Triple-Threat Satellites

The odd, long-nosed rocket that rose from its pad at Cape Canaveral last week contained the most practical crew of explorers yet launched into space: a three-part package of instrument-crammed satellites. Heftiest part of the load (175 lbs.) was Transit IVA, latest of the Navy's navigation satellites, which looked like a bass drum spangled with bright solar cells and patches of white paint. Perched on top of it like the gobs of a three-scoop ice cream cone were a polished aluminum sphere, the Naval Research Laboratory's Greb III solar radiation satellite, and a smaller drum named Injun, built at Dr. James Van Allen's laboratory at the State University of Iowa. Boosted aloft by a Thor-Able-Star rocket, all three satellites soared into space together. Though the launch was successful, the strong springs, meant to shove the satellites apart to follow separate orbits around the earth, did an incomplete job. Transit went its lonely way, but Greb and Injun stuck together.

Injun is one of those miracles of miniaturization for which Van Allen's lab (TIME cover, May 4, 1959) is famous. It weighs only 40 lbs., but packed inside are instruments to measure particles circulating around the earth in the two Van Allen radiation belts, to count fresh particles arriving from the sun or distant space, and to observe several kinds of light from airglow and auroras. Greb III (155 lbs.) is simpler; it is part of the Navy's long-term effort to study solar radiation that ionizes the atmosphere and effects radio transmission. Its job is to keep tabs on X rays coming mostly from solar flares.

Transit IVA, which was built for the Bureau of Naval Weapons by the Applied Physics Laboratory of Johns Hopkins University, is the Navy's fourth and most significant step toward establishing a system of satellites from which ships and airplanes can determine their position anywhere on earth (TIME, April 25, 1960). None of the earlier transits worked very well, but the first signals from Transit IVA promise that it will do far better.

Most interesting improvement on Transit IVA is its nuclear power supply, built for the Atomic Energy Commission by the Martin Co. Tucked under Transit's big drum is a 5-in. white metal ball surrounding a pellet of plutonium 238*, a rare isotope of plutonium that gives off enough alpha radiation to heat itself as it decays. Thermocouples transform this ever-renewed heat into 2.7 watts of electricity for two of Transit's four transmitters. The little generator weighs only 4.6 lbs., but its plutonium fuel, with a half life of 90 years, is expected to supply power for much more than the five years during which an operational transit satellite is expected to function.

* Plutonium 239 is the isotope used in fission bombs.

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