Re: Laser Aperture Size

[Kevin C Houston <hous0042@maroon.tc.umn.edu>]

Kelly:
> Brian:
> >Another problem I may have just spotted is the that the effects of impacts
> >with interstellar matter increases as you approach a light-speed.  Think of
> >it.  Your apparant mass (internal energy, something like that) keeps going
> >up even though you keep pushing your speed infintely closer to c.  While you
> >are only going .999c (I'm making these numbers up to make a point), your
> >impact with that speck of dust feels as if you were going 1000c.

there are two distinct effects 
applicable here.  The first is the apparent mass increase (hydrogens will 
feel like berylliums (7Be).  The second effect is that of space 
contraction.  you will impact seven light-days of space every day at 
..9905 of C. 

Kelly:
> Drag could start geting very noticable at high light speeds.  Probably not
> enough to us for breaking.   .....  Wait a minutte has anyone worked up
> drage figures for these huge sails?  If they were electrically charged and
> reflected all the mass in their path they'ld be slaming into hundreds of
> tons a months.  At high relativistic thats got to generate some usefull
> drag?
>

I did for my initial MARS study, I found that with a 500 Km Radius sail, 
it would generate ~1 G of Decell as long as you stayed above ~.93 of C.
then it drops off rapidly until it accounts for less than .1Garound .88 
of C.  Please Note that this is for a solid sail, and not for a mesh.  a 
charged mesh might behave as a solid sheet, but Iam not certain.


kevin