(Orbiting Astronomical Observatory 3)
OAO-3 was launched in 1972, and proved to be the most successful
of the OAO missions.
It was a collaborative effort between NASA and the UK, and carried
an X-ray detector in addition to an 80 cm UV telescope.
After its launch, it was named Copernicus to mark the 500th
anniversary of the birth of Nicolaus Copernicus.
Copernicus operated until February 1981, and returned high
resolution spectra of hundreds of starsalong with extensive X-ray
Among the significant discoveries made by Copernicus were the
discovery of several long-period pulsars,
with rotation times of many minutes instead of the more typical
second or less.