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Re: starship-design: Both right
In a message dated 7/25/97 5:18:10 PM, you wrote:
>Ken Wharton writes:
>
> > >Until then, I'll leave you with the question: When your spaceship picks
>
> > >up the energ E from some photons, where are you putting the momentum of
>
> > >the photons? It can't be ignored.
>
> >
>
> > The momentum of the photons is not ignored; it speeds up the ship, with
>
> > an absorbed momentum of E/c, where E is the "caught" energy. I showed
>
> > earlier, though, how you could use this same amount of energy (plus part
>
> > of the sail itself as reaction mass) to slow down the ship by a momentum
>
> > equal to 3E/c. The NET momentum loss (with no energy output) is only
>
> > 2E/c, because you absorbed the momentum of the photons in the first
>
> > place.
>
> >
>
> > As for the suggestion about making a heavy-element sail so there would
>
> > be more reaction mass to slow down the ship, don't forget we have to
>
> > speed this thing up before we can slow it down! The lighter the better,
>
> > I think...
>
>
>
>OK, I think I'm satisfied. I agree that as long as you shed mass you
>
>can decelerate even though the beam is still pushing you. I was having
>
>flashbacks to a previous discussion from a couple of years ago where
>
>Kevin (I think) thought he had come up with a way to redirect the beam
>
>using angled reflectors to decelerate without using reaction mass, which
>
>I couldn't swallow. The ensuing flurry of letters was educational for
>
>everyone involved. I'll have to see about making those old letters
>
>available in the archives.
We really must organise this stuff into catagories and such. No I'm not
volenteering. ;)
Kelly