starship-design: Re: Starship design

[Steve VanDevender <stevev@efn.org>]

KellySt@aol.com writes:
 > Glad you liked the site.  We were trying to inspire people.  ;)
 > 
 > We did actually consider something like your design called M.A.R.S.
 > (Microwave Augmented Rocket System).  In M.A.R.S. a microwave sail was used,
 > and the microwaves focused back to drive a deceleration rocket.  I'm not sure
 > where we finished with that, but it had two problems.  Forst the amount of
 > energy causes tremendous waste heat problems.  Secound, the sail is so
 > efficent at producing forward thrust, its difficult to generate enough
 > reverse thrust to counteract it.  Can't remember if its proponent (Kevin
 > Houston) was ever sure it could slow down?

As I recall there was a great deal of debate about this, mostly around
the physically impossible idea of slowing down using beamed power from
Earth without using reaction mass.  If you use some sort of reaction
mass (and in a real sense, a retromirror is reaction mass -- it gains
the forward momentum so the payload can lose its momentum) then you can
slow down.

I suspect that it may be more practical to exploit drag from the
interstellar medium to decelerate down from high relativistic speeds,
then use a fusion rocket or the like to do the final braking into the
target system.  Then you need neither beamed power nor to carry extra
reaction mass that increases power requirements during the boost phase
of the trip.

Of course, this isn't very helpful for the return trip unless the
travelers can build a boost beam in their target system, but I believe
that among the other advances needed for interstellar travel, we'll have
to advance past the notion that explorers should always return from
their trips.