A new automatic star tracker for balloon-borne astronomy instruments

Abstract

The tracking of an astronomical object requires continuous updating of the look angles in azimuth and zenith. The mathematical calculation of these angles needs the position coordinates (latitude and longitude) of the place of observation as the input variables, apart from the celestial co-ordinates of the object. In the case of a balloon-borne platform, the position co-ordinates vary due to float winds both in latitude and longitudinal direction. An accurate pointing thus requires correction of the input position variables continuosuly. We have developed a new microprocessor controlled stand-alone star tracker with a built-in GPS receiver for use in the X-ray astronomy experiments using balloons. GPS receiver provides a highly accurate (~ arcsec) instant longitude and latitude of the balloon platform on continuous basis. Present hardware design is restricted to 12-bit resolution (~5?-). This paper presents some of the technical details of the new system.