Explorer program
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{{otheruses|Explorer (disambiguation)}}
The '''Explorer program''' was the [[United States]]'s first successful attempt to launch an [[satellite|artificial satellite]]. It began as a [[U.S. Army]] proposal to place a scientific satellite into [[orbit]] during the [[International Geophysical Year]]. That proposal was rejected in favor of the U.S. Navy's [[Project Vanguard]]. It was revived as a [[crash program]] to catch up with the [[Soviet Union]] after that nation's launch of [[Sputnik 1]] on [[October 4]], [[1957]]. (''See:'' [[Sputnik crisis]]) [[Explorer 1]] was launched [[January 31]] [[1958]]. Besides being the first U.S. satellite, it is known for discovering the [[Van Allen radiation belt]].
==Explorer at NASA==
[[Image:ISEE-C (ISEE 3) in dynamics test chamber.jpg|thumb|ISEE-C in a dynamic test chamber, 1978]]
The Explorer program was taken over by [[NASA]], which continued to use the name for [[robotic spacecraft]] missions.
Over the years, [[NASA]] has launched a series of "Explorer" [[spacecraft]] carrying a wide variety of scientific investigations. The list below identifies the 79 successful missions as of December 2004. As of this writing, Explorers 50 (IMP-8), 68-71, 73-74, 79-83 (SAMPEX, RXTE, FAST, ACE, TRACE, SWAS, WMAP, RHESSI, CHIPSat, GALEX and SWIFT) are still operating.
NASA's Explorer spacecraft series not only is the longest running series of spacecraft, it has produced highly-durable, well-engineered spacecraft as well. Of the 79 successful Explorer missions depicted, five of them had missions that lasted 10 or more years, the longest of which (IMP-8) has been operational for over 26 years now and still produces valuable information about the solar wind. NASA's [[International Ultraviolet Explorer|IUE]] spacecraft operated for 19 years and produced copious amounts of data for the astronomical community. The ISEE 3/ICE spacecraft operated for 14 years. As of March 2000, of the ten operational Explorer missions, SNOE and TRACE have operated for about two years, ACE two and a half years, FAST for about three and a half, RXTE for over four, EUVE and SAMPEX for nearly eight, and IMP 8 for more than 26. SWAS has been operational for slightly more than one year, having been launched in early December 1998.
; Energetic Particle Explorers
Explorers 12, 14, 15 and 26 were the S 3 series of spacecraft, known as Energetic Particle Explorers. They were [[spin-stabilized satellite|spin-stabilized]], solar-cell-powered spacecraft instrumented to measure [[cosmic ray]] particles, trapped particles, [[solar wind]] [[proton]]s, and magnetospheric and interplanetary magnetic fields.<ref>
{{cite web
| url = http://nssdc.gsfc.nasa.gov/database/MasterCatalog?sc=1961-020A
| title = Explorer 12
| publisher = [[NASA]]
}}</ref>
==Mission History==
<center>
{| border="1" cellspacing="0" cellpadding="2"
|+ '''Explorer Missions'''
|-
! style="background:#efefef;" | Explorer
! style="background:#efefef;" | Name
! style="background:#efefef;" | Launch Date
! style="background:#efefef;" | Mission
! style="background:#efefef;" | End of Data
! style="background:#efefef;" | Re-Entry
|-
|align=center| 1
|align=center| [[Explorer 1]]
|| [[January 31]] [[1958]]
|| Energy particles studies, discovered the [[Van Allen radiation belt]]
| [[May 23]] [[1958]]
| [[March 31]] [[1970]]
|-
|align=center| 2
|align=center| [[Explorer 2]]
|| [[March 5]] [[1958]]
|| Failed to achieve orbit
|align=center| -
|align=center| -
|-
|align=center| 3
|align=center| [[Explorer 3]]
|| [[March 26]] [[1958]]
|| Energy particles studies
| [[June 27]] [[1958]]
| June 27 1958
|-
|align=center| 4
|align=center| [[Explorer 4]]
|| [[July 26]] [[1958]]
|| Energy particles studies
| [[October 5]] [[1958]]
| [[October 23]] [[1959]]
|-
|align=center| 5
|align=center| [[Explorer 5]]
|| [[August 24]] [[1958]]
|| Failed to achieve orbit
|align=center| -
|align=center| -
|-
|align=center| --
|align=center| S-1
|| [[July 16]] [[1959]]
|| Failed to achieve orbit
|align=center| -
|align=center| -
|-
|align=center| 6
|align=center| [[Explorer 6|S-2]]
|| [[August 7]] [[1959]]
|| Magnetosphere research
| [[October 6]] [[1959]]
| [[July 1]] [[1961]]
|-
|align=center| 7
|align=center| [[Explorer 7|S-1a]]
|| [[October 13]] [[1959]]
|| Energy particles studies
| [[August 24]] [[1961]]
| In orbit
|-
|align=center| --
|align=center| S-46
|| [[March 23]] [[1960]]
|| Failed to achieve orbit
|align=center| -
|align=center| -
|-
|align=center| 8
|align=center| [[Explorer 8|S-56]]
|| [[November 3]] [[1960]]
|| Measured atmospheric composition of the ionosphere
|align=center| ?
