Pioneer 4
Pioneer 4 — the first US spacecraft to escape Earth's gravity (launched 3 March 1959). It flew past the Moon on 4 March at about 60,000 km — too far for its photocell to trigger, so it took no lunar data — and carried on into orbit around the Sun, where it remains. Contact held to a then-record 655,000 km.
Key facts
Mission & specifications
Mission
- Operator
- NASA / JPL
- Launched
- March 3, 1959
- Status
- Completed
Trajectory
- Distance from the Sun
- 1.01 AU
- Distance from Earth
- 758,376 km
- Distance from Venus
- 0.605 AU
Mission
Pioneer 4 was the mission that finally worked — after a string of failures, it became the first American spacecraft to escape Earth's gravity. Launched on 3 March 1959, the little cone probe, twin to Pioneer 3, was aimed to fly close past the Moon. Its rocket performed well this time, carrying it clear of Earth and on toward the Moon, which it passed on 4 March at a distance of about sixty thousand kilometres. That was the one disappointment: the pass was farther out than planned, too far for the probe's photoelectric sensor to trigger, so it gathered no close lunar data. But the milestone stood — Pioneer 4 sailed on past the Moon and into orbit around the Sun, where it still travels today, and its signal was tracked to a then-unheard-of 655,000 kilometres, the deepest into space any human object had yet been followed.
- 1959First US Earth-escapeLaunch
Pioneer 4 becomes the first American spacecraft to escape Earth's gravity.
- 1959Lunar flybyFlyby
It passes the Moon farther out than planned — too far to trigger its photocell — then sails on toward solar orbit.
- 1959Last contactMission end
Tracked to a then-record 655,000 km before its signal fades; it still orbits the Sun.
Images
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