Tracking the ESSA-2 Weather Satellite
John Macphail and Charles Taggart set their Crown SS800 data recorder to receive 136.5 MHz image telemetry from ESSA-2 as it passes over Toronto, Canada, March 1, 1966. It was a spin-stabilized operational meteorological satellite. The 132 kg spacecraft launched from from Cape Canaveral, Florida by a Three-Stage Delta rocket on February 28, 1966 into a 113 minute, 1355×1455 km, sun-synchronous 101° inclination polar retrograde orbit. The spacecraft was an 18-sided polygon, 1.07 m in diameter by 56 cm high, made of aluminum alloy and stainless steel reinforced baseplate carrying most of the subsystems and a cover assembly (hat) then covered with 9,100 1×2 cm solar cells for charging 63 nickel-cadmium batteries. Two redundant wide-angle Automatic Picture Transmission (APT) cameras were mounted 180° apart along the side of the cylindrical craft. 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 ±1°. 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 maintain a desired spin rate of 10.9 rpm. The "cartwheel" configuration of the TIROS-9 was selected as the orbital configuration for the ESSA satellites. Therefore, a camera could be pointed at some point on Earth every time the satellite rotated along its axis. The spacecraft operating system was the same as on the TIROS-9. The APT system was designed to transmit an image every 352 s, each photo covering a 5180 km˛ area with 3 km resolution. Its mission was to provide real-time pictures of cloud cover using the automatic picture transmission system. These cloud cover pictures were used by meteorologists for use in weather forecasting and analysis. ESSA-2 was able to transmit two to three images daily to individual ground stations, regardless of their location. The satellite provided useful cloud pictures for more than 4 years before the camera systems were placed in standby mode on March 20, 1970. ESSA-2 was fully deactivated on October 16, 1970. By this time the Environmental Science Services Administration (ESSA) was replaced by the new National Oceanic and Atmospheric Administration (NOAA).
