text: Beacon Explorers Three satellites were planned in this series: Beacon Explorer-A, Beacon Explorer-B, Beacon Explorer-C.
  GEOS series
  A series of three Geodetic Earth Orbiting Satellite (GEOS) were put in orbit: GEOS 1, GEOS 2, GEOS 3.
  Launched spacecraft
  Explorer name numbers can be found in the NSSDC master catalog, typically assigned to each spacecraft in a mission. These numbers were not officially assigned until after 1975.
  Cancelled missions
  Many missions are proposed, but not selected. For example, in 2011, the Explorers Program received 22 full missions solicitations, 20 Missions of Opportunity, and 8 USPI. Sometimes mission are only partially developed but must be stopped for financial, technological, or bureaucratic reasons. Some missions failed upon reaching orbit including WIRE and TERRIERS.
  Examples of missions that were not developed or cancelled were:
  Owl 1 and 2 (cost, 1965)
  MSS A (Magnetic Storm Satellite, Explorer-A, 1970)
  CATSAT (STEDI 3) (cost)
  IMEX (UNEX 2) (cost)
  FAME (MIDEX 4)
  SPIDR (SMEX 8) (technical, 2003)
  GEMS (SMEX 13)
  Recent examples of conclusions of launched missions, cancelled due to budgetary constraints:
  FAST - 2009
  TRACE - 2010 (Solar observatory, see Solar Dynamics Observatory)
  Wilkinson MAP - 2010
  WISE - 2011 (extended in 2013 as NEOWISE mission)
  RXTE - 2012
  Galaxy Evolution Explorer - 2013
  Launch statistics
  Number of launches per decade: