Heao-A

The NASA High Energy Astronomy Observatories (HEAOs) are described along with the capabilities of and the operational plans for HEAO-A. Detailed attention is given to the large-area X-ray array; the X-ray background survey instrument and its low-, medium-, and high-energy detectors; the scanning modulation collimator; and the hard X-ray/low-energy gamma-ray instrument. It is noted that HEAO-A is limited in life to one year and fairly restricted in its pointed-mode capabilities, but is well adapted for studies on every variational time scale, can provide accurate positions for a large set of stronger sources and extragalactic objects, should accurately define the spectral shape of the diffuse background over the range of greatest curvature, and should detect line emission with high sensitivity in extragalactic sources.