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Explorer I

Explorer 1
Explorer1.jpg
Explorer 1 in its orbital configuration, with the launch vehicle's fourth stage attached
Mission type Earth science
Operator Army Ballistic Missile Agency
Harvard designation 1958 Alpha 1
COSPAR ID 1958-001A
SATCAT no. 00004
Mission duration 111 days
Spacecraft properties
Manufacturer Jet Propulsion Laboratory
Launch mass 13.97 kilograms (30.8 lb)
Dimensions 80.75 inches (205.1 cm) length
6.00 inches (15.2 cm) diameter
Power 60 watts
Start of mission
Launch date February 1, 1958, 03:48 (1958-02-01UTC03:48Z) UTC
Rocket Juno I RS-29
Launch site Cape Canaveral LC-26A
End of mission
Last contact May 23, 1958 (1958-05-24)
Decay date March 31, 1970
Orbital parameters
Reference system Geocentric
Regime MEO
Semi-major axis 7,832.2 kilometers (4,866.7 mi)
Eccentricity 0.140
Perigee 358 kilometers (222 mi)
Apogee 2,550 kilometers (1,580 mi)
Inclination 33.24°
Period 114.8 minutes
RAAN 334.6171 degrees
Argument of perigee 311.5310 degrees
Mean anomaly 48.3249 degrees
Mean motion 16.275
Epoch 31 March 1970, 00:50:24 UTC
Revolution no. 58402
Instruments
Cosmic-Ray Detector
Micrometeorite Detector
Satellite Drag Atmospheric Density

Explorer 1 was the first satellite of the United States, launched as part of its participation in the International Geophysical Year. The mission followed the first two satellites the previous year; the Soviet Union's Sputnik 1 and 2, beginning the Cold War Space Race between the two nations.

Explorer 1 was launched on January 31, 1958 at 22:48 Eastern Time (equal to February 1, 03:48 UTC) atop the first Juno booster from LC-26 at the Cape Canaveral Missile Annex, Florida. It was the first spacecraft to detect the Van Allen radiation belt, returning data until its batteries were exhausted after nearly four months. It remained in orbit until 1970, and has been followed by more than 90 scientific spacecraft in the Explorer series.

Explorer 1 was given Satellite Catalog Number 4, and the Harvard designation 1958 Alpha 1, the forerunner to the modern International Designator.

The U.S. Earth satellite program began in 1954 as a joint U.S. Army and U.S. Navy proposal, called Project Orbiter, to put a scientific satellite into orbit during the International Geophysical Year. The proposal, using a military Redstone missile, was rejected in 1955 by the Eisenhower administration in favor of the Navy's Project Vanguard, using a booster advertised as more civilian in nature. Following the launch of the Soviet satellite Sputnik 1 on October 4, 1957, the initial Project Orbiter program was revived as the Explorer program to catch up with the Soviet Union.


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