Technology: A Handy Wrench for Space

With its pistol grip and nubby barrel, the instrument looks like the handy ray gun with which Buck Rogers and Wilma used to zap Killer Kane. It is actually a space-age wrench. Cordless and battery-powered, it was designed by Martin Marietta as a zero-reaction power tool to be used by astronauts for turning nuts and bolts in the weightless conditions of space.

Using an ordinary wrench for such an ordinary job would throw an astronaut for a loop. Newton’s third law of motion is an inexorable reminder that for every action there is an equal and opposite reaction. Thus, in a state of weightlessness, without gravity to anchor the man, an astronaut attempting to put together a space station while in orbit could not hope to use anything as simple as the big wrench with which a car driver changes tires. Every time he tried to exert pressure on nut or bolt, he would turn in the opposite direction. Martin’s new tool, which will be tested on later Gemini flights, is designed to eliminate such reaction almost entirely. The spaceman’s wrench, 10½ in. long, 9 in. high and 5 in. wide across the motor housing, has a built-in reaction absorber. When the astronaut presses the trigger, the motor near the handle compresses a spring with a brief quick twist. As the spring expands, it turns the hollow cylinder that surrounds it. Compression and release of the spring occur, alternately, 1,800 times a second. The turning force of the cylindrical mass is what turns the operating end of the wrench. The rapid rotation and counterrotation of cylinder and motor all but cancel each other out and absorb about 96% of the reaction. This is more than enough to enable an astronaut to turn a nut without being turned himself.