High speed autonomous embedded software for high accuracy star sensors

A star sensor is an embedded system used in modern spacecraft for estimating the orientation of the spacecraft. Star trackers capture image of star in the sky, process them and gave highly accurate attitude in all 3 axis. Basically a star tracker is an electronic camera connected to a microcomputer. First generation star trackers are characterized by acquiring and processing few stars information to estimate attitude with limited software modules. The availability of space qualified microcomputers enables generation shift in the star trackers development for attitude determination onboard. Laboratory for Electro-Optics Systems (LEOS) is actively involved in design and development of indigenous star trackers for different ISRO. Current star trackers employs traditional method of acquiring and processing star image and don´t meet the many spacecraft requirements in terms of number of stars tracking, accuracy and update rate. In order to meet the current generation spacecraft requirements, LEOS has designed and developed second generation star trackers which are characterized by low weight, volume and power. These sensors are based on ERC-32 processor, here after referred as Mark-II sensor. The essential features expected from onboard software are robustness in operations, run-time and ability to give solutions especially during satellite injection with high angular rate. This paper presents the details of state-of-art software designed and developed for these star trackers to provide high accuracy and higher bandwidth with existing hardware limitations even with harsh space environment with limited resources and constraints.