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But the force of that tiny pull could in turn be measured by the microwave communication link.

But because the twin spacecraft were in constant contact with each other through a microwave communication link, that change could still be measured precisely.

The stations employ a wireless, digital microwave communication system that can also be useful in obtaining weather data and in atmospheric and other environmental studies, Kent said.

Officials say the Soviets got the prime turf, with a view of several sensitive buildings, including the White House, because, when the sites were originally agreed upon, the land was available and microwave communication and its interception were not as sophisticated or as prevalent as they are today.

Already used by about 125 big corporations, microwave communication is flexible, and cheaper than any other system.