OV1-9/OV1-10

Orbiting Vehicle 1-9 (also known as OV1-9), launched on 11 December 1966 along with OV1-10, was the ninth (sixth successful) satellite in the OV1 series of the United States Air Force's Orbiting Vehicle program. OV1-9 recorded low-frequency radio emissions and particle radiation in Earth's exosphere; the satellite also collected data on the impact of long-term radiation on biological samples and tissue equivalents. OV1-9 returned the first proof that Earth has an electric field.

Orbiting Vehicle 1-10 (also known as OV1-10), launched on 11 December 1966 along with OV1-9, was the tenth (seventh successful) satellite in the OV1 series of the United States Air Force's Orbiting Vehicle program. Designed to observe atmospheric airglow, X-ray, and cosmic radiation, OV1-10 returned significant data on the Sun as well as on geophysical phenomena in Earth's magnetic field. OV1-10 reentered Earth's atmosphere on 30 November 2002.