Re: Laser Aperture Size

["L. Parker" <lparker@destin.gulfnet.com>]

At 01:31 PM 3/15/96 -0500, you wrote:
>
>!!!  If your getting about a G of decel out of a charged sail, You could
>adgust the sail so it only reflected absorbed enough to keep the sail
>charged.  (It would act like a sheet as long as the voltage could stop the
>mass farther out then the gaps in the mesh.)  Given that that power should
>be much less than the amount to push the ship at 1G.  You'ld cut your
>forward thrust, and THE SAIL WOULD ACT LIKE A BRAKE!  That might be the way
>to get your ship stoped at the target system.
>
>
>Why didn't you follow up on, or talk more about this?  Whats the dragdrop off?
>
It is called magnetic scoop deceleration or an electrostatic drag screen. It
can also be done similarly to the Lorentz Force turning  by simply trailing
charged wires.

For an elastic sail the equation is:

V(s)=2*A*p*m(p)*[(V(s)^2)/M(s)]

for an inelastic sail the equation is:

V(s)=A*p*m(p)*[(V(s)^2)/M(s)]

Where A=scoop field area, p=interstellar ion density, M(p)=proton mass,
V(s)=ship velocity, and M(s)=ship mass. Because of the V(s)^2 factor in
these equations, deceleration eficiency decreases rapidly as the ship
decelerates.

Other than as something to be concerned about as far as drag goes, this
method will not generate sufficient deceleration to be useful in
decelerating from near light speed. As a braking method for a ship that was
accelerated purely via sail to a maximum velocity of about .2c to .3c, it
might be feasible, but you will be looking at a 20 to 25 year deceleration
even then.
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