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toBrian Mansur)

> >>4. Has anyone figured out just how long the accelerator needs to be since

> >>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
> >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

> >>generators that confine magnetics fields have a tendency to blow up.  I 
> >>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
> >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.