Editing EXOSAT (section)

==Satellite operations==

Each of the three axes were stabilized and the optical axes of the three scientific instruments were coaligned. The entrance apertures of the scientific instruments were all located on one face of the central body. Once in orbit the flaps which cover the entrances to the ME and LEIT were swung open to act as thermal and [[stray light|stray-light]] shields for the telescopes and star trackers, respectively.<ref name=Hoff/>

The orbit of Exosat was different from any previous [[X-ray astronomy]] satellite. To maximize the number of sources occulted by the [[Moon]], a highly eccentric orbit (e ~ 0.93) with a 90.6 hr period and an inclination of 73° was chosen.<ref name=White>{{ cite journal |vauthors=White NE, Peacock A |title=The Exosat observatory |journal=Societa Astronomica Italiana, Memorie |volume=59 |issue=1–2 |year=1988 |pages=7–31 |bibcode=1988MmSAI..59....7W }}</ref> The initial apogee was 191,000&nbsp;km and perigee 350&nbsp;km. To be outside the [[Earth]]'s radiation belts, the scientific instruments were operated above ~50,000&nbsp;km, giving up to ~76 hr per 90 hr orbit.<ref name=White/> There was no need for any onboard data storage as Exosat was visible from the ground station at Villafranca, Spain for practically the entire time the scientific instruments were operated.