Explorer 18 (IMP 1, Interplanetary Monitoring Platform) was a solar-cell and chemical-battery powered spacecraft instrumented for interplanetary and distant magnetospheric studies of energetic particles, cosmic rays, magnetic fields, and plasmas. November 27, 1963 at 02:30 UTC · Launch Successful Thor Delta C — United States Air Force, to Elliptical Orbit Space Launch Complex 17B, Cape Canaveral SFS, FL, USA The world's 283rd orbital launch attempt, and 59th of 1963. Data: Launch Library 2, The Space Devs. Image by NASA (NASA Image and Media Guidelines) via The Space Devs.