Explorer 33

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Explorer 33
Mission typeMagnetospheric research
COSPAR ID1966-058A
SATCAT no.2258
Mission duration1,876 days (5 years, 1 month and 21 days)
Spacecraft properties
ManufacturerGoddard Space Flight Center
Launch mass212.0 kilograms (467.4 lb)
Start of mission
Launch dateJuly 1, 1966, 16:02:25 (1966-07-01UTC16:02:25Z) UTC
RocketDelta E1
Launch siteCape Canaveral LC-17A
End of mission
Last contactSeptember 21, 1971 (1971-09-22)
Orbital parameters
Reference systemGeocentric
RegimeHigh Earth
Perigee altitude265,689 kilometers (165,091 mi)
Apogee altitude480,762 kilometers (298,732 mi)
Period38792.0 minutes
RAAN173.5399 degrees
Argument of perigee119.2000 degrees
Mean anomaly21.7899 degrees
Mean motion0.03712071
Epoch12 May 1971, 12:00:00 UTC
Revolution no.142

Explorer 33 (also known as AIMP-D, IMP-D, AIMP 1, Anchored IMP 1, Interplanetary Monitoring Platform-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.[1] 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.[2]

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.[3] Principal investigator James Van Allen used electron and proton detectors aboard the spacecraft to investigate charged particle and X-ray activity.[4] 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.[5]

See also[edit]


  1. ^ J. J. Madden (December 1966). "Interim Flight Report, Anchored Interplanetary Monitoring Platform, AIMP I - Explorer XXXIII" (PDF). NASA Goddard Space Flight Center.
  2. ^ "IMP Chronology". Encyclopedia Astronautica. Archived from the original on January 16, 2010.
  3. ^ "Explorer 33 (NSSDC ID: 1966-058A)". NASA / National Space Science Data Center. April 2, 2008. Retrieved July 4, 2008.
  4. ^ "Explorer 33 – Electron and Proton Detectors". NASA / National Space Science Data Center. April 2, 2008. Retrieved July 4, 2008.
  5. ^ Crooker, N. U.; Feynman, J.; Gosling, J. T. (May 1, 1977). "On the high correlation between long-term averages of solar wind speed and geomagnetic activity". NASA. Retrieved July 4, 2008.

External links[edit]