The first of NASA's
three High Energy Astronomy Observatories, HEAO 1
, launched August 12, 1977 aboard an Atlas rocket
with a Centaur
upper stage, operated until 9 January 1979
. During that time, it scanned the X-ray
sky almost three times over 0.2 keV - 10 MeV, provided nearly constant monitoring of X-ray sources near the ecliptic poles, as well as more detailed studies of a number of objects through pointed observations.
HEAO included four large X-ray and gamma-ray astronomy instruments, known as A1, A2, A3, and A4, respectively (before launch, HEAO 1 was known as "HEAO A"). Inclination was about 22.7 degrees. It re-entered 15 March, 1979.
- The A1, or Large-Area Sky Survey (LASS) instrument, was managed by the Naval Research Laboratory and used large proportional counters to cover the 0.25 to 25 keV energy range.
- The A2, or Cosmic X-ray Experiment (CXE), from the Goddard Space Flight Center, covered the 2-60 keV energy range with high spatial and spectral resolution.
- The A3, or Modulation Collimator (MC) instrument, provided high-precision positions of X-ray sources, accurate enough to permit follow-up observations to identify optical and radio counterparts. It was provided by the Center for Astrophysics (Smithsonian Astrophysical Observatory and the Harvard College Observatory, SAO/HCO).
- The A4, Hard X-ray / Low Energy Gamma-ray experiment, used scintillation counters to cover the energy range from about about 20 keV to 10 MeV. It was provided and managed by the University of California at San Diego, in collaboration with MIT.