Launch and Orbit
The EXOSAT satellite was launched on 26 May 1983 from the Vandenberg complex in the USA on a Thor-Delta rocket and put in a highly eccentric orbit (e~ 0.93) with a 90.6 hr period and an inclination of 73°.
The orbit of EXOSAT was quite different from that of any previous X-ray astronomy satellite. The initial apogee was 191 000 km and the perigee 350 km. The science instruments were operated above 50 000 km, outside the earth's radiation belts. This allowed scientific operations for up to 76 hr per 90 hr orbit, without interruption. EXOSAT was visible from the ground station at Villafranca in Spain for almost the entire time that the science instruments were operated and there was no need for any onboard data storage. The attitude was controlled, to within 1 arc second, using one of two star trackers (each attached to a low energy telescope), three gyros and a sun sensor.