Imagine the Universe!

Satellite Showcase


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).

Imagine the Universe is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

The Imagine Team
Acting Project Leader: Dr. Barbara Mattson
All material on this site has been created and updated between 1997-2012.

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