Space Technology: Fixing Up Telstar

Lobbing a working communications satellite out to the fringes of space was a signal achievement. The task of repairing it in orbit seemed wildly improbable. But when Bell Telephone Laboratories' Telstar sullenly ignored a command after four months of faithful performance, Bell's electronic doctors wasted no time. While unresponsive Telstar circled the earth in silence, they spent six frantic weeks in their labs concocting a cure for its ailment.

Practical experience with Relay, the communications satellite built by RCA, was no help. Relay, which went into orbit on Dec. 13, refused to work properly right from the start; a defective part let most of the power leak out of its storage battery. But Relay still obeyed commands. It was told to throw switches to isolate the faulty transponder (transmitter-receiver). Solar cells were able to recharge the satellite's battery. Last week Relay was in operation, using its spare transponder.

Diagnosis. Telstar, which had no spare transponder, was in much more serious trouble. But its case was not hopeless. Its radio beacon was transmitting normally; so were the host of instruments that report by telemetry on its internal condition. They showed that Telstar's solar cells were generating plenty of electricity. Its temperature was normal, and no intruder, such as a meteorite, had damaged its delicate nervous system. Apparently the only trouble was in the command decoders. Telstar was ablebodied, but without working decoders it could not hear and obey commands.

One clue to Telstar's trouble was the curious manner in which the satellite had quit. Several times before total failure it had reluctantly obeyed a command only after it had been repeated for many minutes. This suggested that the passage of a signal through one of the ailing decoders tended to cure it in much the same way that exercise helps some human ills.

But what disease of space is cured by electrical exercise? The Bell men were aware that transistors behave strangely after they are bathed in powerful radiation. Ions (electrically charged particles) released by the radiation are attracted to electrically charged parts of the transistors. There they form a surface layer that prevents the transistors from working properly. Something of this sort may have happened to Telstar. It was built to resist an expected level of radiation in space, but just before it was launched, the U.S. exploded a powerful nuclear test bomb above the atmosphere near Johnston Island (TIME, July 20). Eminent scientists had dismissed the suggestion that the test would create much high-level radiation, but their forecast was wildly wrong. Telstar's instruments reported long-lasting radiation 100 times as strong as had been expected.

Zero Gate. To find out whether space radiation was the guilty party, Bell engineers hooked up a command decoder just like Telstar's and exposed it to gamma rays in a shielded chamber. It went out of action quickly, and the engineers traced the trouble to a single transistor called the "zero gate" designed to react to short pulses—coded zeros—in command signals. With the zero-counting transistor blocked by ions, the decoder could receive no zeros, and a binary code, which consists only of zeros and ones, is meaningless if deprived of half its vocabulary.