Explorer 26 was a spin-stabilized, solar-cell-powered spacecraft instrumented to measure cosmic-ray particles, trapped particles, solar wind protons, and magnetospheric and interplanetary magnetic fields. December 21, 1964 at 09:00 UTC · Launch Successful Thor Delta C — United States Air Force, to Elliptical Orbit Space Launch Complex 17A, Cape Canaveral SFS, FL, USA The world's 392nd orbital launch attempt, and 99th of 1964. Data: Launch Library 2, The Space Devs. Image by NASA (NASA Image and Media Guidelines) via The Space Devs.