Explorer
A large number of spacecraft - including the very first American satellite launched by the Army Ballistic Missile Agency on January 31, 1958 - have borne the name, "Explorer." All of these vehicles have had important scientific missions. The first explorer missions predated the formation of NASA. Explorers 2 and 5 are counted in the sequence even though they failed to achieve orbit. Following the creation of NASA on October 1, 1958, the agency established the practice of no longer counting failed to orbit launches. The early Explorers performed a large variety of scientific missions ranging from energy particle exploration through atmospheric and ionospheric studies to investigations of micrometeroids, air density, radio astronomy, geodesy, and gamma ray astronomy-including interplanetary and solar monitoring. The Explorer series were relatively small and uncomplicated.
Related QuickLook Pages:
Launch Facts
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| Name | Int'l Desig. | Date | Site | Vehicle | Orbit | Mass(kg) |
| Notes | ||||||
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| Explorer 1 | 1958-[Alpha]1 | 2/1/58 | ESMC | Jupiter C | LEO | 5 kg |
| Discovered Van Allen radiation belts; 1st successful US orbital launch | ||||||
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| Explorer 2 | none | 3/5/58 | ESMC | Jupiter C | FTO | 5 |
| Unsuccessful 4th stage ignition | ||||||
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| Explorer 3 | 1958-[Gamma]1 | 3/26/58 | ESMC | Jupiter C | LEO | 5 |
| Radiation, micrometeoroid data | ||||||
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| Explorer 4 | 1958-[Epsilon]1 | 7/26/58 | ESMC | Jupiter C | LEO | 8 |
| Mapped project Argus radiation | ||||||
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| Explorer 5 | none | 8/24/58 | ESMC | Jupiter C | FTO | 17 |
| Upper stages fired in wrong direction | ||||||
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| Explorer S-1 | none | 7/16/59 | ESMC | Juno 2 | FTO | 41 |
| Destroyed by range safety | ||||||
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| Explorer 6 | 1959-[Delta]1 | 8/7/59 | ESMC | Thor Able | HEO | 64 |
| 1st Earth photo; radiation data | ||||||
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| Explorer 7 | 1959-[Iota]1 | 10/13/59 | ESMC | Juno 2 | LEO | 42 |
| Magnetic field, solar flare data | ||||||
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| Explorer S-46 | none | 3/23/60 | ESMC | Juno 2 | FTO | 16 |
| Upper stage failed to ignite | ||||||
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| Explorer 8 | 1960-[Xi]1 | 11/3/60 | ESMC | Juno 2 | LEO | 41 |
| Ionospheric research | ||||||
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| Explorer S-56 | none | 12/4/60 | Wallops | Scout X1 | FTO | 6 |
| 2nd stage malfunction | ||||||
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| Explorer 9 | 1961-[Delta]1 | 2/16/61 | Wallops | Scout X1 | LEO | 7 |
| 12 foot dia. balloon; atmospheric density studies | ||||||
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| Explorer S-45 | none | 2/24/61 | ESMC | Juno 2 | FTO | 34 |
| 3rd and 4th stage malfunction | ||||||
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| Explorer 10 | 1961-[Kappa]1 | 3/25/61 | ESMC | Delta | HEO | 35 |
| Magnetic field data | ||||||
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| Explorer 11 | 1961-[Nu]1 | 4/27/61 | ESMC | Juno 2 | LEO | 37 |
| Gamma ray data | ||||||
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| Explorer S-45A | none | 5/24/61 | ESMC | Juno 2 | FTO | 33 |
| 2nd stage malfunction | ||||||
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| Explorer S-55 | none | 6/30/61 | Wallops | Scout X1 | FTO | 84 |
| 3rd stage malfunction | ||||||
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| Explorer 12 | 1961-[Upsilon]1 | 8/16/61 | ESMC | Delta | HEO | 38 |
| Radiation and solar wind data | ||||||
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| Explorer 13 | 1961-[Chi]1 | 8/25/61 | Wallops | Scout X1 | LEO | 86 |
| Useless orbit; micrometeoroid research | ||||||
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| Explorer 14 | 1962-B[Gamma]1 | 10/2/62 | ESMC | Delta A | HEO | 40 |
| Magnetosphere studies | ||||||
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| Explorer 15 | 1962-B[Lambda]1 | 10/27/62 | ESMC | Delta A | HEO | 45 |
| Radiation decay data | ||||||
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| Explorer 16 | 1962-B[Chi]1 | 12/16/62 | Wallops | Scout X3 | LEO | 100 |
| Micrometeoroid data | ||||||
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| Explorer 17 | 1963-009A | 4/3/63 | ESMC | Delta B | LEO | 185 |
| Atmospheric research | ||||||
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| Explorer 18 (IMP-A) | 1963-046A | 11/27/63 | ESMC | Delta B | HEO | 62 |
| Radiation data; Interplanetary Monitoring Program | ||||||
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| Explorer 19 | 1963-053A | 12/19/63 | WSMC | Scout X4 | LEO | 7 |
| 12 foot dia. balloon; identical to Explorer 9; atmospheric density studies | ||||||
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| Explorer S-66 (Explorer A) | none | 3/19/64 | ESMC | Delta B | FTO | 54 |
| Insufficient 3rd stage thrust; also known as Ionosphere Beacon | ||||||
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| Explorer 20 | 1964-051A | 8/25/64 | WSMC | Scout X4 | LEO | 44 |
| Ionospheric research | ||||||
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| Explorer 21 (IMP-B) | 1964-060A | 10/4/64 | ESMC | Delta C | HEO | 62 |
| Lower than planned orbit | ||||||
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| Explorer 22 | 1964-064A | 10/10/64 | WSMC | Scout X4 | LEO | 52 |
