ESSA-1 (or OT-3) was a spin-stabilized operational meteorological satellite. Its name was derived from that of its oversight agency, the Environmental Science Services Administration (ESSA).

Launch

ESSA-1 was launched on February 3, 1966, at 07:41 UTC. It was launched atop a Delta rocket from Cape Canaveral, Florida. The spacecraft had a mass of 304 kg at the time of launch. ESSA-1 had an inclination of 97.91°, and an orbited the Earth once every 100 minutes. Its perigee was 702 km and its apogee was 845 km. ESSA-1 had a similar design to that of the TIROS satellite series. It was an 18-sided right prism, measuring 107 cm across opposite corners and 56 cm. It had a reinforced baseplate, which carried most of the subsystems and a cover assembly (hat). ESSA-1 had approximately 10,000 1-cm by 2-cm solar cells, which charged 21 nickel–cadmium batteries. ESSA-1 was designed to take pictures of daytime cloud cover, record them, and transmit them when it was in range of a ground acquisition station. The satellite spin rate and attitude were determined primarily by a magnetic attitude spin coil (MASC). The MASC was a current-carrying coil mounted in the cover assembly. The magnetic field induced by the coil interacted with that of the Earth's magnetic field, and provided the necessary torque to maintain a desired spin rate of 9.225 revolutions per minute (rpm). Five small solid-fuel thrusters mounted on the baseplate provided a secondary means of controlling the spin rate. ESSA-1 operated normally until October 6, 1966, when the camera system failed. The spacecraft was fully deactivated on May 8, 1967, after being left on for an additional period of time for engineering purposes.