Dr. James Van Allen is looking at the cone-shaped Pioneer probe, before it was gold plated and painted with stripes (to maintain temperature during flight). Image Credit: NASA/JPL

Launch Date March 3, 1959 | 05:10:45 UT
Launch Site Cape Canaveral, Florida, USA | Launch Complex 5
Destination Earth's Moon
Type Flyby
Status Partial Success
Nation United States
Alternate Names 00113, 1959-013A


Photograph the Moon during a flyby. It also carried sensors to study radiation in space.


A navigation malfunction send the spacecraft flying past the Moon at twice the planned distance and its camera sensor was not triggered. It did send back 82 hours of valuable scientific data on radiation in space.

In Depth

Although it did not achieve its primary objective to photograph the Moon during a flyby, Pioneer 4 was the first U.S. spacecraft to reach escape velocity.

During the launch, the Sergeants of the second stage did not cut off on time and caused the azimuths and elevation angles of the trajectory to change. The spacecraft thus passed by the Moon at a range of 37,000 miles (59,545 kilometers (instead of the planned 20,000 miles, or 32,000 kilometers) not close enough for the imaging scanner to function.

The closest approach was at 10:25 UT on 4 March 1959.

The spacecraft's tiny radio transmitted information for 82 hours before contact was lost at a distance of 655,000 kilometers from Earth, the greatest tracking distance for a human-made object at the time. The probe eventually entered heliocentric orbit and became the first American spacecraft to do so. Scientists received excellent data on radiation in space.

Key Dates

Mar. 4, 1959: Lunar Flyby


Launch Vehicle: Juno II (no. AM-14)

Spacecraft Mass: 14 pounds (6.1 kilograms)

Spacecraft Instruments:

  1. photoelectric sensor trigger
  2. two Geiger-Mueller counters

Additional Resources

National Space Science Data Center Master Catalog: Pioneer 4

Far Travelers: The Exploring Machines

Selected References

Siddiqi, Asif A. Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, NASA, 2002.

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