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Proceedings Paper

Pointing knowledge accuracy of the star tracker based ATP system
Author(s): Shinhak Lee; Gerardo G. Ortiz; James W. Alexander
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Paper Abstract

The pointing knowledge for the deep space optical communications should be accurate and the estimate update rate needs to be sufficiently higher to compensate the spacecraft vibration. Our objective is to meet these two requirements, high accuracy and update rate, using the combinations of star trackers and inertial sensors. Star trackers are very accurate and provide absolute pointing knowledge with low update rate depending on the star magnitude. On the other hand, inertial sensors provide relative pointing knowledge with high update rates. In this paper, we describe how the star tracker and inertial sensor measurements are combined to reduce the pointing knowledge jitter. This method is based on the 'iterative averaging' of the star tracker and gyro measurements. Angle sensor measurements are to fill in between the two gyro measurements for higher update rate and the total RMS error (or jitter) increases in RSS (Root-Sum-Squared) sense. The estimated pointing jitter is on the order of 150 nrad which is well below the typical requirements of the deep space optical communications. This 150 nrad jitter can be achieved with 8 cm diameter of telescope aperture. Additional expectations include 1/25 pixel accuracy per star, SIRTF class gyros (ARW = 0.0001 deg/root-hr), 5 Hz star trackers with ~5.0 degree FOV, detector of 1000 by 1000 pixels, and stars of roughly 9 to 9.5 magnitudes.

Paper Details

Date Published: 18 April 2005
PDF: 10 pages
Proc. SPIE 5712, Free-Space Laser Communication Technologies XVII, (18 April 2005); doi: 10.1117/12.612037
Show Author Affiliations
Shinhak Lee, Jet Propulsion Lab. (United States)
Gerardo G. Ortiz, Jet Propulsion Lab. (United States)
James W. Alexander, Jet Propulsion Lab. (United States)

Published in SPIE Proceedings Vol. 5712:
Free-Space Laser Communication Technologies XVII
G. Stephen Mecherle, Editor(s)

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