Word: allen
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Dates: during 1950-1959
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GETTING information from a satellite is tricky business. "If you want to measure the temperature up there," says Van Allen, "you can't put a mercury thermometer in your bird. You have to read temperature as an electrical signal." This is done with a tiny "thermistor," whose resistance to current put out by the satellite's batteries varies with temperature. The change affects the frequency of the electronic signal sent out by the satellite's transmitter, thus reporting the temperature to the ground...
...Allen's instrument packages to measure radiation are much more complicated. Their sensing elements are Geiger tubes and scintillation counters that give brief electrical pulses when radiation particles hit them. Some of them are shielded with lead so that they will register only high-energy particles. Others are sensitive only to particles from one direction. The pulses from each instrument are fed to individual audio-frequency (audible sound) oscillators, changing the frequency of the pulses slightly. These modified audio tones are imposed on the high-frequency carrier wave sent out by the satellite's transmitter. Fed into...
When this mixed signal reaches the ground, it is recorded on magnetic tapes. In Van Allen's laboratory the tapes pass through a machine that separates each imposed audio tone from the carrier frequency and records it visually as a jiggly red line on a wide band of graph paper (see chart...
...four lower lines on the chart were made by the instruments of Explorer IV while it was passing through the inner Van Allen belt of heavy radiation. Channel I is from a Geiger tube set up to give a pulse when 64 radiation particles have passed through it, is thus intended to record areas of relatively low radiation. Here the radiation is so heavy that the counter is swamped and no meaningful count is recorded. Its small oscillations are mere radio noise...
...flat parts: the deeper they are, the greater the energy. The depressions come in cycles reflecting the tumbling of the satellite, but some of the energy is recorded when the scintillator is "looking away" from the direction of the radiation. This reveals that the lower part of the Van Allen radiation belt contains particles powerful enough to pass through the shielding around the scintillator...