Design And Performance Of A Day/night Aspect System For The EXITE Balloon-borne Hard X-ray Telescope

We report on the design, development, testing and flight usage of a complete aspect system for the balloon borne Energetic X-ray Imaging Telescope Experiment (EXITE) payload. The aspect systems are designed to provide both real-time and postfacto aspect information for the telescope pointing direction. The aspect system included two independent day-time systems: a sun sensor for determination of the solar azimuth and an integrating CCD TV camera, with deepred filter, for direct detection of bright stars in the day sky. The night-time aspect system included an intensified CCD camera and TV link for direct viewing and recording of the telescope pointing direction. All three systems were tested and used on a successful balloon flight of the EXITE payload from Alice Springs, AUS tralia, on May 9-10, 1989. Real-time aspect was obtained at the 10 arcmin level, sufficient for initial target acquisition and subsequent gyro drift updates for source tracking, for both day and night targets using the sun-semr and intensified TV systems, respectively. Postfacto aspect at the & 3 arcmin level is obtained. Analysis of the near-IR CCD images of bright star fields recorded in daytime at balloon altitudes (4 g/cm2) is in progress and will be reported in a subsequent publication.