Explorer program

The Explorer program was the United States' first successful attempt to launch unmanned space missions. It began as an attempt to place an artificial satellite into orbit during the International Geophysical Year, and became an attempt to catch up with the Soviet Union after that nation's launch of Sputnik I on October 4, 1957.

Over the years, NASA has launched a series of "Explorer" spacecraft carrying a wide variety of scientific investigations. The list below identifies the 74 successful and 4 unsuccessful missions as of this writing (March 2000). As of this writing, Explorers 50 (IMP 8), 67-74 and 77-78 (EUVE, SAMPEX, RXTE, FAST, ACE, SNOE, TRACE, SWAS, FUSE, and IMAGE) are still operating.

NASA's Explorer spacecraft series is not simply the longest running series of spacecraft, it has produced highly-durable (i.e., well-engineered) spacecraft as well. Of the 74 successful Explorer missions depicted, fully five of them had had missions which 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 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. The latest two additions are FUSE (June 1999) and IMAGE (March 2000).

• Explorer 1 - launched February 1, 1958 - detected the Van Allen radiation belt
• Explorer 2[?] - launched March 5, 1958 - Failed
• Explorer 3[?] - launched March 26, 1958
• Explorer 4 - launched July 26, 1958
• Explorer 5[?] - launched August 24, 1958 - Failed
• Explorer 6[?] - launched August 7, 1959
• Explorer 7[?] - launched October 13, 1959
• Explorer 8[?] - launched November 3, 1960
• Explorer 9[?] - launched February 16, 1961
• Explorer 10[?] - launched March 25, 1961
• Explorer 11[?] - launched April 27, 1961
• Explorer 12[?] - launched August 16, 1961
• Explorer 13[?] - launched August 25, 1961
• Explorer 14[?] - launched October 2, 1962
• Explorer 15[?] - launched October 27, 1962
• Explorer 16[?] - launched December 16, 1962
• Explorer 17[?] - launched April 3, 1963
• Explorer 18[?] - launched November 27, 1963
• Explorer 19[?] - launched December 19, 1963
• Explorer 20[?] - launched August 25, 1964
• Explorer 21[?] - launched October 4, 1964
• Explorer 22[?] - launched October 10, 1964
• Explorer 23[?] - launched November 6, 1964
• Explorer 24[?] - launched November 21, 1964
• Explorer 25[?] - launched November 21, 1964
• Explorer 26[?] - launched December 21, 1964
• Explorer 27[?] - launched April 29, 1965
• Explorer 28[?] - launched May 29, 1965
• Explorer 29[?] - launched November 6, 1965
• Explorer 30[?] - launched November 19, 1965
• Explorer 31[?] - launched November 29, 1965
• Explorer 32[?] - launched May 25, 1966
• Explorer 33[?] - launched July 1, 1966
• Explorer 34[?] - launched May 24, 1967
• Explorer 35[?] - launched July 19, 1967
• Explorer 36[?] - launched January 11, 1968
• Explorer 37[?] - launched March 5, 1968
• Explorer 38[?] - launched July 4, 1968
• Explorer 39[?] - launched August 8, 1968
• Explorer 40[?] - launched August 8, 1968
• Explorer 41[?] - launched June 21, 1969
• Explorer 42[?] - launched December 12, 1970
• Explorer 43[?] - launched March 13, 1971
• Explorer 44[?] - launched July 8, 1971
• Explorer 45[?] - launched November 15, 1971
• Explorer 46[?] - launched August 13, 1972
• Explorer 47[?] - launched September 23, 1972
• Explorer 48[?] - launched November 15, 1972
• Explorer 49[?] - launched June 10, 1973
• Explorer 50[?] - launched October 26, 1973
• Explorer 51[?] - launched December 16, 1973
• Explorer 52[?] - launched June 3, 1974
• Explorer 53[?] - launched May 7, 1975
• Explorer 54[?] - launched October 6, 1975
• Explorer 55[?] - launched November 20, 1975
• Explorer 56[?] - launched October 22, 1977
• Explorer 57[?] - launched January 26, 1978
• Explorer 58[?] - launched April 26, 1978
• Explorer 59[?] - launched August 12, 1978
• Explorer 60[?] - launched February 18, 1979
• Explorer 61[?] - launched October 30, 1979
• Explorer 62[?] - launched August 3, 1981
• Explorer 63[?] - launched August 3, 1981
• Explorer 64[?] - launched October 6, 1981
• Explorer 65[?] - launched August 16, 1984
• Explorer 66[?] - launched November 18, 1989
• Explorer 67[?] - launched June 7, 1992
• Explorer 68[?] - launched July 3, 1992
• Explorer 69[?] - launched December 30, 1995
• Explorer 70[?] - launched August 21, 1996
• Explorer 71[?] - launched August 25, 1997
• Explorer 72[?] - launched February 26, 1998
• Explorer 73[?] - launched April 2, 1998
• Explorer 74[?] - launched December 6, 1998
• Explorer 75[?] - launched March 5, 1999 - Failed
• Explorer 76[?] - launched May 18, 1999 - Failed
• Explorer 77[?] - launched June 23, 1999
• Explorer 78[?] - launched March 25, 2000

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"Explorer program" may also refer to the file browser[?] of Windows, called Windows Explorer[?].