Editing Explorer 1 (section)

{{Short description|First satellite launched by the United States (1958)}}
{{About|the U.S. satellite|other uses|Explorer One (disambiguation)}}
{{Other uses|Explorer (disambiguation)}}
{{Use American English|date=February 2021}}
{{Use dmy dates|date=February 2021}}
{{Infobox spaceflight
| name                = Explorer 1
| names_list          = Explorer I<br/>1958 Alpha 1
| image               = Explorer1.jpg
| image_caption       = Explorer 1 in its orbital configuration, with the launch vehicle's fourth stage attached
| image_size          = 

| mission_type        = [[Earth science]]
| operator            = [[Jet Propulsion Laboratory|JPL]] / [[Army Ballistic Missile Agency|ABMA]]
| Harvard_designation = 1958 Alpha 1  
| COSPAR_ID           = 1958-001A
| SATCAT              = 00004
| mission_duration    = 120 days (planned)<br/>111 days (achieved)

| spacecraft          = Explorer I
| spacecraft_type     = Science Explorer
| spacecraft_bus      = Explorer 1
| manufacturer        = [[Jet Propulsion Laboratory]]
| launch_mass         = {{cvt|13.97|kg}}
| dimensions          = {{cvt|203|cm}} length<br/>{{cvt|15.2|cm}} diameter
| power               = 60 [[watt]]s

| launch_date         = 1 February 1958, 03:47:56 [[Greenwich Mean Time|GMT]]
| launch_rocket       = [[Juno I]] (RS-29)
| launch_site         = [[Eastern Range|Atlantic Missile Range]], [[Cape Canaveral Launch Complex 26|LC-26A]]
| launch_contractor   = [[Army Ballistic Missile Agency]]

| entered_service     = 1 February 1958
| last_contact        = 23 May 1958
| destroyed           = 
| decay_date          = 31 March 1970

| orbit_reference     = [[Geocentric orbit]]<ref name="Trajectory"/>
| orbit_regime        = [[Medium Earth orbit]]
| orbit_periapsis     = {{cvt|358|km}}
| orbit_apoapsis      = {{cvt|2550|km}}
| orbit_inclination   = 33.24°
| orbit_period        = 114.80 minutes
| orbit_rev_number    = 58402
| apsis               = gee

| instruments         = Cosmic-Ray Detector<br/>Micrometeorite Detector<br/>Resistance Thermometers<br/>Satellite Drag Atmospheric Density

| programme           = '''[[Explorer program]]'''
| previous_mission    = 
| next_mission        = [[Explorer 2]]
}}

'''Explorer 1''' was the first satellite launched by the [[United States]] in 1958 and was part of the U.S. participation in the [[International Geophysical Year]] (IGY). The mission followed the first two satellites, both launched by the [[Soviet Union]] during the previous year, [[Sputnik 1]] and [[Sputnik 2]]. This began a [[Space Race]] during the [[Cold War]] between the two nations.

Explorer 1 was launched on 1 February 1958 at 03:47:56 [[Greenwich Mean Time|GMT]] (or 31 January 1958 at 22:47:56 Eastern Time) atop the first [[Juno I]] booster from [[Cape Canaveral Launch Complex 26|LC-26A]] at the [[Cape Canaveral Space Force Station|Cape Canaveral Missile Test Center]] of the [[Eastern Range|Atlantic Missile Range]] (AMR), in [[Florida]]. It was the first spacecraft to detect the [[Van Allen radiation belt]],<ref>Paul Dickson, ''Sputnik: The Launch of the Space Race'', Toronto: MacFarlane Walter & Ross, 2001, p. 190.</ref> returning data until its batteries were exhausted after nearly four months. It remained in orbit until 1970.

Explorer 1 was given Satellite Catalog Number 00004 and the Harvard designation 1958 Alpha 1,<ref name="Yost">{{cite book |url=http://www.oosa.unvienna.org/pdf/inf044E.pdf |title=Registration data for United States Space Launches |last=Yost |first=Charles W. |publisher=United Nations Office for Outer Space Affairs |date=6 September 1963 |access-date=30 July 2024}}</ref> the forerunner to the modern [[International Designator]].