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Orbiting Solar Observatory Series

Orbiting Solar Observatory Series

The OSO-3 satellite under construction

The OSO-3 satellite under construction (Credit: Ball Aerospace)

An artist's impression of the OSO-8 satellite in space

An artist's impression of the OSO-8 satellite in space. (Credit: NASA)

The Orbiting Solar Observatory, or OSO for short, Program was a series of scientific satellites which were primarily intended to study the Sun over its 11-year cycle. Eight nearly identical satellites were successfully launched between 1962 and 1975.

Lifetime: March 1962 (first launch, OSO-1) - October 1978 (last satellite, OSO-8, ceases operation)

Portion(s) of spectrum studied: ultraviolet, X-ray, gamma ray (

Country (primary): United States

Primary Science

The OSO satellites were designed to study the Sun in ultraviolet and X-ray light through an 11-year cycle. In particular, they were designed to measure the solar electromagnetic radiation ultraviolet, X-ray and gamma ray.


Each satellite carried a slightly different payload with some combination of ultraviolet, X-ray and gamma-ray spectral capabilities. Use the links from each spacecraft listed below to read about the specific instruments in more detail.


Lifetime: March 1962 - August 1963

Science Highlights

  • Measured extraterrestrial gamma-ray flux between 0.5 and 3.0 MeV

Links to more information


Lifetime: March 1962 - November 1969

Science Highlights

  • First definitive observation of high-energy cosmic gamma rays from both galactic and extragalactic sources.
  • Sky survey showing the celestial distribution of gamma-rays is anisotropic with a cncentration along the galacic equator.
  • Diffuse cosmic X-ray background emission
  • X-ray flare from Scorpius X-1

Links to more information


Lifetime: October 1967 - December 1971

Links to more information


Lifetime: January 1969 - July 1975

Science Highlights

  • Spectrum of the X-ray diffuse background in the 14-200 keV range.

Links to more information


Lifetime: August 1969 - January 1972

Science Highlights

  • Discovered three hard X-ray events coincident with known gamma-ray bursts

Links to more information


Lifetime: September 1971 - July 1974

Science Highlights

  • X-ray all-sky survey.
  • Discovery of 9-day periodicity in Vela X-1, leading to its identification as a high-mass X-ray binary.
  • Gamma-ray observations of solar flares.

Links to more information


Lifetime: June 1975 - October 1978

Science Highlights

  • Detection of an iron lin in the spectrum of a cluster of galaxies.
  • Detection of a black-body spectrum from X-ray bursts.

Links to more information


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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