PIONEER – First to Jupiter, Saturn, and Beyond. 7. 1. Pioneer to the Giant Planets. The space age began in 1957 when the first artificial satellite orbited Earth
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DEDICATION This book is dedicated to all the citizens of the United States of America who have madethis program of interplanetary exploration possible and who, along with all mankind, will benefit from the increased awareness of the universe and how the Earth and its peoples relate to it.
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NASA SP-446PIONEERFIRST TO JUPITER, SATURN, AND BEYOND RICHARD O. FIMMELManager, Pioneer Missions Ames Research Center JAMES VAN ALLEN Professor of Physics University of IowaERIC BURGESSScience Writer Prepared at Ames Research CenterScientific and Technical Information Office 1980NATIONAL AERONAUTICS AND SPACE ADMINISTRATION Washington, D.C. U.S. GOVERNMENT PRINTING OFFICE : 1980Œ0-328-155For sale by the Superintendent of DocumentsU.S. Government Printing Office, Washington, D.C. 20402
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PIONEER Œ First to Jupiter, Saturn, and Beyond 4ContentsForeword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Authors™ Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 1 Œ Pioneer to the Giant Planets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 2 Œ The Pioneer Jupiter / Saturn Mission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26 3 Œ The Pioneer Spacecraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39 4 Œ Pioneer Science at New Frontiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45 5 Œ First into the Outer Solar System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59 6 Œ Results at the New Frontiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .93 7 Œ Images from Jupiter and Saturn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131 8 Œ First Encounter with the Giant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .146 9 Œ Jupiter Revisited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .161 10 Œ Saturn Encounter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18 Epilog Œ Beyond the Outer Giants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .200 Appendix 1 Œ The Imaging Photopolarimeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .205 Appendix 2 Œ Technical Details of Planetary Images . . . . . . . . . . . . . . . . . . . . . . . .207 Appendix 3 Œ Pioneer Team . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .215 Appendix 4 Œ Pioneer Award Recipients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .219 Foreword Some ventures are appropriately named, and Pioneer is surely one of them. The people associated with this program really are pioneers of space exploration. Often it seems that pioneers, being out in front, do not receive the general recognition th athistorically they should deserve. Fortunately, this is not the case with these Pioneer explorations of Jupiter and Saturn. Ma nypeople are beginning to understand the tremendous revolutionary steps we are starting to take into the future as we make important discoveries about the planets of the outer Solar System, as we find out things that we had no glimmering of before these pioneering missions. I anticipate that years from now, when people look back on our time, they will single out the Pioneer program as one of special importance to space science and the broadening of our intellectual horizon.We have now moved out beyond the familiar part of the Solar System to explore planetary objects so unusual that their very existence was something people might accept intellectually but not really in any immediate sense.I like to compare this latter part of the 20thcentury with the 15thand 16thcenturies, the time during which the oceans of Earthwere first explored. The sailing ships first edged their way along the shores of Europe. Then they felt their way around Afri ca.Finally, they struck out across the open oceans and headed for lands so remote, countries so extraordinary, that the reports of the returning explorers were even more incredible than the fictions they replaced. With Pioneer, we felt our way out through the asteroid belt and struck out into the uncharted oceans of the outer Solar System. The excitement of the first flybys of Jupiter and Saturn was a unique experience, enabling us to replace the speculative images of Jupiter and Saturn with actual physical reports. The Pioneers truly initiated a new stage of space exploration, blazing a trail for other spacecraft: the Voyagers, Galileo, other spacecraft yet unnamed, and some even unimagined. Dr. Thomas A. Mutch Associate Administrator for Space ScienceNASA Headquarters
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PIONEER Œ First to Jupiter, Saturn, and Beyond 5Introduction The Pioneer spacecraft have ventured into previously unexplored space far beyond the orbit of Mars, and their missions haveadded greatly to mankind™s knowledge of our Solar System. Throughout history, man has been driven by his innate sense of adventure and curiosity to explore new frontiers, to study what he has found, and to add to his understanding of his place in the cosmos. Author James Michener, in testimony before a Congressional subcommittee, provided an excellent description of this drive and its importance to our civilization:fiI do not for a moment believe that the spiritual well being of our nation depends primarily upon asuccessful space program. I am sure that we could as a nation attain great spiritual reassurance from rebuilding our cities or distributing our farm produce better. But I also believe that there are moments in history when challenges occur of such a compelling nature thatto miss them is to miss the whole meaning of an epoch. Space is such a challenge. We risk great peril if we kill off this spirit of adventure, for we cannot predict how and in what seemingly unrelated