ESSA 8

Description

ESSA 8 was a sun-synchronous operational meteorological satellite designed to provide real-time earth cloudcover TV pictures to properly equipped ground receiving stations for use in weather analysis and forecasting. The satellite had essentially the same configuration as that of a TIROS spacecraft, 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 mickel-cadmium batteries. Two redundant wide-angle Automatic Picture Transmission (APT) cameras were mounted on opposite sides of the spacecraft with their optical axes perpendicular to the spin axis. Projecting downward from the baseplate were a pair of crossed-dipole command reception antennas. A monopole telemetry (136.500 MHz) and tracking (136.770 MHz) antenna extended outward from the top of the cover assembly. The satellite spin rate was controlled by means of a Magnetic Attitude Spin Coil (MASC), with the spin axis maintained normal to the orbital plane (cartwheel orbit mode) to within plus or minus 1 deg. 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 torque necessary to amintain a desired spin rate of 10.9 rpm.