Star Tracker-Based Acquisition, Tracking, and Pointing Technology for Deep-Space Optical communications

This article presents the concept and estimates of the pointing-knowledge accuracy of a star tracker-based acquisition, tracking, and pointing system. The major advantages of this technology are (1) no requirement for a costly groundbased laser beacon, (2) a large mission range beyond the solar system, and (3) a heritage of mature star tracker technology. The key concept is to combine highaccuracy star trackers and high-bandwidth inertial sensors to achieve high-accuracy and high-bandwidth pointing knowledge through the iterative averaging process. The pointing-knowledge bandwidth is divided into three areas (0–10 Hz, 10–50 Hz, and >50 Hz). Signal for each bandwidth are provided by star tracker gyros and angle sensors. Analysis shows that a pointing knowledge of 150 nanoradians (single axis, 1 sigma) can be achieved with an 8-cm-diameter telescope aperture. Additional expectations include 1/25 pixel accuracy per star, Space Infrared Telescope Facility (SIRTF)-class gyros (ARW = 0.0001 deg/root-hr), 5-Hz star trackers with an ∼5.0 degree field of view, a detector of 1000 by 1000 pixels, and stars of roughly 9 to 9.5 magnitudes. This 150-nanoradian pointing knowledge is well below the typical deep-space optical communications requirements of 200 to 300 nanoradians. Furthermore, the link availability can be maintained above 98 percent with a single star tracker.