fields it will manifest itself. A nation which loses its forward thrust is in danger, and one of the most effective ways to retain that thrust is to keep exploring possibilities. The sense of exploration is intimately bound up with human resolve, and for a nation to believe that it is still committed to forward motion is to ensure its continuance.. . . We should be most careful about retreating from the specific challenge of our age. We should be reluctant to turn our back upon the frontier of this epoch. Space is indifferent to what we do; it has no feeling, no design, no interest in whether we grapple with it or not. But we cannot be indifferent to space, because the grand slow march of our intelligence has brought us, in our generation, to a point from which we can explore and understand and utilize it. To turn back now would be to deny our history, our capabilities.fl The Pioneers have been true explorers Œ the first to navigate the asteroid belts, the first to encounter Jupiter and its fierceradiation belts and Saturn and its rings, and they will be the first manmade objects to leave our Solar System. They have probed new frontiers and explored regions of the Solar System very different from those of the inner system near Earth. Originally, the Pioneer missions were intended to explore only Jupiter and the interplanetary space beyond Mars, but as the mission progressed an opportunity to reach Saturn also developed and the pathway was opened to another unexplored planet. To carry out their missions, the Pioneers have traveled enormous distances and have operated effectively for extended periods. In so doing, the engineering accomplishments of this mission have matched the scientific accomplishments. Pioneers 10and11have been in space over 8 years and 7 years, respectively, and have traveled 4.6 billion kilometers and 4.1 billion kilometers, respectively. All of the spacecraft systems continue to operate reliably after the years in deep space and in spit eof encounters with hostile radiation environments.The mission has continued far beyond achieving its original objectives. The spacecraft continue to send data as they reach toward the boundaries of the Solar System. To undertake a mission of such length called for great and continued dedication on the part of scientists and engineers who had to devote a major portion of their professional careers to the mission. The Pioneers and the people who made them possible have clearly met the challenge of which Michener spoke.C. A. SyvertsonDirectorAmes Research Center
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PIONEER Œ First to Jupiter, Saturn, and Beyond 6Authors™ Preface The success of Pioneer 11 in its encounter with Saturn and the continued mission of Pioneers 10and 11into the outer SolarSystem necessitated an updating of the earlier publications (SP-349, Pioneer Odyssey, Encounter with a Giant, and SP- 349/396, Pioneer Odyssey). Results from further analyses of data from the encounters with Jupiter, interplanetary results, and results from Pioneer 11 ™s encounter with Saturn are included. Because the bibliography associated with this mission has now become extremely large and continues to grow, it is published separately as NASA Technical Memorandum 81233, available from NASA Scientific and Technical Information Facility, P.O. Box 8757, Baltimore / Washington International Airport, Maryland, 21240.In the preparation of this book, the authors gratefully acknowledge having drawn upon the work of many others too numerousto mention individually. Many scientists and project staff personnel were interviewed during research to assemble material for the book. Of particular importance was valuable assistance in the form of initial suggestions and later comments on all or parts of the drafts of the book by Robert R. Nunamaker, John W. Dyer, and John H. Wolfe. The reviews by principal investigators and members of their teams are also appreciated.Personnel from Ames Research Center, the Pioneer Project Staff, the Technical Information Division, and the Phototechnology Branch were particularly helpful in providing information and research material and in producing the book.The authors are also indebted to personnel of the Lunar and Planetary Laboratory and the Optical Sciences Center of theUniversity of Arizona for astronomical information and photographs and for the production of images of Jupiter and Saturn reproduced in this book. Special thanks must be given to Edward Beshore, James J. Burke, Bruce DaCosta, Joseph S. Gotobed, Robert Kingston, Robin Strickland (computer processing), Charles Blenman, Jr., Lyn R. Doose, Charles KenKnight, and John W. Fountain (photographic processing). Additional thanks must be given to William Swindell, University of Arizona, for use of material written for the earlier Pioneer publications and incorporated into this new publication.Richard O. FimmelJames A. Van Allen Eric Burgess August 1980
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PIONEER ΠFirst to Jupiter, Saturn, and Beyond 8As Pioneersped away from Saturn, the view was of a crescent-shaped planet crossed by dark rings and their shadow bands.Ahead was the large satellite Titan, which Pioneerwould pass at a distance of almost 354,000 km on September 2nd. As it did so, the spacecraft obtained the first images of the largest satellite in our Solar System. With Titan shrinking into a sta r-like object behind it, and having explored the two giants, Jupiter and Saturn, for the first time, Pioneerstill had not completedits mission. The spacecraft headed out of our Solar System toward the distant stars, seeking information about interplanetary space to the orbit of Pluto and beyond.During the first decade of space exploration, scientists concentrated on the inner Solar System (Figure 1-1), but at thebeginning of the second decade scientists and space technologists began to consider missions to the outer planets, particularly to the gaseous giants Jupiter and Saturn. These two planets are perhaps the most important in the Solar System because, after the Sun, they contain most of the matter in the Solar System. Jupiter alone accounts for over two-thirds of the planetary mass of the Solar System.Figure 1-1. Planets of the Solar System consist of two types: small, dense inner planets with solid surfaces Mercury, Venus, Ea rth withits Moon, and Mars and large, mainly gaseous outer planets Jupiter, Saturn, Uranus, and Neptune, some of which have satellites aslarge as the smaller inner planets. Pluto, the outermost known planet, has not been observed well enough from Earth to be accu ratelyclassified. Spacecraft have opened new vistas of our Solar System. Note the detail in the best ground based photographs compa redwith the photographs of planets taken from spacecraft.