HEAO-3

Mission type	Astronomy
Operator	NASA
COSPAR ID	1979-082A
SATCATno.	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 CanaveralLC-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 ofNASA's threeHigh Energy Astronomy Observatories,HEAO 3 was launched 20 September 1979 on anAtlas-Centaur launch vehicle, into a nearly circular, 43.6 degree inclinationlow 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 acryogenic high-resolution germaniumgamma-ray spectrometer, and two devoted tocosmic-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 withatomic mass between 7 and 56, and the flux of each element withatomic number (Z) between Z = 4 and Z = 50;

(3) to search for super-heavy nuclei up toZ = 120 and measure the composition of the nuclei with Z >20.

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.Thegamma-ray spectrometer was especially designed to search for the 511 keVgamma-ray line produced by theannihilation ofpositrons in stars, galaxies, and theinterstellar medium (ISM), nuclear gamma-ray line emission expected from the interactions ofcosmic rays in the ISM, the radioactive products of cosmicnucleosynthesis, 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-purityGegamma-ray detectors with a total volume of about 100 cm${\displaystyle {}^3}$, enclosed in a thick (6.6 cm average)caesium iodide (CsI)scintillation shield in active anti-coincidence^[2] 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/cm²-s, depending on the energy. Key experimental parameters were (1) a geometry factor of 11.1 cm²-sr, (2) effective area ~75 cm${\displaystyle {}^2}$ at 100 keV, (3) a field of view of ~30 degFWHM 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 itscryogen was exhausted.^[3][4] The energy resolution of the Ge detectors was subject to degradation (roughly proportional to energy and time) due to radiation damage.^[5] The primary data are available at from the NASA HESARC^[6] 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.^[7] The experiment was proposed, developed, and managed by theJet Propulsion Laboratory of the California Institute of Technology, under the direction of Dr.Allan S. Jacobson.

The HEAO C-2 experiment measured the relative composition of the isotopes of the primary cosmic rays between beryllium and iron (Z from 4 to 26) and the elemental abundances up to tin (Z=50). Cerenkov counters andhodoscopes, together with the Earth's magnetic field, formed a spectrometer. They determined charge and mass of cosmic rays to a precision of 10% for the most abundant elements over the momentum range from 2 to 25 GeV/c (c=speed of light). Scientific direction was by Principal Investigators Prof. Bernard Peters and Dr. Lyoie Koch-Miramond. The primary data base has been archived at the Centre Etudes Nuclearires de Saclay and the Danish Space Research Institute. Information on the data products is given by Engelman et al. 1985.^[8]

The purpose of the HEAO C-3 experiment was to measure the charge spectrum of cosmic-ray nuclei over the nuclear charge (Z) range from 17 to 120, in the energy interval 0.3 to 10 GeV/nucleon; to characterize cosmic ray sources; processes of nucleosynthesis, and propagation modes. The detector consisted of a double-ended instrument of upper and lower hodoscopes and three dual-gap ion chambers. The two ends were separated by a Cerenkov radiator. The geometrical factor was 4 cm²-sr. The ion chambers could resolve charge to 0.24 charge units at low energy and 0.39 charge units at high energy and high Z. The Cerenkov counter could resolve 0.3 to 0.4 charge units. Binnset al.^[9] give more details.The experiment was proposed and managed by theSpace Radiation Laboratory of theCalifornia Institute of Technology (Caltech), under the direction of Principal Investigator Prof.Edward C. Stone, Jr. of Caltech, and Dr. Martin H. Israel, and Dr. Cecil J. Waddington.

The HEAO 3 Project was the final mission in theHigh Energy Astronomy Observatory series, which was managed by the NASAMarshall Space Flight Center (MSFC), where the project scientist was Dr. Thomas A. Parnell, and the project manager was Dr. John F. Stone. Theprime contractor wasTRW.

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• HEAO Program
• High Energy Astronomy Observatory 1
• Einstein Observatory (HEAO 2)

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• Gamma-ray telescopes
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