Explorer 11

Explorer 11 (also known as S15) was the orbital spacecraft that carried the first gamma ray telescope. This was the earliest beginnings of gamma-ray astronomy. Launched on April 27, 1961 by a Juno II rocket the satellite returned data until November 17, when power supply problems ended the science mission. During the spacecraft's seven month lifespan it detected twenty-two events from gamma-rays and approximately 22,000 events from cosmic radiation.

The telescope used a combination of a sandwich scintillator detector along with a Cherenkov counter to measure direction of events. Since the telescope could not be aimed the spacecraft was set in an end over end tumble to give a rough scan of the celestial sphere, with emphasis on the galactic plane, the Galactic Center, the Sun, and other known radio noise sources.

The gamma-ray events observed by Explorer 11 seemed to suggest a random distribution 'background' of gamma-rays. Later telescopes observed point sources in addition to the background noise of gamma-rays.

External links

* [http://library01.gsfc.nasa.gov/cgi-bin/gdprojs/searchAlpha.pl?letter=E Goddard Project Historical Missions]
* [http://legacy.gsfc.nasa.gov/docs/heasarc/missions/explorer11.html Explorer 11]
* [http://nssdc.gsfc.nasa.gov/database/MasterCatalog?sc=1961-013A S15]
* [http://www.friends-partners.org/partners/mwade/lvs/junoii.htm Juno II]
* [http://legacy.gsfc.nasa.gov/Images/explorer/explorer-11_small.gifGIF image]