Explorer I

Part of the Explorer program

Explorer I was the first United States satellite. It consisted of the fourth stage of the Jupiter C rocket, and was built by the Army Ballistic Missile Agency and JPL. The satellite provided preliminary information on the environment and conditions in space outside Earth's atmosphere. It resulted in the discovery of the Van Allen radiation belts, named after the cosmic ray instrument scientist, Dr. James A. Van Allen.

Spacecraft
The spacecraft was built within the fourth stage section of the rocket. It consisted of a lower fiberglass ring with external temperature sensors mounted onto it along with four turnstile antenna wires for the high power transmitter. Above that were the science instruments and just below the nose cone was the low power transmitter and batteries. The nose cone held another temperature guage.

Payload
Instruments included a cosmic ray and micrometeorite package, a micrometeorite impact microphone, micrometeorite erosion guages, and internal and external temperature guages.

Status as of
Circled the Earth more than 58,000 times before re-entering the Earth's atmosphere over the South Pacific March 31, 1970.

Country of Origin	United States
Customer/User	US Army
Manufacturer(s)	Army Ballistic Missile Agency, Jet Propulsion Laboratory
Size	2.05 m long x 16.5 cm diameter
Orbit	347 x 1859 km @ 33.2 degrees inclination
Design Life	~ 4 months operational

Launch Facts

Name	Int'l Desig.	Date	Site	Vehicle	Orbit	Mass(kg)
Notes
Explorer 1	1958-[Alpha]1	1/31/58	ESMC	Jupiter C	LEO	5 kg
Discovered Van Allen radiation belts; 1st successful US orbital launch