| Ionospheric and geodetic data | ||||||
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| Explorer 23 | 1964-074A | 11/6/64 | Wallops | Scout X4 | LEO | 134 |
| Micrometeoroid data | ||||||
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| Explorer 24 | 1964-076A | 11/21/64 | WSMC | Scout X4 | LEO | 9 |
| 12 foot dia. balloon; atmospheric density studies | ||||||
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| Explorer 25 | 1964-076B | 11/21/64 | WSMC | Scout X4 | LEO | 40 |
| Radiation data | ||||||
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| Explorer 26 | 1964-086A | 12/21/64 | ESMC | Delta C | MEO | 46 |
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| Explorer 27 | 1965-032A | 4/29/65 | Wallops | Scout X4 | LEO | 60 |
| Battery failed in 1968; ionospheric research and geodetic data | ||||||
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| Explorer 28 (IMP-C) | 1965-042A | 5/29/65 | ESMC | Delta C | HEO | 58 |
| Magnetic field, radiation data | ||||||
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| Explorer 29 (GEOS A) | 1965-089A | 11/6/65 | ESMC | Delta E | LEO | 175 |
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| Explorer 30 | 1965-093A | 11/19/65 | Wallops | Scout X4 | LEO | 57 |
| Solar radiation data | ||||||
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| Explorer 31 | 1965-098B | 11/29/65 | WSMC | Thor Agena B | LEO | 99 |
| Ionospheric research; data correlated with Alouette 2 | ||||||
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| Explorer 32 (AE-B) | 1966-044A | 5/25/66 | ESMC | Delta C | LEO | 225 |
| Atmospheric Explorer; aeronomy experiments | ||||||
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| Explorer 33 | 1966-058A | 7/1/66 | ESMC | Delta E | VHO | 93 |
| Intended to enter lunar orbit | ||||||
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| Explorer 34 (IMP-F) | 1967-051A | 5/24/67 | WSMC | Delta E | HEO | 75 |
| Radiation, magnetic field data | ||||||
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| Explorer 35 (IMP-E) | 1967-070A | 7/19/67 | ESMC | Delta E | Lunar | 104 |
| Earth magnetic tail measurements | ||||||
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| Explorer 36 | 1968-002A | 1/11/68 | WSMC | Delta E | LEO | 209 |
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| Explorer 37 | 1968-017A | 3/5/68 | Wallops | Scout B | LEO | 198 |
| Solar Explorer B; radiation data; off-nominal orbit | ||||||
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| Explorer 38 (RAE 1) | 1968-055A | 7/4/68 | WSMC | Delta J | MEO | 190 |
| Radio Astronomy Explorer; Earth, solar, cosmic radio emission data | ||||||
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| Explorer 39 | 1968-066A | 8/8/68 | WSMC | Scout B | LEO | 9 |
| Air Density Explorer; atmospheric density and temperature data | ||||||
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| Explorer 40 | 1968-066B | 8/8/68 | WSMC | Scout B | LEO | 70 |
| Injun Explorer; radiation data | ||||||
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| Explorer 41 (IMP G) | 1969-053A | 6/21/69 | WSMC | Delta E | HEO | 174 |
| Cislunar radiation data | ||||||
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| Explorer 42 (SAS-1, Uhuru) | 1970-107A | 12/12/70 | San Marco | Scout B | LEO | 143 |
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| Explorer 43 (IMP I) | 1971-019A | 3/13/71 | ESMC | Delta M-6 | HEO | 288 |
| Earth magnetosphere research | ||||||
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| Explorer 44 (Solrad 10) | 1971-058A | 7/8/71 | Wallops | Scout B | LEO | 118 |
| Solar radition data | ||||||
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| Explorer 45 | 1971-096A | 11/15/71 | San Marco | Scout B | MEO | 52 |
| Studies magnetosphere, energetic particles | ||||||
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| Explorer 46 | 1972-061A | 8/13/72 | Wallops | Scout D1 | LEO | 136 |
| Micrometeoroid tests | ||||||
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| Explorer 47 (IMP-H) | 1972-073A | 9/23/72 | ESMC | Delta 1604 | VHO | 376 |
| Investigated cislunar radiation, Earth's magnetosphere, interplantary magnetic field | ||||||
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| Explorer 48 (SAS B) | 1972-091A | 11/15/72 | San Marco | Scout D1 | LEO | 185 |
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| Explorer 49 (RAE 2) | 1973-039A | 6/10/73 | ESMC | Delta 1913 | Lunar | 328 |
| Radio Astronomy Explorer; measured galactic, stellar radio noise | ||||||
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| Explorer 50 (IMP-J) | 1973-078A | 10/26/73 | ESMC | Delta 1604 | VHO | 371 |
| Solar flare and radiation monitor | ||||||
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| Explorer 51 (AE-C) | 1973-101A | 12/16/73 | WSMC | Delta 1900 | MEO | 658 |
| Atmospheric Explorer; upper atmospheric research | ||||||
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| Explorer 52 (Hawkeye) | 1974-040A | 6/3/74 | WSMC | Scout E1 | HEO | 27 |
| Solar wind experiments | ||||||
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| Explorer 53 | 1975-037A | 5/7/75 | San Marco | Scout F1 | LEO | 195 |
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| Explorer 54 (AE-D) | 1975-096A | 10/6/75 | WSMC | Delta 2910 | MEO | 676 |
| Atmospheric Explorer; atmospheric research | ||||||
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| Explorer 55 (AE-E) | 1975-107A | 11/20/75 | ESMC | Delta 2910 | LEO | 721 |
| Atmospheric Explorer | ||||||
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| Explorer (DAD) | none | 12/5/75 | WSMC | Scout F1 | FTO | 71 |
| Dual Air Density; air density experiments | ||||||
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