Bubbles for Space

Ideas for gizmos to put in satellites are as common as scientists' notebooks, and they range from TV cameras to dogs and chimpanzees. William J. O'Sullivan Jr. of the National Advisory Committee for Aeronautics favors satellites that can do useful jobs with no instruments at all.

One of his satellites, which he prefers to call a sub-satellite, is so light that it can be carried almost as an afterthought by any orbit-bound rocket. It is a balloon of plastic film .00025 in. thick, bonded to aluminum foil .0005 in. thick and packed in a doughnut-shaped container. To inflate the balloon, O'Sullivan provides a capsule of nitrogen gas at 2,000 Ibs. pressure per square inch. The whole apparatus weighs only .69 lb.

Sphere of Nothing. When the rocket reaches the orbit, the nitrogen inflates the balloon and pops it out of its container. When all the gas has left the capsule, the balloon is erected into a sphere 30 in. in diameter. The pressure inside it (.2 lb.) is enough to stretch the wrinkles out of the aluminum film and make it mirror smooth. After doing this job, the nitrogen escapes into the vacuum outside. O'Sullivan wants to get rid of it because the balloon may be punctured by a meteor, and a jet of gas escaping from it might push it off its regular orbit.

O'Sullivan's modest sphere would not be conspicuous to the naked eye, but it could be picked up easily with low-power moonwatch telescopes. Its great virtue would be its short life. Even on a comparatively high orbit, the tenuous bubble of nothing would be slowed by faint traces of air on the threshold of space. Following a circular course 300 miles above the earth, it would live for only about ten days, and its rapid changes of speed and altitude would measure air density much more accurately than the slow responses of heavier satellites.

Corner Satellite. A more ambitious NACA satellite is made of the same aluminized film and weighs only 8.7 lbs. When inflated by a 1/2-lb. bottle of gas, it erects into a "corner reflector" 12 ft. in diameter.

Corner reflectors are peculiar shapes made of two or three mutually intersecting surfaces of electrically conducting material. They re: ect radio or radar waves with extraordinary efficiency; small ones stand out on a radarscope as if they were heavy bombers. The NACA plan is to put one of these large but almost immaterial objects on an orbit so high that residual air will not slow it appreciably. At twilight it will look as bright as the North Star, and radars pointed at it will show it plainly. They can follow it on its course and measure its distance and direction continuously.

If shot away from the earth at escape velocity (25,000 m.p.h.), a cheap 8.7-lb. corner reflector can be followed far into space. It can be watched by radar, says the NACA, as it circles the moon and heads back to earth. Its behavior will check the calculations of astronavigators and explore the spaceways for vehicles of the future, carrying instruments or men.

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