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Explorer program

This article is about the space exploration program. "Explorer program" may also refer to the file browser of Windows, called Windows Explorer.

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 an 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 I on October 4, 1957. (See: Sputnik crisis) Explorer 1 was launched February 1 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 unmanned space 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 J), 67-74 and 77-83 (EUVE, SAMPEX, RXTE, FAST, ACE, SNOE, TRACE, SWAS, FUSE, IMAGE, WMAP, HESSI, 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, fully five of them had had missions which lasted 10 or more years, the longest of which (IMP J) 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 of 2000, of the ten operational Explorer missions, SNOE and TRACE have operated for about two year, 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.

Mission History

Explorer Missions
Explorer Name Launch Date Mission
1 Explorer 1 February 1 1958 Energy particles studies, discovered the Van Allen radiation belt
2 Explorer 2 March 5 1958 Failed to achive orbit
3 Explorer 3 March 26 1958 Energy particles studies
4 Explorer 4 July 26 1958 Energy particles studies
5 Explorer 5 August 24 1958 Failed to achive orbit
-- S-1 July 16 1959 Failed to achive orbit
6 S-2 August 7 1959 Magnetosphere research
7 S-1a October 13 1959 Energy particles studies
-- S-46 March 23 1960 Failed to achive orbit
8 S-56 November 3 1960 Measured atmospheric composition of the ionosphere
-- S-56 December 4 1960 Failed to achive orbit
9 S-56a February 16 1961 Atmospheric density measurments
-- S-45 February 24 1961 Failed to achive orbit
10 P-14 March 25 1961 Investigated field magnetic field between the earth
11 S-15 April 27 1961 Gamma ray astronomy
-- S-45a May 25 1961 Failed to achive orbit
-- S-55 June 30 1961 Failed to achive orbit
12 EPE A August 16 1961 Energetic particles research
13 S-55a August 25 1961 Micrometeoroids research
14 EPE B October 2 1962 Energetic particles research
15 EPE C October 27 1962 Energetic particles research
16 S-55b December 16 1962 Micrometeoroids research
17 AE A April 3 1963 Atmospheric research
18 IMP A November 27 1963 Magnetospheric research
19 AD A December 19 1963 Atmospheric density measurments
20 IE A August 25 1964 Ionosphere research
21 IMP B October 4 1964 Magnetospheric research
22 BE B October 10 1964 Ionospheric and geodetic research
23 Explorer 23 November 6 1964 Micrometeoric research
24 AD B November 21 1964 Atmospheric density measurments
25 Injun 4 (IE B) November 21 1964 Ionospheric research
26 EPE D December 21 1964 High energy particle observations
27 IMP C April 29 1965 Magnetospheric research
28 IMP C May 29 1965 Magnetospheric research
29 GEOS A November 6 1965 Geodetic earth monitoring
30 Solrad 8 (SE A) November 19 1965 Solar radiation monitoring
31 DME A November 29 1965 Ionospheric research
32 AE B May 25 1966 Atmospheric research
33 IMP D July 1 1966 Magnetospheric research
34 IMP F May 24 1967 Magnetospheric research
35 IMP E July 19 1967 Magnetospheric research
36 GEOS B January 11 1968 Geodetic earth monitoring
37 Solrad 9 (SE B) March 5 1968 Solar radiation monitoring
38 RAE A July 4 1968 Radio astronomy
39 AD C August 8 1968 Atmospheric density measurments
40 Injun 5 (IE C) August 8 1968 Magnetospheric Research
41 IMP G June 21 1969 Magnetospheric research
42 SAS A December 12 1970 X-Ray Astronomy
43 IMP H March 13 1971 Magnetospheric research
44 Solrad 10 (SE C) July 8 1971 Solar radiation monitoring
45 SSS A November 15 1971 Magnetospheric research
46 MTS A August 13 1972 Micrometeoroids research
47 IMP I September 23 1972 Magnetospheric research
48 SAS B November 15 1972 X-Ray Astronomy
49 RAE B June 10 1973 Radio astronomy
50 IMP J October 26 1973 Magnetospheric research
51 AE C December 16 1973 Atmospheric research
52 Injun 6 (IE D) June 3 1974 Magnetospheric research
53 SAS C May 7 1975 X-Ray Astronomy
54 AE D October 6 1975 Atmospheric research
55 AE E November 20 1975 Atmospheric research
56 ISEE 1 October 22 1977 Magnetospheric research
57 IUE January 26 1978 Ultraviolet astronomy
58 HCMM April 26 1978 Thermal mapping of the earth
59 ISEE 3 (ICE) August 12 1978 Magnetospheric research
60 SAGE February 18 1979 Stratospheric aerosol and ozone data
61 Magsat October 30 1979 Mapped the near surface magnetic field of the Earth
62 DE 1 August 3 1981 Magnetospheric research
63 DE 2 August 3 1981 Magnetospheric research
64 SME October 6 1981 Atmospheric research
65 CCE August 16 1984 Magnetospheric research
66 COBE November 18 1989 Microwave astronomy
67 EXUV June 7 1992 Ultraviolet astronomy
68 SAMPEX July 3 1992 Magnetospheric research
69 XTE December 30 1995 X-ray astronomy
70 FAST August 21 1996 Auroral phenomena
71 ACE August 25 1997 Solar/interplanetary/interstellar partical research
72 SNOE February 26 1998 Atmospheric research
73 TRACE April 2 1998 Solar observatory
74 SWAS December 6 1998 Submillimeter astronomy
75 WIRE March 5 1999 InfraRed astronomy, primary mission failed due to loss of coolant
76 TERRIERS May 18 1999 Atmospheric research, satellite failed shortly after achiving orbit
77 FUSE June 23 1999 Ultraviolet astronomy
78 IMAGE March 25 2000 Magnetospheric research
79 WMAP June 30 2001 Microwave astronomy
80 RHESSI February 5 2002 X-ray and gamma ray solar flare imaging
81 CHIPSat January 13 2003 Ultraviolet spectroscopy and astronomy
82 GALEX April 28 2003 Ultraviolet astronomy
83 SWIFT November 20 2004 Gamma ray astronomy

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