Popular name for the NASA satellite HEAO-2, the second High Energy Astronomical Observatory, launched in 1978 November. It was the first X-ray astronomy mission that could take images of the X-ray sky, for which it used grazing-incidence mirrors with a collecting area of approximately 200 cm2. Einstein had four instruments, each covering the energy range 0.1–4 keV (0.3–12 nm) for X-ray imaging and spectroscopy. It operated until 1981 April.
http://heasarc.gsfc.nasa.gov/docs/einstein/heao2.html Information page at Goddard Space Flight Center.
Subjects: Astronomy and Astrophysics.