Educated Satellites

Satellites are getting more sophisticated. The first few tumbled any which way through space; now they are expected to perform all sorts of complicated maneuvers. The Air Force's Discoverer II, whose re-entry capsule came to earth embarrassingly close to northern Russia last week (see NATIONAL AFFAIRS), was as full of busy gadgets as a watch is full of works. The main purpose of its gadgetry was the seemingly simple task of keeping the satellite horizontal in relation to the surface of the earth below --a necessary step toward effective photographic reconnaissance.

Its heart was an inertial-reference package made by Dynamics Corp. of America. Through an intricate system of tiny gyroscopes, it gave Discoverer II a continuous sensing of its motion and attitude in space. When the second-stage rocket separated, the inertial-reference package squirted jets of high-pressure helium out of orifices in the rocket's side, bringing it to a horizontal attitude. Then the rocket motor fired, driving the second stage into an orbit.

Once in orbit, the little jets went back into action. To keep the satellite horizontal, they had to make it turn just as fast as it circled the earth: one revolution, one turn. This was done by an infrared scanner, which watched the line of the horizon ahead and released little spurts of gas to keep the satellite's attitude stable. This complicated operation seems to have worked well. As Discoverer II circled the earth, its directional radio signals kept at a steady level. If Discoverer had not been stabilized properly, they would have fluctuated as the satellite wobbled.

Paddle Wheels for Power. Oddest-looking satellite yet is one scheduled for launching next month by the National Aeronautics and Space Administration to test the possibility of sending a probe to the neighborhood of Venus. There is no point in such a probe unless radio communication can be maintained across 25 million miles, the nearest approach of Venus. Transmission over this distance requires a lot of power. Chemical batteries are too feeble. Nuclear-powered batteries are promising but have not been developed sufficiently. The best bet is solar cells, which capture energy from sunlight.

The paddle-wheel satellite is designed to make the most of the sun's energy. Its main body will be a 28-in. sphere covered with a thin metal skin. Out of it will protrude four paddlelike surfaces carried on branching supports and arranged in such a way that one of them will always face fairly accurately toward the sun. Both surfaces of the paddles will be covered with a mosaic of cells made of thin sheets of a photoelectric material (probably silicon) that turns sunlight into electricity. The paddles will be folded when the satellite is in the nose of its launching rocket and will snap into position as soon as it is spaceborne. The array of solar batteries is expected to develop as much as 400 watts, about enough to run a small toaster. Most of the energy will be stored in nickel-cadmium batteries. When triggered by a signal from the earth, the batteries will power the satellite's radio transmitter.

The first paddle-wheel satellite will not try for Venus, but will follow a long elliptical orbit that will take it about 30,000 miles from the earth. It will carry various instruments, but its principal job will be to answer promptly when spoken to. If all goes well, it will draw on its stored solar power and speak in a loud radio voice. Then its designers can judge whether a transmitter of this type can be made loud enough to be heard from Venus.

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