- 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