A US astronomy satellite, also known as OAO-3, which carried a 0.81-m telescope for ultraviolet spectroscopy of hot stars at wavelengths of 70–300 nm. Three small X-ray detectors were also carried. Copernicus was launched in 1972 August and operated until 1980. It studied interstellar matter, mainly by observing absorption features from interstellar gas superimposed on stellar spectra. Its name commemorated the 500th anniversary of the birth of Nicolaus Copernicus in 1973.

http://heasarc.gsfc.nasa.gov/docs/copernicus/copernicus.html Information page at Goddard Space Flight Center.