Explorer 33 (IMP-D)

Explorer 33 (IMP-D) was a spin-stabilized spacecraft instrumented for studies of interplanetary plasma, energetic charged particles (electrons, protons, and alphas), magnetic fields, and solar X rays at lunar distances. The spacecraft failed to achieve lunar orbit but did achieve mission objectives. Explorer 33 was also known as Interplanetary Monitoring Platform D (IMP-D) or Anchored Interplanetary Monitoring Platform 1 (AIMP-1).