(a)Mercury (Pie du Midi Observatory)(f)Saturn (Catalina Observatory)(j)Moon, Tycho ( Lunar Orbiter)(b)Venus (Lick Observatory)(g)Uranus (Catalina Observatory)(k)Mars ( Viking 1 )(c)Moon, Tycho (Lick Observatory)(h)Mercury ( Mariner 10)(l)Jupiter ( Pioneer 10)(d)Mars (Catalina Observatory)(i)Venus ( Mariner 10)(m)Saturn ( Pioneer 11 )(e)Jupiter (Catalina Observatory) (a)(d)(e)(b)(c)
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PIONEER Œ First to Jupiter, Saturn, and Beyond 10Both giant planets (Figure 1-2) are unusual by terrestrial standards Œ thedensity of Jupiter is only slightly greater than water while that of Saturn is sufficiently low that the planet would float in water. Jupiter™s mass is 317.8 times that of Earth. Its gravity affects the orbits of other planets and may have prevented the asteroids from coalescing into a planet. Jupiter™s gravitational force pulls many comets into distorted orbits; some short period comets appear to have become controlled by Jupiter so that their orbits at their most distant points from the Sun are about the distance of the Jovian orbit. Saturn also has collected a family of comets.Despite their size, Jupiter and Saturn were not large enough to become stars. Their masses were insufficient to raise internal temperatures high enough to trigger nuclear reactions in their cores. However, had they been some 100 times larger, the Solar System might have been a triple star system, and nighttime would have been infrequent on Earth. As it is, both giant planets emit more energy than they absorb from the Sun, energy that is probably generated as these planets continue to cool following their primordial gravitational collapse eons ago, soon after the Solar System formed.In 1608, spectacle maker Hans Lippershey, of Middleburgh, Holland, invented an astounding instrument. He happened to pick up two lenses and looked through them, discovering that objects viewed through the lenses appeared nearer. He experimented further with a convex and a concave lens at opposite ends of a tube. His spyglass engendered considerable excitement and word of his invention spread across Europe.Two men, Galileo and Simon Marius, using the idea of Lippershey™s spyglass, constructed a device which came to be known as a telescope in about 1611 and trained it on the heavens.Figure 1-2. Jupiter and Saturn are dominant planets of our Solar System. The terrestrial planets Mercury, Venus, Earth, and Mars are relatively small compared with the planets of the outer Solar System, Jupiter, Saturn, Uranus, and Neptune. (l)(m)Figure 1-1 concluded
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PIONEER Œ First to Jupiter, Saturn, and Beyond 11Figure 1-4. Each year as Earth moves in its orbit away from Jupiter, the times of eclipse of Jupiter™s satellites become late because light takes about 16 minutes longer to cross Earth™s orbit. In 1675, the Danish astronomer Roemer determined the velocity of light from this effect. The discovery of the satellites of Jupiter (Figure 1-3) is usually credited to Galileo,who published The Starry Messengerrelating the results of observations he madeat Padua on January 7, 1610. Galileo made a staggering number of observations at that time Œ figreat, unusual, and remarkable spectacles, a host of stars.fl The StarryMessengerdescribed what Galileo considered the most important discovery of all,the moons of Jupiter. Some historians, however, claim that Simon Marius of Auerbach, Germany, first discovered the Jovian satellites on December 29, 1609, but he did not publish his observations.Both men, looking at Jupiter, were astounded to discover that the bright planet possessed a system of satellites Œ an undreamed of condition in the Aristotelian philosophy of an Earth-centered universe then holding sway over most human thought. In fact, some scientists of that day claimed the luminous objects were defects of the new instrument, not real objects. These satellites were later given the names Io, Europa, Ganymede, and Callisto by Marius, but are often referred to as the Galilean satellites. Today the satellites are frequently identified by the Roman numerals I, II, III, and IV, respectively. In 1675, Ole Roemer, observing Jupiter™s satellites, made one of the most important discoveries in physics. He noted that the eclipses of Jovian satellites occur progressively later as the Earth moves away from Jupiter and progressively earlier as it moves toward Jupiter. He explained that this effect is evidence for the finite velocity of light. Light traveling across Earth™s orbit, when Earth is farthest from Jupiter, takes 16 minutes and 40 seconds to cover the additional distance. From this, he estimated the velocity of light to be about 300,000 km/sec (186,000 mps) (Figure 1-4).Figure 1-3. Jupiter and its four Galilean satellites. The photograph at top shows a typical configuration; right to left, the satellites Europa, Ganymede, and Callisto. Io is obscured by the planet. (Photographs: Catalina Observatory, University of Arizona)
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