Passage to a Ringed World - NASA's History Office

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PLANETARY MISSION OPERATIONS Function Primary Activities THE JPL WAY Mission Planning Generate a mission plan and mission phase plans. Generate mission and flight rules and constraints. Integrated Sequence Generate detailed timelines of activities. Generate integrated files of valid com- Development mands. Generate sequence and realtime command loads for radiation to the spacecraft. Mission Control Configure and control the ground system. Monitor in real time the spacecraft’s and payload’s activities, health and safety. Navigation Predict and reconstruct the spacecraft’s trajectory. Design maneuvers to correct the trajectory to achieve mission objectives. Spacecraft Analysis and Plan, design and integrate engineering activities. Maintain the health and safety Sequence Input Development of the spacecraft through non-realtime analyses and anomaly identification and resolution. Payload Analysis and Generate a science operations plan. Design and integrate instrument observa- Sequence Input Development tions. Maintain the health and safety of the payload through non-realtime analyses and anomaly identification and resolution. Science Processing Generate and archive processed data in support of payload analysis and for the purpose of scientific research. Database Management Provide throughout the mission realtime accessible engineering and science telemetry and ancillary data for non-realtime spacecraft and instruments analyses. Data Acquisition Acquire the downlink signal. Generate Doppler and ranging tracking data. Extract and digitize the original information from the modulated subcarrier of the radio signal. Eliminate bit errors. Digital Processing Perform telemetry decommutation.* Display and convert telemetry channels data. Data Transport Ensure that communications are in place and functioning so that data can be routed to the project database and scientists. Computer and Communication Implement and administer computer and communication systems. Administration Training Train personnel on the processes and on the use of the ground data system. System Engineering Design a mission operations system that matches the requirements, takes constraints into account and has acceptable performance. *Decommutation is the process by which a single telemetry signal is separated into its component signals. AN ENSEMBLE EFFORT 123
124 PASSAGE TO A RINGED WORLD Saturn, gathering energy from two flybys of Venus, one flyby of Earth and one of Jupiter. Upon arrival at Saturn, the spacecraft will be placed into orbit around Saturn and a four-year tour of the Saturn system will begin. The Huygens Probe will be delivered on the first (nominal) or second (backup) flyby of Titan. Multiple close Titan flybys will be used during the tour for gravity assists and studies of the satellite. The tour also includes icy satellite flybys for satellite studies and orbits at a variety of inclinations and orientations with respect to the Sun–Saturn line for ring, atmospheric, magnetospheric and plasma science studies. Spacecraft and Payload The Cassini spacecraft is a three-axis stabilized spacecraft. The Huygens Probe and the Orbiter instruments are affixed to the body of the spacecraft. There are 18 science instrument subsystems, which are divided into four groups: optical remote sensing; microwave remote sensing; fields, particles and waves; and Probe instruments. Orbiter instruments that serve multiple investigations are called facility instruments. Facility instruments are provided by the Jet Propulsion Laboratory (JPL), the NASA Goddard Space Flight Center or by JPL and ASI. The facility instruments, except for the Ion and Neutral Mass Spectrometer (INMS), are operated by a JPL team called the distributed operations interface element. Instruments that serve individual investigations are provided and operated by a Principal Investigator (the INMS is operated like a Principal Investigator instrument). The Huygens Titan Probe is operated from the Huygens Probe Operations Centre in Darmstadt, Germany. Capabilities and Constraints The Cassini–Huygens mission scientific objectives involve complex mission, spacecraft and payload demands. In addition, mission operations must fit within certain inherent constraints. However, operational capabilities built into the spacecraft can help to keep operations simple. Operational Capabilities Robustness. Robustness is provided by redundant engineering subsystem assemblies, healthy margins of Orbiter consumables and fault-protection software that provides protection for the spacecraft and the mission in the event of a fault. Automation. Automation is provided by the onboard inertial vector propagator, which generates turn profiles, bringing the spacecraft from its last commanded attitude and rate to a possibly time-varying target attitude and rate. The target attitude is obtained by applying an offset to a base attitude, which is defined by primary and secondary pointing constraints as follows: • Primary constraint — Align a spacecraft fixed vector (primary body vector) with a specified inertial vector (primary inertial vector). • Secondary constraint — Align a spacecraft fixed vector (secondary body vector) with a specified inertial vector (secondary inertial vector). Flexibility. Flexibility is provided by the capability of storing telemetry data on a solid-state recorder for later playback and by trigger-command capabilities. Most instruments operate from commands stored in their memories; a trigger command is issued from the central computer to initiate a preestablished series of instrument-internal commands. Inherent Constraints Cost. The major operational constraint of the Cassini–Huygens mission is that mission operations and data analysis activities must be conducted within fixed budgets (within both the U.S. and the European space communities). Thermal. At Sun range closer than 2.7 astronomical units (AU), thermal constraints make it necessary to use the Cassini’s high-gain antenna to shade the spacecraft from the Sun — except for infrequent turns away from the Sun (off-Sun turns), such as those used for trajectory correction maneuvers. The allowable duration of the off-Sun turns roughly scales with the square of the Sun range. For example, at 0.61 AU, the spacecraft could withstand a transient off-Sun duration of 30 minutes. Telecommunications. While the highgain antenna is used to shade the spacecraft, telecommunications mostly will be restricted to one of
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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
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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
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
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Page 90 and 91: CHAPTER 7 Space mission design aims
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Page 130 and 131: CHAPTER 10 Mission operations are t
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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
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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
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Page 164 and 165: APPENDIX F Peralta, F. and S. Flana
Page 168: National Aeronautics and Space Admi
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