Launched on 13 November 1978 from Cape Canaveral Florida on an Atlas-Centaur SLV-3D, HEAO-B (later to become known as the Einstein Observatory) carried the first imaging, extra-solar X-ray telescope (PI, R. Giacconi). A set of 4 Wolter type 1 nested mirrors focused X-rays up to 8 keV in energy. Angular resolution was 5 arcseconds on axis, degrading to 1.5 arcminutes at the edge of the 1 degree field of view (see details in Giacconi et al. 1979, ApJ, 230, 540). The Einstein Observatory satellite re-entered the Earth's atmosphere and burned up on March 25, 1982

Einstein employed a turntable by which different detectors could be placed at the telescope focus. X-ray imaging was the principal aim of the mission. Both an imaging proportional counter (IPC) and micro-channel plate detector (HRI) were included.
The HRI's angular resolution was that of the mirrors, but energy resolution was poor. The IPC recorded the energy of each event but angular resolution was approximately 40 arcseconds at best. A third detector, the solid state spectrometer (SSS) provided a factor of approximately 3 better energy resolution but no spatial information since it recorded all events occurring in its 6 arcminute field of view. A monitoring proportional counter (MPC) was coaligned with the telescope to monitor variability of the brighter X-ray sources. The observatory included two high-resolution spectrometers. The objective grating spectrometer (OGS) was a set of gold diffraction gratings which could be inserted into the telescope light path. The dispersed spectrum was recorded by one of the imagers. The focal-plane crystal spectrometer (FPCS) was a curved-crystal Bragg spectrometer which operated at the telescope focus. Effective area of these spectrometers was very small (about 1 sq. cm or less), so they were used on only the brightest sources.

The SSS had a lifetime of 11 months due to a limited onboard cryogen supply. The observatory itself lost its ability to point after only 2.5 years in orbit. Operations ceased in April 1981 after the exhaustion of the attitude-control gas. Einstein accomplished 5600 observations. By virtue of its ability to focus X-rays from point sources onto a small region of a detector and as a result of the much lower background associated with the small region of interest, the Einstein Observatory sensitivity was several hundred times greater than any previous X-ray mission. It was the first X-ray NASA mission to have a Guest Observer program.

With the dramatic improvement in sensitivity and the ability to image with angular resolution of a few arcseconds, for the first time astronomers studied the structure of supernova remnants, detected unexpectedly strong coronal emission from normal stars, resolved the distribution of compact sources in external galaxies (M31 and the Magellanic Clouds), detected hot gaseous coronae in early type galaxies, detected cooling gas in the cores of galaxy clusters, discovered X-ray jets co-aligned with radio jets, and found extensive structure in the hot gas of galaxy clusters. Deep observations of blank fields resolved 25% of the diffuse background into discrete active galactic nuclei. The Einstein Observatory made unique contributions to the study of all classes of astronomical objects and paved the way for future, more powerful missions.