HEAO Program

The High Energy Astronomy Observatory Program was a NASA program of the late 1970s and early 1980s that included a series of three large low-Earth-orbiting spacecraft for X-ray and Gamma-Ray astronomy and Cosmic-Ray investigations. After launch, they were denoted HEAO 1, HEAO 2 (also known as The Einstein Observatory), and HEAO 3, respectively. The large (~3000 kg) satellites were 3-axis stabilized to arc-minute accuracy, with fixed solar panels. All three observatories were launched from Cape Canaveral, Florida on Atlas-Centaur SLV-3D launch vehicles into near-circular orbits with initial altitudes slightly above 500 km.

HEAO 1, launched August 12, 1977, was a sky survey mission that included four large X-ray and gamma-ray astronomy instruments, known as A1, A2, A3, and A4, respectively. Inclination was about 22.7 degrees. It re-entered the Earth's atmosphere and burned up on March 15, 1979.

HEAO 2, more commonly known as the Einstein Observatory, launched 13 November 1978 into a 23.5 deg inclination orbit. It carried a single large grazing-incidence focusing X-ray telescope, providing unprecedented levels of sensitivity (hundreds of times better than previously achieved) and arc-second angular resolution for pointed observations of known objects, and operated over the 0.2 to 3.5 keV energy range. HEAO 2 differed from HEAO 1 and HEAO 3 in that it was used for pointed, deep, small-field-of-view observations rather than sky-survey studies.

A suite of four focal plane instruments were provided:

as well as a 1-20 keV Monitor Proportional Counter (MPC), a Broad Band Filter Spectrometer (BBFS), and an objective grating spectrometer (OGS). The observatory re-entered the Earth's atmosphere and burned up on March 25, 1982.

HEAO 3, launched on 20 September 1979 into a 43.6-degree inclination orbit, carried three experiments, known as C1, C2, and C3. The first was a cryogenically cooled germanium (Ge) high-resolution gamma-ray spectrometer, while the C2 and C3 experiments were large cosmic-ray instruments. The satellite re-entered the Earth's atmosphere and burned up on December 7, 1981.

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