[extropy-chat] unidirectional thrust

[Keith Henson]

At 08:11 PM 15/03/05 -0800, Mike Lorrey wrote:

>--- Hal Finney <hal at finney.org> wrote:
> > I thought Dirk was wrong at first, in fact I had a message all typed
> > up, but then I thought.what if I'm wrong?  And then I decided that I
> > *was* wrong! I think Dirk's analysis is correct. Let me make it more
> > concrete.
> >
> > Let's suppose a lifter will work in outer space.  We'll use a
> > photovoltaic
> > panel and some kind of DC-to-DC pulsed transformer to get the 30 kV
> > we need.
> >
> > Looking at the first chart on the lifter page at
> > <http://jnaudin.free.fr/lifters/data/index.htm>, he can lift about
> > 35 grams with Lifter v4.0, for 132.9 Watts.  That's a force of
> > .035 kg times 9.8 m/s/s or about .3 Newtons.  A random solar panel,
> >
><http://www.wholesalesolar.com/products.folder/module-folder/kyocera/KC167.html>,
> > can generate 167 Watts and weighs 16 kg.  We'll add 4 kg for the
> > transformer (this is all hand-wavey) and get a 20 kg device that we
> > can shoot into space and it will start accelerating all by itself.
> > .3 Newtons over 20 kg is about .015 m/s/s acceleration that our
> > device will deliver. It's small, but it builds up. After 1 day, it's
> > going over a kilometer per second! And velocity increases by a km/s
> > every day. Meanwhile we are putting in 132.9 Watts the whole time,
> > which is 132.9 J/s times 86400 s/day or 11.5 MJ per day. Well, after
> > two days we are at 2 km/s so our kinetic energy is m*v*v/2 or 40
> > MJ. But we've only used 2 * 11.5 MJ or 23 MJ. So Dirk is right, we
> > are over unity already, even with a primitive lifter like Naudin
> > has designed.  And it gets worse every day.
>
>The error you start off with is that you are using the thrust it
>demonstrates at atmospheric pressure, using atmosphere as the
>dielectric medium. Try first adjusting the thrust to that predicted by
>the dielectric value for vacuum. Fix that error and you wind up well
>within the realm of mundane sub-unity efficiency.... lets try again.

Mike, it doesn't matter how small the thrust is, unless the thrust declines 
in a specific way with velocity, any such drive will go over unity eventually.

Mind you, I *wish* such a thing existed and would be delighted if it 
did.  But energy to thrust doesn't work--another way to put it is "wrong 
units."

Unfortunately.

Keith Henson