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First Beep. With this work well underway and no satellite launching expected for some time, Van Allen was not a man to sit around idly. He got aboard the Navy icebreaker Glacier and headed for Antarctica to measure cosmic rays near the South Magnetic Pole. On Oct. 4, when the Glacier was wallowing southward across the Pacific, a report that the Russians had launched a satellite came over the ship's radio. Van Allen went to work on the Glacier's 20-mc. receiver, and within half an hour it yielded vigorous beeping sounds. That was Sputnik I. The Russians had won the first heat in the race into space.
The free world was crying for U.S. satellite action. But the Vanguard program still sputtered and faltered. Suddenly, Van Allen got a radio message from Pickering. The Army had at last got permission to try its satellite. He asked if Van Allen would approve transfer of his instruments to Jupiter-C.
Van Allen instantly cabled his approval, wired Ludwig to pack up all his apparatus and rush it to the Jet Propulsion Laboratory at Pasadena. Then he flew back from New Zealand. In Pasadena, he and Pickering decided that the payload—basically a Geiger counter to detect cosmic rays in space and two incredibly light but powerful radio transmitters—would have to be modified in one respect. It contained a miniature tape recorder to record the cosmic-ray data during a trip around the earth and then transmit it quickly when triggered by a coded signal sent up from the ground. Designed for Vanguard, this elegant apparatus would not work in Explorer I, which would spin too fast. So it was removed, requiring Explorer I to broadcast continuously.
Mysterious Silence. On Jan. 31, 1958, a Jupiter-C, fired from Cape Canaveral, put Explorer I into a fine orbit. With two massive Sputniks to compete with, the U.S. pinned its hopes for outdoing the Russians on the superiority of Van Allen's instruments.
Van Allen waited in Iowa City. In a few days, long, wide paper tapes with wiggly red pen lines began to arrive from monitoring stations in the U.S. The cosmic-ray count that they showed was not unusual. But after two or three weeks, tapes began to dribble in from stations in South America. "As soon as we started looking at them, we saw the most remarkable situation." Over the U.S., where the satellite swooped low, the rate was about 40 counts a second. But over the equatorial region, where the satellite was rising to its highest point, the counting rates were much smaller. During some two-minute stretches there were no counts at all. Says Van Allen: "My first thought was, 'Great guns! Something's gone wrong with the apparatus!' But then we got later North American tapes and everything seemed normal again."
All sorts of suggestions were made to explain the Explorer's peculiar behavior over the equatorial region. Perhaps a weird magnetic field was shunting all cosmic rays away from the equator. Maybe the alternation of sunlight and shade was affecting the Geiger counter. No explanation really worked.