TIMELINE OF EARTH SCIENCE SATELLITES By vinsond Feb 1, 1958 Explorer 1; US; Decayed 31 May 1970. Discovered Van Allen belts Period: Feb 1, 1958 to Dec 16, 1962 Timeline of EARTH SCIENCE SATELLITES Mar 5, 1958 Explorer 2; US, Failed to orbit Mar 17, 1958 Vanguard I, US Oldest artificial satellite in orbit Mar 26, 1958 Explorer 3; US; Decayed 28 June 1958 Apr 27, 1958 Sputnik; Soviet Union; Fail to orbit Jul 26, 1958 Explorer 4; US; Measured electrons & protons in radiation belts. Also measured data on Operation Argus nuclear explosion Feb 17, 1959 Vanguard II; US; Still in Orbit Aug 7, 1959 Explorer 6; US; Decayed 1 July 1961 Sep 18, 1959 Vanguard III; US; Still in orbit Apr 27, 1961 Explorer 11; US; Still in orbit Apr 16, 1962 Explorer 900;US; Still in orbit Apr 24, 1962 Kosmos 3; Soviet Union; Still in orbit Oct 27, 1962 Explorer 15; US; Still in orbit