Syncom 3 was the first geostationary satellite. (The earlier geosynchronous Syncom 2 had an orbit inclined to the equator.) It was an experimental geosynchronous communications satellite placed over the equator at 180 degrees longitude in the Pacific Ocean. The satellite provided live television coverage of the 1964 Olympic games in Tokyo, Japan and conducted various communications tests. Operations were turned over to the Department of Defense on 1 January 1965, Syncom 3 was to prove useful in the DoD's Vietnam communications.
Syncom 3 was launched from Cape Kennedy on 19 August 1964 and injected into an elliptical orbit inclined 16 degrees to the equator following a third stage yaw maneuver. The apogee motor was fired to remove most of the remaining inclination and to provide a circular near-synchronous orbit of 35,670 km x 35,908 km. The spacecraft next carried out a series of attitude and velocity maneuvers to align itself with the equator at an inclination of 0.1 degrees and to slow its speed so it drifted west to the planned location at 180 degrees longitude where its speed at altitude was synchronized with the Earth. These maneuvers were completed by 23 September, and Syncom 3 was used in a variety of communications tests, including the transmission of the Olympics, transmissions between the Philippines, USNS Kingsport, and Camp Roberts, California, and teletype transmissions to an aircraft on the San Francisco-Honolulu route. Satellite operations were turned over to the Department of Defense on 1 January 1965 and it was operated by the DoD through 1966. It was turned off in April 1969.
The Syncom satellites were 71 cm diameter, 39 cm high cylinders. The fully fueled mass of the spacecraft was 68 kg. The nozzle of the solid propellant apogee motor (1000-lb-thrust designed to impart a velocity increase of 1431 meters/sec) extended from the bottom of the cylinder and a co-axial slotted array communications antenna from the top. The total height including the nozzle was 64 cm. The radial exterior was covered with 3840 P-on-n silicon solar cells which provided direct power of 29 watts the 99 percent of the time the spacecraft was in sunlight. Nickle-cadmium rechargeable batteries provided power when the spacecraft was in the Earth's shadow. No active thermal control was required. Most of the central interior of the spacecraft consisted of the tanks and combustion chamber for the apogee motor, around this were arranged two hydrogen peroxide and two nitrogen tanks and the electronics. Attitude and velocity control was provided by nitrogen jets to align the spin axis and hydrogen peroxide jets to position the satellite. Each system had two jets, one parallel and one perpendicular to the spin axis.
Syncom employed a redundant, frequency-translation, active repeater communication system designed to handle one two-way telephone or 16 one-way teletype channels. The dual transponders utilized 2-watt traveling wave tubes. Selection of receiver and transmitter was made by ground command. One receiver had a 13 megacycle bandwidth for TV transmission, the other a 5 megacycle bandwidth. The receiving gain was 2 dB through the slotted dipole antenna. Signals were received on two frequencies near 7360 megacycles and retransmitted on 1815 megacycles. The slotted dipole transmitting antenna radiated a pancake-shaped beam 25 degrees wide with its plane perpendicular to the spacecraft spin axis. There were also four whip antennas oriented normal to the spin axis for telemetry and command.
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