Passage to a Ringed World - NASA's History Office

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address the challenges of the mission. More people will share in the discoveries, the costs and the benefits. About three quarters of a million people from more than 80 countries have involved themselves in the Cassini– Huygens mission by requesting that their signatures be placed aboard the spacecraft for the trip to the Saturn system. What will the mission bring to these people? The answers are varied: satisfaction of curiosity, a sense of participation, aesthetic inspiration, perhaps even understanding of our place in this vast universe. The Spacecraft At the time of launch, the mass of the fully fueled Cassini spacecraft will be about 5630 kilograms. Cassini consists of several sections. Starting at the bottom of the “stack” and moving upward, these are the lower equipment module, the propellant tanks together with the engines, the upper equipment module, the 12-bay electronics compartment and the highgain antenna. These are all stacked vertically on top of each other. Attached to the side of the stack is an approximately three-meter-diameter, disk-shaped spacecraft — the Huygens Titan Probe. Cassini–Huygens accommodates some 27 scientific investigations, supported by 18 specially designed instruments: 12 on the Orbiter and six on the Probe. Most of the Orbiter’s scientific instruments are installed on one of two body-fixed platforms — the remotesensing pallet or the fields and particles pallet — named after the type of instruments they support. The big, 11-meter-long boom supports sensors for the magnetometer experiment. Three thin 10-meter-long electrical antennas point in orthogonal directions; these are sensors for the Radio and Plasma Wave Science experiment. At the top of the stack is the large, four-meter-diameter high-gain antenna. Centered and at the very top of this antenna is a relatively small low-gain antenna. A second low-gain antenna is located near the bottom of the spacecraft. Two-way communication with Cassini will be through NASA’s Deep Space Network (DSN) via an X-band radio link, which uses either the four-meterdiameter high-gain antenna or one of the two low-gain antennas. The highgain antenna is also used for radio and radar experiments and for receiving signals from Huygens. The electrical power for the spacecraft is supplied by three radioisotope thermoelectric generators. Cassini is a three-axis-stabilized spacecraft. The attitude of the spacecraft is changed by using either reaction wheels or the set of 0.5-newton thrusters. Attitude changes will be done frequently because the instruments are body-fixed and the whole spacecraft must be turned in order to point them. Consequently, most of the observations will be made without a real-time communications link to Earth. The data will be stored on two solid-state recorders, each with a capacity of about two gigabits. Scientific data will be obtained primarily by using one or the other of two modes of operation. These modes have been named after the functions they will carry out and are called the “remote-sensing mode” and the “fields and particles and downlink mode.” During remote-sensing operations, the recorders are filled with images and spectroscopic and other data that are obtained as the spacecraft points to various targets. During the fields and particles and downlink mode, the high-gain antenna is pointed at Earth and the stored data are transmitted to the DSN. Also, while in this mode, the spacecraft is slowly rolled about the axis of the high-gain antenna. This allows sensors on the fields and particles pallet to scan the sky and determine directional components for the various quantities they measure. Mission Overview The Cassini–Huygens mission is designed to explore the Saturn system and all its elements — the planet Saturn and its atmosphere, its rings, its magnetosphere, Titan and many of the icy satellites. The mission will pay special attention to Saturn’s largest moon, Titan, the target for Huygens. The Cassini Orbiter will make repeated close flybys of Titan, both for gathering data about Titan and for gravity-assisted orbit changes. These maneuvers will permit the achievement of a wide range of desirable characteristics on the individual orbits that make up the tour. In turn, this ability to change orbits will enable close flybys of icy satellites, re- A MISSION OF DISCOVERY 5
Cassini Saturn Orbiter Fields and Particles Instruments Cassini Saturn Orbiter Remote-Sensing Instruments Huygens Titan Probe Instruments 6 PASSAGE TO A RINGED WORLD CASSINI–HUYGENS SCIENCE INVESTIGATIONS Instrument Investigations Cassini Plasma Spectrometer In situ study of plasma within and near Saturn’s magnetic field Cosmic Dust Analyzer In situ study of ice and dust grains in the Saturn system Dual Technique Magnetometer Study of Saturn’s magnetic field and interactions with the solar wind Ion and Neutral Mass Spectrometer In situ study of compositions of neutral and charged particles within the magnetosphere Magnetospheric Imaging Instrument Global magnetospheric imaging and in situ measurements of Saturn’s magnetosphere and solar wind interactions Radio and Plasma Wave Science Measurement of electric and magnetic fields, and electron density and temperature in the interplanetary medium and within Saturn’s magnetosphere Cassini Radar Radar imaging, altimetry, and passive radiometry of Titan’s surface Composite Infrared Spectrometer Infrared studies