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starship-design: Re: Decelerating a Starship

In a message dated 8/4/97 12:49:39 PM, you wrote:

>I'm not sure if you're the appropriate person to e-mail this to, but
>I was just browsing the following web page:
>This web page noted:
>>Decelerating into the target star system. 
>>Now for the bad news - you have to slow down. We can't pre-load
>>a deceleration course track into the target star with fuel across
>>interstellar distances. ...
>This simply is not true!  It is indeed possible to pre-load a
>deceleration course track.  The trick is that this deceleration
>course track is travelling at relativistic velocities, catching
>up with the starship.
>The basic idea is to launch a bunch of fuel packets after the
>starship has launched at relativistic speeds.  IMO, the best
>launch method would be RPB propulsion.  These packets travel
>faster than the starship to catch up with it when it reaches
>the destination system.
>The big advantages this scheme has are:
>1.  The starship's initial launch mass is minimized (obviously).
>2.  The fuel packets may be launched over a period of years, and
>    yet arrive at the destination over a period of weeks by
>    progressively launching faster and faster packets.  This
>    minimizes the power needed of the particle beams.  (Compare
>    to the dubious concept of transmitting a laser or microwave
>    beam over interstellar distances.)
>3.  The deceleration phase is almost identical to the acceleration
>    phase (from the perspective of the starship), so the same
>    ramjet/scoops/whatever can be used.  This can simplify the design.
>Anyway, I haven't seen this idea floated around before, but I know
>someone must have thought of this before me.  It's just too simple
>and elegant a concept!
>    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo

I'm a good one to mail too.  I also forwarded your comments to the main group
masil list.

A couple problems.  One your talking about firing pellets to within a few
hundred miles at a distence of light years.  Given any drift due to
interstellar megnetic fields (which we know little about) or loss of charge
due to interaction with the interstellar medium, etc..  And your fuel will
wind up scatted all over the star system.

Secound.  To avoid the deta-v gain from scooping up fuel thats going faster
then you (your are trying to slow down) the fuel has to be at a relativly
slow velocity.  (Ideally slightly slower than you at all points of the
deceleration.)  But if it was that slow, it would have to be launched decades
to centuries ahead of time.  Also any course speed deviation by the ship and
it will miss the fuel stream.

No I still can't see how that could be a viable option.  But keep submiting,
we've been chewing over weirder ideas.  Some might even work out.  :)