Design of Optical System for Autonomous APS Star Sensors

摘要

The modern spacecrafts harassed by the "lost-in-space" problem frequently desire for retrieving their orientations autonomously while performing missions especially in deep space. Star sensor becomes a preferred assistant which determines the attitudes with very high accuracy. Autonomous APS star sensors have been the development trends in virtue of their lighter weight, smaller size, less power, and the ability to acquire attitude knowledge autonomously. By analyzing the principle of attitude measurement applying star identification algorithm, the requirements for the aberration correction and imaging quality of their optical systems are discussed. The statistics of star numbers in different orientations is analyzed making use of guide star catalogs established with various limiting star magnitudes and fields of view (FOV). The method to determine parameters of the optical system including aperture size, FOV, focal length and spectrum range is introduced. These parameters meeting the demand of the Pyramid identification algorithm utilized in this paper to realize the autonomous attitude reorganization in any orientations are calculated. Accordingly, a star camera is designed with STAR 1000 APS as its detector. Its focal length, aperture diameter and circular field of view are 43.56mm, 27.3mm and 20 degrees, respectively. Structure selection and aberration correction schemes are presented. Aberrations including coma, astigmatism, and distortion and lateral color are corrected, and spherical aberration and longitudinal color are controlled. This camera is telecentric in the image field which assures that the star identification is still valid even though the image plane suffers from a deviation as a result of the environmental alteration and manufacture errors.