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Explorer 41 (IMP-G) was a spin-stabilized spacecraft placed into a high-inclination, highly elliptic orbit to measure energetic particles, magnetic fields, and plasma in cislunar space. The line of apsides and the satellite spin vector were within a few degrees of being parallel and normal, respectively, to the ecliptic plane. Initial local time of apogee was about 1300 h. Initial satellite spin rate was 27.5 rpm. The basic telemetry sequence was 20.48 s. The spacecraft functioned very well from launch until it decayed from orbit on December 23, 1972. Data transmission was nearly 100% for the spacecraft life except for the interval from November 15, 1971, to February 1, 1972, when data acquisition was limited to the vicinity of the magnetotail neutral sheet.

Alternate Names

  • 03990
  • Explorer 41
  • IMP 5
  • PL-691K

Facts in Brief

Launch Date: 1969-06-21
Launch Vehicle: Delta
Launch Site: Vandenberg AFB, United States
Mass: 175 kg

Funding Agency

  • NASA-Office of Space Science Applications (United States)


  • Space Physics

Additional Information

Questions and comments about this spacecraft can be directed to: Coordinated Request and User Support Office



NameRoleOriginal AffiliationE-mail
Ms. Della StewartGeneral ContactNASA Goddard Space Flight Center
Mr. B. H. FererGeneral ContactNASA Goddard Space Flight Center
Mr. Harold H. LevyGeneral ContactNASA Goddard Space Flight Center
Dr. Frank B. McDonaldProject ScientistNASA Goddard Space Flight Center
Dr. Alois W. SchardtGeneral ContactNASA Headquarters
Mr. Paul ButlerProject ManagerNASA Goddard Space Flight Center
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