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Re: MARS
toBrian Mansur)
> >>4. Has anyone figured out just how long the accelerator needs to be since
it
> >>has to be linear? More to the point, can we keep the linear accelerator
> >>short enough and, therefore, light enough to produce relativistic exhaust
> >>velocities?
> >Some long time ago I figured out that it would probably be too long, the
> >formulas are not so easy to integrate so at that time I used some
repeating
> >summation. I assumed that we would not have a constant acceleration of the
> >mass, but a constant power input. This means that initially it accelerates
> >fast but at the end much slower. Relativistic effects do make this
> >difference worse.
===
> What I mean is has anyone thought about what it would
> be like, structurally, to push what amounts to a 10 km
> long acceleration tower at 10 m/s^2? For that matter,
> speaking of other starship structures, what would it be
> like to push a ram scoop (a really tall wire mesh cone)
> at the same rate?
MOst people skip over it, but it would probably be impossible.
> >>5. Can we even produce the magnetic fields in an accelerator necessary to
> >>get an exhaust velocity of .9996c for .62kg/sec. or even a .75c exhaust
> >>velocity using say a 1km long accelerator? My understanding is that
field
> >>generators that confine magnetics fields have a tendency to blow up. I
hope
> >>I'm wrong but I thought you might know if this concern applies to the
> >>designs we've discussed.
> >I think we should not worry about that too much, for me this is just a
> >problem for the gigantic-energy stack (i.e. problems involving creation
and
> >containment of gigangtic energies).
> Unfortunately, the hardware involved in accomplishing
> energy containment for our accelerator will up our ship
> dry mass. A 10km long ion accelerator is not going to be
> terribly light as it is. I originally was under the
> impression that we could keep the ship dry weight at
> 100,000 t o 250.000 tones. Sadly, it seems that we
> are putting more and more mass into the engine structure
> which exponentially increases our fuel/RM problems.
You are correct on all counts.
Depressing isn't it.
Kelly