jeh@dcs.simpact.com (04/25/91)
For some reason my newsreader refuses to let me follow up to the referenced article, so this posting lacks a proper "References:" header. No doubt this is evidence of a conspiracy to suppress discussion of the technologies therein revealed... :-) The "rectified centrifuge" described in detail in the article, and the "Dean drive" briefly mentioned, are indeed close cousins. The Dean Drive was much-discussed in the pages of _Astounding Science Fiction_ (now _Analog_) in the mid-50s to the early 60s. Norman Dean actually got a patent on his invention. Several prototypes were built which would pull themselves along the ground. Some appeared to exhibit an antigravity effect, in that if you put the box on a scale, noted the weight and then turned the drive on, the scale would read slightly lower. None ever managed to lift clear of the ground and stay there, however. Allow me to quote from an article, "Lost Technologies of the Fifties", by George M. Ewing (from _Pyrotechnics_ number 42): "Of course the Dean Drive, and the Farrell Drive [invented at Michigan State, also patented, also demonstrated to work for travel on the ground], and that secret Marine Corps drive that was on the cover of _Popular Science_ magazine all work, but they're NOT space drives, they're static friction devices. The difference between static and dynamic friction causes a one-way ratcheting action, just like the effect of a good ski wax on cross-country skis. They work fine for pulling a piece of farm machinery out of the mud or running a military landing craft up on a beach, but in a zero-friction state like in space they just sit there and buzz and shake. Next question." Briefly, the Dean Drive (like the "rectified centrifuge") works by moving a mass rapidly in one direction and then moving it slowly back for the next shot. The rapid movement causes a large, brief "impulse" of reaction force which can overcome static friction. The reaction from the slower return stroke is of lower magnitude, so it does not overcome static friction, so the box moves in just one direction. But the reaction from the slower return stroke is still there, and although it has less force, it lasts longer, so everything sums to zero. --- Jamie Hanrahan (x1116), Simpact Associates, San Diego CA Internet: jeh@dcs.simpact.com, or if that fails, jeh@crash.cts.com Uucp: ...{crash,scubed,decwrl}!simpact!jeh