Mirrors (first draft)

[Brian Mansur <bmansur@oc.edu>]

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.

MASER BEAM REDIRECTING MIRROR:
     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.
     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.
     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 
out.
     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.

SHIELDING:
     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?

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.