From: Doug Jones (djones@xcor.com)
Date: Thu May 09 2002 - 19:53:54 MDT
"Robert J. Bradbury" wrote:
>
> I'm not sure I understand this paper fully, but it looks
> like progress in laser power densities are leading us
> into the realm where one can accelerate protons to
> produce an Isp of 10^7 seconds. (I know that means
> nothing to most of the people on the list but to
> the rocketry intelligentsia its significant).
>
> At any rate, slide 16, which is rather difficult to
> interpret, seems to suggest that one can manage a
> trip to Mars within 3 weeks with a propulsion
> system such as they propose.
Only if they can increase the input power by a factor of about 55 from
the already absurd 1 megawatt. These guys have a solution in search of
a problem, and do *not* understand that real limitation on non-thermal
rockets is power, not reaction mass or exhaust velocity. For minimum
power system mass, you must match the exhaust velocity to the mission
delta-V requirement; if you grind through the calculations, the best
performance comes with much less exhaust velocity which allows the power
supply to be used more efficiently.
A good discussion of the tradeoffs is at http://www.neofuel.com/optimum/
-- Doug Jones, Rocket Plumber XCOR Aerospace
This archive was generated by hypermail 2.1.5 : Sat Nov 02 2002 - 09:13:57 MST