of temperature and composition of surfaces, atmospheres and rings within the Saturn system Imaging Science Subsystem Multispectral imaging of Saturn, Titan, rings and icy satellites to observe their properties Radio Science Instrument Study of atmospheric and ring structure, gravity fields and gravitational waves Ultraviolet Imaging Spectrograph Ultraviolet spectra and low-resolution imaging of atmospheres and rings for structure, chemistry and composition Visible and Infrared Mapping Spectrometer Visible and infrared spectral mapping to study composition and structure of surfaces, atmospheres and rings Aerosol Collector and Pyrolyser In situ study of clouds and aerosols in Titan’s atmosphere Descent Imager and Spectral Radiometer Measurement of temperatures of Titan’s atmospheric aerosols and surface imagery Doppler Wind Experiment Study of winds by their effect on the Probe during descent Gas Chromatograph and Mass Spectrometer In situ measurement of chemical composition of gases and aerosols in Titan’s atmosphere Huygens Atmospheric Structure Instrument In situ study of Titan’s atmospheric physical and electrical properties Surface Science Package Measurement of the physical properties of Titan’s surface
Page 1: Passage to a Ringed World The Cassi
Page 4 and 5: On the Cover: A collage of images s
Page 6 and 7: FOREWORD This book is for you. You
Page 8 and 9: ACKNOWLEDGMENTS This book would not
Page 10 and 11: Three separate images, taken by Voy
Page 12 and 13: descent to the surface. The Huygens
Page 16 and 17: Participant Nations* * First flag i
Page 18 and 19: PROBING A MOON OF MYSTERY Huygens
Page 20 and 21: TOUR T18-3 TARGETED SATELLITE FLYBY
Page 22 and 23: SATURN CASSINI-HUYGENS MISSION SCIE
Page 24 and 25: Cassini-Huygens designed to determi
Page 26 and 27: In this diagram from his book, Syst
Page 28 and 29: This Voyager 1 image shows Saturn
Page 30 and 31: An Extended Atmosphere From Liquid
Page 32 and 33: Haze layers are also observed above
Page 34 and 35: IN THE EYE OF THE BEHOLDER Taken fr
Page 36 and 37: This spectacular view of the edge o
Page 38 and 39: the interaction was described as a
Page 40 and 41: have a signature of a tone decreasi
Page 42 and 43: CONSTITUENTS OF THE TITAN ATMOSPHER
Page 44 and 45: The processes of plate tectonics an
Page 46 and 47: tan was accreting, it is possible t
Page 48 and 49: Surface Science. The highest resolu
Page 50 and 51: This enhanced Voyager 2 image shows
Page 52 and 53: 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
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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
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CHAPTER 7 Space mission design aims
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(SOI) propulsive maneuver to initia
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the tour cannot continue. Of course
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crease inclination to this value. T
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This illustration shows the main de
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discussed earlier) and data handlin
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of the spacecraft! Below the oxidiz
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• Opening or shutting thermal lou
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management subsystem and the Probe
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falls below its storage temperature
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The Cassini-Huygens spacecraft stan
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The Imaging Science Subsystem (ISS)
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• Map the composition and thermal
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cise distance between the surface f
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• Study the interaction of the ma
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• Study the erosional and electro
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midway out on the magnetometer boom
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The RPWS instrument will be used to
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altitudes down to 40 kilometers abo
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dex. A group of platinum resistance
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CHAPTER 10 Mission operations are t
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PLANETARY MISSION OPERATIONS Functi
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two low-gain antennas 1 and will pr
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During much of Cassini’s orbital
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articulation control subsystem’s
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AFTERWORD It has been said that in
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Developments tied to the Cassini-Hu
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APPENDIX A Command. A data transact
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APPENDIX A 138 PASSAGE TO A RINGED
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APPENDIX A Plasma wave. A wave char
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APPENDIX A 142 PASSAGE TO A RINGED
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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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