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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.
Nation: USA
Type / Application: Astronomy, X-Ray, Gamma
Operator: NASA
Contractors: TRW
Configuration: HEAO Bus
Power: Solar cells, batteries
Mass: 2720 kg
Orbit: 428 km × 447 km, 22.7
Satellite COSPAR Date LS Launch Vehicle Remarks
HEAO 1 1977-075A 12.08.1977 CC LC-36B Atlas-SLV3D Centaur-D1AR


  • NSSDC Master Catalog: HEAO 1
Further HEAO missions: