HEAO 1 (High-Energy Astronomy Observatory 1) was the first in a series of three
satellite observatories designed to continue the X-ray and gamma-ray studies initiated by ANS, OAO 3, UK 5, the
OSO series, the SAS series, and
the gamma-ray burst discoveries of the Vela satellites.
This mission was specifically designed to map and survey the celestial sphere for X-ray
and gamma-ray sources in the energy range of 150 eV to 10 MeV, to establish the size and
precise location of X-ray sources to determine the contribution of discrete sources to the
X-ray background, and to measure time variations of X-ray sources.
This observatory consisted of a common spacecraft equipment module (SEM), which carried
most of the spacecraft operational equipment, and a unique experiment module (EM), which
carried some elements of the electrical distribution system in addition to the four
experiments: Large Area X-ray Survey, Cosmic X-ray Background Experiment, Scanning
Modulation Collimator, and Hard X-ray and Low Energy Gamma-Ray Experiment.
Continuous celestial scans were made perpendicular to the satellite-sun vector during
the initial phase of the mission. Scan rate was 0.03 rpm. The entire celestial sphere
would be scanned in 6 months. When passing over the South Atlantic Anomaly (SAA) of the
inner Van Allen Belt, high-voltage supplies were turned off or reduced to prevent damage
caused by saturation effects.
The six-sided HEAO 1 was 5.68 m high and 2.67 m in diameter, and weighed 2552 kg,
which included 1220 kg experiments. Downlink telemetry was at a data rate of 6.5 kb/s for
real-time data and 128 kb/s for either of the two tape recorder systems. The mission
lifetime was 12 August 1977, to 9 January 1979.
HEAO 1 featured following instruments:
- Large Area Sky Survey experiment (LASS) - covered the energy range 0.25 to 25.0 keV.
- Cosmic X-ray Experiment (CXE) - designed to study the large scale structure of the
galaxy and the universe, yielding high quality spatial and spectral data over the energy
range 2-60 keV.
- Modulation Collimator (MC) - designed to measure positions of X-ray sources with
sufficient precision to identify optical and/or radio counterparts;
- Hard X-Ray / Low Energy Gamma Ray Experiment.
