Science: Steering with Mouse Burps

One bedeviling problem facing space scientists is the difficulty of building the enormous chemical rocket engines needed to propel the ever growing payloads the U.S. wants to hurl deep into space. Last week the problem came closer to solution, not with the development of a big new chemical rocket but with the Air Force announcement that the U.S. had for the first time successfully tested an ion rocket engine in space.

Under development by Electro-Optical Systems Inc. of Pasadena, Calif., for the past four years, the ion rocket is likely to prove to be the Mighty Mouse of the space age. On earth it develops no more thrust than several milli-pounds (engineers call it the “milli-mouse burp”), barely enough to lift a one-carat diamond an inch off a desk. But in frictionless, gravity-free space, such burps can propel the biggest payloads. And the ion rocket’s assignment is just that: to take over the task of propelling huge space cargoes to the planets and back after the mighty chemical rockets lift them clear of the earth’s gravitational pull.

The ion engine tested in a 30-minute, 3,200-mile flight over the Pacific got its thrust by passing vaporized cesium metal through a hot tungsten filter. This action strips electrons from the cesium, speeds the positively charged ions out the rear of the engine. The great advantage of this process is that it requires remarkably little fuel—only one-tenth of that for a conventional chemical rocket. Even the smallest ion engine could keep a satellite on its right course for more than ten years by giving it gradual nudges. On a 300-day trip to Mars, a full-scale ion rocket could push five times as much cargo as a chemical rocket, still have enough left to get back to earth.