Explorer program

The Explorer program was the United States's first successful attempt to launch an 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

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 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, solar-cell-powered spacecraft instrumented to measure cosmic ray particles, trapped particles, solar wind protons, and magnetospheric and interplanetary magnetic fields.

Mission History

Explorer Missions

Explorer	Name	Launch Date	Mission	End of Data	Re-Entry
1	Explorer 1	January 31 1958	Energetic particle studies, discovered the Van Allen radiation belt	May 23 1958	March 31 1970
2	Explorer 2	March 5 1958	Failed to achieve orbit	-	-
3	Explorer 3 (Gamma 1)	March 26 1958	Energetic particle studies	June 27 1958	June 27 1958
4	Explorer 4	July 26 1958	Energetic particle studies	October 5 1958	October 23 1959
5	Explorer 5	August 24 1958	Failed to achieve orbit	-	-
7x	Explorer 7x (S 1)	July 16 1959	Measure earth's radiation balance, destroyed by range safety	-	-
6	S-2 (Able 3)	August 7 1959	Magnetosphere research	October 6 1959	July 1 1961
7	S 1A	October 13 1959	Energetic particle studies	August 24 1961	In orbit
--	S 46	March 23 1960	Analyze electron and proton radiation energies, failed to achieve orbit	-	-
8	S 30	November 3 1960	Measured atmospheric composition of the ionosphere	December 27 1960	In orbit
--	S 56	December 4 1960	Atmospheric density measurements, failed to achieve orbit	-	-
9	S 56A	February 16 1961	Atmospheric density measurements	April 9 1964	April 9 1964
--	S 45	February 24 1961	Ionosphere research, failed to achieve orbit	-	-
10	P 14	March 25 1961	Investigated field magnetic field between the earth	March 27 1961	June 1 1968
11	S 15	April 27 1961	Gamma ray astronomy	November 17 1961	In orbit
--	S 45A	May 25 1961	Ionosphere research, failed to achieve orbit	-	-
--	S 55 (Meteoroid Satellite-A, Micrometeorite Explorer)	June 30 1961	Micrometeoroid research, failed to achieve orbit	-	-
12	EPE-A (S 3, Energetic Particle Explorer-A)	August 16 1961	Energetic particle research	December 6 1961	September 1 1963
13	S 55A	August 25 1961	Micrometeoroid research	August 28 1961	August 28 1961
14	EPE-B (Energetic Particle Explorer-B)	October 2 1962	Energetic particle research	August 11 1963	July 1 1966
15	EPE-C (Energetic Particle Explorer-C)	October 27 1962	Energetic particle research	January 30 1963	January 15 1978
16	S 55B	December 16 1962	Micrometeoroid research	July 22 1963	November 24 1966?
17	AE-A (Atmosphere Explorer-A)	April 3 1963	Atmospheric research	July 10 1963	November 24 1966?
18	IMP-A (IMP 1, Interplanetary Monitoring Platform-A)	November 27 1963	Magnetospheric research	May 10 1965	December 30 1965
19	AD-A (Atmospheric Density-A)	December 19 1963	Atmospheric density measurements	May 10 1981	May 10 1981
20	IE-A (S 48, TOPSI, Ionosphere Explorer-A)	August 25 1964	Ionosphere research	December 29 1965	In orbit
21	IMP-B (IMP 2, Interplanetary Monitoring Platform-B)	October 4 1964	Magnetospheric research	October 13 1965	January 30 1966
22	BE-B (S 66, Beacon Explorer-B)	October 10 1964	Ionospheric and geodetic research	February 1970	In orbit
23	S 55C (Explorer 23)	November 6 1964	Micrometeoric research	November 7 1965	June 29 1983
24	AD-B (Atmospheric Density-B)	November 21 1964	Atmospheric density measurements	October 18 1968	October 18 1968
