# Re: Laser Aperture Size

```At 9:28 PM 3/16/96, L. Parker wrote:
>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.
>>
>>
>>
>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.

Ouch, if we could get down to .2-.3 I'ld figure we could do the rest by
rocket.  But if we're talking about that kind of time to get down to .3c it
won't help much.

Kelly

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Kelly Starks                       Internet: kgstar@most.fw.hac.com
Sr. Systems Engineer
Magnavox Electronic Systems Company
(Magnavox URL: http://www.fw.hac.com/external.html)

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