ESSA 1

Description

ESSA 1 was a spin-stabilized operational meteorological spacecraft designed to take and record daytime cloudcover pictures on a global basis for subsequent playback to a ground acquisition station. The satellite had essentially the same configuration as that of the TIROS series, i.e., an 18-sided right prism, 107 cm across opposite corners and 56 cm high, with a reinforced baseplate carrying most of the subsystems and a cover assembly (hat). Electrical power was provided by approximately 10,000 1- by 2-cm solar cells that were mounted on the cover assembly and by 21 nickel-cadmium batteries. Two redundant wide-angle cameras were mounted on opposite sides of the spacecraft and canted 75 deg from the spacecraft spin axis. A pair of crossed-dipole command and receiving antennas projected out and down from the baseplate. A monopole telemetry and tracking antenna extended up from the top of the cover assembly. The satellite was placed in a cartwheel orbital mode, with its spin axis maintained normal to the orbital plane. 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 current interacted with the earth's magnetic field to provide the necessary torque to maintain a desired spin rate of 9.225 rpm. Five small solid-fuel thrusters mounted around the baseplate provided a secondard means of controlling the spacecraft spin rate. The satellite performed normally after launch until October 6, 1966, when the camera system failed. The spacecraft was deactivated on May 8, 1967, after being left on for an additional time period for engineering purposes.