To Shush a Satellite

U.S. spacemen were justifiably proud when their grapefruit-sized Vanguard I, the first U.S. satellite, continued to circle the earth long after later-launched rivals, both U.S. and Russian, bit the atmosphere. Now their pride has soured; Vanguard I has become a bore and a nuisance. Its radio voice, powered by solar cells, is still on the air after 4 1/2 years. Its reports translate to nothing more important than "Here I am." And unstoppable broadcasts, which may well persist for 1,000 years, clutter up a precious radio channel.

Such channels are already scarce, and they will get scarcer still as more and gabbier satellites for communication, navigation and weather watching take to space. Many of the newcomers will have radio transmitters powered by solar cells, and unless they are silenced in some way, like Vanguard they will broadcast long after their original jobs are done. But to shush a satellite and clear its radio channel is not as simple as it sounds. A radio signal could be sent from the ground to tell the satellite to turn itself off, but this would require tying up a standby radio channel and force the satellite to carry heavy special equipment for one brief moment of use.

To keep the radio spectrum clear of outmoded but garrulous space vehicles, the National Aeronautics and Space Administration is turning to the small electronic timekeepers that Bulova Watch Co. developed for its Accutron wrist watches. To measure time, these timers use a transistor-controlled tuning fork that runs indefinitely on a tiny trickle ( eight-millionths of a watt) of electric power; a battery the size of a dime will keep one of them humming for a year. The whole apparatus weighs less than three ounces, and it can easily be set to turn off a satellite's transmitter after any desired time interval.

Bell Telephone Laboratories' famous Telstar carries a timer that will silence its beacon transmitter after 17,700 hours--about two years. Bulova engineers are now working on timers that will turn instruments off and on again automatically. This will permit a satellite to take periodic readings of space conditions over long periods of time without demanding exclusive use of a radio channel.

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