Syncom space satellite

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.