trh@atari.UUCP (T R Hall) (04/08/90)
>> Even _*IF*_ one mode is more "efficient" than the other, _*WHY NOT >>USE BOTH AT THE SAME TIME!!??*_ ... > > Stability issues are one possible reason. The Space Studies Institute > mass-driver people eventually settled on an all-attractive scheme, as > I recall, because it naturally stabilized the projectile, while schemes > using repulsive drive as well needed active stabilization. Thank you. In my zeal over the magnetic forces, I conveniently ignored the purely mechanical aspects. You're right; it's kind of like the difference between pulling or pushing a trailer. Pulling IN to a point (the center of the coil) is, of course, more stable than pushing OUT from the same point. TRH
logajan@ns.network.com (John Logajan) (04/08/90)
henry@utzoo.uucp (Henry Spencer) writes: >>>>> In case #2, you have the projectile being "pushed" in REPULSIVE (or >>>>> opposing) mode and also being "pulled" in ATTRACTIVE (or aiding) mode. >> Even _*IF*_ one mode is more "efficient" than the other, _*WHY NOT >>USE BOTH AT THE SAME TIME!!??*_ ... > >Stability issues are one possible reason. The Space Studies Institute >mass-driver people eventually settled on an all-attractive scheme, as >I recall, because it naturally stabilized the projectile, while schemes >using repulsive drive as well needed active stabilization. I think it was Paul Dietz who mentioned stability to me in a private post. (Sorry if I am attributing it to the wrong author.) I speculated in reply that if an off center projectile is drawn in to an attractive magnet, that it will pick up momentum that will vector it into the side of the barrel also. The next stage will amplify this and so on. It is not so obvious then, that attractive mode is more stable than repulsive mode. Unless there is some additional non-obvious damping mechanism in attractive mode, I would say they both needed some sort of side to side motion restraint. -- - John Logajan @ Network Systems; 7600 Boone Ave; Brooklyn Park, MN 55428 - logajan@ns.network.com, john@logajan.mn.org, 612-424-4888, Fax 424-2853
chuck@mitlns.mit.edu (04/09/90)
-Message-Text-Follows- In article <1990Apr8.062629.6589@ns.network.com>, logajan@ns.network.com (John Logajan) writes... >henry@utzoo.uucp (Henry Spencer) writes: >>>>>> In case #2, you have the projectile being "pushed" in REPULSIVE (or >>>>>> opposing) mode and also being "pulled" in ATTRACTIVE (or aiding) mode. >>> Even _*IF*_ one mode is more "efficient" than the other, _*WHY NOT >>>USE BOTH AT THE SAME TIME!!??*_ ... >> >>Stability issues are one possible reason. The Space Studies Institute >>mass-driver people eventually settled on an all-attractive scheme, as >>I recall, because it naturally stabilized the projectile, while schemes >>using repulsive drive as well needed active stabilization. > >of the barrel also. The next stage will amplify this and so on. > >It is not so obvious then, that attractive mode is more stable than repulsive >mode. Unless there is some additional non-obvious damping mechanism >in attractive mode, I would say they both needed some sort of side to >side motion restraint. > The difference is that the imbalances become worse as you move off axis. For a small displacement an attractive coil will tend to pull the slug on axis. You are correct that this requires a lateral acceleration which without damping will cause the projectile to oscillate. The repulsive coil however will take a small displacement and make it larger in a single stage. Since the lateral forces become larger as you move off axis you get into trouble fast. This is a case where the exp(ikt) solution is alot better than the exp(kt). Or am I imagining that ... 8-) Chuck Parsons CHUCK@MITLNS.MIT.EDU