Passage to a Ringed World - NASA's History Office

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PROBING A MOON OF MYSTERY Huygens’ encounter with Titan is planned for November 2004, about three weeks before the Orbiter makes its first flyby of Saturn’s largest satellite. The Probe, which consists of a descent module enveloped by a conical thermal-protection shell almost three meters in diameter, carries six science instruments designed to make in situ mea- Saturn Orbit Insertion July 1, 2004 ameter and is a very bluntly shaped conical capsule with a high drag coefficient. The shield is covered with a special thermal-ablation material to protect the Probe from the enormous flux of heat generated during atmospheric entry. On the aft side is a protective cover that is primarily designed to reflect away the heat radiated from the hot wake of the Probe as it decelerates in Titan’s upper atmosphere. Atmospheric entry is a tricky affair — entry at too shallow an angle can cause the Probe to skip out of the atmosphere and be lost. If the entry is too steep, that will cause the Probe measurements to begin at a lower altitude than is desired. After the Probe has separated from the Orbiter, the electrical power for its whole mission is provided by five lithium–sulfur dioxide batteries. The Probe carries two S-band transmitters and two antennas, both of which will transmit to the Orbiter during the surements of Titan’s atmospheric and surface properties. Probe’s descent. One stream of telemetry is delayed by about six seconds with respect to the other to avoid data loss if there are brief transmission outages. Once the Probe has decelerated to about Mach 1.5, the aft cover is pulled off by a pilot parachute. An 8.3-meter-diameter main parachute is then deployed to ensure a slow and stable descent. The main parachute slows the Probe and allows the decelerator and heat shield to fall away. To limit the duration of the descent to a maximum of two and a half hours, the main parachute is jettisoned at entry +900 seconds and replaced by a smaller, three-meter-diameter drogue chute for the remainder of the descent. The batteries and other resources are sized for a maximum mission duration of 153 minutes. This Titan Probe Entry and Orbiter Flyby November 27, 2004 Probe Release November 6, 2004 corresponds to a maximum descent time of two and a half hours, with at least three minutes — but possibly up to half an hour or more — on the surface, if the descent takes less time than expected. The instrument operations are commanded by a timer in the top part of the descent and on the basis of measured altitude in the bottom part of the descent. The altitude is measured by a small radar altimeter during the last 10–20 kilometers. Throughout the descent, the Huygens Atmospheric Structure Instrument (HASI) will measure more than half a dozen physical properties of the atmosphere. The HASI will also process signals from the Probe’s radar altimeter to gain information about surface properties. The Gas Chromatograph and Mass Spectrometer (GCMS) will determine the chemical composition A MISSION OF DISCOVERY 9
10 PASSAGE TO A RINGED WORLD of the atmosphere as a function of altitude. The Aerosol Collector and Pyrolyser (ACP) will capture aerosol particles, heat them and send the effused gas to the GCMS for analysis. The optical radiation propagation in the atmosphere will be measured in all directions by the Descent Imager and Spectral Radiometer (DISR). The DISR will also image the cloud formations and the surface. As the surface looms closer, the DISR will switch on a bright lamp and measure the spectral reflectance of the surface. Altitude, kilometers 1000 500 300 192 170 0 Instruments’ Inlet Port Opens Decelerator Jettisons Throughout its descent, the Doppler shift of Huygens’ telemetric signal will be measured by the Doppler Wind Experiment (DWE) equipment on the Orbiter to determine the atmospheric winds, gusts and turbulence. In the proximity of the surface, the Surface Science Package (SSP) will activate a number of its devices to make measurements near and on the surface. If touchdown occurs in a liquid, such as in a lake or a sea, the SSP will measure the liquid’s physical properties. The Orbital Tour. After the end of the Probe mission, the Orbiter will start its nearly four-year tour, consisting of more than 70 Saturn-centered orbits, connected by Titan-gravityassist flybys or propulsive maneuvers. The size of these orbits, their orientation to the Sun–Saturn line and their inclination to Saturn’s equator are dictated by the various scientific requirements, which include Titan ground-track coverage; flybys of icy satellites, Saturn, Titan, or ring occultations; orbit inclinations; and ringplane crossings. DESCENT INTO THE MURKY DEPTHS Main Chute Deploys Drogue Chute Deploys 0 2.5 Time, Hours After Entry As Huygens’ descent into Titan slows, it releases a small parachute, which then deploys the main parachute. The decelerator shield jettisons and the Probe drifts to about 40 kilometers above the surface. Then, a smaller, drogue chute carries Huygens the rest of the way to the 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 14 and 15: address the challenges of the missi
Page 16 and 17: Participant Nations* * First flag i
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
Page 64 and 65: Before the advent of spacecraft exp
Page 66 and 67: 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
Page 168:
National Aeronautics and Space Admi
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