Paddle-Wheel Satellite

The U.S.'s Explorer VI, shot into orbit from Cape Canaveral last week (see NATIONAL AFFAIRS), was the most sophisticated satellite the U.S. has launched. Rigid arms like paddle wheels, whirling through the sunlight of empty space, were its most spectacular feature, designed to test the possibility of capturing enough energy from the sun to send messages across millions of miles (TIME, April 27). Such a durable source of energy is crucial to proposed space probes to Venus or farther planets, for there is little point in sending out space probes unless their transmitters can send information back to earth.

At launch, the two aluminum arms were folded against the satellite's side. As the solid-fueled third stage was about to fire some 150 miles above the earth, they snapped out into position. Each arm branched in two directions and each branch carried a flat paddle about the size of a checkerboard, covered with 2,000 silicon-based solar cells mounted on a thin plastic honeycomb (an elaboration of the light-collecting window in Vanguard I, which still draws in enough energy to keep the tiny satellite busily broadcasting 17 months after it was launched). At 22,000 m.p.h., the new 142-lb. satellite went into orbit (rotating 171 times a minute), and the cells began to convert sunlight into electricity.

Other Tasks. But Explorer VI had more to do than absorb energy from the sun. Purposely programed for the most eccentric orbit ever achieved by an earth satellite, it settled almost exactly into its planned path, first reached its record apogee some 26,400 miles straight out into space from the Cape of Good Hope, its perigee a narrow 157 miles over Singapore. With so great a range of altitude, it will pierce both of the newly discovered Van Allen radiation belts (TIME. May 12, 1958 et seq.), collect comprehensive data on phenomena ranging from the earth's ionosphere to cosmic dust.

To accomplish these tasks, Explorer VI's 1/161n. aluminum skin shrouds the most intricate and talented collection of scientific instruments yet sent into space --all in a 29-in. by 26-in. ball that moves through its complete orbit once every twelve hours. One hoped-for result is the first relatively detailed map of the Van Allen belts, which present a formidable barrier to interplanetary flight. Previous earth satellites have not gone high enough to examine the enormous breadth of the Van Allen radiation. Pioneer IV obtained valuable information, but made only one trip through the belts before falling into orbit around the sun. Several devices in Explorer VI are studying the belts' range and fluctuating intensities. In one experiment, high-energy particles are measured by a 2-in. cube that holds seven tiny, gas-filled cylinders shielded with lead. The particles' passage ionizes the gas, creates electrical impulses of varying strength that are transmitted to earth.

Ears & Eyes. Another possible hazard for space travelers is cosmic dust--micro-meteorites. Behind metal plates on the sides of Explorer VI, microphones listen for micrometeoric impacts, register their intensity and frequency. The problem of communication with future space probes or space argonauts is complicated by the fact that radio waves are distorted and deflected when they penetrate the shell of the ionosphere. The satellite carries equipment to study their behavior.

Other eyes look into subjects of more immediate importance to men on earth. A small mirror housed in a tube peers down from one side of Explorer VI and gathers impressions of the cloud layers over the earth. An electronic counter digests the mirror's impressions and turns them into radio signals, which eventually become crude photographs of the earth's weather patterns. Two magnetometers watch the earth's magnetic field, may help map the field and explain its curious storms and their effect on earth communications.

To keep the interior of the paddle-wheel satellite at an even temperature range as it passes from the cool shadow of the earth into the blazing heat of the naked sun, Explorer VI has on its outer skin a patch of black-carbon paint. A thermostat actuates a small shield that alternately covers and uncovers the patch as heat requirements dictate. Since the satellite uses electricity much faster than the paddle wheels can make it signals from the earth periodically shut of the largest of Explorer VI's three radio transmitters. A memory device called Telebit takes over, stores up what the satellite learns during its silence. When the transmitter is turned on again, Telebit spills out the stored information in the digital transmission system, a coding method so concise that data collected during a 4 1/2-hour period can be sent in a few seconds.

Kick in Reserve. Explorer VI is expected to hold its hip-swinging orbit for at least a year. During that time it may illuminate problems of the universe from Einstein's theory on the curvature of space to the question whether man can really get past the Van Allen radiation belts by entering space above the earth's poles. At week's end a spokesman for the National Aeronautics and Space Administration reported: "The paddle wheel is doing well. It is converting solar energy into electrical energy. The signals are coming in loud and clear." If its perigee edges in too close to the earth, the paddle-wheel satellite still has a 5-lb. kick rocket that can be fired to elongate its orbit; last week's launching was such a perfect shot that the kicker was not fired.

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