Satellite with a Memory

As the Army's first satellite, Explorer I, speeds around the earth, it wastes most of its radio broadcasts on the unheeding ocean, where only a few ship's operators are listening. Explorer III, which started its orbiting last week, is a higher stage of satellite evolution. It has a memory, and if asked, will tell all it knows.

Explorer Ill's memory is a midget tape recorder (weight, 1/2 Ib.; diameter, 2.5 in.) designed by Graduate Student George Ludwig of the State University of Iowa and fitted for space by the Jet Propulsion Laboratory at Pasadena. While the satellite circles the earth, a delicate solenoid moves forward a magnetic tape in jumps of five-thousandths of an inch, one jump per second. As the tape moves, the satellite's instruments record upon it the number of cosmic rays they are detecting. All this time the satellite's low-power radio transmitter is sending its signal, but the high-power transmitter is silent.

Extracting from Explorer III the cosmic-ray information that it "remembers" is the job of the Naval Research Laboratory, which has seven minitrack stations along the 75th meridian from Camp Stewart, Ga., south to Santiago, Chile. When the satellite passes over the line, one of the crewmen of the nearest station presses a button, sending into the sky a special coded radio signal, and the satellite will pay attention to nothing else. When it gets the proper word, it snaps into sudden action. Its high-power transmitter goes on the air. Its tape reverses and races past the playback head, sending to the minitrack station all the cosmic-ray information that it has gathered in its circuit. After this brief (5 sec.) spasm, the sophisticated little instrument starts all over again, recording on the freshly erased tape the data of its next earth orbit. The burst of information from the tape sounds like a high-pitched screech, but skilled interpreters can tell by analyzing the record how many cosmic rays were hitting the satellite at any point.

This file is automatically generated by a robot program, so reader's discretion is required.