| in orbit
|-
|align=center| --
|align=center| S-56
|| [[December 4]] [[1960]]
|| Failed to achieve orbit
|align=center| -
|align=center| -
|-
|align=center| 9
|align=center| S-56a
|| [[February 16]] [[1961]]
|| Atmospheric density measurements
|align=center| ?
| [[April 9]] [[1964]]
|-
|align=center| --
|align=center| S-45
|| [[February 24]] [[1961]]
|| Failed to achieve orbit
|align=center| -
|align=center| -
|-
|align=center| 10
|align=center| P-14
|| [[March 25]] [[1961]]
|| Investigated field magnetic field between the earth
|align=center| ?
| [[June 1]] [[1968]]
|-
|align=center| 11
|align=center| [[Explorer 11|S-15]]
|| [[April 27]] [[1961]]
|| Gamma ray astronomy
|align=center| ?
| In orbit
|-
|align=center| --
|align=center| S-45a
|| [[May 25]] [[1961]]
|| Failed to achieve orbit
|align=center| -
|align=center| -
|-
|align=center| --
|align=center| S-55
|| [[June 30]] [[1961]]
|| Failed to achieve orbit
|align=center| -
|align=center| -
|-
|align=center| 12
|align=center| EPE A
|| [[August 16]] [[1961]]
|| Energetic particles research
|align=center| ?
| [[September 1]] [[1963]]
|-
|align=center| 13
|align=center| S-55a
|| [[August 25]] [[1961]]
|| Micrometeoroids research
|align=center| ?
| In orbit
|-
|align=center| 14
|align=center| EPE B
|| [[October 2]] [[1962]]
|| Energetic particles research
|align=center| ?
| [[July 1]] [[1966]]
|-
|align=center| 15
|align=center| EPE C
|| [[October 27]] [[1962]]
|| Energetic particles research
|align=center| ?
|[[January 15]] [[1978]]
|-
|align=center| 16
|align=center| S-55b
|| [[December 16]] [[1962]]
|| Micrometeoroids research
|align=center|?
|[[November 24]] [[1966]]?
|-
|align=center| 17
|align=center| [[Explorer 17|AE A]]
|| [[April 3]] [[1963]]
|| Atmospheric research
| [[July 10]] [[1963]]
| [[November 24]] [[1966]]?
|-
|align=center| 18
|align=center| IMP A
|| [[November 27]] [[1963]]
|| Magnetospheric research
|align=center|?
|[[December 30]] [[1965]]
|-
|align=center| 19
|align=center| AD A
|| [[December 19]] [[1963]]
|| Atmospheric density measurements
|align=center|?
|[[May 10]] [[1981]]
|-
|align=center| 20
|align=center| IE A
|| [[August 25]] [[1964]]
|| Ionosphere research
|align=center|?
|In orbit
|-
|align=center| 21
|align=center| IMP B
|| [[October 4]] [[1964]]
|| Magnetospheric research
|align=center|?
|[[January 30]] [[1966]]
|-
|align=center| 22
|align=center| BE B (S-66)
|| [[October 10]] [[1964]]
|| Ionospheric and geodetic research
|align=center|?
|In orbit
|-
|align=center| 23
|align=center| Explorer 23 (S-55c)
|| [[November 6]] [[1964]]
|| Micrometeoric research
|align=center|?
|[[June 29]] [[1983]]
|-
|align=center| 24
|align=center| AD B
|| [[November 21]] [[1964]]
|| Atmospheric density measurements
|align=center|?
|[[October 18]] [[1968]]
|-
|align=center| 25
|align=center| Injun 4 (IE B)
|| [[November 21]] [[1964]]
|| Ionospheric research
|align=center|?
|In orbit
|-
|align=center| 26
|align=center| EPE D
|| [[December 21]] [[1964]]
|| High energy particle observations
|align=center|?
|In orbit
|-
|align=center| 27
|align=center| IMP C
|| [[April 29]] [[1965]]
|| Magnetospheric research
|align=center|?
