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RE: starship-design: Re: FTL travel

> Ben Franchuk writes:
>  > Finding the equation just recently  Power (in watts) = ISP
> ( impulse )
>  > * 9.8 ( g ) * N ( newtons of thrust ) / 2. Any propulsion system
>  > would require MAMMOTH amounts of power. Heat dissipation
> is the limiting
>  > factor here.
> As has been pointed out before, fuel is the real limiting factor.
> Fusion power is barely capable of driving a ship to
> relativistic speeds
> with large, but not completely untenable, fuel-to-payload ratios.
> Talking about building an interstellar spacecraft that uses fission
> power is just plain ludicrous.  There isn't enough fissible
> material in
> the solar system to power a spacecraft at 1 g acceleration for a whole
> year.

Steve is correct, several fission rocket engines have been built and tested
(NERVA). They had nowhere near enough power for interstellar applications,
but would work reasonably well interplanetary. The major reason they were
dropped was that nobody wanted NASA using nuclear powered engines to launch
craft into orbit, which was the purpose of the program at the time.

Even though this is a (mostly) mature technology, it wouldn't be worth the
effort to build such an engine now when we have several different plasma
engines testing and at least one fusion design in the early experimental
phase. All of these designs offer between 2 and 50 times the power of any
fission engine ever built.

Not even the fusion design as currently envisioned is capable of maintaining
1G constant acceleration all the way to Mars, much less anywhere farther
away. I suppose if you drastically reduced the payload fraction, it could be
done, but the amount of fuel consumed would probably not make it practical.