Pioneer 4
Pioneer 4 was a NASA, Army Ballistic Missile Agency and JPL lunar-flyby probe launched on March 3, 1959. It carried two Geiger-Mueller counters and a photoelectric sensor trigger. Its March 4 passage about 60,000 kilometers from the Moon was too distant for the intended optical experiment, but radiation measurements were returned. It became the first U.S. spacecraft to escape Earth and enter solar orbit, transmitting for 82 hours.
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Identity
- Aliases
- Pioneer 4Pioneer P-4Juno II Pioneer 4 Lunar Flyby Probe
- Name
- Pioneer 4
- Status
- completed
Details
- Astronauts
- -
- Description
- Pioneer 4 was a NASA, Army Ballistic Missile Agency and JPL lunar-flyby probe launched on March 3, 1959. It carried two Geiger-Mueller counters and a photoelectric sensor trigger. Its March 4 passage about 60,000 kilometers from the Moon was too distant for the intended optical experiment, but radiation measurements were returned. It became the first U.S. spacecraft to escape Earth and enter solar orbit, transmitting for 82 hours.
- Destination
- Heliocentric orbit after a lunar flyby at approximately 60,000 km range; first U.S. spacecraft to escape Earth’s gravity and return Van Allen Belt data
- End Date
- 1959-03-06
- Outcome
- Lunar-flyby mission with a missed primary imaging objective. Pioneer 4 passed the Moon at about 60,000 km rather than the planned 32,000 km, so the imaging scanner did not function. It nevertheless returned excellent Van Allen Belt data, became the first U.S. spacecraft to reach Earth escape velocity and enter heliocentric orbit, and transmitted for 82 hours.
- Programs
- Start Date
- 1959-03-03
- Vehicle Families
Links
- Official Url
- https://science.nasa.gov/mission/pioneer-4/
Assets & Meta
- Creation Time
- August 14, 2026 at 17:41:44 UTC
- Updated Time
- October 17, 2026 at 14:02:02 UTC
Other
- Affiliations
- Space Stations
- -
- Vehicles