RE: RE: starship-design: Modular Ship Design

["L. Clayton Parker" <lparker@cacaphony.net>]

Kelly,

> -----Original Message-----
> I think I figured out that to get a .4C delta-V you needed
> something like a
> 40-100 to 1 fuel ratio. (hence my interest in a no tank fuel).
> That only gets
> you about 4 months at 1G.  Magnifying that to get more delta-v
> would require
> staggering fuel quantities!  The engines might need to weigh an
> order of mag
> more then the unfueled ship!

Yep! I was in fact expecting fuel ratios around 400 to 1 even using second
generation ACMF (AIMSTAR) which with a fuel ratio of only 4 to 1 can get to
0.35% C (Reference:
http://antimatter.phys.psu.edu/AIMSTAR/AIMSTAR-98-3404_04.html). If we use
the table on this page as a starting point, then we can assume that raising
the fuel mass by a factor of 100 while holding payload mass constant would
give us a final cruise velocity of 35.0% c. The only problem here is that
even AIMSTAR does not provide 1 g of acceleration (more like 0.1 g).
However, thirty or forty years from now could be quite a different story.

It is possible through a combination of minor (single order of magnitude)
improvements and the use of multiple engines (another order of magnitude) to
get up to 1 g of acceleration even out of AIMSTAR. I have never seen the
figures for VASIMIR, they were apparently yanked from the web soon after
they were posted. But I get the impression that although it is ready for
flight testing, its PEAK performance is probably not as high as what was
expected of the first ACMF design. Given the trip times to Mars claimed in
the NASA release, it just about exactly matches the ICAN II figures posted
at Penn State. AIMSTAR is a second generation _concept_ that significantly
improves upon ICAN based upon the initial ICAN experiments carried out at
JPL.

Lee Parker