Passage to a Ringed World - NASA's History Office

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AFTERWORD It has been said that in making scientific and technological advances, each generation of scientists and engineers stands on the shoulders of the previous generation. This is true of all types of exploration, and it is true with the Cassini–Huygens mission. On the Shoulders of Giants The story begins in late 1609, when Galileo Galilei built a telescope and had the inspiration to aim it at the sky. Galileo’s discoveries about the Moon, Venus, Jupiter and the Milky Way were a quantum leap forward in our understanding of the universe, but he was puzzled by Saturn. With his telescope’s poor optics, Galileo could only see that Saturn looked like a “triple” planet. To add to the mystery, the planet lost its “companions” a few years later! Fast forward more than 40 years: Christiaan Huygens turned his telescope toward Saturn and discovered a real companion to the planet — like the four discovered around Jupiter by Galileo — a satellite now called Titan. Huygens also recognized for the first time the great ring surrounding Saturn. He realized that the plane of the ring is tilted with respect to the plane of the planet’s orbit, so that about every 14 years, Earth crosses through the plane and the ring can disappear temporarily — explaining Galileo’s puzzling observation. Shortly thereafter, Jean-Dominique Cassini discovered four additional satellites and spied a “gap” in the ring, making it two rings separated by what is now called the Cassini division. Over the next century, more satellites were discovered. And two centuries later, James Clerk Maxwell, well-known for his explanation of electromagnetism, showed that the rings were not solid disks but were instead composed of myriad particles, each in its own orbit. Astrophysical techniques, in development since the 1860s, enabled in 1932 the discovery of methane and ammonia in Saturn’s atmosphere — and thus a great advancement in understanding the nature of Saturn and the other “gas giants” — Jupiter, Uranus and Neptune. This was followed by Gerard Kuiper’s surprising discovery in 1943–44 of a dense atmosphere, unknown among other planetary satellites, on Titan. The birth of space exploration in 1957, and the National Aeronautics and Space Administration in 1958, led to dreams of human and robotic exploration of the planets. The wanderlust of the Renaissance was reborn as both scientists A F T E R W O R D 131
132 PASSAGE TO A RINGED WORLD and the public became interested in visiting distant worlds. Ground-based planetary astronomy experienced a rebirth, as new techniques and the need for more information about the planets to be explored pushed the science along. The evolution of planetary exploration began with the first steps to the Moon, was followed by the exploration of Venus and Mars and continued in plans for exploring the outer planets (that is, Jupiter and beyond). Fanciful “Grand Tour” missions to the outer planets were proposed. Pioneers 10 and 11 explored Jupiter and its environment in 1973 and 1974, respectively. The success of Pioneer 10 permitted the retargetting, after Jupiter, of Pioneer 11 to arrive at Saturn in 1979, just as Voyager 1 was arriving at Jupiter. The Voyagers, 1 and 2, carried out a thorough reconnaissance of Jupiter and then Saturn. Following the success at Saturn, Voyager 2 was able to complete the Grand Tour, missing only tiny Pluto in its travels. The contributions of these missions, complemented by the continuing developments of science and technology, have brought us to the Cassini–Huygens mission. We can only guess, and not well, at what the Cassini–Huygens spacecraft will find. Surely, many questions raised by previous observations will be answered. But the answers, as always in science, will only generate more questions. And, it is safe to predict there will be some unimaginable surprises. Technology — the Bridge from the Ethereal to the Material As technology has improved through history, our understanding of natural phenomena has also improved. And, this technology has affected our daily lives. Improved telescopes provided more knowledge about Saturn and Titan, generating more questions — which drove the development of technology in optics. This has not only helped us do remote-sensing science better, it has allowed eyeglass wearers to see better, via improved lens materials and coatings. The development of auxiliary instruments changed astronomy from a descriptive science into a “measuring” science, uncovering new mysteries for us to puzzle over, like Titan’s atmosphere. Improvements in detectors, from eyeballs through photography to electronic imagers, have made possible the permanent, unbiased recording of images. Digitized images can be transmitted, without loss of detail, across the solar system — and soon, directly into your home, with the image quality on your television matching that in a movie theater. Advancements in detectors and image-analysis software have been applied in diverse areas: helping patients with limited night vision “see” in the dark; enabling doctors to analyze magnetic resonance, positron emission and X-ray images; and protecting airport personnel from exposure to radiation from security devices.
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Passage to a Ringed World The Cassi
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On the Cover: A collage of images s
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FOREWORD This book is for you. You
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ACKNOWLEDGMENTS This book would not
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Three separate images, taken by Voy
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descent to the surface. The Huygens
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address the challenges of the missi
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Participant Nations* * First flag i
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PROBING A MOON OF MYSTERY Huygens
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TOUR T18-3 TARGETED SATELLITE FLYBY
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SATURN CASSINI-HUYGENS MISSION SCIE
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Cassini-Huygens designed to determi
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In this diagram from his book, Syst
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This Voyager 1 image shows Saturn
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An Extended Atmosphere From Liquid
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Haze layers are also observed above
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IN THE EYE OF THE BEHOLDER Taken fr
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This spectacular view of the edge o
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the interaction was described as a
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have a signature of a tone decreasi
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CONSTITUENTS OF THE TITAN ATMOSPHER
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The processes of plate tectonics an
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tan was accreting, it is possible t
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Surface Science. The highest resolu
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This enhanced Voyager 2 image shows
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Voyager 1 captured this striking im
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Prometheus and Pandora, two tiny sa
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In the stellar occultation experime
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scattering than are larger particle
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In fact, Saturn’s rings — as we
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The satellites of Saturn comprise a
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Before the advent of spacecraft exp
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The bright surface of Saturn’s mo
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Galilean satellites. Most of what i
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duced that one hemisphere is compos
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patches on the surface. Although it
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Artist’s conception of Ithaca Cha
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An artist’s rendition of Saturn
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The MAPS Instruments Coordinated ob
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field reverses direction across the
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SATURN’S MAGNETIC FIELD Saturn’
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Solar Wind Magnetosheath Titan neut
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per atmosphere. Energetic particles
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and plasma wave emissions from narr
Page 90 and 91: CHAPTER 7 Space mission design aims
Page 92 and 93: (SOI) propulsive maneuver to initia
Page 94 and 95: the tour cannot continue. Of course
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Page 118 and 119: • Study the interaction of the ma
Page 120 and 121: • Study the erosional and electro
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Page 130 and 131: CHAPTER 10 Mission operations are t
Page 132 and 133: PLANETARY MISSION OPERATIONS Functi
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Page 136 and 137: During much of Cassini’s orbital
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Page 142 and 143: Developments tied to the Cassini-Hu
Page 144 and 145: APPENDIX A Command. A data transact
Page 146 and 147: APPENDIX A 138 PASSAGE TO A RINGED
Page 148 and 149: APPENDIX A Plasma wave. A wave char
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Page 152 and 153: APPENDIX B H O 2 + Water molecule w
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Page 156 and 157: APPENDIX D 148 PASSAGE TO A RINGED
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Page 160 and 161: APPENDIX F 152 PASSAGE TO A RINGED
Page 162 and 163: APPENDIX F 154 PASSAGE TO A RINGED
Page 164 and 165: APPENDIX F Peralta, F. and S. Flana
Page 168: National Aeronautics and Space Admi
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