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).[1]
Spacecraft
The 290 lb (130 kg) 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.[1]
Launch
Launch of ESSA-4.
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,[2] into Sun-synchronous orbit. 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).
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.[1] One of the APTs failed after launch, but the other performed normally.[3]
Legacy and status
ESSA 4 was turned operationally off on December 6, 1967, being finally deactivated on May 5, 1968.[3]
Payloads are separated by bullets ( · ), launches by pipes ( | ). Crewed flights are indicated in underline. Uncatalogued launch failures are listed in italics. Payloads deployed from other spacecraft are denoted in (brackets).
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