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RE: starship-design: LINAC efficiency

> There's a problem with ramscoops.  Yes, you can sweep up interstellar
> hydrogen and fuse it for thrust.  But once your ship is at speed,
> sweeping up that hydrogen induces drag.  If you're trying to put that
> hydrogen into a fusion reactor, you have to bring it up to
> the speed of
> the ship to get it in there; eventually, the thrust you get from the
> hydrogen only matches the drag of the ramscoop.
> ......(clip)

Steve puts it rather succinctly, for more in-depth treatment try NASA's
website "Warp Drive When?" by Marc Millis. There are some excellent
PowerPoint slides there that illustrate the mass vs. velocity problem as
well as the basis for Marc's reasoning that reaction drives, although useful
at the moment, just won't cut it for long term interstellar travel.

I would like to clarify a term however. What I meant by reaction drive is a
classical rocket - whether it is chemical, nuclear, fusion or antimatter is
irrelevant - they are all rockets. By "reactionless" I actually meant
REACTANTLESS, a slightly different animal. Carrying propellant, as Steve
points out, is a terrible drag as is trying to scoop it out of space.

Ideally, we would discover two things:

1) A source of propulsive energy extraneous to the ship,
2) A method of nullifying the effects of inertia

These two things alone would make interstellar travel possible in
"real-time", i.e. Alpha Centauri would only be 4 years away, not fifty. Warp
drive, worm holes and hyper space, although nice, are not absolutely