|Mission type||Space Physics|
|Mission duration||~4 months|
|Launch mass||37.6 kilograms (83 lb)|
|Dry mass||37.6 kilograms (83 lb)|
|Start of mission|
|Launch date||16 August 1961, 23:21UTC|
|Launch site||Cape Canaveral LC-17B|
|End of mission|
|Last contact||6 December 1961|
|Decay date||1 September 1963|
|Perigee altitude||790 kilometers (490 mi)|
|Apogee altitude||77,620 kilometers (48,230 mi)|
Explorer 12 (also known as S3) was a United States Satellite built to measure the solar wind, cosmic rays, and the earth's magnetic field. It was launched on August 16, 1961, aboard a Thor-Delta booster. Explorer 12 was the first of three S3 series spacecraft. It ceased transmitting on December 6 due to power failure.
Explorer 12 was designed to study space physics, and so had a multitude of instruments including a cosmic-ray detector, a particle trapper, and a magnetometer. Good data was recorded for 90% of the mission.
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