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Because of the Doppler effect, the resulting tone decreases steadily in pitch, or frequency, as a satellite approaches and passes beyond the Kettering antenna. At the moment that the satellite reaches its point of closest approach the frequency of the tone becomes identical with the difference between the frequencies of the satellite transmitter and the signal generator. By recording the closest approach time on successive days, determining when Russian controllers turn on satellite transmitters, and noting when signals suddenly change pitch (during the firing of retrorockets) or are permanently silenced, there is little that Perry and his students cannot deduce about a satellite's origin, orbit and landing site.
22½° Miss. Even their latest coup, the Kettering boys had a list of impressive accomplishments, many of which were reported in modest letters to British science publications. In 1964, Perry predicted re-entry time for Cosmos 32 more accurately than did NASA's sophisticated space-tracking network. Before the Russians announced the launch of the three-man Voskhod 1, and before it was detected by the mighty Jodrell Bank radio telescope, Perry blandly telephoned word of the flight to the British space-tracking network. When Voskhod 2 returned to earth, the Kettering trackers calculated that it had landed some 22½° in latitude or about 700 miles from its intended touchdown point; the Russians did not admit until a year later that the craft had landed far from its intended target.
Perry originally established Kettering's space-tracking project to demonstrate the Doppler effect to his physics class. Its purpose nowadays is to help stimulate student interest in physics and mathematics. "When you talk space and rockets to these kids," he explains, "they listen." But the teacher clearly enjoys the project just as much as the youngsters. He proudly allows visitors to riffle through pictures of satellites photographed as they passed over the school grounds, then plays tapes of telemetry signals and voice conversations picked up from space on the Kettering receiver. His favorite is the voice of Lady Astronaut Valentina Tereshkova calling "Seagull, over and out" to an entranced ground controller.