One of the longest programs in history provided America with it's first satellite. From late January 1958 to October 1981 there were 59 missions designated "Explorer". The missions were not ALL Earth orbital and had many and various tasks assigned to them.
Mind you, NASA did not exist when that first flight took place.
Hence, the numbering system for the "Explorer" missions is not confirmed. In addition, flights involving international co-operation were not designated with the name "Explorer".
What follows is a list of those craft that WERE designated "Explorer", their launch date, and their purpose or result.
NOTE : Interspersed within the chronology are other significant achievements in spaceflight to add some "colour" to this otherwise droll listing!
Explorer 1
31 January 1958
1st US satellite, discovered Van Allen radiation belt
[img width= height=]http://www.hq.nasa.gov/office/pao/History/sputnik/exlaunch1958.jpg[/img]
Launch of America's first space craft
Explorer 2
5 March 1958
Failed to reach orbit, booster failure
Explorer 3
26 March 1958
Study of radiation belt
Explorer 4
26 July 1958
Spatial study of Argus radiation
Explorer 5
24 August 1958
Failed to reach orbit, booster failure
Explorer 6
7 August 1959
Magnetosphere studies
Explorer 7
13 October 1959
Micrometeoroid studies
Explorer 8
3 November 1960
Study of ionospheric composition
Explorer 9
16 February 1961
Study of upper thermosphere and lower exosphere
Explorer 10
25 February 1961
Study of interplanetary magnetic field near Earth
12 APRIL 1961 : YURI GAGARIN BECOMES FIRST MAN IN SPACE
Explorer 11
27 April 1961
Gamma ray study
Explorer 12
16 August 1961
Magnetospheric studies
Explorer 13
25 August 1961
Micrometeoroid studies
20 FEBRUARY 1962 : JOHN GLENN IS FIRST AMERICAN IN ORBIT
Explorer 14
2 October 1962
Study of charged particles and magnetic fields
Explorer 15
27 October 1962
Study of enhanced radiation belt
Explorer 16
16 December 1962
Micrometeoroid study
Explorer 17
3 April 1963
Global atmospheric physics mission
16 MAY 1963 : FINAL MERCURY MISSION SPLASHED DOWN
Explorer 18 (Interplanetary Monitoring Platform; IMP)
26 November 1963
Charged particles and magnetic fields in cislunar space
Explorer 19
19 December 1963
Air density of upper atmosphere
Explorer 20
25 August 1964
Probe of topside of the ionosphere
Explorer 21 (IMP-2)
4 October 1964
Magnetic fields reaction to solar plasma and solar wind
12 OCTOBER 1964 : USSR LAUNCHES 1ST 3-MAN MISSION
Explorer 22 (Beacon Explorer; BE)
9 October 1964
Ionospheric and geodetic research
Explorer 23
6 November 1964
Micrometeoroid penetration
Explorer 24
21 November 1964
Radiation air density studies in upper atmosphere
Explorer 25
21 November 1964
Same as Explorer 24
Explorer 26
21 December 1964
High-energy particle study
18 MARCH 1965 : ALEXEI LEONOV FIRST MAN TO WALK IN SPACE
Explorer 27 (BE-2)
29 April 1965
Variations in electron density and orbital perturbations
Explorer 28 (IMP-3)
29 May 1965
Earth magnetosphere research
Explorer 29 (GEOS-1)
6 November 65
Part of US Geodetic satellite program, studied gravitational field
Explorer 30 (Solrad-1)
19 November 1965
Monitored solar x-rays
Explorer 31 (Direct Measurements Satellite; DME)
29 November 1965
Sounded the topside of the ionosphere
Explorer 32
25 May 1966
Structure & phyics of the upper atmosphere
Explorer 33 (IMP-4)
1 July 1966
Solar plasma and magnetic fields
27 JANUARY 1967 : APOLLO 1 CREW LOST IN PAD FIRE AT KSC
Explorer 34 (IMP-5)
24 May 1967
Solar & galactic radiation, solar plasma
Explorer 35 (IMP-6)
19 July 1967
Solar plasma flux measured from Lunar orbit
Explorer 36 (GEOS-2)
11 January 1968
Same as Explorer 29
Explorer 37 (Solrad-2)
5 March 1968
Monitored Solar X-ray emissions
Explorer 38 (Radio Asytonomy Explorer; RAE)
4 July 1968
Monitored low-frequency cosmic radio noise
Explorer 39
8 August 1968
Radio beacon study of solar radiation in upper atmosphere
Explorer 40
8 August 1968
Same as Explorer 39
Explorer 41 (IMP-7)
21 June 1969
Environmental studies within & beyond the magnetosphere
20 JULY 1969 : FIRST MANNED LUNAR LANDING
Explorer 42 (Small Astronomy Satellite; SAS)
12 December 1970
Mapped the universe in x-ray wavelengths
Explorer 43 {IMP-8}
13 March 1971
Study of cislunar environment
Explorer 44 (Solrad-3)
8 July 1971
Monitored solar flux
Explorer 45
15 November 1971
Measured meteoriod penetration & impact velocity
Explorer 46
13 August 1972
Same as Explorer 45
Explorer 47 (IMP-9)
22 September 1972
Same as Explorer 43
Explorer 48 (Gamma Ray Explorer; GRE)
16 November 1972
Gamma-radiation study
7 DECEMBER 1972 : FINAL APOLLO MISSION LAUNCHED TO THE MOON
Explorer 49 (RAE-2)
19 June 1973
From Lunar orbit, measured radio signal intensity
Explorer 50 (IMP-10)
25 October 1973
Particle & field interaction in distant magnetotail
Explorer 51
15 December 1973
Solar ultraviolet activity & atmospheric physics
Explorer 52 (Hawkeye)
3 June 1974
Interaction of solar wind with geomagnetosphere over polar caps
Explorer 53
7 May 1975
Study of x-ray emissions from extragalactic sources
15 JULY 1975 : 1ST INTERNATIONAL MANNED FLIGHT APOLLO-SOYUZ
Explorer 54
6 October 1975
Ultraviolet activity & atmospheric composition
Explorer 55
20 November 1975
Structure & behaviour of atmosphere & ionosphere
Explorer 56
18 February 1979
Global database of stratospheric aerosols & ozone
12 APRIL 1981 : 1ST SHUTTLE MISSION 20 YRS. AFTER GAGARIN
Explorer 57
3 August 1981
Solar-terrestrial interactions
Explorer 58
3 August 1981
Same as Explorer 57
Explorer 59 (Solar Mesosphere Explorer)
6 October 1981
Reactions between sunlight & ozone in the atmosphere
Credit : Image from NASA.
