Realization of a faster, cheaper, better star tracker for the new millennium

Abstract

The Advanced Stellar Compass (ASC) is a second generation star tracker consisting of a CCD camera and its associated microcomputer. It is a true, multi-star tracker which was designed for the Orsted mission, a precision mapper of the Earth's magnetic field. The ASC operates by matching the star images acquired by the camera to internal star initial attitude acquisition (solving the lost in space problem) is performed, and then the attitude of the camera is calculated in celestial coordinates by averaging the position of a large number of star observations for each image. The ASC features high accuracy, a smooth response to changing star fields, high boresight stability, low power and mass, robust autonomy, quaternion output and low cost. It is readily adapted to a wide range of missions, four of which are cited. Key parameters of the ASC for the Orsted and Astrid II satellites are: mass as low as 900 g; power consumption as low as 5.5 W; a single axis, relative, attitude angle error of less than 1.4 arcsec, RMS (which is close to 1 /spl sigma/) and a twist, or roll angle, relative accuracy of less than 13 arcsec, RMS, as measured at the Mauna Kea, Hawaii observatories of the university of Hawaii in June 1996.