Share this page:

Explorer 1

The First U.S. Satellite

William Pickering, the director of NASA's Jet Propulsion Laboratory, scientist James Van Allen and rocket pioneer Wernher von Braun hold up a model of the Explorer 1 spacecraft during a press conference for the satellite's successful launch into space.
› Larger view
Explorer Spacecraft

A model of the Explorer series of spacecraft. Image credit: NASA/JPL-Caltech
› Larger view
Cosmic-Ray Detector

Explorer 1's payload principally consisted of a cosmic-ray detector, which gave the satellite added notoriety when it lead to the finding that Earth is surrounded by radiation belts (later named Van Allen belts in honor of their discoverer) held in place by the planet's magnetic field. Here, the instrument's designer, George Ludwig, poses with his creation. Image credit: NASA/JPL-Caltech
› Larger view
Launch of Explorer

Through the combined efforts of JPL and the Army Ballistic Missile Ballistic Agency, Explorer 1 launched from Cape Canaveral, Fla., on Jan. 31, 1958. There was a nail-biting wait before tracking stations confirmed that Explorer 1 had successfully gone into orbit around Earth. With the launch of Explorer 1, the United States entered the space age.
› Larger view
Prepping Explorer

In late 1957, teams at JPL worked on the complex pieces required to build the Explorer 1 satellite. Here, Explorer 1 is test-mated before launch by engineers (from left) John Small, Gene Hendricks and Dee Trimble. Explorer 1 was launched successfully on Jan. 31, 1958, and became the first satellite to carry science instruments.
› Larger view
Getting Ready for Launch

On Jan. 20, 1958, technicians lowered the Explorer 1 satellite payload onto the launch vehicle's fourth-stage motor. The photo was taken in the gantry at Launch Complex 26, Patrick Air Force Base, Florida. Explorer 1 launched successfully on Jan. 31, 1958. Image courtesy: NASA/JPL-Caltech
› Larger view
JPL Ground Antenna

On March 22, 1956, preliminary satellite tracking tests began in a field near JPL. The prototype Microlock ground receiving station included the antenna, instrumentation built into a 25-foot van, generators, and other equipment. Less than two years later, the Microlock receiving station helped tracked the successful orbit of Explorer 1. Image courtesy: NASA/JPL-Caltech
› Larger view

Mission Summary

Explorer 1 became the first successfully satellite launched by the United States when it was sent to space on January 31, 1958. A quick response to the Soviet Union's launch of Sputnik 1, Explorer 1's success marked the beginning of the U.S. Space Age.

The satellite, which was designed, built and operated by the NASA Jet Propulsion Laboratory, carried a cosmic ray detector, which lead to Explorer Principal Investigator Dr. James Van Allen's discovery of radiation belts around Earth held in place by the planet's magnetic field. The findings were later named Van Allen belts in honor of their discoverer.

Mission Events

January 31, 1958: Explorer 1 launches successfully into space, marking the beginning of U.S. space exploration.

May 23, 1958: Explorer 1 makes its final transmission to Earth.

May 31, 1958: After more than 58,000 Earth orbits, Explorer 1 enters Earth's atmosphere and blows up.

Key Discoveries

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 State 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.

Scientific Instrument(s)

- Cosmic-ray detector
- Micrometeorite detector

Fast Facts

Type:	Orbiter

Status:	Past

Launch Date:	January 31, 1958 10:48 p.m. EST (03:48 UTC, February 1)

Launch Location:	Cape Canaveral Air Force Station, Florida

Mission End Date:	May 31, 1958

Target:	Earth

Resources

› Mission Website

› NASA Mission Website

› Interactive

› Fast Facts

› The World of Explorer 1

	Cassini Probe to Take Photo of Earth From Deep Space › Read more
	The Turbulent, High-Energy Sky Is Keeping NuSTAR Busy › Read more
	Warm Ocean Causing Most Antarctic Ice Shelf Mass Loss › Read more