Explorer 33
Explorer 33 — meant to be the first US spacecraft in orbit around the Moon (launched 1 July 1966). Its rocket stages gave it too much speed for its retrorocket to put it into lunar orbit, so it was left in a huge, elongated Earth orbit reaching beyond the Moon's. From there it measured the magnetic fields, plasma and energetic particles between Earth and Moon until September 1971. (Its orbit is drawn to its initial published size; its orientation and position on it are representative.)
Key facts
Mission & specifications
Mission
- Operator
- NASA
- Launched
- July 1, 1966
- Status
- Completed
Trajectory
- Distance from the Sun
- 0.998 AU
- Computed from the cached position
- Distance from Earth
- 4,164,630 km
- Computed from cached positions
- Distance from Venus
- 0.281 AU
- Computed from cached positions
Mission
Explorer 33, also called IMP-D and the first Anchored Interplanetary Monitoring Platform, was planned to be the first US spacecraft in orbit around the Moon. It was a 93 kg octagonal drum with four solar-cell paddles and two magnetometer booms, built to study magnetic fields, plasma and energetic particles near the Moon, and to map the Moon's gravity from orbit. It was launched from Cape Kennedy on 1 July 1966, and its Delta rocket's second and third stages both gave too much thrust: about 21 m/s more speed toward the Moon than its small retrorocket was able to remove. Instead of entering lunar orbit, it was put into a highly elongated Earth orbit whose far point lay beyond the Moon. It came within 35,000 km of the Moon on its first orbit and within 40,000 to 60,000 km on later passes in 1966. From that orbit it nevertheless did most of what it had been built for, measuring the magnetic fields and radiation between Earth and the Moon. In January 1967 engineers at Goddard restored power to a blacked-out circuit by remote command — the most distant repair of a spacecraft made until then. Its experiments worked until September 1971, and no data came after 21 September.
- 1966Explorer 33 launches toward the Moon on a Delta rocketLaunch
Its second and third stages give it about 21 m/s more speed than planned.
- 1971Last dataMission end
After five years measuring fields and particles from a long Earth orbit.
Images
Images from open archives · credit shown per image