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starship-design: Re: Starship design

In a message dated 9/29/97 7:11:11 PM, you wrote:

>I was really interested in your Starship design page, as this has always
>been an interest of mine.  I was delighted that people were thinking about 
>actual designs for interstellar vehicles. 
>One of the points made was, in relation to light sail craft, was that 
>there really wasn't any practical way to use the light from earth or
>to deaccelerate the ship.  Perhaps there is.
>Imagine if you will a craft that is shaped somewhat like an umbrella.  The
>"covering" of the umbrella is a light sail.  Lasers from the solar system 
>would be used to accelerate it towards its destination.  Deacceleration
>would be accomplished by reconfiguring the sail so that all light would
>be focused on the "handle" of the umbrella, which would be a thermo-electric
>generator.  The shaft leading to the top would be a magnetic accelerator.
>Very small pieces of iron would be used as reaction mass to slow the
>pushed out at a very high velocity.  Note that the velocity of the "exhaust"

>would be arbitrarily high, dependent upon the amount of power obtained from 
>the light-gathering generators and the efficiency of the rail-gun drive.  
>This design is very similar to the fuel/sail concept mentioned in your web 
>page, but it differs in that it does not depend on the starship carrying a
>source of power to slow it down.  All power would be beamed to it until it
>became close enough to the target star to use its light to obtain power.  
>Given the type of propulsion used, the concept of "specific impulse" becomes
>meaningless.  Theoretically, if (1)beamed enough power (2)that it could
>and (3)the magnetic accelerator was powerful enough, it could essentially 
>"create" reaction mass if the "exhaust" was accelerated to relativistic
>speeds, since its mass would increase.  Of course, this would be incredibly 
>wasteful of energy considering the momentum generated, but since the power 
>comes from outside the ship and is essentially free, who cares?
>I haven't tried working out any math on such a model, but so far as I know
>is not something that your group has discussed.  Maybe the concept is 
>terminally flawed for reasons I do not see, but any feedback that you might
>have on this would be welcome if you have the time.

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?

We alsao toyed with some related ideas.  I came up with on where the beam was
focused back and reflected forward as a narror beam through the center of the
ship.  That beam is reflected backwards off a plasma sheet formed ahead of
the ship.  The plasma would blast forward (possible rocket thrust their) and
the reversed beam could push backwards on a deceleration sail behind it.  But
we did know how much power, or mass, it would take to refect the beam; and ir
seemed a little complicated.

If you figure out how to make any of these work give us a e-mail.  ;)

Thanks again for the interest.