Re: RE: starship-design: Timothy's beamed power paper

[KellySt@aol.com]

> In a message dated 7/23/97 2:07:30 AM, TLG.van.der.Linden@tip.nl 
> (Timothy van der Linden) wrote:
>
>Lee,
>
>Hoping that Zenon did quote your entire letter, here my comment
>
>> In rergards to shielding the cargo aeas of sail powered craft I think 
>> you are worrying too much. 
>
>In my summary it is just on of many points. It is a problem that may arise,
>but surely not the biggest.
>
>> I seem to remember that Forward performed all 
>> of these calculations. I will look them up to be sure. But, anything 
>> with sufficient power to require a lot of shielding on the cargo will 
>> MELT THE SAIL.
>
>True, but you got me thinking about something...
>
>I think most of us are still assuming that the sail is a mirror. This can be
>true, but if so, it will not decelerate the ship unless we can make a
>retro-mirror (or plasma-cloud mirror) work. (Kelly would you care writing a
>short explanation about the plasma-cloud mirror for the new members?)

Ok.
Imagine a parabolic sail hung in frount of the ship like a parachute.  Its
shape is adjusted to keep the reflected microwaves focused backward into a
smallar ring sail behind the ship (I.E. closer to Sol).  The smaller sail
focuses the beam forward into a beam passing through the middle of a ring
shaped ship.  Because of the two reflections your net thrust is zero.  But
then the focused microwave beam hits the plasma mirror the ship magnetically
suspend in the volume inside the ring.  The beam is reflected backwards where
it hits a drag sail.  The plasma is reflected (blasted) forward and is lost.
 Net thrust is from the drag sail, toward the microwave source.

Note this assumes you can economically replace the plasma mirror mass.  If
you lose to much mass, you wouldn't be able to carry enough to sustain the
mirror durring the deceleration phase.

Oh, note that the mirror plasma will get hot!  Probably enough to explode
outward in all directions.  This blast presure might be tapable to provide a
bit of rocket thrust.  My gut feel is that woldn't work thou.




>The beaming concept looks nice, but its most essential problem is
>deceleration. Using the "sail" as an energy collector to power some engine
>(Kelly has a "simple" solution for that too) is the only option besides a
>retro-reflection-mirror.
>
>  <snip>

Well Kevin had tinkered with the idea of using the microvave beam to power a
reverse thrust rocket motor  (M.A.R.S. - Microwave Augmented Rocket System)
but I'm not sure where thats at.

My idea was Fuel/Sail.  You weave the sail out of a solid fussion fuel like
Lithium-6.  Lithium is a stiff metal, and should be adaptable as a sail
material.  The microwave beam accelerates the sail, which outweight the ship
by a fantastic amount.  After your boosted to cruse speed you pull in the
sail into a solid plug in frount of the ship (for impact sheilding).  When
you reach the star system, you burn the fuel in fusion motors to decelerate
you into the system.  

Since the sail can be any size you want.  I scaled it to about 400 times the
dry weight of the ship.  That would let it decelerate from about 40%-43%(?)
of light speed.  Giving you a quick trip.  For the ride back you mine more
lithium-6.  Burn it all accelerating back toward Sol.  They deploy a
compartivly tiny drag sail to decelerate you down into Sol (assuming someone
will turn on the beam again).

Kelly