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Proceedings Paper

Cassini star tracking and identification architecture
Author(s): Valerie C. Thomas; James W. Alexander; Edwin W. Dennison; Patrick G. Waddell; Giuseppe Borghi; Dorico Procopio
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Paper Abstract

The Cassini spacecraft will perform a detailed examination of the Saturnian system, including the release of a probe to study Saturn's largest satellite, Titan. The star tracker for the Cassini mission must provide accurate data during the entire flight including four years of measurement in a harsh radiation environment. The star tracker will provide autonomous star identification over the entire celestial sphere using a 4,000 entry on-board star catalog. Three axis attitude reference will be determined by measurements of two to five stars in the tracker field of view which will allow the gyroscopes to be powered off during the cruise phase of the flight. When the gyros are operational, attitude updates will be provided. The Cassini star tracker consists of a CCD based star camera, called the stellar reference unit (SRU), which is being designed and built by Officine Galileo. The operation of the SRU, including functional modes, exposure times, and areas of the CCD to digitize is under the control of the Cassini Attitude and articulation control subsystem (AACS) flight computer (AFC). The raw digital pixel data is transmitted from the SRU through a dedicated direct memory access (DMA) interface to the AFC memory for subsequent processing. All pixel processing and centroiding is performed within the AFC. Once the initial attitude has been determined, the AFC algorithms will choose which stars within the SRU field of view to track in order to maintain attitude knowledge. The SRU will have a 15 degree field of view and will provide 60 (mu) rad (3 (sigma) ) 2-axis position measurement accuracy for stars of approximately 6.05 visual magnitude and brighter. The required 1 mrad (3 (sigma) ) twist accuracy is provided by star separation.

Paper Details

Date Published: 5 July 1994
PDF: 12 pages
Proc. SPIE 2221, Acquisition, Tracking, and Pointing VIII, (5 July 1994); doi: 10.1117/12.178934
Show Author Affiliations
Valerie C. Thomas, Jet Propulsion Lab. (United States)
James W. Alexander, Jet Propulsion Lab. (United States)
Edwin W. Dennison, Jet Propulsion Lab. (United States)
Patrick G. Waddell, Jet Propulsion Lab. (United States)
Giuseppe Borghi, Officine Galileo (Italy)
Dorico Procopio, Officine Galileo (Italy)

Published in SPIE Proceedings Vol. 2221:
Acquisition, Tracking, and Pointing VIII
Michael K. Masten; Larry A. Stockum; Morris M. Birnbaum; George E. Sevaston, Editor(s)

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