TIROS 9

Description

TIROS 9 (Television and InfraRed Observation Satellite) was a sun-synchronous meteorological spacecraft designed to develop improved capabilities for obtaining and using TV cloudcover pictures from satellites to test the TOS (TIROS Operational System) concept. The spin-stabilized spacecraft was in the form of 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 supplied to the spacecraft from approximately 9000 1- by 2-cm silicon solar cells mounted on the cover assembly and by 21 nickel-cadmium batteries. A single monopole antenna for reception of ground commands extended from the top of the cover assembly. A pair of crossed-dipole telemetry antennas (235 MHz) projected down and diagonally out from the baseplate. TIROS 9 was the first of the so-called 'Cartwheel' meteorological TV satellites. That is, the spacecraft spin axis was maintained normal to the orbital plane. The satellite was still equipped with small solid-fuel thrusters as in the case of previous TIROS spacecraft. However, the system was used only as a backup. The satellite spin rate and attitude were primarily determined by a Quarter-Orbit Magnetic Attitude Control (QOMAC) system. The system used the torque developed by interaction of the earth's magnetic field with a current-carrying loop mounted in the satellite. The spacecraft carried two identical wide-angle TV cameras with 1.27-cm vidicons for taking earth cloudcover pictures. The pictures were transmitted directly to either of two ground receiving stations or stored in a tape recorder on board for subsequent playback if the spacecraft was beyond communication range. A failure in the spacecraft guidance system placed the spacecraft in an unplanned elliptical (700 to 2500 km) orbit. The TV system operated normally unitl April 1, 1965, when one of the wide-angle TV cameras failed. The other camera operated normally until July 26, 1965, and sporadically until February 15, 1967. TIROS 9 was the first satellite in the TIROS series to be placed in a near-polar orbit, therby increasing TV coverage to the entire daylight portion of the globe.