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X-ray Astronomy Satellites & Missions

We present here the many satellites which have detected electromagnetic radiation between 0.01 and 50 keV by the decade in which the satellite was launched. You will see, as you go through the 1960s, 70s, 80s, and 90s, that the sensitivity increase in the detectors has developed greatly during the over 30 years of X-ray astronomy. In addition, our ability to focus X-rays has developed enormously -- allowing us to obtain high-quality images of many fascinating celestial objects.

NOTE: We include here only missions which detected non-solar X-rays (intentionally or not).

Vela 5B
Vela 5B
Credit: NASA


The first satellite which detected cosmic X-rays (not to be confused with the first detection of cosmic X-rays!) was called the Third Orbiting Solar Observatory, or OSO-3. Even its name tells you that it was intended primarily to observe the Sun, which it did very well during its 2 year lifetime, but it also detected a flaring episode from the source Sco X-1 and it measured the diffuse cosmic X-ray background. In fact, none of the satellites launched in the 1960s were dedicated to cosmic X-ray astronomy... so all of the discoveries they made were just little gifts from the missions as they did their "real" jobs. For example, the Vela satellites were launched to watch for whether or not countries on Earth exploded any nuclear bombs in the atmosphere!

Vela 5B May 1969 - June 1979
Vela 5A May 1969 - 1979
OSO 5 January 1969 - July 1975
ESRO-2B May - December 1968
OGO 5 March 1968 - June 1971
OSO 4 October 1967 - December 1971
OSO 3 March 1967 - November 1969
Credit: NASA


The decade of the 1970s was a very busy one for X-ray astronomy. The first orbiting mission which was dedicated to celestial X-ray astronomy was Uhuru, launched in 1970. Uhuru had a simple complement of instrumentation covering the energy range 2-20 keV. It provided the first comprehensive view of the entire X-ray sky. The final catalog of point sources Uhuru detected contained 339 objects, which were primarily binary stellar systems, supernova remnants, Seyfert galaxies and clusters of galaxies.

Many important missions followed Uhuru in the 1970s, including ANS, Copernicus, SAS-3, Ariel V, and OSO 8. These missions discovered X-ray bursts, numerous pulsars, and obtained the first detailed X-ray spectra. Another great leap forward occurred in 1977 with the launch of NASA's first High Energy Astrophysical Observatory ( HEAO-1). HEAO-1 carried 4 major instruments, covering the energy band 0.2 keV to 10 MeV. It generated a catalog of approximately 850 point sources during its 18 month lifetime, allowed the first comprehensive measurement of the diffuse X-ray background, and performed time variability studies on millisecond time scales. This mission was followed by HEAO-2 (also known as the Einstein Observatory), which was the first mission to use grazing incidence focusing optics for celestial astronomy (which increased the detection sensitivity by a factor of nearly 1000!).

Ariel 6 June 1979 - February 1982
P78-1 February 1979 - September 1985
Hakucho February 1979 - 1984
HEAO 2 November 1978 - April 1981
Venera 12 September 1978 - April 1980
Venera 11 September 1978 - February 1980
ISEE-3 August 1978 - 1982
HEAO 1 August 1977 - January 1979
Apollo-Soyuz July 1975
OSO 8 June 1975 - September 1978
SAS 3 May 1975 - 1979
Aryabhata April 1975
Salyut-4 December 1974 - February 1977
Ariel 5 October 1974 - March 1980
ANS August 1974 - 1976
Skylab July - August 1973
Copernicus August 1972 - late 1980
TD-1A March 1972 - 1973
OSO 7 September 1971 - July 1974
Cosmos 428 June - July 1971
Uhuru December 1970 - March 1973
Vela 6A & 6B April 1970 - 1979
Credit: NASA


During the 1980s, as NASA struggled to recover from the Space Shuttle Challenger accident, the European, Japanese, and Russian Space Agencies continued to launch successful X-ray astronomy missions. In particular, this decade saw the launches of the European X-ray Observatory Satellite (EXOSAT), Granat, the Kvant module, Tenma, and Ginga. These missions were more modest in scale than the HEAO program in the 1970s, and were directed toward in-depth studies of known phenomena.

Granat December 1989 - November 1998
Phobos 2 July 1988 - March 1989
Phobos 1 July - September 1988
Kvant May 1987 - 2001
Ginga February 1987 - November 1991
Spacelab-2 July - August 1985
Spartan-1 June 1985
Spacelab-1 November - December 1983
EXOSAT May 1983 - April 1986
Astron March 1983 - June 1989
Tenma February 1983 - late 1984
Venera 14 November 1981 - March 1983
Venera 13 October 1981 - March 1983
Credit: NASA


In the 1990s the ROSAT survey detected more than 100,000 X-ray objects, the ASCA mission made the first sensitive measurements of the X-ray spectra from these objects, and RXTE studied their timing properties. These have been supplemented by a host of other missions, with other primary goals, but which contain instruments sensitive to high-energy cosmic radiation (such as Ulysses and Wind). Both individually and collectively, these satellites have provided an unprecedented view of the X-ray Universe. Satellites launched late in the decade, Chandra and XMM, had an order of magnitude improvement in sensitivity for imaging, and promise new and exciting breakthroughs in the journey of X-ray astronomy exploration.

XMM December 1999 -
Chandra August 1999 -
Beppo SAX April 1996 - April 2002
RXTE December 1995 -
Wind November 1994 -
ALEXIS April 1993 -
ASCA February 1993 - March 2001
DXS January 1993
EURECA August 1992 - July 1993
BBXRT December 1990
Ulysses October 1990 -
ROSAT June 1990 - February 1999
Credit: NASA


As the 21st century began, XMM-Newton, the Chandra X-ray Observatory, and RXTE were the work-horses of X-ray astronomy. In early 2000 X-ray astronomy suffered from the loss of Astro-E, which was to provide high resolution spectroscopy through innovative X-ray micro-calorimeters. But astronomers anticipated its replacement in Astro-E2 in the middle of the decade. Astronomers also looked forward to the useful data from the X-ray telescope aboard Swift.

(formerly Astro-E2)
July 2005 -

The Next Generation

Beyond 2010, NASA anticipates launching revolutionary missions to explore new frontiers in astronomy. The joint NASA-ESA Laser Interferometer SpaceAntenna (LISA) ( will detect and measure gravitational radiation from coalescing black holes, from stars being being ripped apart as they fall into a black hole, and from thousands of binary star systems in our Galaxy. Constellation-X ( will provide high resolution X-ray spectroscopy to probe matter as it falls into a black hole, as well as probe the nature of dark matter and dark energy by observing the formation of clusters of galaxies. All of this is part of NASA's Beyond Einstein ( program.

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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