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Re: Mirrors (first draft)

At 5:12 PM 3/4/96, Brian Mansur wrote:
>Brian 5:10 CT 3/4/96
>Okay, here it is.  The mirror paper.
>First off.  I'd like to thank everyone for the comments on the MARS Hybrid
>II (first draft). Although it has been mangled and shot through, I think it
>still has a chance of working.  This is because I'm already assuming a
>miracle in robotics to make it happen.  Why not a few more?  But to make it
>more believable, here are some ideas on the mirrors to perhaps add (or
>eliminate) credibility.
>     This component of my hybrid design was originally meant to be
> disassembled and launched aboard a protective pathfinder shell.  This is
>because the mirror will have to be precision crafted to reflect maser energy
>back to the Asimov during its deceleration phase.  Whether or not the mirror
>will be curved overall I am not knowledgable enough to determine.  But to
>allow flexiblitity for the design, I planned on making the entire mirror a
>composite of individually targetable mirrors of say 10km to a side.

Thats kind of the problem with these big structures.  They won't stay
precice under these loads.  They will flex.  Probably need to be flexible
like fabric.

>     Since the total reflective area will span a diameter of at least
>1000km, this mirror will also have to be extremely thin.  I figure that by
>the time we decide to launch this mission, we should have come up with some
>superstrong, superlightweight  plastics for the support structure and
>reflective surface.  This is necessary to make this array light enough to
>push.  A point of confusion for me is just what a microwave reflector would
>be like in terms of the reflective surface.  I have heard that a reflective
>sail could be made like chicken wire with spaces of say 1 mm between wires.
> That would certainly lighten the load.

A looser mesh than that, possibly up to 1/2 cm mesh.  But varies alot
depeding on transmitted frequency and dopler shift.

>     Refiguring my reflector ideas, I decided that the mirror could be
>protected against the interstellar debris using a lightweight solid shield.
> See Shielding below for an explanation.   If this can be accomplished, then
>we could use the mirror as its own sail, pushing it via masers.  It would be
>heavy but that is actually good because it means less acceleration during
>the Asimov's decel phase and so less distance between the two to aim across.
>     Aiming the array would be accompished by applying the same kinds of
>gyros that are employed on the masers to keep the beams on target from the
>Sol end.  I hope this is adaption can be made because my entire deceleration
>scheme really depends on it.  I note that these gyros will need some kind of
>protection from the maser beam and that is something I've not yet worked
>     In flight course corrections will be needed for this reflector to work.
> This will have to be accomplished with onboard rockets.  Just how powerful
>they must be and how much fuel they must carry depends on how light we can
>get the mirror structure.  If the mirror is chicken wire, this shouldn't be
>much of a problem.
>     Here's my proposal on shielding.  Make a bag out of chicken wire and
>fill it with superlightweight ping pong balls or with a superlightweight
>foam.  These substances would act like a dust or gas barrier but would stay
>inside the bag.  Anything that hits the bag will probably cause a sizable
>explosion so replenishment of these materials will be needed.  Robots can
>scout the surface of the bag to patch and reknit gaping holes.   The size of
>the bag depends on how much shielding we want.
>     It just occured to me that this idea may not work very well because the
>chemical structural of the pp balls or the foam will probably be altered by
>the tremendous heat from collisions.  Kelly, I believe, had proposed keeping
>a plasma in a bag several km in thickness.  I don't know how to contain
>plasma in such a thin bag as chicken wire even it the wire was producing a
>hefty field.  Also, how do we keep the plasma a plasma.  How about a "less"
>energetic charged dust cloud.  Would that stay in a magnetic field better?
> Could we keep it charged.  Wouldn't we have static electricity problems?

My shield wasn't a plasma shield.  I just assumed the ship launched a cloud
of electrostatically charged dust ahead of the ship.  Given the charge.
The cloud would spread out a bit, but wouldn't clump up on the ship.  Dust
plowing back past the ship would need to be scooped up before it got out
past the sides, and relaunched forward.

On the other hand your huge frontal area mirrors wouldn't need to worry
about that.  You might even just ignore the shield and assume a certain %
of the mirror mesh will be eroded during the flight, and carry extra

>So much for bolstering my hybid design.  By the way.  From now on I'm going
>to officially call it an ARGOSY class starship.  Since I'll probably have
>nothing better to do over spring break (like relaxing?), I'll see if I can
>improve my design.  Expect to see a lot of ideas borrowed from the Explorer
>design.  I should at least be able to give the group a decent description
>along with a critic of the problems associated with the thing.  Oh, and a
>long list of assumptions as well.

Great!  I was hoping we'ld get a fleet of compeating ship designs!  We can
try to cross link our pages when they are uploaded by Dave.

Let me know if you want copies or help.



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