PTTI-Aided Ephemeris Calculation and Rapid Data Link Acquisition for Manned Space Flight

Alfred Anderman

Abstract:	Complexity of future manned space flight mission control can be significantly reduced by integrating GPS, the PTTl source, into telemetry, tracking and command (TT&C). Future telecommunications, space tracking electronic intelligence, metrology, navigation, and data acquisition will thereby be sewed, including: 1) On-board ephemeris determination, 2) Reduced synchronization time for time division multiple access (TDMA) links, and 3) In-flight clock calibration, increasing on-board autonomy and reducing ground support costs. Manned space transportation through the first quarter of the 21 "' century will probably depend on a mix of vehicles, including the Advanced Manned Launch System (AMLS), the Personnel Launch System (PLS), and continued use of the Shuttle Fleet. Precise Ephemeris is important on-board for mission success, status monitoring, also for rendezvous and docking. Use of GPS can eliminate ground based tracking/processing, enhancing autonomy and reducing communications bandwidth. GPS time can simplify complicated functions used in bandwidth efficient time division multiple access (TDMA) communications, such as: I) Precise and real-time synchronization of receive reference timing, 2) Transmit-timing and acquisition control, 3) Unique synchronization word (UW) detection, and 4) Elastic buffering. High clock accuracy provides increased signal-to-noise (S/N) ratio during acquisition, permitting narrower acquisition frequency and time windows. Spaceborne systems requirements to provide capabilities such as: 1) Refinement of the GEM-72 gravity model based on satellite tracking observations from ATS-6 to GEOS-3, 2) Relativistic clock experiments, 3) NASA crustal dynamics program for developing space geodetic techniques to study the earth's crust, its gravity field, and earthquake mechanisms, and 4) Multi-disciplinary space geodetic tracking for studying global climatic changes are also reviewed.
Published in:	Proceedings of the 24th Annual Precise Time and Time Interval Systems and Applications Meeting December 1 - 3, 1992 Ritz-Carlton Hotel McLean, Virginia
Pages:	137 - 152
Cite this article:	Anderman, Alfred, "PTTI-Aided Ephemeris Calculation and Rapid Data Link Acquisition for Manned Space Flight," Proceedings of the 24th Annual Precise Time and Time Interval Systems and Applications Meeting, McLean, Virginia, December 1992, pp. 137-152.
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