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).

Background

ESSA 4 was launched to replace ESSA 2, launched February 3, 1966, which had drifted into an orbit of limited usefulness. The satellite was financed, managed, and operated by the Environmental Science Services Administration (ESSA).

Spacecraft

The cartwheel-shaped spacecraft carried two Automatic Picture Transmission (APT) systems, with which it could instantly transmit photos of Earth's cloudcover to APT ground stations.

Launch

ESSA-4 was launched on January 26, 1967, at 17:31 UTC. It was launched atop a Delta rocket from Vandenberg Space Launch Complex 2, into

Sun-synchronous orbit A Sun-synchronous orbit (SSO), also called a heliosynchronous orbit, is a nearly polar orbit around a planet, in which the satellite passes over any given point of the planet's surface at the same local mean solar time. More technically, it is ...

. ESSA-4 had an inclination of 102°, and an orbited the earth once every 113.4 minutes. Its perigee was and its apogee was . The satellite properly aligned itself with respect to the Earth during its 18th orbit, whereupon its first photos were transmitted. A two-week spacecraft checkout and evaluation program ensued. One of the APTs failed after launch, but the other performed normally.

Legacy and status

ESSA 4 was turned operationally off on December 6, 1967, being finally deactivated on May 5, 1968.

References

{{DEFAULTSORT:Essa-4 Spacecraft launched in 1967 Weather satellites of the United States