Officially known as Satellite 1958 Alpha, Explorer I was sent aloft as part of the United States program for the International Geophysical Year 1957-1958, on the evening of January 31, 1958. It was designed and built by the Jet Propulsion Laboratory of the California Institute of Technology under the direction of Dr. William H. Pickering. The satellite instrumentation it carried was designed and built by Dr. James Van Allen of the State University of Iowa.

Explorer I was the United States's "answer" to the Soviet launch of Sputnik I, on October 4, 1957.

Once in orbit, the cosmic ray equipment of the satellite indicated a much lower cosmic ray count than had been anticipated. Dr. Van Allen theorized that the equipment may have been saturated by very strong radiation from a belt of charged particles trapped in space by the earth's magnetic field. The existence of what we now know as the Van Allen Belt was confirmed by Explorer III, which was launched on March 26, 1958. The discovery of the Van Allen Belts was the most important discovery made by Explorer I, and probably one of the most outstanding discoveries of the International Geophysical Year.

Characteristics

Total Weight 30.8 pounds (14 kilograms)
Weight of Instrumentation 18.35 pounds

Length 80 inches (203 centimeters)
Diameter 6.25 inches (15.9 centimeters)

Launch Vehicle Jupiter-C rocket

Orbit Perigee 220 miles (354 kilometers)
Orbit Apogee 1,563 miles (2,515 kilometers)
Orbit Period 114.8 minutes

Instrumentation cosmic-ray detection package, internal temperature sensor, three external temperature sensors, nose-cone temperature sensor, micrometeorite impact microphone, micrometeorite erosion guages

Last Transmission May 23, 1958
Entered Earth's Atmosphere March 31, 1970

Questions or comments about this page?

The Robinson Library
Science.--Physics.--Geophysics. Cosmic Physics.

Search This Site | Usage Guidelines | About the Library | Contact Information | Navigation Help