8. Project Relay. Relay was a medium-altitude (820 miles to 4,612 miles) communications satellite, much like
Telstar, and was developed by Radio Corporation of America (RCA) for NASA. Relay I was launched on 13
December 1962 by a Thor Delts booster. The Relay satellite weighed 172 pounds and was 33 inches high, with
a maximum breadth of 29 inches. Relay's RF power output was greater than Telstar's-10 watts compared with
2.5 watts. Relay's transponders (transmitter-receiver combinations) also differed from Telstar's since they
contained frequency triplers, while Telstar changed from receive frequency to transmit frequency by heterodyne
mixing. These differences in circuitry plus various construction differences allowed an evaluation of the
various techniques involved by comparing Telstar and Relay performance. Much of the ground station
equipment used with Telstar was also used with Relay--AT&T's facility at Andover, Maine and the stations at
Goonhilly Downs, England and Pleumer-Bodou, France, for instance. Immediately after Relay was launched,
telemetry data indicated low power supply voltage. After waiting for some time to see if the power supply
voltage might stabilize, the satellite was commanded to switch to the other transponder. After the switch, the
satellite functioned normally. It was used to relay television signals from the US to Europe, and to establish the
first link via satellite between the US and South America when contact was established with a station in Brazil.
9. Project SYNCOM.
a. In the SYNCOM series, two satellites were successfully launched into orbits having periods of very
nearly 24 hours. The 24-hour period caused the satellites to appear to be almost motionless over the equator,
providing a permanent link for a pair of ground stations. SYNCOM I apparently was damaged by the firing of
the apogee rocket motor that was to circularize its orbit, and radio contact was lost immediately after the motor
was fired. However, both SYNCOM II and III were successfully orbited and functioned satisfactorily as real-
time repeaters in overseas operations. SYNCOM II drifted north and south of the equator in a figure 8 pattern,
but SYNCOM II was in a nearly perfect equatorial synchronous orbit SYNCOM III, then, was more easily
tracked by the ground terminal.
b. Owing to the size and weight limitations imposed on the satellite to achieve this type of orbit, each
SYNCOM satellite was relatively small. Its package, without antenna or final stage motor, was a cylinder 28
inches in diameter and 15-1 inches high. The weight of the communications package, plus the burned-out final
stage motor, was only 86 pounds, of which the communications package alone weighed approximately 50
pounds. Because of the small size and the great distances involved, SYNCOM did not have the
communications capacity nor the output power that some of the low-altitude communications satellites possess.
The communication-handling capacity of synchronous satellites has increased as the state-of-the-art advanced,
and we now are able to place larger satellites into synchronous orbits.
c. One of the advantages of the SYNCOM type of satellite is the elimination of the technical problems
involved with antenna tracking of a continuously moving satellite. This is an advantage of the synchronous
orbit wherein the satellite appears to hang motionless in the sky.
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