Passage to a Ringed World - NASA's History Office

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The RPWS instrument will be used to investigate electric and magnetic waves in space plasma at Saturn. The solar wind is a plasma; plasma may be “contained” within magnetic fields (that is, the magnetospheres) of bodies such as Saturn and Titan. The RPWS instrument will measure the electric and magnetic fields in the interplanetary medium and planetary magnetospheres and will directly measure the electron density and temperature of the plasma in the vicinity of the spacecraft. The major components of the RPWS instrument are an electric field sensor, a magnetic search coil assembly and the Langmuir probe. The electric field sensor is made up of three deployable antenna elements mounted on the upper equipment module of the Cassini Orbiter. Each element is a collapsible beryllium copper tube that is rolled up during launch and subsequently unrolled to its 10-meter length by a motor drive. The magnetic search coil assembly includes three orthogonal coils about 25 millimeters in diameter and 260 millimeters long. The magnetic search coils are mounted on a small platform attached to a support for the HGA. The Langmuir probe, which measures electron density and temperature, is a metallic sphere 50 millimeters in diameter. The probe is attached to the same platform by a one-meter deployable boom. Signals from the sensors go to a number of receivers, which provide low and high time and frequency resolution measurements. The instrument ranges are one hertz to 16 megahertz for electric fields; one hertz to 12.6 kilohertz for magnetic fields; electron densities of 5–10,000 electrons per cubic centimeter; and electron temperatures equivalent to 0.1– 4 electron volts. Probe Instruments Overview The Huygens Probe, provided by the European Space Agency (ESA), will fly to the Saturn system aboard the Cassini–Huygens spacecraft. Carrying six science instruments, the Probe will study the atmosphere and surface of Saturn’s largest satellite, Titan, descending through Titan’s atmosphere and landing — either on solid land or in a liquid lake or ocean. Many countries have participated in the development of the Huygens Probe’s six instruments. The instruments are the Huygens Atmospheric Structure Instrument (HASI), the Aerosol Collector and Pyrolyser (ACP), the Gas Chromatograph and Mass Spec- trometer (GCMS), the Descent Imager and Spectral Radiometer (DISR), the Doppler Wind Experiment (DWE) and the Surface Science Package (SSP). These instruments comprise 39 sensors; the total mass of the science payload is 48 kilograms. Once the Probe has separated from the Orbiter, it is wholly autonomous. The instruments are turned on in a preprogrammed sequence after the Probe’s heat shield is released. Probe instrument operation is controlled by timers, acceleration sensors, altimeters and a Sun sensor. All instruments use time-based operation from the beginning of the descent down to 20 kilometers. Three of the instruments, the DISR, the HASI and the SSP, use measured altitude below 20 kilometers. Up to three hours of Probe data will be relayed to the Orbiter for later transmission to Earth. Probe Instrument Descriptions Huygens Atmospheric Structure Instrument. The Huygens Atmospheric Structure Instrument (HASI) investigates the physical and electrical properties of Titan’s atmosphere, including temperature, pressure and atmospheric density as a function of altitude and wind gusts — and in the event of a landing on a liquid surface — wave motion. Comprising a variety of sensors, the HASI will also measure the ion and electron conductivities of the atmosphere and search for electromagnetic wave activity. Atmospheric pressure is measured by the deflection of a diaphragm. A tube inlet is mounted on a stub extending outside the Probe. Thermometers mounted on the stub measure atmospheric temperature. The Cassini–Huygens spacecraft, with thermal blankets on, in its flight-ready state. TOOLS OF DISCOVERY 115
Huygens Atmospheric Structure Instrument – HASI Gas Chromatograph and Mass Spectrometer – GCMS Aerosol Collector and Pyrolyser – ACP Descent Imager and Spectral Radiometer – DISR Doppler Wind Experiment – DWE Surface Science Package – SSP 116 PASSAGE TO A RINGED WORLD HUYGENS PROBE INSTRUMENTS Measurements Temp: 50–300 K; Pres: 0–2000 mbar; Grav: 1 μg–20 mg; AC Efield: 0–10 kHz, 80 dB at 2 μVm –1 Hz –0.5 ; DC E-field: 50 dB at 40 mV/ m; electrical conductivity: 10 –15 Ω/ m to ∞; relative permittivity: 1–∞; acoustic: 0–5 kHz, 90 dB at 5 mPa Mass range: 2–146 amu; Dynamic range: >10 8 ; Sensitivity: 10 –12 mixing ratio; Mass resolution: 10 –6 at 60 amu 2 samples: 150–45 km, 30–15 km altitude Upward and downward spectra: 480–960 nm, 0.87–1.7 μm; resolution 2.4–6.3 nm; downward and side-looking images: 0.66–1 μm; solar aureole photometry: 550 nm, 939 nm; surface spectral reflectance (Allan Variance)1/2: 10 –11 (in 1 s), 5 × 10 –12 (in 10 s), 10 –12 (in 100 s), corresponding to wind velocities of 2 m/s to 200 m/s, Probe spin Gravity: 0–100 g; Tilt: ±60°; Temp: 65–100 K; thermal conductivity: 0–400 mW m –1 K –1 ; speed of sound: 150–2000 m/s; liquid density: 400–700 kg m –3 ; refractive index: 1.25–1.45 To determine the density of the atmosphere, an accelerometer measures acceleration along the spin axis. Three additional accelerometers measure acceleration along all three axes of the Probe over a range of ±20 g. A microphone is also part of the HASI; it senses acoustic noise from sources such as thunder, rain or wind gusts. A permittivity and wave analyzer, consisting of an array of six elec- Techniques Direct measurements using “laboratory” methods Chromatography and mass spectrometry; 3 parallel chromatographic columns; quadrupole mass filter; 5 electron impact sources 3-step pyrolysis; 20°C, 250°C, 650°C Spectrometry, imaging, photometry and surface illumination by lamp Doppler shift of Huygens Probe telemetry signal, signal attenuation Impact acceleration; acoustic sounding, liquid relative permittivity, density and index of refraction trodes, is mounted on two deployable booms. Measurements of the magnitude and phase of the received signal give the permittivity and electronic conductivity of the atmosphere and the surface. Electromagnetic signals such as those of lightning can also be detected. The instrument also processes the signal from the Probe’s radar altimeter to obtain information on surface topography, roughness and electrical properties. Partner Nations Italy, Austria, Finland, Germany, France, The Netherlands, Norway, Spain, US, UK US, Austria, France France, Austria, Belgium, US US, Germany, France Germany, France, Italy, US UK, Italy, The Netherlands, US Aerosol Collector and Pyrolyser. The Aerosol Collector and Pyrolyser (ACP) captures aerosol particles from Titan’s atmosphere using a deployable sampling device extended in the air flow below the nose of the Probe. The samples are heated in ovens to vaporize the volatiles and decompose the complex organic materials. The products are then passed to the GCMS for analysis. The ACP will obtain samples at two altitude ranges. The first sample, at
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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
Page 74 and 75: Artist’s conception of Ithaca Cha
Page 76 and 77: An artist’s rendition of Saturn
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Page 82 and 83: SATURN’S MAGNETIC FIELD Saturn’
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Page 86 and 87: per atmosphere. Energetic particles
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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
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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
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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
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Page 156 and 157: APPENDIX D 148 PASSAGE TO A RINGED
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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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