The timeline of first Earth observation satellites shows, in chronological order, those successful Earth observation satellites, that is, Earth satellites with a program of Earth science. Sputnik 1, while the first satellite ever launched, did not conduct Earth science. Explorer 1 was the first satellite to make an Earth science discovery when it found the Van Allen belts.
| Satellite | Country | Date | Organisation | Notes |
|---|---|---|---|---|
| Sputnik 2 | Soviet Union | 3 November 1957[1] | Korolev Design Bureau | Researched charged particles near Earth |
| Explorer 1 | United States | 1 February 1958 | U.S. Army Ballistic Missile Agency | Decayed 31 May 1970. Discovered Van Allen belts. |
| Explorer 2 | United States | 5 March 1958 | U.S. Army Ballistic Missile Agency | Failed to orbit. |
| Vanguard 1 | United States | 17 March 1958 | U.S. Naval Research Laboratory | Oldest artificial satellite in orbit, along with its upper stage. |
| Explorer 3 | United States | 26 March 1958 | U.S. Army Ballistic Missile Agency | Decayed 28 June 1958. |
| Vanguard TV-5 | United States | 29 April 1958 | U.S. Naval Research Laboratory | Failed to orbit. |
| Sputnik 3 | Soviet Union | 15 May 1958 | Korolev Design Bureau | Decayed 6 April 1960. |
| Vanguard SLV-1 | United States | 28 May 1958 | U.S. Naval Research Laboratory | Failed to orbit. |
| Vanguard SLV-2 | United States | 26 June 1958 | U.S. Naval Research Laboratory | Failed to orbit. |
| Explorer 4 | United States | 26 July 1958 | U.S. DARPA | Measured electrons & protons in radiation belts. Also measured data on Operation Argus nuclear explosions. |
| Explorer 5 | United States | 24 August 1958 | U.S. DARPA | Failed to orbit. |
| Vanguard SLV-3 | United States | 26 September 1958 | U.S. Naval Research Laboratory | Failed to orbit. |
| Beacon 1 | United States | 23 October 1958 | NASA/U.S. Army | Failed to orbit. |
| Vanguard II | United States | 17 February 1959 | NASA/U.S. Naval Research Laboratory | Still in orbit. |
| Vanguard SLV-5 | United States | 14 April 1959 | NASA | Failed to orbit. |
| Vanguard SLV-6 | United States | 22 June 1959 | NASA | Failed to orbit. |
| Explorer S-1 | United States | 16 July 1959 | NASA | Failed to orbit. |
| Explorer 6 | United States | 7 August 1959 | Jet Propulsion Laboratory | Decayed 1 July 1961. |
| Beacon 2 | United States | 15 August 1959 | NASA/U.S. Navy | Failed to orbit. |
| Vanguard III | United States | 18 September 1959 | U.S. Naval Research Laboratory | Still in orbit. |
| Explorer 7 | United States | 13 October 1959 | NASA | Still in orbit. |
| Satellite | Country | Date | Organisation | Notes |
|---|---|---|---|---|
| Explorer 8 | United States | 3 November 1960 | Jet Propulsion Laboratory | Ionospheric studies; decayed from orbit on 28 March 2012. |
| Explorer 9 | United States | 16 February 1961 | Langley Research Center (NASA) | Thermosphere and exosphere studies; decayed from orbit on 9 April 1964. |
| Explorer S-56a | United States | 25 February 1961 | ||
| Explorer 10 | United States | 25 March 1961 | NASA | Magnetic field and plasma studies; decayed from orbit on June 1, 1968. |
| Explorer 11 | United States | 27 April 1961 | NASA | Gamma ray detection |
| Explorer 12 | United States | 16 August 1961 | NASA | Solar wind, cosmic ray and magnetic field studies |
| Explorer 13 | United States | 25 August 1961 | ||
| Kosmos 3 | Soviet Union | 24 April 1962 | Decayed from orbit on 17 October 1962. | |
| Ariel 1 | United Kingdom | 26 April 1962 | NASA-SERC | Ionospheric studies; decayed from orbit on 24 May 1976. |
| Kosmos 5 | Soviet Union | 28 May 1962 | ||
| Kosmos 8 | Soviet Union | 18 August 1968 | Micrometeoroid detection; discovered meteoroid flux | |
| Alouette 1 | Canada | 29 September 1962 | DRDC | Ionospheric studies |
| TAVE | United States | 29 September 1962 | ||
| Explorer 14 | United States | 2 October 1962 | NASA | Particle and field detection |
| Explorer 15 | United States | 27 October 1962 | NASA | |
| Explorer 900 | United States | 16 December 1962 |