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Showcase COS-B


The Mission

COS-B was launched on 9 August 1975 into an orbit of ~100,000 km, with a period of 37 hours. The orbital plane was inclined at ~90 deg to the Earth's equator. The satellite spun on its axis at a rate of ~10 rpm. Sun and Earth sensors were used for attitude measurements from which the pointing direction could be determined with a precision of about 0.5 deg. The timing accuracy was 0.5 ms or better. The satellite was operated in a pointing mode with its spin axis directed towards fixed points in the sky for periods of four to five weeks early in the mission and up to 3 months in later observations. In total, 64 observations (or pointings) were made. The mission ended on 25 April 1982.

artist concept of COS-B in orbit
Credit: NASA

The Instrumentation

The experiment consisted of a spark chamber, triggered by a scintillation counter telescope. Beneath the telescope was an energy calorimeter which absorbed the secondary particles produced by the incident photons. The detector could detect gamma-rays in the energy range of 30 MeV to 4 GeV. The experiment is described in detail by Bignami et al. (1975).

Alongside the gamma-ray detector was mounted a proportional counter, sensitive to 2-12 keV X-rays. This detector was intended to provide synchronization for possible short-period pulsations of gamma-ray emission from pulsating X-ray sources. The pulsar synchronizer was also used for monitoring the intensity of radiation from X-ray sources.

The Science Results

The scientific objectives of COS-B were to study the sources of extra-terrestrial gamma radiation at energies above ~30 MeV. Specifically, the mission was to

Study the spectrum and distribution of galactic gamma-rays
Determine the flux and distribution of extragalactic gamma-ray emission
Study known point sources
Search for new point sources.

The results of COS-B observations of extragalactic gamma-rays, resolved galactic sources, gamma-ray pulsars, binary systems, large-scale galactic emission, and localized gamma-ray sources allowed the field of gamma-ray astronomy to move from the "discovery" phase into the "exploration" phase. Truly, a valuable new window into our Universe had been opened.

Additional References

K. Bennett, Nuclear Physics B (Proc. Suppl) 14B (1990) 23-34.

G.F. Bignami, Space Sci. Instr. 1 (1975) 245.

Much of the information found here was condensed from "COS-B: The Highlights" (Bennett 1990).


A service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA/GSFC

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