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Pioneer 4

Scientist James Van Allen inspecting the cone-shaped Pioneer 4 probe prior to launch.
Scientist James Van Allen inspecting the cone-shaped Pioneer 4 probe prior to launch. Photo: NASA/JPL

Launched on March 3, 1959, NASA’s 13-pound Pioneer 4 probe passed by the Moon at a distance of 37,000 miles (60,000 km). It failed to photograph the Moon as planned, but Pioneer 4 became the first U.S.-built spacecraft to escape Earth’s gravity and enter into a heliocentric orbit, where it remains to this day. A fine addition to our spaceflight museum.

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