kilometers from stored and returned the data, before the Earth. During its five-year, 3.2-billion-kilo- atmosphere and the pressure of the planet meter journey, the NEAR mission provided the destroyed it. For months thereafter, because most detailed profile yet of a small celestial the high-gain antenna was inoperative, scien- body. It began a yearlong orbit of Eros on 14 tists and technicians coaxed the data back to February 2000 and collected ten times more Earth for analysis. Today, Galileo continues data than originally planned. The data include to transmit scientific measurements back to a detailed model culled from more than 11 mil- Earth. The result has brought a reinterpreta- lion laser pulses; radar and laser data on tion of human understanding about Jupiter Eros’s weak gravity and solid but cracked inte- and its moons. rior; x-ray, gamma-ray, and readings on its composition and spectral properties; and Most significant in terms of results has been about 160,000 images covering all of the 34- the discovery of a frozen ocean of water cov- kilometer bouldered, cratered, dusty-terrain ering Europa, one of the principal moons of asteroid. Jupiter. On 13 August 1996, data from Galileo

8 Deep Space Chronicle Finally, in 1997, NASA launched the Cassini NEAR spacecraft orbit of Eros in February spacecraft on its voyage to Saturn. In some 2000. respects a sister spacecraft to the remarkable Galileo vehicle at Jupiter, this spacecraft will •A discussion, with results, of planet flybys linger for several years collecting all manner introduces attempts on Mars, Jupiter, of data about Saturn and its moons. Once it Saturn, Uranus, and Neptune. arrives in 2003, Cassini is expected to provide a similar level of stunning scientific data •A detailed bibliography is enclosed, and the about the Saturnine system to the rich har- author highly recommends Andrew Wilson’s vest that Galileo brought to the human race Solar System Log for more details regarding about Jupiter and its moons. particular missions.

Conclusion We are pleased to publish Asif A. Siddiqi’s monograph on all planetary missions under- The Deep Space Chronicle provides a ready taken during the twentieth century. He is reference of deep space missions attempted also the author of the recently published since the opening of the space age in 1957 pathbreaking book Challenge to Apollo: The and documents the development, testing, and Soviet Union and the , 1945–1974 implementation of robotic spacecraft. Here (NASA SP-2000-4408). He has created in are a few of its features: Deep Space Chronicle a factual reference source that will prove useful to all who are •A list of significant “firsts” takes readers interested in planetary exploration. from the American Able 1 lunar probe in August 1958, to the Russian Mars 2 space- craft impact on Mars in November 1971, to Roger D. Launius the American Sojourner’s wheeled touch- NASA Chief Historian down on Mars in 1997, to the American

Foreword 9