High Energy Astronomy Observatory 3
| Mission type | Astronomy |
|---|---|
| Operator | NASA |
| COSPAR ID | 1979-082A |
| SATCAT no. | 11532 |
| Spacecraft properties | |
| Manufacturer | TRW |
| Dry mass | 2,660.2 kilograms (5,865 lb) |
| Start of mission | |
| Launch date | 20 September 1979, 05:27:00 UTC |
| Rocket | Atlas SLV-3D Centaur-D1AR |
| Launch site | Cape Canaveral LC-36B |
| End of mission | |
| Decay date | 7 December 1981 |
| Orbital parameters | |
| Reference system | Geocentric |
| Regime | Low Earth |
| Eccentricity | 0.00134 |
| Perigee altitude | 486.4 kilometres (302.2 mi) |
| Apogee altitude | 504.9 kilometres (313.7 mi) |
| Inclination | 43.6° |
| Period | 94.50 minutes |
The last of NASA's three High Energy Astronomy Observatories, HEAO 3 was launched 20 September 1979 on an Atlas-Centaur launch vehicle, into a nearly circular, 43.6 degree inclination low Earth orbit with an initial perigeum of 486.4 km. The normal operating mode was a continuous celestial scan, spinning approximately once every 20 min about the spacecraft z-axis, which was nominally pointed at the Sun. Total mass of the observatory at launch was 2,660.0 kilograms (5,864.3 lb).
HEAO 3 included three scientific instruments: the first a cryogenic high-resolution germanium gamma-ray spectrometer, and two devoted to cosmic-ray observations. The scientific objectives of the mission's three experiments were:
- (1) to study intensity, spectrum, and time behavior of X-ray and gamma-ray sources between 0.06 and 10 MeV; measure isotropy of the diffuse X-ray and gamma-ray background; and perform an exploratory search for X-and gamma-ray line emissions;
- (2) to determine the isotopic composition of the most abundant components of the cosmic-ray flux with atomic mass between 7 and 56, and the flux of each element with atomic number (Z) between Z = 4 and Z = 50;
- (3) to search for super-heavy nuclei up to Z = 120 and measure the composition of the nuclei with Z >20.