|In orbit
|-
|align=center| 28
|align=center| IMP C
|| [[May 29]] [[1965]]
|| Magnetospheric research
|align=center|?
|[[July 4]] [[1968]]
|-
|align=center| 29
|align=center| [[Geodetic Earth Orbiting Satellite|GEOS A]]
|| [[November 6]] [[1965]]
|| Geodetic earth monitoring
|align=center|?
|In orbit
|-
|align=center| 30
|align=center| [[Solrad]] 8 (SE A)
|| [[November 19]] [[1965]]
|| Solar radiation monitoring<br>(Cover for covert [[ELINT]] mission)
|align=center|?
|In orbit
|-
|align=center| 31
|align=center| DME A
|| [[November 29]] [[1965]]
|| Ionospheric research
|align=center|?
|In orbit
|-
|align=center| 32
|align=center| [[Explorer 32|AE B]]
|| [[May 25]] [[1966]]
|| Atmospheric research
|March 1967
|[[February 22]] [[1985]]
|-
|align=center| 33
|align=center| [[Explorer 33|IMP D]]
|| [[July 1]] [[1966]]
|| Magnetospheric research
| [[September 21]] [[1971]]<ref>{{cite web
|url=http://nssdc.gsfc.nasa.gov/nmc/masterCatalog.do?sc=1966-058A
|title=Explorer 33 (NSSDC ID: 1966-058A)
|publisher=NASA / National Space Science Data Center
|date=2008-04-02
|accessdate=2008-07-04
}}</ref>
|In orbit
|-
|align=center| 34
|align=center| IMP F
|| [[May 24]] [[1967]]
|| Magnetospheric research
|align=center|?
|[[May 3]] [[1969]]
|-
|align=center| 35
|align=center| [[Explorer 35|IMP E]]
|| [[July 19]] [[1967]]
|| Magnetospheric research
|[[June 24]] [[1973]]
|align=center|?
|-
|align=center| 36
|align=center| [[Geodetic Earth Orbiting Satellite|GEOS B]]
|| [[January 11]] [[1968]]
|| Geodetic earth monitoring
|align=center|?
|In orbit
|-
|align=center| 37
|align=center| Solrad 9 (SE B)
|| [[March 5]] [[1968]]
|| Solar radiation monitoring<br>(Cover for covert ELINT mission)
|align=center|?
|[[November 16]] [[1990]]
|-
|align=center| 38
|align=center| RAE A
|| [[July 4]] [[1968]]
|| Radio astronomy
|align=center|?
|In orbit
|-
|align=center| 39
|align=center| AD C
|| [[August 8]] [[1968]]
|| Atmospheric density measurements
|align=center|?
|[[June 22]] [[1981]]
|-
|align=center| 40
|align=center| Injun 5 (IE C)
|| [[August 8]] [[1968]]
|| Magnetospheric Research
|align=center|?
|In orbit
|-
|align=center| 41
|align=center| IMP G
|| [[June 21]] [[1969]]
|| Magnetospheric research
|align=center|?
|[[December 23]] [[1972]]
|-
|align=center| 42
|align=center| [[Uhuru (satellite)|SAS A]]
|| [[December 12]] [[1970]]
|| X-Ray Astronomy
|March 1973
|[[April 5]] [[1979]]
|-
|align=center| 43
|align=center| IMP H
|| [[March 13]] [[1971]]
|| Magnetospheric research
|align=center|?
|[[October 2]] [[1974]]
|-
|align=center| 44
|align=center| Solrad 10 (SE C)
|| [[July 8]] [[1971]]
|| Solar radiation monitoring<br>(Cover for covert ELINT mission)
|align=center|?
|[[December 15]] [[1979]]
|-
|align=center| 45
|align=center| SSS A
|| [[November 15]] [[1971]]
|| Magnetospheric research
|align=center|?
|[[January 10]] [[1992]]
|-
|align=center| 46
|align=center| MTS A
|| [[August 13]] [[1972]]
|| Micrometeoroids research
|align=center|?
|[[November 2]] [[1979]]
|-
|align=center| 47
|align=center| IMP I
|| [[September 23]] [[1972]]
|| Magnetospheric research
|align=center|?
|In orbit
|-
|align=center| 48
|align=center| [[Second Small Astronomy Satellite|SAS B]]
|| [[November 15]] [[1972]]
|| X-Ray Astronomy
|align=center|?
|[[August 20]] [[1980]]
|-
|align=center| 49
|align=center| [[Explorer 49|RAE B]]
|| [[June 10]] [[1973]]
|| Radio astronomy
|align=center|?
