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*To*: bmansur@oc.edu, David@interworld.com, hous0042@maroon.tc.umn.edu, jim@bogie2.bio.purdue.edu, lparker@destin.gulfnet.com, rddesign@wolfenet.com, stevev@efn.org, T.L.G.vanderLinden@student.utwente.nl, zkulpa@zmit1.ippt.gov.pl*Subject*: Re: MARS*From*: KellySt@aol.com*Date*: Sun, 3 Mar 1996 19:01:45 -0500

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

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