25	Injun 4 (IE-B, Ionosphere Explorer-B)	November 21 1964	Ionospheric research	December 1966	In orbit
26	EPE-D (Energetic Particle Explorer-D)	December 21 1964	High energy particle observations	December 27 1967	In orbit
27	BE-C (Beacon Explorer-C)	April 29 1965	Magnetospheric research	July 20 1973	In orbit
28	IMP-C (IMP 3, Interplanetary Monitoring Platform-C)	May 29 1965	Magnetospheric research	May 12 1967	July 4 1968
29	GEOS 1 (GEOS-A)	November 6 1965	Geodetic earth monitoring	June 23 1978	In orbit
30	SOLRAD 8 (SE-A)	November 19 1965	Solar radiation monitoring (Cover for covert ELINT mission)	November 5 1967	In orbit
31	DME A	November 29 1965	Ionospheric research	October 1 1969	In orbit
32	AE-B (Atmosphere Explorer-B)	May 25 1966	Atmospheric research	March 1967	February 22 1985
33	IMP-D (AIMP 1, Anchored IMP 1, Interplanetary Monitoring Platform-D)	July 1 1966	Magnetospheric research	September 21 1971	In orbit
34	IMP-F (IMP 4, Interplanetary Monitoring Platform-F)	May 24 1967	Magnetospheric research	May 3 1969	May 3 1969
35	IMP-E (AIMP-E, AIMP 2, Anchored IMP 2, Interplanetary Monitoring Platform-E)	July 19 1967	Magnetospheric research	June 24 1973	?
36	GEOS 2 (GEOS-B)	January 11 1968	Geodetic earth monitoring	July 1 1982	In orbit
37	Solrad 9 (SE B)	March 5 1968	Solar radiation monitoring (Cover for covert ELINT mission)	April 30 1974	November 16 1990
38	RAE-A (RAE 1, Radio Astronomy Explorer-A)	July 4 1968	Radio astronomy	?	In orbit
39	AD-C (Atmospheric Density-C)	August 8 1968	Atmospheric density measurements	June 23 1971	June 22 1981?
40	Injun 5 (Injun C, IE-C, Ionosphere Explorer-C)	August 8 1968	Magnetospheric Research	June 1971	In orbit
41	IMP-G (IMP 5, Interplanetary Monitoring Platform-G)	June 21 1969	Magnetospheric research	December 23 1972	December 23 1972
42	SAS-A (Small Astronomy Satellite-A, SAS 1)	December 12 1970	X-Ray Astronomy	January 4 1975	April 5 1979
43	IMP-H (IMP 6, Interplanetary Monitoring Platform-H)	March 13 1971	Magnetospheric research	October 2 1974	October 2 1974
44	Solrad 10 (SE-C, SOLRAD-C)	July 8 1971	Solar radiation monitoring (Cover for covert ELINT mission)	June 30 1973	December 15 1979
45	SSS-A (S-Cubed A)	November 15 1971	Magnetospheric research	September 30 1974	January 10 1992
46	Meteoroid Technology Satellite (MTS, METEC)	August 13 1972	Micrometeoroids research	November 4 1974	November 2 1979
47	IMP-I (IMP 7, Interplanetary Monitoring Platform-I)	September 23 1972	Magnetospheric research	October 31 1978	In orbit
48	SAS-B (Small Astronomy Satellite-B, SAS 2)	November 15 1972	X-Ray Astronomy	June 8 1973	August 20 1980
49	RAE-B (RAE 2, Radio Astronomy Explorer-B)	June 10 1973	Radio astronomy	April 26 1977	In Lunar orbit
50	IMP J (IMP 8, Interplanetary Monitoring Platform-J)	October 26 1973	Magnetospheric research	Operational (34 years)	In orbit
51	AE-C (Atmosphere Explorer-C)	December 16 1973	Atmospheric research	?	December 12 1978
52	Hawkeye 1, Injun 6 (IE-D, Ionosphere Explorer-D)	June 3 1974	Magnetospheric research	April 28 1978	April 28 1978
53	SAS-C (Small Astronomy Satellite-C, SAS 3)	May 7 1975	X-Ray Astronomy	April 7 1979	April 9 1979
54	AE-D (Atmosphere Explorer-D)	October 6 1975	Atmospheric research	January 29 1976	March 12 1976
55	AE-E (Atmosphere Explorer-E)	November 20 1975	Atmospheric research	September 25 1980	June 10 1981
56	ISEE 1 & 2 (International Sun-Earth Explorer-A & B)	October 22 1977	Magnetospheric research	September 26 1987	September 26 1987
