Smithsonian Institution photograph #80-4976 by D. Penland	Milestone: First Successful United States Satellite
	Date of Milestone: 1958
	Spacecraft: Explorer 1
	Operated by: NASA Jet Propulsion Laboratory
	Spacecraft Location: Smithsonian Institution, National Air and Space Museum, Milestones of Flight Gallery

Explorer 1 became America's first satellite on January 31, 1958. Following the Soviet success with Sputnik and the embarrassing failure in December 1957 of the first American attempt to launch a satellite, the U.S. Army launched a scientific satellite using a rocket that had been developed to test guided missile components.

Explorer 1 carried an instrument package developed by a team at the State University of Iowa under the direction of Professor James A. Van Allen. Data returned by Explorer 1 and Explorer 3 (launched in March 1958) provided evidence that the Earth is surrounded by intense bands of radiation, now called the Van Allen radiation belts. This was the first major scientific discovery of the space age.

Design Features (in comparison to Sputnik 1):

Sputnik 1	Explorer 1

• More than twice the size of a basketball, Sputnik was larger and heavier than Explorer. Only the striped section of Explorer contained the payload; the rear half was a solid-fuel rocket motor.
• Sputnik’s sphere was polished to a high sheen to aid in tracking by telescope. Explorer’s light and dark stripes helped control its temperature.
• Despite Sputnik’s streamlined appearance, it tumbled while in orbit. Explorer spun about its long axis, which extended its four flexible antennas.
• Sputnik contained two radio transmitters, which sent back the “beep-beep-beep” heard round the world. Explorer contained a cosmic ray detector, radio transmitter, and temperature and micrometeoroid sensors.

People:

Three key Explorer 1 team members triumphantly display a full-scale model of the satellite after its successful launch.

From left to right:

William H. Pickering, director of the Jet Propulsion Laboratory, which designed and built Explorer.

James A. Van Allen, University of Iowa physicist who directed the design and creation of Explorer’s instruments.

Wernher von Braun, head of the U.S. Army Ballistic Missile Agency team that designed and built the Jupiter-C rocket.

Explorer 1
Identical backup for the original satellite

This satellite was built as a backup-an identical unit for the original Explorer 1. It could have been launched if the first one had failed. The striped portion contains the instruments, radios, and batteries. It is attached to a single solid-propellant rocket motor, which served as the launch vehicle's fourth stage.

Transferred from the Jet Propulsion Laboratory and NASA

More Information:

• Learn more about Sputnik 1 and the events leading to the launch of Explorer 1.
• Learn more about the U.S.-Soviet competition in space in the Space Race exhibition (Gallery 114).