High Energy Astronomy Observatory 3
HEAO 3
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| 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 |
| Perigee | 486.4 kilometres (302.2 mi) |
| Apogee | 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 perigee 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:
The HEAO "C-1" instrument (as it was known before launch) was a sky-survey experiment, operating in the hard X-ray and low-energy gamma-ray bands. The gamma-ray spectrometer was especially designed to search for the 511 keV gamma-ray line produced by the annihilation of positrons in stars, galaxies, and the interstellar medium (ISM), nuclear gamma-ray line emission expected from the interactions of cosmic rays in the ISM, the radioactive products of cosmic nucleosynthesis, and nuclear reactions due to low-energy cosmic rays. In addition, careful study was made of the spectral and time variations of known hard X-ray sources.
The experimental package contained four cooled, p-type high-purity Ge gamma-ray detectors with a total volume of about 100 cm, enclosed in a thick (6.6 cm average) caesium iodide (CsI) scintillation shield in active anti-coincidence to suppress extraneous background. The experiment was capable of measuring gamma-ray energies falling within the energy interval from 0.045 to 10 MeV. The Ge detector system had an initial energy resolution better than 2.5 keV at 1.33 MeV and a line sensitivity from 1.E-4 to 1.E-5 photons/sq cm-s, depending on the energy. Key experimental parameters were (1) a geometry factor of 11.1 sq cm-sr, (2) effective area ~75 cm at 100 keV, (3) a field of view of ~30 deg FWHM at 45 keV, and (4) a time resolution of less than 0.1 ms for the germanium detectors and 10 s for the CsI detectors. The gamma-ray spectrometer operated until 1 June 1980, when its cryogen was exhausted. The energy resolution of the Ge detectors was subject to degradation (roughly proportional to energy and time) due to radiation damage. The primary data are available at from the NASA HESARC and at JPL. They include instrument, orbit, and aspect data plus some spacecraft housekeeping information on 1600-bpi binary tapes. Some of this material has subsequently been archived on more modern media. The experiment was proposed, developed, and managed by the Jet Propulsion Laboratory of the California Institute of Technology, under the direction of Dr. Allan S. Jacobson.
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