57	IUE	January 26 1978	Ultraviolet astronomy	September 30 1996	In orbit
58	HCMM (AEM-A, Applications Explorer Mission-A, Heat Capacity Mapping Mission)	April 26 1978	Thermal mapping of the earth	September 30 1980	?
59	ISEE 3 (International Sun-Earth Explorer-C, ICE)	August 12 1978	Magnetospheric research	May 5 1997	In heliocentric orbit
60	SAGE (AEM-B, Applications Explorer Mission-B, Stratospheric Aerosol and Gas Experiment)	February 18 1979	Stratospheric aerosol and ozone data	January 7 1982	April 11 1989
61	MAGSAT (AEM-C, Applications Explorer Mission-C, Magnetic Field Satellite)	October 30 1979	Mapped the near surface magnetic field of the Earth	May 6 1980	June 11 1980
62	DE 1 (DE-A, Dynamics Explorer-A)	August 3 1981	Magnetospheric research	February 28 1991	In orbit
63	DE 2 (DE-B, Dynamics Explorer-B)	August 3 1981	Magnetospheric research	1983	February 19 1983
64	SME	October 6 1981	Atmospheric research	April 4 1989	March 5 1991
65	AMTPE/CCE (Active Magnetospheric Particle Tracer Explorers/Charge Composition Explorer)	August 16 1984	Magnetospheric research	July 12 1989	?
66	COBE	November 18 1989	Microwave astronomy	December 23 1993	In orbit
67	EUVE	June 7 1992	Ultraviolet astronomy	January 30 2002	In orbit
68	SAMPEX	July 3 1992	Magnetospheric research	operational?	In orbit
69	RXTE	December 30 1995	X-ray astronomy	Operational (11 years)	In orbit
70	FAST	August 21 1996	Auroral phenomena	operational?	In orbit
71	ACE	August 25 1997	Solar/interplanetary/interstellar particle research	Operational (11 years)	In L1 orbit
72	SNOE	February 26 1998	Atmospheric research	December 13 2003	December 13 2003
73	TRACE	April 2 1998	Solar observatory	Operational (10 years)	In orbit
74	SWAS	December 6 1998	Submillimeter astronomy	July 2004 hibernation August 2005 after Deep Impact sub-mission	In orbit
75	WIRE	March 5 1999	InfraRed astronomy, primary mission failed due to loss of coolant	operational?	In orbit
76	TERRIERS	May 18 1999	Atmospheric research, satellite failed shortly after achieving orbit	May 18 1999	In orbit
77	FUSE	June 23 1999	Ultraviolet astronomy	October 18 2007	In orbit
78	IMAGE	March 25 2000	Magnetospheric research	December 18 2005	In orbit
79	HETE-2	October 9 2000	UV, X-Ray, and gamma ray astronomy	Operational (7 years)	In orbit
80	WMAP	June 30 2001	Microwave astronomy	Operational (6 years)	In L2 orbit
81	RHESSI	February 5 2002	X-ray and gamma ray solar flare imaging	Operational (6 years)	In orbit
82	CHIPSat	January 13 2003	Ultraviolet spectroscopy and astronomy	April 11 2008	In orbit
83	GALEX	April 28 2003	Ultraviolet astronomy	Operational (5 years)	In orbit
84	SWIFT	November 20 2004	Gamma ray astronomy	Operational (3 years)	In orbit
85	THEMIS	February 17 2007	Magnetospheric research	Operational	In orbit
86	THEMIS	February 17 2007	Magnetospheric research	Operational	In orbit
87	THEMIS	February 17 2007	Magnetospheric research	Operational	In orbit
88	THEMIS	February 17 2007	Magnetospheric research	Operational	In orbit
89	THEMIS	February 17 2007	Magnetospheric research	Operational	In orbit
90	AIM	April 25 2007	Noctilucent cloud observation	Operational	In orbit

References

See also

• Small Explorer program

External links

• NASA Explorer program missions page
• Explorer Program Profile by NASA's Solar System Exploration
• 1957 Video (30 minutes) on launch and impact of Explorer
• Master list of Names, Initialisms, and Abbreviations for un-manned satellites