Re: EUREKA!!!!!!!!!! (ha ha ha ha ha ha) >:-)

[Kevin C Houston <hous0042@maroon.tc.umn.edu>]

On Wed, 15 Nov 1995 KellySt@aol.com wrote:

> I still have questions about momentum transfer vs power absorbsion. This
> neat conversion of absorbed power and momentum bothers me.  I would think
> that converting the power would use up the energy that would generate the
> thrust.  Maybe I'm confused?
> 

Not at all, if you reflect, you get twice the momentum that you'd get if 
you absorbed.  so there is no violation of energy conservation.

> 
> 
> If the back side of the sail/collector was mirrored, and the frount side of
> the inner sail elements had the rectennas.  Then durring the accel phase
> all sail elements can be trimed to reflect almost all the power straight
> back at Sol for max thrust.  (Note you'll need a slight outward thrust to
> hold the sails out to the sides.)
> 
> Durring the decel phase.  The outer sails are trimed to reflect their
> energy inward toward frount of the inner sails.  The inner sails are trimed
> to reflect the energy hiting their back inward toward other sails or
> dumping it.  But this foward and outward thrust, serves to support them
> against  backward and inward thrurst from the energy pouring inward and
> back from the outer sails onto the frount of the inner sails.  The frount
> of the inner sails have the rectenna arrays.  Which absorb and convert the
> microwaves.
> 
> Good news.
> The sails have max reflectivity durring accel phase.
> 
> Only the inner sail array needs the more complecated rectenna and power
> conversion/transmition/cooling equipment.  (The outer segments are just
> wire mesh.)  So servicing and costs can be minimized.
> 
> Bad news
> The expensive power converters are going to be face first into the inter
> stellar medium, and they are going to be operating at much higher power
> densities.  Cooling is going to be much harder.
> 

1) about power converters (schottsky <sp?> diodes) being face first into 
the "wind"  we are going to need a lot of tension wires to keep the 
antenna from blowing apart, so if they were on the front, they would 
effectivly shield the diodes.

2) about cooling, angling the antennas requires more surface area, 
allowing for _smaller_ power densities, and more surface to radiate the heat.

> 
> Weird thought.  Am I right that microwaves can impart thier momentum on
> ions directly?  Could you channel the power via waveguides, and feed the
> reaction mass into the power stream and get it to accelerate the plasma
> directly?  I can't remenber it clearly, but I think their is some such
> mechanism.  If so, you could avoid the heating problems of the power
> conversion step.

Agreed, this should be looked into.  Not sure if this is possible with 
microwaves, I'm having difficulty seeing how the microwaves could be 
reflected into the reaction chamber without the inner sail elements 
getting in the way of the outer ones.  but if it could be made to work, 
it would solve the heat problem neatly.