ESSA-4

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

Mission type	Weather
Operator	NASA
COSPAR ID	1967-006A
SATCAT no.	S02657
Spacecraft properties
Launch mass	290 kg (640 lb)
Start of mission
Launch date	21 January 1967, 17:31 GMT
Rocket	Thor-Delta E
Launch site	Vandenberg Space Launch Complex 2
Entered service	21 January 1967
End of mission
Deactivated	5 May 1968
Orbital parameters
Reference system	Geocentric orbit
Regime	Low Earth orbit
Eccentricity	0.00740
Perigee altitude	1,338 km (831 mi)
Apogee altitude	1,443 km (897 mi)
Inclination	102°
Period	113.48 minutes
ESSA program ← ESSA-3 ESSA-5 →

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).^[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]