Passage to a Ringed World - NASA's History Office

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Surface Science. The highest resolution, clearest images of Titan’s surface will come from the Descent Imager and Spectral Radiometer on the Huygens Probe. This camera will take over 500 images under the haze layer — where the atmosphere may be very clear — during the Probe’s journey to the surface. If the Probe survives a landing on liquid, aerosol drifts or ice, chemical samples may be analyzed using the gas chemical analyzer. The camera will image the surface, while information on the atmosphere will be relayed by the Huygens Atmospheric Structure Instrument and Doppler Wind Experiment instrument. The Probe’s surface science instrumentation will measure deceleration upon impact, test for liquid surface (if waves are present, the instrument can detect the bobbing motion) or fluffy surface and conduct investigations of liquid density, optical refractivity and thermal and electrical properties. The Cassini Orbiter instruments have the capability to penetrate the hazy atmosphere for data gathering. The Orbiter’s radar can map the surface through the clouds with high-resolution swaths in a manner similar to the Magellan mission’s mapping of Venus’ cloud-enshrouded surface. The radar will provide data on the extent of liquid versus dry land and map surface features at high resolution (hundreds of meters) in narrow swaths. The Orbiter’s camera and visible and infrared radiometer can provide global coverage by imaging through long-wavelength “windows,” where atmospheric aerosols do not block sunlight. The combined set of data from these instruments will allow scientists to determine the dominant geological processes — cratering, volcanism and erosion. Titan’s spin vector and reference features for making maps will be established, and data from the radar altimeter will provide estimates of the relative eleva- tions. If large bodies of liquid exist, winds may be detected through measurements of the surface roughness. Interior Structure. Titan’s interior structure can be determined indirectly. As it passes close to Titan, the Cassini Orbiter’s path will be altered by the Artist’s conception of the Huygens Probe descending through Titan’s atmosphere. This artist’s rendering illustrates the Cassini Orbiter’s radar as it maps swaths of Titan’s surface. THE MYSTERIOUS TITAN 39
40 PASSAGE TO A RINGED WORLD satellite’s gravitational field. The resulting change in the Orbiter’s velocity will be detected on Earth as a Doppler shift in the spacecraft’s radio signal. Understanding the basic structure of Titan’s gravitational field allows scientists to determine the satellite’s moment of inertia, thereby establishing whether Titan has a differentiated core and layered mantle. Titan’s eccentric orbit carries it to varying distances from Saturn. As Titan gets nearer and farther from Saturn, the shape of the satellite changes due to tidal forces. This may cause a detectable change in Titan’s gravitational field that can be measured by flying close to Titan a number of times when the satellite is at different locations in its orbit. Such deformation is a measure of the rigidity of Titan, as it flexes because of tidal forces, which can then be used to infer whether or not it has a liquid layer in the mantle. A World of Its Own The interaction between Titan’s atmosphere and magnetosphere is very complex and many questions still remain. Most of the progress to date has been made using Voyager 1 results, combined with computer modeling. Questions concerning precise interaction, such as the importance of ionization, neutral particle escape, shape of the Titan wake and how the interaction varies over the Titan orbit could all soon be answered by the Cassini–Huygens mission. With over 40 flybys planned, the Cassini Orbiter should be able to answer the question of whether or not Titan has a significant internal magnetic field. Understanding Titan’s methane–hydrocarbon cycle is a major goal for Cassini–Huygens. Investigating the circulation of the atmosphere and the transport of these hydrocarbons is important to understanding Titan’s climate and weather in many time domains: over days, over seasons and over the age of the solar system. The source of atmospheric methane is an intriguing puzzle — methane in Ti- tan’s atmosphere will be depleted by irreversible photolysis in less than 10 million years, so there needs to be a replenishing source of methane at or near the surface. Titan presents an environment that appears to be unique in the solar system, with a thick, hazy atmosphere; a possible ocean of hydrocarbons; and a surface coated with precipitates from the atmosphere — similar to the scenario that scientists believe led to the origin of life on Earth. In the three centuries since the discovery of Titan, we have come to see it as a world strangely similar to our own — yet located about one and a half billion kilometers from the Sun. When the Cassini Orbiter and Huygens Probe arrive at Titan, they will provide us with our first close-up view of Saturn’s largest satellite. With the Probe’s slow descent through Titan’s atmosphere — with images of the surface and chemical composition data — and the Orbiter’s radar maps of the moon’s surface, we will once again be shown another world.
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 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 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
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 106 and 107:
management subsystem and the Probe
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falls below its storage temperature
Page 110 and 111:
The Cassini-Huygens spacecraft stan
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The Imaging Science Subsystem (ISS)
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• Map the composition and thermal
Page 116 and 117:
cise distance between the surface f
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• 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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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
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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
Page 164 and 165:
APPENDIX F Peralta, F. and S. Flana
Page 168:
National Aeronautics and Space Admi
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