3rd High Energy Astronomy Observatory
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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 . HEAO 3 included three scientific instruments: the first a
cryogenic In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th IIR International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of “cryogenics” and “cr ...
high-resolution germanium gamma-ray spectrometer, and two devoted to
cosmic-ray Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...
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.


The Gamma-ray Line Spectrometer Experiment

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
positron The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. It has an electric charge of +1 '' e'', a spin of 1/2 (the same as the electron), and the same mass as an electron. When a positron collides ...
s in stars, galaxies, and the
interstellar medium In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstella ...
(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^3, enclosed in a thick (6.6 cm average)
caesium Caesium (IUPAC spelling) (or cesium in American English) is a chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of , which makes it one of only five elemental metals that a ...
iodide (CsI)
scintillation Scintillation can refer to: *Scintillation (astronomy), atmospheric effects which influence astronomical observations *Interplanetary scintillation, fluctuations of radio waves caused by the solar wind *Scintillation (physics), a flash of light pro ...
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/cm2-s, depending on the energy. Key experimental parameters were (1) a geometry factor of 11.1 cm2-sr, (2) effective area ~75 cm^2 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.


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 hodoscopes, 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.


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 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. Binns ''et al.''W. R. Binns, et al., Nuc. Instr. and Meth., v. 185, pp. 415–426, 1981 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 Edward Carroll Stone (born January 23, 1936) is an American space scientist, professor of physics at the California Institute of Technology, and former director of the NASA Jet Propulsion Laboratory (JPL). Biography Stone was born in Knoxvil ...
, Jr. of Caltech, and Dr. Martin H. Israel, and Dr. Cecil J. Waddington.


Project

The HEAO 3 Project was the final mission in the High Energy Astronomy Observatory series, which was managed by the NASA
Marshall Space Flight Center The George C. Marshall Space Flight Center (MSFC), located in Redstone Arsenal, Alabama (Huntsville postal address), is the U.S. government's civilian rocketry and spacecraft propulsion research center. As the largest NASA center, MSFC's first ...
(MSFC), where the project scientist was Dr. Thomas A. Parnell, and the project manager was Dr. John F. Stone. The prime contractor was TRW.


See also

* HEAO Program *
High Energy Astronomy Observatory 1 HEAO-1 was an X-ray telescope launched in 1977. HEAO-1 surveyed the sky in the X-ray portion of the electromagnetic spectrum (0.2 keV – 10 MeV), providing nearly constant monitoring of X-ray sources near the ecliptic poles and more detailed stu ...
*
Einstein Observatory Einstein Observatory (HEAO-2) was the first fully imaging X-ray telescope put into space and the second of NASA's three High Energy Astrophysical Observatories. Named HEAO B before launch, the observatory's name was changed to honor Albert E ...
(HEAO 2)


References

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