Passage to a Ringed World - NASA's History Office

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Cassini–Huygens designed to determine the present state of these bodies and the processes operating on or in them, but it is also equipped to discover the interactions that occur among and between them. These interactions within the Saturn system are important. An analogy can be drawn to a clock, which has many parts. However, a description of each part and the cataloging of its properties, alone, completely misses the “essence” of a clock. Rather, the essence is in the interactions among the parts. So it is for much of what the Cassini– Huygens mission will be studying in the Saturn system. It is the ability to do “system science” that sets apart the superbly instrumented spacecraft. The very complex interactions that are in play in systems such as those found at Jupiter and Saturn can only be addressed by such instrument platforms. This is because the phenomena to be studied are often sensitive to a large number of parameters — a measurement might have to take into account simultaneous dependencies on location, time, directions to the Sun and planet, the orbital configurations of certain satellites, magnetic longitude and latitude and solar wind conditions. To deal with such complexity, the right types of instruments must be on the spacecraft to make all the necessary and relevant measurements — and all the measurements must be made essentially at the same time. Identical conditions very seldom, if ever, recur. Thus, it would be totally impossible for a succession, or even a fleet, of “simple” spacecraft to obtain the same result. Furthermore, requiring the instruments to operate simultaneously has a major impact on spacecraft resources such as electrical power. This demand — and the need for a broadly based, diverse collection of instruments — is the reason that the Cassini–Huygens spacecraft is so large. Both the Huygens Probe and the Cassini Orbiter will study Titan. While the formal set of scientific objectives is the same for both, the Cassini–Huygens mission is designed so that a synergistic effect will be realized when the two sets of measurements are combined. In other words, the total scientific value of the two sets of data together will be maximized because of certain specific objectives for the Probe and the Orbiter. Each time the Orbiter flies by Titan, it will make atmospheric and surface remote-sensing observations that include re-observations along the flight path of the Probe. The Probe’s measurements will be a reference set of data for calibrating the Orbiter’s observations. In this way, the Probe and Orbiter data together can be used to study the spatial and seasonal variations of the composition and dynamics of the atmosphere. Launch: Ending and Beginning Launch is both an ending and a beginning. Nowhere is there a more profound test of the work that has been done, nor a more dramatic statement to mark a shift in program priorities. Nowhere is there more hope — or more tension. A successful launch is everything. These will be our thoughts as we survey the scene at Cape Canaveral Air Station in Florida. It is October 6, 1997. The launch vehicle is the Titan IVB with two stout Solid Rocket Motor Upgrades (SRMUs) attached. An additional Centaur rocket — the uppermost stage — sits on top of the propulsion stack. This system puts Cassini–Huygens into Earth orbit and then, at the right time, sends it on its interplanetary trajectory. The “core” Titan vehicle has two stages. The SRMUs are anchored to the first, or lower, stage. These “strap-on” rockets burn solid fuel; the Titan uses liquid fuel. The Centaur is a versatile, high-energy, cryogenic-liquid-fueled upper stage with two multiple-start engines. The Titan IVB/ SRMU–Centaur system is capable of placing a 5760-kilogram payload into a geostationary orbit. On top of all this propulsive might sits Cassini– Huygens, protected for its trip through the lower atmosphere by a 20-meterlong payload fairing. Lift-off is from Cape Canaveral Air Station, launch complex 40. It is early in the morning. The launch sequence begins with the ignition of the two solid-rocket motors, which lift the whole stack off the pad. About 10 seconds A MISSION OF DISCOVERY 15
16 PASSAGE TO A RINGED WORLD after lift-off, the stack continues to accelerate and then it starts to tilt and rotate. The rotation continues until the required azimuth is reached. At plus two minutes, the first stage of the Titan is ignited, at an altitude of approximately 58,520 meters. A few seconds later, the two solid-rocket motors, now spent, are jettisoned. One and a half minutes pass, and at 109,730 meters, the payload fairing is released. About five and a half minutes into the flight, the Titan reaches an altitude of 167,330 meters. Here the first stage of the Titan separates and the second stage fires. At launch plus nine minutes, the second stage has burnt out and drops away. Now it is the Centaur’s turn to fire. It boosts the remaining rocket–spacecraft stack into a “parking” orbit around Earth and turns off its engines. Some 16 minutes later, the Centaur ignites for a second time. This burn lasts between seven and eight minutes, and when it is over, the Centaur separates from the spacecraft. The Cassini–Huygens spacecraft is now on an interplanetary trajectory, heading first for Venus, then Venus again, around to Earth, to Jupiter — and at last, Saturn!
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 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
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
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Artist’s conception of Ithaca Cha
Page 76 and 77:
An artist’s rendition of Saturn
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The MAPS Instruments Coordinated ob
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field reverses direction across the
Page 82 and 83:
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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