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Large Area Cosmic X-Ray Survey (A-1)

NSSDCA ID: 1977-075A-01

Mission Name: HEAO 1
Principal Investigator:Dr. Herbert D. Friedman


This instrument was a modular assembly of seven large-area, thin-window, proportional counter sensor modules to record incident X-ray fluxes. The objectives were to map the celestial sphere in the energy range from .15 to 20 keV with greater sensitivity than achieved previously, and to measure the spectra, location, and time variations of X-ray sources with a 0.1- to 1-deg angular resolution. Each of the sensor modules consisted of a proportional counter body frame on which was mounted a window support structure, counter back structure with integral control counter, collimator assembly, and electronic subassemblies. A honeycomb cell construction for the basic counter provided X-ray collimation of 80-deg by 4-deg FWHM. A back layer of the three-layered counter provided anticoincident protection against charged particle events. The front layer was the main X-ray sensor for most of the energy ranges. The collimator for each of the counters viewed the sky. The collimator on sensor modules 1 through 4 provided 1-deg by 4-deg FWHM FOV, on sensor modules 5 and 6 provided 1-deg by 0.5-deg FWHM FOV, and on sensor module 7 provided 8-deg by 2-deg FWHM FOV. Each of the sensors included movable radioactive calibration sources to provide a check on counter operation and channel position. There was also a magnet assembly to deflect low-energy radiation belt electrons. The control counter was a small counter at the back of the assembly that shared the counting gas with the main counter. It was excited by an Fe 55 source and served to generate the proper operating voltage on the main counter to compensate for gas density changes and high-voltage drifts. For more details, see H. Friedman, Proc. Roy. Soc. Lon., v. A 366, p. 423, 1979.

Alternate Names

  • Large Area X-Ray Survey Experiment

Facts in Brief

Mass: 450 kg
Power (avg): 22.4 W

Funding Agency

  • NASA-Office of Space Science (United States)


  • Astronomy: X-Ray

Additional Information

Questions and comments about this experiment can be directed to: Dr. Cynthia Y. Cheung



NameRoleOriginal AffiliationE-mail
Dr. Herbert D. FriedmanPrincipal InvestigatorUS Naval Research Laboratory
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