The Pioneer 4 mission was the second of two early attempts by the United States to send a spacecraft to the moon. Designed primarily to photograph the moon up close, Pioneer 4 did in fact fly past the moon, but at a much farther distance than planned. Because of the trajectory error, the camera sensor failed to trigger.

Pioneer 4 did provide extensive and valuable data on radiation and the tracking of space objects. After 82 hours of transmissions from Pioneer 4's tiny radio and and 655,000 miles of travel -- the farthest tracking distance for a human-made object at the time -- contact was lost on March 6, 1959.

Scientific Instruments

- Geiger tube detector