High Energy Astronomy Observatory 3

HEAO-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 (1979-09-20UTC05:27) UTC
Rocket	Atlas SLV-3D Centaur-D1AR
Launch site	Cape Canaveral LC-36B
End of mission
Decay date	7 December 1981 (1981-12-08)
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).^[1]

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.