Extending CubeSAT star tracker operation to very low-Earth orbit using a 2D-morphological clutter filter

CubeSAT star trackers, deployed on very small nanosatellites, measure spacecraft vehicle attitude (body orientation). Very low Earth orbit (VLEO) at 90 km creates severe challenges for detecting stars in the presence of the Earth’s bright limb clutter. In this work, we examine a camera with an active-pixel CMOS focal plane to develop a cluttered background mitigation algorithm that improves star-field detection performance, which is applicable to a wide range of deployed CubeSAT star trackers through firmware upgrades. Lab measurements of the point spread function (PSF) across the field of view determine the structure element needed for a 2D morphological clutter filter needed to reject the Earth’s bright limb and cirrus clouds. Ground-based night sky star field scenes with cirrus clouds demonstrate the clutter filter efficacy in combating the bright Earth limb. Future analysis of data from the 85-kft balloon flight the test article has taken will give us an opportunity to test our clutter algorithm on clutter more comparable to what we expect at VLEO.