Editing Explorers Program (section)

==Cancelled missions==
[[File:WISE artist concept (PIA17254, crop).jpg|thumb|200px|WISE was restarted after it was turned off]]
[[File:Thor-Able III Explorer 6.jpg|thumb|right|200px|[[Explorer 6]] on a [[Thor-Able|Thor-Able III]] launch in August 1959]]
[[File:ISEE-C (ISEE 3) in dynamic test chamber.jpg|thumb|200px|right|ISEE-C in a dynamic test chamber, 1978]]
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.<ref>{{cite web|url=http://explorers.larc.nasa.gov/EX/ |title=Science Office for Mission Assessments: Explorer 2011 |website=Explorers.larc.nasa.gov |access-date=2016-02-24}}</ref> <!-- Missions of Opportunity (MO) are small collaborative missions with spacecraft not operated by NASA, such as an additional instrument. Examples of this include [[Astro-H]], [[CINDI]], [[TWINS]], and [[HETE-2]].  -->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.{{citation needed|date=September 2024}}

Examples of missions that were not developed or cancelled were:<ref name=skyrocket/>
*Owl 1 and 2 (cost, 1965)<ref>{{cite web|url=http://space.skyrocket.de/doc_sdat/explorer_owl.htm |title=Explorer: Owl 1, 2 |publisher=Space.skyrocket.de |access-date=2018-04-28}}</ref>
*MSS A (Magnetic Storm Satellite, Explorer-A, 1970)<ref>{{cite web|url=http://space.skyrocket.de/doc_sdat/explorer_mss-a.htm |title=Explorer: MSS A |publisher=Space.skyrocket.de |access-date=2018-04-28}}</ref><ref>{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=MSS-A |title=NASA - NSSDCA - Spacecraft - Details |publisher=Nssdc.gsfc.nasa.gov |date=2017-03-21 |access-date=2018-04-20}}</ref>
*CATSAT (STEDI 3) (cost)<ref name="nap" />
*IMEX (UNEX 2) (cost)<ref name="nap" />
*[[Full-sky Astrometric Mapping Explorer|FAME]] (MIDEX 4)
*SPIDR (SMEX 8) (technical, 2003)<ref name="nap" />
*[[Gravity and Extreme Magnetism|GEMS]] (SMEX 13)

Recent examples of conclusions of launched missions, cancelled due to budgetary constraints:
*[[Fast Auroral Snapshot Explorer|FAST]] - 2009
*[[TRACE]] - 2010 (Solar observatory, see [[Solar Dynamics Observatory]])
*[[Wilkinson Microwave Anisotropy Probe|Wilkinson MAP]] - 2010
*[[Wide-field Infrared Survey Explorer|WISE]] - 2011 (extended in 2013 as NEOWISE mission)
*[[Rossi X-ray Timing Explorer|RXTE]] - 2012
*[[GALEX|Galaxy Evolution Explorer]] - 2013