Exosat factsheet

Observing and detecting X-ray sources

Name Exosat stands for European X-ray Observatory Satellite.

Description Exosat was the first ESA mission entirely devoted to study the Universe at X-ray wavelengths. It observed a wide variety of objects, including active galactic nuclei, X-ray binary systems, supernova remnants, and clusters of galaxies.

Launch 26 May 1983 (Thor-Delta rocket at Vandenburg Airforce Base, United States).

Status Completed (1986).

Journey By placing the satellite in an elliptical orbit, scientists were able to operate the instruments for 76 hours of each revolution.

Notes Exosat's payload consisted of three instruments: two low-energy telescopes, a medium-energy proportional counter, and a gas scintillation proportional counter. These detected X-rays in the 0.05 to 50 keV band.

Exosat was actively making observations until April 1986 but the natural decay of the orbit caused the satellite to enter the Earth's atmosphere on 6 May of that year.

All the data that Exosat retrieved is still available for study, and is still leading to new discoveries.

The results that Exosat obtained were very useful to scientists, and led to several new discoveries. The most important of these was the discovery of 'quasi-periodic' oscillations in X-ray binary systems, a phenomenon unknown before Exosat.

Exosat was unusual at the time because it featured an on-board computer. This not only processed much of the data before returning it to Earth, but also allowed scientists to alter the on-board data handling programs after launch. This is now a standard part of spacecraft control.

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