View source for High Energy Astronomy Observatory 3

{{Infobox spaceflight
| name                  = HEAO-3
| image                 = File:HEAO-3_observatory_artist's_view_0102165.jpg
| image_caption         = 
| insignia              =

| mission_type          = Astronomy 
| operator              = [[NASA]] 
| website               = 
| COSPAR_ID             = 1979-082A
| SATCAT                = 11532
| mission_duration      =

| spacecraft_bus        = 
| manufacturer          = [[TRW Inc.|TRW]]
| dry_mass              = {{convert|2660.2|kg}}
| launch_mass           = 
| power                 =

| launch_date           = {{start-date|20 September 1979, 05:27:00}}&nbsp;UTC 
| launch_rocket         = [[Atlas-Centaur|Atlas SLV-3D Centaur-D1AR]]
| launch_site           = [[Cape Canaveral Air Force Station|Cape Canaveral]] [[Cape Canaveral Air Force Station Space Launch Complex 36|LC-36B]]
| launch_contractor     =

| decay_date            = {{end-date|7 December 1981}}

| orbit_epoch           = 
| orbit_reference       = [[geocentric orbit|Geocentric]]
| orbit_regime          = [[low Earth orbit|Low Earth]]
| orbit_periapsis       = {{convert|486.4|km}}
| orbit_apoapsis        = {{convert|504.9|km}}
| orbit_eccentricity    = 0.00134
| orbit_inclination     = 43.6°
| orbit_period          = 94.50 minutes
| apsis                 = gee
}}
[[Image:HEAO-3 diagram.gif|thumb|Diagram of HEAO 3 Satellite]]

The last of [[NASA|NASA's]] three [[HEAO Program|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&nbsp;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 {{convert|2660.0|kg|lb}}.<ref>{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1979-082A |title=NSSDC ID:1979-082A |access-date=2008-02-25}}</ref>

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 [[Atomic number|Z]] = 120 and measure the composition of the nuclei with Z >20.

==The Gamma-ray Line Spectrometer Experiment==
[[File:HEAO-C_in_clean_room.jpg|thumb|HEAO 3 in the clean room]]
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 spectroscopy#Semiconductor detectors|gamma-ray spectrometer]] was especially designed to search for the 511 keV [[gamma-ray]] line produced by the [[annihilation]] of [[positron]]s in stars, galaxies, and the [[interstellar medium]] (ISM), nuclear gamma-ray line emission expected from the interactions of [[cosmic ray]]s 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 [[germanium|Ge]] [[Gamma spectroscopy#Semiconductor detectors|gamma-ray detectors]] with a total volume of about 100&nbsp;cm<math>^3</math>, enclosed in a thick (6.6&nbsp;cm average) [[caesium]] iodide (CsI) [[scintillation counter|scintillation]] shield in active anti-coincidence<ref>L. E. Peterson, ''Instrumental Technique in X-Ray Astronomy'', in Annu. Rev. Astron. Astrophys. 13, 423 (1975)</ref> 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/cm<sup>2</sup>-s, depending on the energy.  Key experimental parameters were (1) a geometry factor of 11.1 cm<sup>2</sup>-sr, (2) effective area ~75&nbsp;cm<math>^2</math> at 100 keV, (3) a field of view of ~30 deg [[Full width at half maximum|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.<ref>Wheaton, W.A. et al., "The HEAO 3 Background: Spectrum Observed by a Large Germanium Spectrometer in Low Earth Orbit", in AIP conference Proceedings #186, ''High Energy Radiation Background in Space'',1987, Eds Rester & Trombka, p. 304-322.</ref><ref>{{cite web|url=http://heasarc.gsfc.nasa.gov/docs/heao3/heao3.html |title=The HEAO-3 Satellite |access-date=2007-12-07 |date=2003-06-26 |publisher=NASA/GSFC }}</ref>  The energy resolution of the Ge detectors was subject to degradation (roughly proportional to energy and time) due to radiation damage.<ref>Mahoney, W.A., Ling, J.C., and Jacobson, A.S. ''Nuc. Instr. & Meth.'',178:363,(1980)</ref>  The primary data are available at from the NASA HESARC<ref>{{cite web|url=http://heasarc.nasa.gov/docs/heao3/heao3.html |archive-url=https://web.archive.org/web/20040109191203/http://heasarc.nasa.gov/docs/heao3/heao3.html |url-status=dead |archive-date=2004-01-09 |title= HEAO 3}}</ref> 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.<ref>For more detailed information on the data base, contact Dr. James C. Ling, Mail Stop 169–337, JPL, 4800 Oak Grove Drive, Pasadena, Ca 91109</ref> 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]].

==The Isotopic Composition of Primary Cosmic Rays Experiment==
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 and [[hodoscope]]s, 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.<ref>Engelman et al. Astron. & Astrophys., v. 148, pp. 12–20, 1985</ref>

==The Heavy Nuclei Experiment==
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 cm<sup>2</sup>-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.  Binns ''et al.''<ref>W. R. Binns, et al., Nuc. Instr. and Meth., v. 185, pp. 415–426, 1981</ref> give more details.
The experiment was proposed and managed by the Space Radiation Laboratory of the [[California 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.

==Project==
The HEAO 3 Project was the final mission in the [[HEAO Program|High Energy Astronomy Observatory]] series, which was managed by the NASA [[Marshall Space Flight Center]] (MSFC), where the project scientist was Dr. Thomas A. Parnell, and the project manager was Dr. John F. Stone.  The [[Prime contractor (US Government)|prime contractor]] was [[TRW Inc.|TRW]].

==See also==
{{commons category|HEAO 3}}
{{Portal|Spaceflight}}
* [[HEAO Program]]
* [[High Energy Astronomy Observatory 1]]
* [[Einstein Observatory]] (HEAO 2)

==References==
{{Reflist}}

{{TRW}}
{{Space observatories}}
{{Orbital launches in 1979}}

{{Use dmy dates|date=July 2019}}

[[Category:1979 in spaceflight]]
[[Category:Gamma-ray telescopes]]
[[Category:Space telescopes]]
[[Category:X-ray telescopes]]
[[Category:Spacecraft launched in 1979]]