Model of the Pioneer 4 space probe in front of a map of its trajectory. Pioneer 4 launched on 3rd March 1959 on a mission to photograph the Moon during a close fly-by. It didnt achieve this goal as a longer than planned burn of the second stage engine set it on a trajectory that was too far from the lunar surface. However Pioneer 4 did become the first US spacecraft to leave Earths orbit. After passing the Moon, Pioneer 4 went into a heliocentric orbit.