||This article contains orbital elements but does not include an epoch, or date when those elements, which typically vary over time, were correct.|
|Mission type||Magnetospheric research|
|Mission duration||1,876 days (5 years, 1 month and 21 days)|
|Manufacturer||Goddard Space Flight Center|
|Launch mass||212.0 kilograms (467.4 lb)|
|Start of mission|
|Launch date||July 1, 1966, 16:02:25UTC|
|Launch site||Cape Canaveral LC-17A|
|End of mission|
|Last contact||September 21, 1971|
|Perigee||265,689 kilometers (165,091 mi)|
|Apogee||480,762 kilometers (298,732 mi)|
|Argument of perigee||119.2000 degrees|
|Mean anomaly||21.7899 degrees|
|Epoch||12 May 1971 12:00:00|
Explorer 33 (also known as AIMP-D or IMP-D) was a spacecraft in the Explorer program launched by NASA on July 1, 1966 on a mission of scientific exploration. Originally intended for a lunar orbit, mission controllers worried that the spacecraft's trajectory was too fast to guarantee lunar capture. Consequently, mission managers opted for a backup plan of placing the craft into an eccentric Earth orbit with a perigee of 265,679 km and an apogee of 480,762 km — still reaching distances beyond the Moon's orbit.
Despite not attaining the intended lunar orbit, the mission met many of its original goals in exploring solar wind, interplanetary plasma, and solar X-rays. Principal investigator James Van Allen used electron and proton detectors aboard the spacecraft to investigate charged particle and X-ray activity. Astrophysicists N. U. Crooker, Joan Feynman, and J. T. Gosling used data from Explorer 33 to establish relationships between the Earth's magnetic field and the solar wind speed near Earth.
- J. J. Madden (December 1966). "Interim Flight Report, Anchored Interplanetary Monitoring Platform, AIMP I - Explorer XXXIII". NASA Goddard Space Flight Center.
- "IMP Chronology". Encyclopedia Astronautica.
- "Explorer 33 (NSSDC ID: 1966-058A)". NASA / National Space Science Data Center. 2008-04-02. Retrieved 2008-07-04.
- "Explorer 33 – Electron and Proton Detectors". NASA / National Space Science Data Center. 2008-04-02. Retrieved 2008-07-04.
- Crooker, N. U.; Feynman, J.; Gosling, J. T. (1977-05-01). "On the high correlation between long-term averages of solar wind speed and geomagnetic activity". NASA. Retrieved 2008-07-04.
- AIMP-D Technical Summary Description
- Second Interim Flight Report - AIMP-I - Explorer XXXIII
- Observations of the earth's magnetic tail and neutral sheet at 510,000 km by Explorer 33 - 1966
- Observations of the earth's magnetic tail and neutral sheet at 510,000 km by Explorer 33 - 1967
- Mapping of the earth's bow shock and magnetic tail by Explorer 33
- Energetic particles in the outer magnetosphere - Explorer 33