c. Further application will result from the existence of the satellites in sufficient number to satisfy the long-
haul strategic requirements. Once this has been achieved, their use will be economically justifiable on the
shorter tactical links as well.
LEARNING EVENT 6: PAST EFFORTS AND RESULTS IN SPACE COMMUNICATIONS
The following brief summaries constitute a chronological history of satellite communications efforts. In these,
as in discussions of most communications satellite systems, orbital altitude are given in miles. Unless otherwise
indicated, these figures represent nautical miles. A nautical mile is approximately 1.11 statute miles.
1. Project Communications Moon Relay (CMR). The moon, being a natural satellite of the Earth, offers the
possibility of being used for communications purposes. The US Navy demonstrated in 1951 that it was feasible
to use the moon as a reflector of electromagnetic radiation to communicate between distant points on the Earth's
surface. By 1956, the feasibility of CMR had been sufficiently demonstrated so the chief of Naval Operations
directed the establishment of a two-way telegraph and facsimile CMR link between Washington and Hawaii. In
November 1959, the system was successfully used when solar disturbances in the ionosphere disrupted
conventional HF circuits between Washington and Hawaii. Transmitter and receiver sites for each end of the
CMR link were located some distance apart to minimize mutual interference. For instance, the Washington
transmitter site was located at Annapolis, Maryland, and the receiver site was located at Cheltenham, Maryland-
a distance of several miles.
2. Project Score. On 18 December 1958, the Score satellite was successfully launched. This was the first
satellite designed purely for communications purposes. As a practical demonstration of its capability, President
Eisenhower recorded a Christmas message which was rebroadcast to the world via the satellite. Score operated
for 12 days, during which time 97 contacts were made. The altitude of Score varied from 110 miles to 920
miles. Since this was a relatively low-altitude orbit, the ground terminals had to be relatively close to each
other in order that both stations in each communicating pair could "see" the satellite. Score was designed to
receive message traffic as it passed over one station, record the message, and retransmit the traffic as it passed
over another station. This technique of recording messages for later transmission is known as store-and-
forward.
3. Project Courier. The more refined communications satellite, Courier, was the joint responsibility of the US
Army Signal Corps and the US Air Force. Courier was designed with a dual capability-that of recording and
retransmitting traffic, as in the earlier Score, and functioning as a direct relay. The first launch attempt failed
because of booster difficulties, but Courier IB was successfully put into orbit on 4 October 1960. The satellite
weighed 500 pounds and had a diameter of 52 inches. Courier's altitude varied from 598 to 755 miles, with a
total operating time of only 18 days. The experiment was considered highly successful because it demonstrated
the feasibility of high-capacity store-and-forward satellite communications. The ground equipment associated
with this test is still in use and will continue to be used in a modified form for other tests.
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