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Ground performance of the High-Energy Focusing Telescope (HEFT) attitude control system

The High Energy Focusing Telescope (HEFT) is a balloon-borne, hard x-ray/gamma ray (20-70 keV) astronomical experiment. HEFT's 10 arcminute field of view and 1 arcminute angular resolution place challenging demands on its attitude control system (ACS). A microprocessor-based ACS has been developed to manage target acquisition and sidereal tracking. The ACS consists of a variety of sensors and actuators, with provisions for 2-way ground communication, all controlled by an on-board computer. Ground based pointing performance measurements indicate 1σ jitter of 7" and gyro drift rates of <1" s-1. Jitter is expected to worsen in the flight environment, but star tracker data are expected to reduce drift rates significantly, enabling a predicted 1σ absolute attitude determination of ≥4.7". HEFT is scheduled for flight in Spring 2004.