Passage to a Ringed World - NASA's History Office

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• Opening or shutting thermal louvers (which resemble Venetian blinds) to cool or heat electronics in one of the bays of the upper equipment module. • Using small radioisotope heater units to raise the temperatures of selected portions of the spacecraft that would otherwise cool to unacceptably low temperatures. • Installing on the spacecraft thermal blankets (gold or black in color) to prevent heat from escaping to space. • Installing thermal shields above the RTGs to keep them from radiating excessive heat to sensitive science instruments. • Taking advantage of the orientation of the spacecraft to keep most of the spacecraft in the shadow of the high-gain antenna or the Huygens Probe. From launch until Cassini–Huygens is well beyond the distance of Earth, the spacecraft is oriented to point the high-gain antenna at the Sun, thereby shading most of the rest of the spacecraft. Deviations from this orientation are permitted for a maximum of half an hour for each occurrence until the spacecraft reaches a distance of 2.7 AU (405 million kilometers) from the Sun. After that time, the heat input from the Sun will have diminished sufficiently to permit almost any spacecraft orientation. Although they are not a part of the TCS responsibility, several instruments have radiator plates to cool their detectors. Even at the distance of Saturn from the Sun, spacecraft orientations that point those radiator plates in the same half of the sky as the Sun can severely degrade the data collected by some of the science instruments. In at least one case, it is even necessary to simultaneously avoid having Saturn illuminate the radiator plate(s). New Technology. Whereas previous interplanetary spacecraft used onboard tape recorders, Cassini will pioneer a new solid-state data recorder with no moving parts. The recorder will be used in more than 20 other NASA and non-NASA missions. Similarly, the main onboard computer, which directs Orbiter operations, uses a novel design incorporating new families of electronic chips. Among them are very high speed integrated circuit (VHSIC) chips. The computer also contains powerful new application-specific integrated circuit (ASIC) parts, each replacing a hundred or more traditional chips. Also on the Orbiter, the power system will benefit from an innovative solidstate power switch that will eliminate the rapid fluctuations or “transients” that can occur with conventional power switches. This will significantly extend component lifetime. Past interplanetary spacecraft have used massive mechanical gyroscopes to provide inertial reference during periods when Sun and star references were unavailable. Cassini employs hemispherical resonator gyroscopes that have no moving parts. These devices utilize tiny “wine glasses” about the size of a dime that outperform their more massive counterparts both in accuracy and in expected lifetime. Huygens Probe Design The Huygens Probe, supplied by the European Space Agency (ESA), will scrutinize the clouds, atmosphere and surface of Saturn’s moon Titan. It is designed to enter and brake in Final European Space Agency inspection of the Huygens Probe prior to shipment to the United States for integration with the Cassini Orbiter. VEHICLE OF DISCOVERY 95
The Huygens Probe carries six science investigations to study the clouds, atmosphere and surface of Titan. Three separate parachutes are carried in the Probe’s parachute compartment. The heat shield, front shield and back cover are jettisoned before data collection begins. 96 PASSAGE TO A RINGED WORLD 3 Titan’s atmosphere and parachute a fully instrumented robotic laboratory down to the surface. The Huygens Probe system consists of the Probe it- 4 2 5 1 2 3 4 5 Heat Shield Front Shield Back Cover Parachute Compartment Descent Module with Scientific Instruments self, which will descend to Titan, and the Probe support equipment, which will remain attached to the orbiting spacecraft. 1 The Probe will remain dormant throughout the 6.7-year interplanetary cruise, except for health checks every six months. These checkouts will follow preprogrammed descent scenario sequences as closely as possible, and the results will be relayed to Earth for examination by system and payload experts. Prior to the Probe’s separation from the Orbiter, a final health check will be performed. The “coast” timer will be loaded with the precise time necessary to turn on the Probe systems (15 minutes before the encounter with Titan’s atmosphere), after which the Probe will separate from the Orbiter and coast to Titan for 22 days with no systems active except for its wakeup timer. The Probe system is made up of a number of engineering subsystems, some distributed between the Probe and the Probe support equipment on the Orbiter. The Huygens payload consists of a complement of six science instrument packages. Probe Support Equipment. The Probe support equipment includes the electronics necessary to track the Probe, recover the data gathered during its descent and process and deliver the data to the Orbiter, from which the data will be transmitted or “downlinked” to the ground. The Probe engineering subsystems are the entry subsystem, the inner structure subsystem, the thermal control subsystem, the electrical power subsystem, the command and data
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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
Page 54 and 55: Prometheus and Pandora, two tiny sa
Page 56 and 57: In the stellar occultation experime
Page 58 and 59: scattering than are larger particle
Page 60 and 61: In fact, Saturn’s rings — as we
Page 62 and 63: The satellites of Saturn comprise a
Page 64 and 65: Before the advent of spacecraft exp
Page 66 and 67: The bright surface of Saturn’s mo
Page 68 and 69: Galilean satellites. Most of what i
Page 70 and 71: duced that one hemisphere is compos
Page 72 and 73: patches on the surface. Although it
Page 74 and 75: Artist’s conception of Ithaca Cha
Page 76 and 77: An artist’s rendition of Saturn
Page 78 and 79: The MAPS Instruments Coordinated ob
Page 80 and 81: field reverses direction across the
Page 82 and 83: SATURN’S MAGNETIC FIELD Saturn’
Page 84 and 85: Solar Wind Magnetosheath Titan neut
Page 86 and 87: per atmosphere. Energetic particles
Page 88 and 89: 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
Page 96 and 97: crease inclination to this value. T
Page 98 and 99: This illustration shows the main de
Page 100 and 101: discussed earlier) and data handlin
Page 102 and 103: of the spacecraft! Below the oxidiz
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Page 108 and 109: falls below its storage temperature
Page 110 and 111: The Cassini-Huygens spacecraft stan
Page 112 and 113: The Imaging Science Subsystem (ISS)
Page 114 and 115: • Map the composition and thermal
Page 116 and 117: cise distance between the surface f
Page 118 and 119: • Study the interaction of the ma
Page 120 and 121: • Study the erosional and electro
Page 122 and 123: midway out on the magnetometer boom
Page 124 and 125: The RPWS instrument will be used to
Page 126 and 127: altitudes down to 40 kilometers abo
Page 128 and 129: dex. A group of platinum resistance
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 140 and 141: AFTERWORD It has been said that in
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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APPENDIX C 146 PASSAGE TO A RINGED
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APPENDIX D 148 PASSAGE TO A RINGED
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APPENDIX D 150 PASSAGE TO A RINGED
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APPENDIX F 152 PASSAGE TO A RINGED
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APPENDIX F 154 PASSAGE TO A RINGED
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APPENDIX F Peralta, F. and S. Flana
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National Aeronautics and Space Admi
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