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 The Environmental Science Services Administration (ESSA) was a United States Federal executive agency created in 1965 as part of a reorganization of the United States Department of Commerce. Its mission was to unify and oversee the meteorologica ...

(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

(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 Delta commonly refers to: * Delta (letter) (Δ or δ), a letter of the Greek alphabet * River delta, at a river mouth * D (NATO phonetic alphabet: "Delta") * Delta Air Lines, US * Delta variant of SARS-CoV-2 that causes COVID-19 Delta may also r ...

rocket from

Vandenberg Space Launch Complex 2 Space Launch Complex 2 (SLC-2) is an active rocket launch site at Vandenberg Space Force Base, in California, USA. It consists of two launch pads. The East pad (SLC-2E, originally LC 75-1-1) was used for Delta, Thor-Agena and Thorad launches betw ...

, 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 ...

. ESSA-4 had an inclination of 102°, and an orbited the earth once every 113.4 minutes. Its

perigee An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any ell ...

was and its

apogee An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any el ...

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