Fast access method for onboard star catalog

Rao, Nagendra G and Bhat, Seetharama M and Alex, TK (2005) Fast access method for onboard star catalog. In: Journal of guidance, control, and dynamics, 28 (5). pp. 1032-1037.

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Abstract

A new method to retrieve the star data from the onboard catalog is presented. A query to find stars that lie within a cone of uncertainty angle of a given unit vector is answered quickly. If stars are present, a set of catalog numbers is returned along with the nearest neighbor to the center of the cone. An index to the star catalog is formed with a hash function that maps the given unit vector to an index in a hash table. The hash function preserves the stars’ closeness even after their translation to the hash table and thus facilitates the query of a star with a noisy measurement. The proposed organization of the star catalog, other data structures used, and their access methods are described. When subjected to a numerical simulation test with 10,000 random star vectors corrupted with noise, all of the queries are answered correctly. A hash table of 5773-word (16-bit) size is required for a star catalog containing 1613 stars (10,485 words). This method requires only 2.2 average catalog accesses and 2.0-μs process time per query, compared to a traditional binary search that requires 24 accesses and 3.8 μs.

Item Type:	Journal Article
Publication:	Journal of guidance, control, and dynamics
Publisher:	American Institute of Aeronautics and Astronautics
Additional Information:	Copyright of this article belongs to American Institute of Aeronautics and Astronautics.
Department/Centre:	Division of Mechanical Sciences > Aerospace Engineering(Formerly Aeronautical Engineering)
Date Deposited:	16 May 2007
Last Modified:	10 Jan 2012 05:54
URI:	http://eprints.iisc.ac.in/id/eprint/10772

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