A method for identifying image data coming from two optical channels in a split field of view star camera

Abstract

Split FOV (Field of View) star tracker was developed by Texas A&M University together with the University of Rome “La Sapienza”. A 50% splitter was used to combine light beams from two separate FOVs, while only a single objective lens and optical detector are used. In this way, double FOV configuration allows increased accuracy in attitude determination by taking advantage of the ability to examine two orthogonal FOVs simultaneously. There is a demand for optical tag due to each frame contained overlapping star images coming from separate FOVs. In this paper we propose a method for identifying two FOVs by tagging the images with different shaped diffraction patterns. We insert a circular diaphragm in the optical channel 1# and non-circular (elliptical or rectangular) in the channel 2#, so that images with distinctive features are produced at CCD photosensitive surface - circular Airy disc for the FOV-1# and elliptical contour (with side lobe or distortion) for FOV-2#. The effects of elliptical sampling window and the signal-to-noise ratio on the accuracy of the centroid estimate for star spots with a Gaussian intensity distribution were discussed theoretically. The optical tagging has one limitation. There is possibility for a star image tagged by non-circular contour, which is confused with smearing trail due to high angular velocity operation (e.g. greater than 1°/s).