|In Lunar orbit
|-
|align=center| 50
|align=center| IMP J
|| [[October 26]] [[1973]]
|| Magnetospheric research
|'''Operational (34 years)'''
|In orbit
|-
|align=center| 51
|align=center| AE C
|| [[December 16]] [[1973]]
|| Atmospheric research
|align=center|?
|[[December 12]] [[1978]]
|-
|align=center| 52
|align=center| [[Explorer 52|Hawkeye 1, Injun 6 (IE D)]]
|| [[June 3]] [[1974]]
|| Magnetospheric research
|[[April 28]] [[1978]]
|[[April 28]] [[1978]]
|-
|align=center| 53
|align=center| [[Third Small Astronomy Satellite|SAS C]]
|| [[May 7]] [[1975]]
|| X-Ray Astronomy
|align=center|?
|[[April 9]] [[1979]]
|-
|align=center| 54
|align=center| AE D
|| [[October 6]] [[1975]]
|| Atmospheric research
|align=center|?
|[[March 12]] [[1976]]
|-
|align=center| 55
|align=center| AE E
|| [[November 20]] [[1975]]
|| Atmospheric research
|align=center|?
|[[January 10]] [[1981]]
|-
|align=center| 56
|align=center| ISEE 1
|| [[October 22]] [[1977]]
|| Magnetospheric research
|align=center|?
|[[September 26]] [[1987]]
|-
|align=center| 57
|align=center| [[International Ultraviolet Explorer|IUE]]
|| [[January 26]] [[1978]]
|| Ultraviolet astronomy
|[[September 30]] [[1996]]
|In orbit
|-
|align=center| 58
|align=center| HCMM
|| [[April 26]] [[1978]]
|| Thermal mapping of the earth
|align=center|?
|align=center|?
|-
|align=center| 59
|align=center| ISEE 3 ([[International Cometary Explorer|ICE]])
|| [[August 12]] [[1978]]
|| Magnetospheric research
|[[May 5]] [[1997]]
|In [[heliocentric]] orbit
|-
|align=center| 60
|align=center| SAGE
|| [[February 18]] [[1979]]
|| Stratospheric aerosol and ozone data
|align=center|?
|[[April 11]] [[1989]]
|-
|align=center| 61
|align=center| [[Magsat]]
|| [[October 30]] [[1979]]
|| Mapped the near surface magnetic field of the Earth
|align=center|?
|[[June 11]] [[1980]]
|-
|align=center| 62
|align=center| DE 1
|| [[August 3]] [[1981]]
|| Magnetospheric research
|align=center|?
|align=center|?
|-
|align=center| 63
|align=center| DE 2
|| [[August 3]] [[1981]]
|| Magnetospheric research
|align=center|?
|align=center|?
|-
|align=center| 64
|align=center| [[Solar Mesosphere Explorer|SME]]
|| [[October 6]] [[1981]]
|| Atmospheric research
|[[April 4]] [[1989]]
|[[March 5]] [[1991]]
|-
|align=center| 65
|align=center| [[Charge Composition Explorer|CCE]]
|| [[August 16]] [[1984]]
|| Magnetospheric research
|align=center|?
|align=center|?
|-
|align=center| 66
|align=center| [[COBE]]
|| [[November 18]] [[1989]]
|| Microwave astronomy
|operational?
|In orbit
|-
|align=center| 67
|align=center| [[Extreme Ultraviolet Explorer|EUVE]]
|| [[June 7]] [[1992]]
|| Ultraviolet astronomy
|[[January 30]] [[2002]]
|In orbit
|-
|align=center| 68
|align=center| [[Solar Anomalous and Magnetospheric Particle Explorer|SAMPEX]]
|| [[July 3]] [[1992]]
|| Magnetospheric research
|operational?
|In orbit
|-
|align=center| 69
|align=center| [[Rossi X-ray Timing Explorer|RXTE]]
|| [[December 30]] [[1995]]
|| X-ray astronomy
|'''Operational (11 years)'''
|In orbit
|-
|align=center| 70
|align=center| [[Fast Auroral Snapshot Explorer|FAST]]
|| [[August 21]] [[1996]]
|| Auroral phenomena
|operational?
