History
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; however, that proposal was rejected in favor of the U.S. Navy's Project Vanguard. The Explorer program was later reestablished 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.
The Explorer program was transferred to NASA, which continued to use the name for an ongoing series of relatively small space missions, typically an artificial satellite with a science focus. Over the years, NASA has launched a series of Explorer spacecraft carrying a wide variety of scientific investigations.
Explorer satellites have made important discoveries: Earth's magnetosphere and the shape of its gravity field; the solar wind; properties of micrometeoroids raining down on the Earth; much about ultraviolet, cosmic, and X-rays from the solar system and universe beyond; ionospheric physics; Solar plasma; solar energetic particles; and atmospheric physics. These missions have also investigated air density, radio astronomy, geodesy, and gamma ray astronomy. Various space telescopes have made a variety of discoveries, including the first known Earth Trojan asteroid.
The Explorers Program Office at Goddard Space Flight Center in Greenbelt, Maryland, provides management of the multiple scientific exploration missions in the Explorer space flight program. The missions are characterized by relatively moderate cost, and by small to medium sized missions that are capable of being built, tested and launched in a short time interval compared to the large observatories.
Explorer categories have included MIDEX, SMEX, UNEX, and others. A subprogram called Missions of Opportunity (MO) has funded instruments on non-NASA missions.
THEMIS/ARTEMIS, Swift, RHESSI, ACE, AIM, IBEX, and NuSTAR are active missions as of 2012. In 2012, GALEX switched to University funding to continue its mission. IRIS is a future mission.
Hibernating missions include ISEE-3/ICE, SWAS, and WISE. GEMS (SMEX) was planned, but was cancelled in 2012.
Read more about this topic: Explorer Program
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