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From: chuck@mitlns.mit.edu
Newsgroups: sci.physics,sci.electronics
Subject: Re: Coilguns -- help me Spock!
Message-ID: <1990Apr8.200108.4975@athena.mit.edu>
Date: 8 Apr 90 22:46:18 GMT
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Organization: M.I.T. Lab for Nuclear Science
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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