How Zero Gravity Feels

An artificial satellite on an orbit around the earth is in "free fall." So is a rocket cruising through space with its motor cold. People on board a satellite or rocket would feel weightless, and space medicine experts have long feared that unaccustomed freedom from gravitation will upset human organs or nerves.

Weightlessness is easy to achieve on earth, but only for short intervals. The simplest way is to jump off something, even a chair. While the jumper is in free fall, his body as a whole is pulled by the earth's gravitation, but the parts of his body feel weightless. In the same way a person in a rapidly descending elevator feels his stomach rise. Actually it does rise: the elevator's fall has made the stomach lose weight, and the elastic tissues that support it have pulled it upward. When the elevator stops descending, gravity resumes control. The stomach regains its weight and settles back into place.

A better system is to fly an airplane over a curved course in a part of a gentle outside loop. If the speed and sharpness of the curve are correct, centrifugal force exactly balances the earth's gravitation. Everything in the airplane, including the pilot, suddenly becomes weightless.

At the International Astronautical Congress at Rome, Dr. Siegfried J. Gerathewohl of the U.S. Air Force School of Aviation Medicine told about experiments with weightlessness made with a two-place, T-33 jet-trainer, which by flying the proper curve at high speed could keep its occupants weightless for 40 seconds at a time.

Hundreds of men, said Dr. Gerathewohl, made "zero gravity'' flights without alarming effects. As the airplane noses over its curve, the passenger begins to feel a "floating" sensation. A ball tossed in the hand falls more slowly. When it does not fall at all. gravity is suspended. At this point about half of the men who made the test felt pleasant, elated sensations. One of them wished he could live forever at zero gravity.

Some of the others felt such unpleasant effects as pressure on the eyeballs, sweating, headaches. Dr. Gerathewohl said of his own experience: "There's a feeling of flotation and lack of orientation when you close your eyes. You have a sense of complete relaxation."

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