Explorer 1

Explorer 1

Explorer 1 in its orbital configuration, with the launch vehicle's fourth stage attached
Names	Explorer I 1958 Alpha 1
Mission type	Earth science
Operator	JPL / Army Ballistic Missile Agency
Harvard designation	1958 Alpha 1
COSPAR ID	1958-001A
SATCAT no.	00004
Mission duration	120 days (planned) 111 days (achieved)
Spacecraft properties
Spacecraft	Explorer I
Spacecraft type	Science Explorer
Bus	Explorer 1
Manufacturer	Jet Propulsion Laboratory
Launch mass	13.97 kg (30.8 lb)
Dimensions	203 cm (80 in) length 15.2 cm (6.0 in) diameter
Power	60 watts
Start of mission
Launch date	1 February 1958, 03:47:56 GMT
Rocket	Juno I (RS-29)
Launch site	Atlantic Missile Range, LC-26A
Contractor	Army Ballistic Missile Agency
Entered service	1 February 1958
End of mission
Last contact	23 May 1958
Decay date	31 March 1970
Orbital parameters
Reference system	Geocentric orbit[1]
Regime	Medium Earth orbit
Perigee altitude	358 km (222 mi)
Apogee altitude	2,550 km (1,580 mi)
Inclination	33.24°
Period	114.80 minutes
Revolution no.	58402
Instruments
Cosmic-Ray Detector Micrometeorite Detector Resistance Thermometers Satellite Drag Atmospheric Density
Explorer program 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 GMT (or 31 January 1958 at 22:47:56 Eastern Time) atop the first Juno booster from LC-26A at the Cape Canaveral Missile Test Center of the Atlantic Missile Range (AMR), in Florida. It was the first spacecraft to detect the Van Allen radiation belt,^[2] 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,^[3] the forerunner to the modern International Designator.