A flexible auto-tracking pre-programmed orientation system

Abstract

The details of an orientation system used for balloon-borne hard X-ray telescope fabricated at the Tata Institute of Fundamental Research, Bombay, are given. The servo-stabilized orientable platform is used to point and stabilize the detector axis in any desired direction of the sky during a flight for making pointed mode astronomical observations. The auto-tracking and pre-programmed control system updates the on-board pre-stored steering information to produce correct demand angles every minute for both the azimuth and elevation drives. The telescope's proper angular orientation with overall pointing accuracy of ±0.3°is acquired by actuating the respective torque motors. The novel feature of this system is its capability to acquire and track a large number of selected X-ray sources and background regions in a preplanned observation sequence for long durations and also to correct for balloon drifts with minimum command operations. A variety of command controls are incorporated in the orientation system to update on-board controller status and decide accordingly on the observation scheme as well as to acquire unscheduled X-ray sources with the coordinates calculated at the ground station.