High Energy Astrophysical Observatory (HEAO)

Series of three NASA orbital observatories. HEAO-1, launched in August 1977, successfully completed the most accurate all-sky survey of x-ray sources up to that time. Discovered the `Cygnus Superbubble' created by a series of supernovae. HEAO-2 (later known as EINSTEIN), launched in 1978, was the first true x-ray astronomy satellite. HEAO-3, launched in September 1979, carried a gamma ray spectro...