Since opening its doors in 1958, one of the core objectives of NASA has been to explore worlds beyond our own. On March 3, 1959, the young space agency achieved a thrilling milestone when it launched Pioneer 4, the first American spacecraft to travel beyond Earth orbit.

Not long after its inception, NASA planned two lunar flyby missions, Pioneer 3 and Pioneer 4. Developed by the Jet Propulsion Laboratory in California, these conical-shaped spacecrafts were relatively small, weighing in at roughly 13 pounds. The designs for Pioneer 3 and 4 were similar. One key difference was the addition of a voltage monitor in Pioneer 4, which was added after the radio transmitter in Pioneer 3 failed.

Pioneer 3 was intended to be the first spacecraft to leave Earth orbit, but a premature first stage engine shut down led to a failed attempt to break through Earth’s atmosphere.

Unlike Pioneer 3, Pioneer 4 successfully broke free from Earth’s atmosphere and traveled to the Moon. However, it did not pass close enough to trigger the image sensor. Pioneer 4 came within 37,000 miles of the lunar surface, roughly 17,000 miles off the planned trajectory.

Pioneer 4 did not achieve its primary mission objective to photograph the Moon. It did, however, provide important data regarding the Earth’s radiation belts and the tracking of space objects

NASA reports that contact was lost on March 6, after transmitting for 82 hours and traveling 655,000 miles (the farthest tracking of a human-made object at that point in time). Pioneer 4 ultimately entered heliocentric orbit. In doing so, it became the nation’s first spacecraft to orbit the Sun.

The Pioneer 4 mission may not have gone exactly to plan, but it proved to be a monumental flight that helped pave the path for later lunar expeditions.

Learn more about Pioneer 4