Explorer IV

Explorer IV sped into space with a double task firmly impressed on its electronic senses. It must report on the belt of radiation, probably particles from the sun, that was found by Explorer III about 600 miles above the earth's surface. And it must tell U.S. scientists more than they yet know about cosmic rays.

Little is known about the radiation belt. Explorer III, with a single Geiger counter, reported only that the radiation was strong enough to jam the counter's tube. The more sophisticated instruments of Explorer IV, two Geiger counters and two scintillation counters, are designed to measure the radiation accurately and tell what kind it is. They will report over two radio transmitters, a high-powered one on 108.03 megacycles, a low-powered one at 108 megacycles, both with chemical batteries. Explorer IV has no solar battery, no magnetic tape, no mouse.

Explorer IV was fired northeast from Cape Canaveral, its course shaving Cape Hatteras and passing just to the east of New England, Nova Scotia and Newfoundland. The earlier Explorers, fired somewhat south of due east, never came farther north than the latitude of Atlanta, but Explorer IV reaches 51DEG north. As the earth turns inside its orbit, it will pass over most of western Europe, southern Russia (but not Moscow), all of the U.S. and Japan, most of China, all of the tropics and most of the land in the Southern Hemisphere except Antarctica.

The northerly orbit permits Explorer IV to report more fully on cosmic rays, which vary in intensity from the poles to the equator. But the satellite got less launching throw (205 m.p.h. less than Explorer III) from the west-to-east turning of the earth.

The new satellite's radio signals were picked up all around the earth on its first trip, which took about in minutes. Its high point is 1,400 miles above the earth, its low point 170 miles. It will probably stay up for several years.

Explorer IV raised the Army's satellite batting average to .750; only Explorer II was a dud. The launching vehicle was the old reliable Jupiter-C--a Redstone rocket as the first stage, topped with assemblies of small solid-propellant rockets. The propellant in the third and fourth stages had more punch, permitting the weight of the final satellite to be raised to 38.43 lbs., a gain of 7 lbs.

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