AUTONOMOUS SPIN AXIS AND SPIN RATE CONTROL OF HAMSAT

摘要

HAMSAT is a micro satellite for providing satellite based Amateur Radio Services to the Indian as well as the international community of Amateur Radio Operators. HAMSAT is a spin stabilized satellite with a nominal spin rate of 4 rpm. It was launched into a sun synchronous orbit of 624 km altitude as an auxiliary payload by Polar Satellite Launch Vehicle on May 5th of 2005. Autonomous control of spin rate and spin axis is desirable for small satellites in order to reduce ground support. First time, the Negative Bdot control law has been used to align the spin axis of HAMSAT along the orbit normal. As the variation of earth's magnetic field along orbit normal is nearly zero, the spin axis is maintained to the orbit normal within very good accuracy. The spacecraft has been made totally autonomous with Spin axis orientation by Negative Bdot control law and Spin rate control using Cross product law. The satellite has been functioning normally for the last 2 years unattended except for monitoring the health of the satellite once in a while. This paper describes Autonomous Attitude Control System (AACS) of HAMSAT and On-Orbit results of AACS.