Passage to a Ringed World - NASA's History Office

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altitudes down to 40 kilometers above the surface, will be obtained primarily by direct impact of the atmosphere on a cold filter target. The second sample will be obtained at about 20 kilometers by pumping the atmosphere through the filter. After each collection, the filter will be transferred to an oven and heated to three successively higher temperatures, up to about 650 degrees Celsius, to vaporize and pyrolyze the collected material. The product at each temperature will be swept up by nitrogen carrier gas and transferred to the GCMS for analysis. Gas Chromatograph and Mass Spectrometer. The Gas Chromatograph and Mass Spectrometer (GCMS) provides a quantitative analysis of the composition of Titan’s atmosphere. Atmospheric samples are transferred into the instrument by dynamic pressure as the Probe descends through the atmosphere. The Mass Spectrometer constructs a spectrum of the molecular masses of the gas driven into the instrument. Just prior to landing, the inlet port of the GCMS is heated to vaporize material on contact with the surface. Following a safe landing, the GCMS can determine Titan’s surface composition. The GCMS uses an inlet port to collect samples of the atmosphere and has an outlet port at a low pressure point. The instrument contains three chromatographic columns. One column has an absorber chosen to separate carbon monoxide, nitrogen and other gases. Another column has an absorber that will separate nitriles and other highly polar compounds. The third is to separate hydrocarbons up to C . The mass range 8 is 2–146 amu. The Mass Spectrometer serves as the detector for the Gas Chromatograph, for unseparated atmospheric samples and for samples provided by the ACP. Portions of the GCMS are identical in design to the Orbiter’s INMS. Descent Imager and Spectral Radiometer. The Descent Imager and Spectral Radiometer (DISR) uses several instrument fields of view and 13 sensors, operating at wavelengths of 350– 1700 nanometers, to obtain a variety of imaging and spectral observations. The thermal balance of the atmosphere and surface can inferred by measuring the upward and downward flux of radiation. Solar aureole sensors will measure the light intensity around the Sun resulting from scattering by aerosols, permitting calculations of the size and number density of suspended particles. Infrared and visible imagers will observe the surface during the latter stages of the descent. Using the Probe’s rotation, the imagers will build a mosaic of pictures of the Titan landscape. A side-looking visible imager will view the horizon and take pictures of the clouds, if any exist. For spectral measurements of the surface, a lamp will be turned on shortly before landing to provide enough light for measuring surface composition. The DISR will obtain data to help determine the concentrations of atmospheric gases such as methane and argon. DISR images will also determine if the local surface is solid or liquid. If the surface is solid, DISR will reveal topographic details. If the surface is liquid, and waves exist, DISR will photograph them. DISR sensors include three framing imagers, looking downward and horizontally; a spectrometer dispersing light from two sets of optics looking downward and upward; and four solar aureole radiometers. The spectral range of the imagers is 660– 1000 nanometers; the spectrometer’s range is 480–960 nanometers; the aureole radiometers operate at 475– 525 and 910–960 nanometers, with two different polarizations. Separate downward- and upwardlooking optics are linked by fiberoptic bundles to an infrared grating spectrometer. The infrared detectors have a spectral range of 870–1700 nanometers. There are also two violet photometers, looking downward and upward with a bandwidth of 350–470 micrometers. To provide reference and timing for the other measurements, the DISR uses a Sun sensor to measure the solar azimuth and zenith angle relative to the rotating Probe. The interior of the Huygens Probe, showing its science instruments. TOOLS OF DISCOVERY 117
118 PASSAGE TO A RINGED WORLD Doppler Wind Experiment. The Dop- pler Wind Experiment (DWE) uses two ultrastable oscillators (USOs), one on the Probe and one on the Orbiter, to give Huygens’ relay link a stable carrier frequency. Orbiter measurements of the shift in Probe frequency (Doppler shift) will provide information on the Probe’s motion from which a height profile of the zonal wind (the component of wind along the line of sight) and its turbulence can be derived. The output frequency of each USO is set by a rubidium oscillator. The signal (which is like a very high precision clock) received from the Probe is compared with that of the Orbiter USO, and the difference in frequency is recorded and stored for transmission to Earth. This information is used to determine the Doppler velocity be- PROBING TITAN’S DEPTHS Like the Cassini Orbiter, Huygens represents an internationalcollaboration. The partners involved in the Probe effort are Austria, Belgium, the European Space Agency, Finland, France, Germany, Italy, The Netherlands, Norway, Spain, the United Kingdom and the United States. The Huygens science instruments comprise a total of 39 sensors. The total mass of the Probe science payload is 48 kilograms. Once the Probe separates from the Orbiter, it is wholly autonomous. The instruments will turn on in a preprogrammed sequence after the Probe cover is released. Probe operation is controlled by timers, acceleration sensors, altimeters and a Sun sensor. As much as three hours of tween the Probe and the Orbiter. Modulation of this signal will provide additional data on the Probe spin rate, spin phase and parachute swing. Winds will be measured to a precision of one meter per second. Surface Science Package. The Surface Science Package (SSP) contains a number of sensors to determine the physical properties and composition of Titan’s surface. Some of the SSP sensors will also perform atmospheric measurements during descent. During descent, measurements of the speed of sound will give information on atmospheric composition and temperature. An accelerometer records the deceleration profile at impact, indicating the hardness of the surface. Tilt sensors (liquid-filled tubes with electrodes) will measure any pendulum motion of the Probe during Probe data will be relayed to the Orbiter and later transmitted to Earth. Radar Altimeter Antenna HASI Stud Gas Chromatograph and Mass Spectrometer descent, indicate the Probe orientation after landing and measure any wave motion. If the surface is liquid, an opening at the bottom of the Probe body, with a vent extending upward along the Probe axis, will admit liquid, which will fill the space between a pair of electrodes. The capacitance between the electrodes gives the dielectric constant of the liquid; the resistance gives the electrical conductivity. A float with electrical position sensors determines the liquid’s density. A sensor to measure the refractive index of the liquid has light-emitting diode (LED) light sources, a prism with a curved surface and a linear photodiode detector array. The position of the light/dark transition on the detector array indicates the refractive in- Aerosol Collector and Pyrolyser Huygens Atmospheric Structure Instrument (HASI) Deployable Booms Surface Science package “Top Hat” Batteries
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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
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In the stellar occultation experime
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scattering than are larger particle
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In fact, Saturn’s rings — as we
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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
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
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Page 102 and 103: of the spacecraft! Below the oxidiz
Page 104 and 105: • Opening or shutting thermal lou
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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
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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 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
Page 154 and 155: APPENDIX C 146 PASSAGE TO A RINGED
Page 156 and 157: APPENDIX D 148 PASSAGE TO A RINGED
Page 158 and 159: APPENDIX D 150 PASSAGE TO A RINGED
Page 160 and 161: APPENDIX F 152 PASSAGE TO A RINGED
Page 162 and 163: 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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