Passage to a Ringed World - NASA's History Office

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management subsystem and the Probe data relay subsystem. Entry Subsystem. The entry subsystem functions only during the release of the Probe from the Orbiter and its subsequent entry into the Titan atmosphere. It consists of three main elements: the spin–eject device that propels the Probe away from the Orbiter; a front shield covered with special thermal protection material that protects the Probe from the heat generated during atmospheric entry; and an aft cover, also covered with thermal protection material, to reflect away heat from the wake of the Probe during entry. The Probe will be targeted for a highlatitude landing site on the “day” side of Titan and released from the Orbiter on November 6, 2004. The spin–eject device will impart a relative velocity of about 0.3 meter per second and a spin rate (for stabilization) of about seven revolutions per minute. The Probe’s encounter with Titan is planned for November 27, when it will enter the atmosphere at a velocity of 6.1 kilometers per second. The entry phase will last about three minutes, during which the Probe’s velocity will decrease to about 400 meters per second. Three parachutes will be used during the Probe’s descent. When the onboard accelerometers detect a speed of Mach 1.5 near the end of the deceleration phase, the two-meter-diameter pilot chute will deploy, pulling off the aft cover. This will be followed immediately by deployment of the 8.3-meter-diameter main parachute. About 30 seconds after deployment of the main chute, the Probe’s velocity will have dropped from Mach 1.5 to Mach 0.6, and the front heat shield will be released. At this point, scientific measurements can begin. About 15 minutes later, the main chute will be released and a smaller, three-meter drogue chute will permit the Probe to reach Titan’s surface, about two and a half hours after data taking starts. The Probe will hit the surface at a velocity of about seven meters per second and is expected to survive the impact. The Probe will continue to transmit data for an additional 30–60 minutes. Inner Structure Subsystem. The inner structure of the Probe consists of two aluminum honeycomb platforms and an aluminum shell. It is linked to the front heat shield and the aft cover by fiberglass struts and pyrotechnically operated release mechanisms. The central equipment platform carries, on both its upper and lower surfaces, the boxes containing the electrical subsystems and the science experiments. The upper platform carries the parachutes (when stowed) and the antennas for communication with the Orbiter. Thermal Control Subsystem. At different times during the mission, the Probe will be subjected to extreme thermal environments requiring a variety of passive controls to maintain the required temperature conditions. For instance, during the two Venus flybys, the solar heat input will be high. The Probe will get some protection from the shadow of the high-gain antenna, and when the antenna is off Sun-point for maneuvers or communication, the Probe will be protected by multilayer insulation that will burn off during the later atmospheric entry. The Probe will be at its coldest just after it separates from the Orbiter. To ensure that none of the equipment AQ60 tiles, similar to those used on the Space Shuttle, will help to dissipate heat during the Huygens Probe’s descent through Titan’s atmosphere. VEHICLE OF DISCOVERY 97
98 PASSAGE TO A RINGED WORLD SPACECRAFT SUBSYSTEMS MASS AND POWER Mass, Power, Subsystem or Component kilograms watts Comments on Power Usage Engineering Subsystems Structure Subsystem 272.6 0.0 Radio Frequency Subsystem 45.7 80.1 During downlinking of data Power and Pyrotechnics Subsystem 216.0 39.1 Shortly after launch Command and Data Subsystem 29.1 52.6 With both strings operating Attitude and Articulation Control Subsystem 150.5 115.3 During spindown of spacecraft (Engine Gimbal Actuator) 31.0 During main engine burns Cabling Subsystem 135.1 15.1 Maximum calculated power loss Propulsion Module Subsystem (dry)* 495.9 97.7 During main engine burns Temperature Control Subsystem 76.6 117.8 During bipropellant warmup 6.0 Temperature fluctuation allowance 2.0 Radiation and aging allowance 20.0 Operating margin allowance Mechanical Devices Subsystem 87.7 0.0 Packaging Subsystem 73.2 0.0 Solid-State Recorders 31.5 16.4 Both recorders reading and writing Antenna Subsystem 113.9 0.0 Orbiter Radioisotope Heater Subsystem 3.8 0.0 Science Instrument Purge Subsystem 3.1 0.0 System Assembly Hardware Subsystem 21.7 0.0 Total Engineering Mass* Science Instruments 1756.6 Radio Frequency Instrument Subsystem 14.4 82.3 Both S-band and K -band operating a Dual Technique Magnetometer 8.8 12.4 Both scalar and vector operations Science Calibration Subsystem 2.2 44.0 In magnetometer calibration mode Imaging Science (narrow-angle camera) 30.6 28.6 Active and operating Imaging Science (wide-angle camera) 25.9 30.7 Active and operating Visible and Infrared Mapping Spectrometer 37.1 24.6 In imaging mode Radio and Plasma Wave Science 37.7 17.5 During wideband operations Ion and Neutral Mass Spectrometer 10.3 26.6 Neutral Mass Spectrometer operating Magnetospheric Imaging Instrument 29.0 23.4 High-power operations Cosmic Dust Analyzer 16.8 19.3 Operating with articulation Cassini Radar 43.3 108.4 Operating in imaging mode Cassini Plasma Spectrometer 23.8 19.2 Operating with articulation Ultraviolet Imaging Spectrograph 15.5 14.6 On in sleep state Composite Infrared Spectrometer 43.0 43.3 Active and operating Total Science Mass 338.2 Huygens Probe (including Probe support) 350.0 249.8 During Probe checkouts Launch Vehicle Adaptor Mass 136.0 0.0 TOTALS* 2580.7 680.5 Power available at middle of tour * Note that the masses given above do not include approximately 3141 kilograms of propellant and pressurant.
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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
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
Page 104 and 105: • Opening or shutting thermal lou
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
Page 134 and 135: two low-gain antennas 1 and will pr
Page 136 and 137: During much of Cassini’s orbital
Page 138 and 139: articulation control subsystem’s
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
Page 150 and 151: APPENDIX A 142 PASSAGE TO A RINGED
Page 152 and 153: APPENDIX B H O 2 + Water molecule w
Page 154 and 155: 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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