Living History: January 31, 1958, 1st US Satellite in Orbit

Explorer I is the first U.S. satellite to go into orbit. It was launched Jan. 31, 1958, by a Jupiter C rocket from Cape Canaveral, Fla. (NASA photo.)

Living History:

WASHINGTON, Jan. 30, 2009 -- On Jan. 31, 1958, Explorer I was the first U.S. satellite to go into orbit. It was launched by a Jupiter-C rocket from Cape Canaveral, Fla., in response to the launch of the Soviet satellite Sputnik 1. It was the first spacecraft to detect the Van Allen radiation belt.

The primary science instrument on Explorer 1 was a cosmic ray detector designed to measure the radiation environment in Earth orbit. Once in space this experiment, provided by Dr. James Van Allen of the University of Iowa, revealed a much lower cosmic ray count than expected. Van Allen theorized that the instrument may have been saturated by very strong radiation from a belt of charged particles trapped in space by Earth's magnetic field. The existence of these radiation belts was confirmed by another U.S. satellite launched two months later, and they became known as the Van Allen Belts in honor of their discoverer.

Explorer 1 was designed and built by the Jet Propulsion Laboratory of the California Institute of Technology under the direction of Dr. William H. Pickering. The Jupiter-C rocket was modified by the Army Ballistic Missile Agency to accommodate a satellite payload under the direction of Dr. Wernher von Braun. The Jupiter-C launch vehicle consisted of a modified version of the Redstone rocket's first stage and two upper stages of clustered Sergeant rockets later designated as Juno boosters for space launches.

May 23, 1958 - Signal ended when batteries ran out

March 31, 1970 - Burned up on re-entry over Pacific Ocean

Orbited Earth once every 114.8 minutes after launch, or 12.54 orbits per day

Completed 58,000 orbits times before returning to Earth in March 1970

Orbit path took it as close as 354 kilometers (220 miles) to Earth and as far as 2,515 kilometers (1,563 miles) from Earth

(Report from a NASA, Jet Propulsion Laboratory news release.)

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