The Small Explorer program (SMEX) is an effort within "NASA to fund "space exploration missions that cost no more than US$120 million. Extending the larger "Explorers program, it was started in 1989.
The first set of three SMEX missions were launched between 1992 and 1998. The second set of two missions were launched in 1998 and 1999. These missions were managed by the Small Explorer Project Office at NASA's "Goddard Space Flight Center (GSFC). In early 1999, that office was closed and with the announcement of opportunity for the third set of SMEX missions NASA converted the program so that each mission was managed by its Principal Investigator, with oversight by the GSFC Explorers Project.
As of 2017, NASA is funding a competitive study of five candidate heliophysics Small Explorers missions, with the expectation that one finalist proposal will be selected as a mission for flight in 2022. The proposals are Mechanisms of Energetic Mass Ejection – eXplorer (MEME-X), Focusing Optics X-ray Solar Imager (FOXSI), Multi-Slit Solar Explorer (MUSE), Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites (TRACERS), and Polarimeter to Unify the Corona and Heliosphere (PUNCH).
|"SAMPEX||SMEX-1||Explorer-68||3 July 1992||Ended: 30 June 2004
Reentered: 13 November 2012
|"TOMS-EP||2 July 1996|||
|"FAST||SMEX-2||Explorer-70||21 August 1996||Ended: 4 May 2009|
|"SWAS||SMEX-3||Explorer-74||6 December 1998||Ended: 21 July 2004|
|"TRACE||SMEX-4||Explorer-73||2 April 1998||Ended: 21 June 2010|
|"WIRE||SMEX-5||Explorer-75||5 March 1999||Spacecraft equipment failure
Reentered: 10 May 2011
|"RHESSI||SMEX-6||Explorer-81||5 February 2002||Operational|
|"GALEX||SMEX-7||Explorer-83||28 April 2003||Ended: May 2012
Decommissioned: 28 June 2013
|SPIDR||SMEX-8||Cancelled, instrument not sensitive as expected|
|"AIM||SMEX-9||Explorer-90||25 April 2007||Operational|
|"IBEX||SMEX-10||Explorer-91||19 October 2008||Operational|
|"NuSTAR||SMEX-11||Explorer-93||13 June 2012||Operational|
|"IRIS||SMEX-12||Explorer-94||28 June 2013||Operational|
|"GEMS||SMEX-13||Cancelled, expected cost overrun|
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