ESSA-4 (or TOS-B) was a spin-stabilized operational meteorological satellite. Its name was derived from that of its oversight agency, the Environmental Science Services Administration (ESSA).
ESSA-4 was launched on January 26, 1967 at 17:31 UTC. It was launched atop a Delta rocket from Vandenberg Air Force Base, California, U.S.. The spacecraft had a mass of 285 kilograms (628 lb) at the time of launch. ESSA-4 had an inclination of 102°, and an orbited the earth once every 113.4 minutes. Its perigee was 1,328 kilometers (825 mi) and its apogee was 1,443 kilometers (897 mi).