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PART

By JORDAN McQUAY

Some inłeresłing applicałions of arłificial earth sałelliłes as space Communications relay stałions as well as for television transmissions.

Fig. 14. The łour paddle whecli on *'Ex-

plorer VI" carry 8000 »olar celi* lor power.

62

THE previous parts of this series have covered some of the spoci fic elec-tronic equipmcnt used in outer space. This. the concluding article, will cover the application of satellites as Communications relays and as part of a television transmission system.

Communications Relays

Although satellites and space probes provide a wealth of scientific and en-\ironmentaI data. specially equipped electronics payloads can provide a number of direct communication serv-ices. Chief among these is the use of satellites as space relay stations.

First use of a satellite as a radio relay station occurred accidentally dur-ing the one-day flight of “Pioneer I” in October 1958. The electronics payload included a command receiver, which was supposed to trigger a reverse rocket and thus propel the vehicle further into space. Although the rocket

failed to function on command. the command signals were instantaneously rebroadcast by the data transmitter aboard the “Pioneer I.” These command signals were heard half-way around the world!

Not so accidental was the “talking” satellite known as “Project Score”— for Signal Communications by Orbital fielay Fquipment. Carried aboard an “Atlas” missile and operated success-fully during December 1958. this electronics payload had been specifically designed as a radio relay station for operation in the upper atmosphere. This was also the first step toward futurę “courier” satellites for military types of communication requiring ex-treme security of operat ion.

The payload consisted essentially of an FM messenger receiver (150 mc.), a control switching Circuit, a commer-cial-type magnetic tape recorder, an FM message transmitter (132 mc.).

and a battery power supply. The nav-load also included a beacon or tracking transmitter (108 mc.). See Fig. 15.

The FM message receiver operated continuously. Other components of the payload were not in operat ion ercept when activated by the control Circuit. When the appropriate command signal was received from a ground station, the control Circuit triggered any one of three operating conditions:    (1)

turned on the tape recorder to rerr''ve messages from ground stations: (2) turned on the tape recorder to phty buck, and turned on the FM message transmitter to broadcast the recorded tape: or (3) connected the output of the message receiver directly to the FM message transmitter.

With conditions 1 and 2. the electronics payload functioned as a delayed repeater, with no limitation on the time between receipt and rebroadcast of a message. With condition 3. the payload functioned as an instantaneous radio relnw

The payload accepted and relayed voice messages and as many as seven tcletypewriter channels. It was loaded. switched, and triggered successfully throughout the 12-day period of its existence—proving the feasibility of space relay stations.

Other. morę sophisticated, payloads are being developed for use during the next two years. These will feature re-fined circuitry and expanded operating bandwidths up to about 100 kc. By 1965, bandwidths of from 4 to 5 mc. will be achieved. making possible the long-distance relay of television signals by space relay stations aboard orbiting satellites.

ELECTRONICS WC4LD