Editing Explorer 2 (section)

{{Short description|1958 American failed space mission which attempted to place a satellite into orbit}}
{{about|the U.S. Army exploratory satellite|other uses|Explorer Two (disambiguation)}}
{{Use American English|date=February 2021}}
{{Use dmy dates|date=February 2021}}
{{Infobox spaceflight
| name                = Explorer 2
| names_list          = Explorer II
| image               = Juno-1 explorer-2.jpg
| image_caption       = Launch of Explorer 2 satellite
| image_size          = 300px

| mission_type        = [[Earth science]]
| operator            = [[Jet Propulsion Laboratory|JPL]] / [[Army Ballistic Missile Agency]]
| Harvard_designation = 
| COSPAR_ID           = 
| SATCAT              = 
| mission_duration    = Failed to orbit<br/>120 days (planned)

| spacecraft          = Explorer II
| spacecraft_type     = Science Explorer
| spacecraft_bus      = [[Explorer 1]]
| manufacturer        = [[Jet Propulsion Laboratory]]
| launch_mass         = {{cvt|14.22|kg}}
| dimensions          = {{cvt|203|cm}} length<br/>{{cvt|15.2|cm}} diameter
| power               = 60 [[watt]]s

| launch_date         = 5 March 1958, 18:27:57 [[Greenwich Mean Time|GMT]]<ref name="JSR1"/>
| launch_rocket       = [[Juno I]] (RS-26)
| launch_site         = [[Eastern Range|Atlantic Missile Range]], [[Cape Canaveral Launch Complex 26|LC-26A]]
| launch_contractor   = [[Army Ballistic Missile Agency]]

| entered_service     = 
| last_contact        = 
| destroyed           = Failed to orbit
| decay_date          = 

| orbit_reference     = [[Geocentric orbit]] (planned) <ref name="Trajectory">{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/displayTrajectory.action?id=1958-001A|title=Trajectory: Explorer-1 1958-001A|publisher=NASA|date=14 May 2020|access-date=13 February 2021}} {{PD-notice}}</ref>
| orbit_regime        = [[Medium Earth orbit]]
| orbit_periapsis     = {{cvt|358|km}}
| orbit_apoapsis      = {{cvt|2550|km}}
| orbit_inclination   = 32.24°
| orbit_period        = 114.80 minutes
| apsis               = gee

| instruments         = Geiger counter<br/>Micrometeorite Detector<br/>Satellite Drag Atmospheric Density<br/>Resistance Thermometers<br/>Thermometers

| programme           = '''Explorer program'''
| previous_mission    = [[Explorer 1]]
| next_mission        = [[Explorer 3]]
}}

'''Explorer 2''' was an American unmanned space mission within the [[Explorer program]]. Intended to be a repetition of the previous [[Explorer 1]] mission, which placed a satellite into medium Earth orbit, the spacecraft was unable to reach orbit due to a failure in the launch vehicle during launch.

Explorer 2 was launched from Cape Canaveral Missile Test Center of the Atlantic Missile Range (AMR), [[Cape Canaveral Launch Complex 26|LC-26A]] in Florida on 5 March 1958 at 18:27:57 GMT by a [[Juno I]] launch vehicle.<ref name="jsr">{{cite web|url=http://www.planet4589.org/space/lvdb/launch/Redstone|title=Launch Vehicle Database - Redstone|publisher=Jonathan's Space Report|access-date=13 February 2021|archive-date=10 October 2007|archive-url=https://web.archive.org/web/20071010035912/http://www.planet4589.org/space/lvdb/launch/Redstone|url-status=dead}}</ref> The Juno I had its origins in the United States Army's [[Project Orbiter]] in 1954. The project was canceled in 1955 when the decision was made to proceed with [[Project Vanguard]].