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Re: starship-design: Deceleration scheme

On Tue, 29 Jul 1997 16:17:32 -0700 Steve VanDevender <stevev@efn.org>
>The efficiency problem shows up in other areas.  Another blast from 
>past I'll have to dig up is the derivation of fuel-to-payload ratios 
>various possible fuel sources.  In summary, for a self-powered 
>to get to high relativistic speeds (I defined that as 0.8 c or 
>you need 4-5 times as much matter+antimatter as payload just to boost 
>to about 0.8 c (square to get the amount need to decelerate again;
>square again for the amount needed for a round trip without 
>And it's much worse for anything else.  Fusion would probably require
>lugging an ice moon around for fuel, at best.
>Has anyone else thought of using a lightsail and beamed power to
>accelerate, and a ramscoop to decelerate?  I think the concept has 
>by before, but it seems to me to be the best combination.  You don't
>have to carry much fuel, except for maneuvering; you get free braking
>_and_ more fuel from the ramscoop, and maybe you can even afford to
>build another beamer in the target system for a return trip.  This 
>turns the main disadvantage of a ramscoop (drag against the 
>medium) into an advantage.  There's almost no need to fuse the 
>hydrogen unless you want improved braking efficiency once you get 
>down to low speed.
Sigh, I'm beginning not to like the sail concept as much.  It is simple
and elegant, but between the deceleration problems, plus the difficulties
of such mega-structure operation, and the power beam generation problems,
I think the use of matter-antimatter and/or fusion ideas may be the
ultimate best way to go.