|In orbit
|-
|align=center| 71
|align=center| [[Advanced Composition Explorer|ACE]]
|| [[August 25]] [[1997]]
|| Solar/interplanetary/interstellar particle research
|'''Operational (11 years)'''
|In [[Lissajous orbit]]
|-
|align=center| 72
|align=center| [[Student Nitric Oxide Explorer|SNOE]]
|| [[February 26]] [[1998]]
|| Atmospheric research
|[[December 13]] [[2003]]
|[[December 13]] [[2003]]
|-
|align=center| 73
|align=center| [[TRACE]]
|| [[April 2]] [[1998]]
|| Solar observatory
|'''Operational (10 years)'''
|In orbit
|-
|align=center| 74
|align=center| [[Submillimeter Wave Astronomy Satellite|SWAS]]
|| [[December 6]] [[1998]]
|| Submillimeter astronomy
|July 2004 hibernation<br>August 2005 after Deep Impact sub-mission
|In orbit
|-
|align=center| 75
|align=center| [[Wide Field Infrared Explorer|WIRE]]
|| [[March 5]] [[1999]]
|| InfraRed astronomy, primary mission failed due to loss of coolant
|operational?
|In orbit
|-
|align=center| 76
|align=center| TERRIERS
|| [[May 18]] [[1999]]
|| Atmospheric research, satellite failed shortly after achieving orbit
|align=center|?
|In orbit
|-
|align=center| 77
|align=center| [[Far Ultraviolet Spectroscopic Explorer|FUSE]]
|| [[June 23]] [[1999]]
|| Ultraviolet astronomy
|[[October 18]] [[2007]]
|In orbit
|-
|align=center| 78
|align=center| [[IMAGE]]
|| [[March 25]] [[2000]]
|| Magnetospheric research
|[[December 18]], [[2005]]
|In orbit
|-
|align=center| 79
|align=center| [[HETE]]
|| [[October 9]] [[2000]]
|| UV, X-Ray, and gamma ray astronomy
|'''Operational (7 years)'''
|In orbit
|-
|align=center| 80
|align=center| [[WMAP]]
|| [[June 30]] [[2001]]
|| Microwave astronomy
|'''Operational (6 years)'''
|In L2 orbit
|-
|align=center| 81
|align=center| [[RHESSI]]
|| [[February 5]] [[2002]]
|| X-ray and gamma ray solar flare imaging
|'''Operational (6 years)'''
|In orbit
|-
|align=center| 82
|align=center| [[CHIPSat]]
|| [[January 13]] [[2003]]
|| Ultraviolet spectroscopy and astronomy
|[[April 11]] [[2008]] <ref>[http://www.redorbit.com/news/space/1417075/chipsat_quietly_shut_down/ CHIPSat quietly shut down]</ref>
|In orbit
|-
|align=center| 83
|align=center| [[GALEX]]
|| [[April 28]] [[2003]]
|| Ultraviolet astronomy
|'''Operational (5 years)'''
|In orbit
|-
|align=center| 84
|align=center| [[Swift Gamma-Ray Burst Mission|SWIFT]]
|| [[November 20]] [[2004]]
|| Gamma ray astronomy
|'''Operational (3 years)'''
|In orbit
|-
|align=center| 85
|align=center| [[THEMIS (satellite)|THEMIS]]
|| [[February 17]] [[2007]]
|| Magnetospheric research
|'''Operational'''
|In orbit
|-
|align=center| 86
|align=center| [[THEMIS (satellite)|THEMIS]]
|| [[February 17]] [[2007]]
|| Magnetospheric research
|'''Operational'''
|In orbit
|-
|align=center| 87
|align=center| [[THEMIS (satellite)|THEMIS]]
|| [[February 17]] [[2007]]
|| Magnetospheric research
|'''Operational'''
|In orbit
|-
|align=center| 88
|align=center| [[THEMIS (satellite)|THEMIS]]
|| [[February 17]] [[2007]]
|| Magnetospheric research
|'''Operational'''
|In orbit
|-
|align=center| 89
|align=center| [[THEMIS (satellite)|THEMIS]]
|| [[February 17]] [[2007]]
|| Magnetospheric research
|'''Operational'''
|In orbit
|-
|align=center| 90
|align=center| [[Aeronomy of Ice in the Mesosphere|AIM]]
| [[April 25]] [[2007]]
| Noctilucent cloud observation
|'''Operational'''
|In orbit
|}
</center>
== References ==
{{reflist}}
== See also ==
* [[Small Explorer program]]
== External links ==
* [http://explorers.gsfc.nasa.gov/missions.html NASA Explorer program missions page]
* [http://solarsystem.nasa.gov/missions/profile.cfm?MCode=Explorer_Moon Explorer Program Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]
* [http://w3.armed.us/explorer 1957 Video (30 minutes) on launch and impact of Explorer]
* [http://www.cira.colostate.edu/cira/RAMM//hillger/acronyms.htm Master list of Names, Initialisms, and Abbreviations for un-manned satellites]
{{Explorer program}}
{{NASA planetary exploration programs}}
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