From: dbessell@jessica.stmic.tas.edu.au (David Bessell)
Newsgroups: sci.physics,sci.physics.plasma
Subject: Re: ??? Plasma mirror propulsion...
Date: Wed, 17 Sep 1997 04:05:59 GMT
Message-ID: <341f561c.5558901@phyllis>
References: <5rfjov$1ha$1@jupiter.cs.uml.edu>


On 27 Jul 1997 09:51:27 -0400, aufsj@IMAP2.ASU.EDU wrote:

>
>: : Is there some big fundamental flaw I'm missing? Has this idea
>: : been fleshed out before?
>
>: Can't say I'm an expert on plasma mirrors, but if I were to
>: hazard a guess I'd say further calculations would show that you
>: spend exactly as much energy blueshifting the radiation in front
>: of the mirror as is gained redshifting the radiation behind.
>
> If there were such a relationship, couldn't one simply ensure
>that more energy is 'behind' it than in 'front' of it? Put a powerful
>energy source behind and head in a direction with less energy "in the
>way" and you should get the unbalanced force with the results as
>promulgated by Newton. There seems to be a very clear analogy to sailing
>(for example, you could head 'into' powerful energy sources by tacking).
Tacking in a sailing vessel requires pressure on the keel and rudder
to prevent slipping sideways. This is not possible in space without
expending energy.