Re: RETRO MIRROR SCHEMES

[Brian Mansur <bmansur@oc.edu>]

Brian

On March 7, 1996 at 9:21 AM, Kevin Houston proposed in Orbit B this idea.

>Kevin:
>I've got an idea rolling around my head, and I think it's time to let it 
out.

>First, attach a asimov-sized sail and maser cannons (just like Tim/Kelly
>proposed) to several large asteroids (for mass) and blast the hell out of
>it to get it up to .5 C. once it is on it's way, wait until it is in
>position, (time unknown, still working on it) and start a one light-year
>long maser blast.  after this amount of energy is on it's way, the Asmiov
>begins it's journey.  after one year, the maser beam cuts off from Sol.
>The tail end of this beam catches up to Asimov at the half-way point,
>just as the retransmitted beam from the (for lack of a better word)
>reflector.  The reflector speeds up, and crashes into TC, while the
>asimov slows down. the maser beam from earth is still only on for about
>two years (not counting the time needed to accelerate the reflector)

>one of the nice things about this system is that the reflector can be
>accelerated at just about any rate, (within reason) as it is un-manned.
>given that we won't need large RM tanks, or a Kilometer long ion engine,
>I think the entire weight of the Asimov can be drastically reduced to
>crew support sections only.  While in-system, the Asimov uses a
>visible-light solar sail to move around.  This system still requires a
>construction project to build the return masers.

>Comments?  Suggestions? Flames?  ;)

Brian
ISN'T THIS EXACTLY WHAT I'VE BEEN SUGGESTING ALL FOR THE LAST THREE DAYS!!!
I THINK ITS BRILLIANT!!!  sorry for shouting Kev.

Problems with aiming the reflected beam, however.  Since the distances 
between the reflector (we are callin it a retro-mirror) and the Asimov could 
get to an excess of 10,000 AU, I propose refocusing the beam into a tight 
shot about between 100 to 1000km.

Talking about refocusing beams.  At worst, the beam from Sol can be allowed 
to stray  + or - 1000km.  This could be more easily accomplished (or 
eliminated dare I hope) if we had  a refocusing mirror aparatus station (of 
a similar configuration to the retro-mirror) somewhere  along the way to TC. 
 Because of losses in the reflecting, I figure that there would be power 
transfer losses of say 30% per station.  I get this number from the idea 
that the primary beam gathering mirror would be made of aluminum.  It is a 
reflector good for  85+% transmission.  Use silver for better %ages.

The primary mirror refocuses into a small (10 - 100 km) precision mirror 
that beams the refocused energy into a final dish that accurately aims using 
your gyros.  The thing works like a telescope getting a precision shot to 
TC.  I assume that we lose 30% through the whole process.  Depending on how 
many refocusing stations we go through, we may expect 1% of our original 
beam from Sol to reach the Asimov.

This rating is disgusting, but fortunately I have already calculated for 
gathering 1E20 W (from closer than Mercury orbit) assuming 1% ever get to 
the Asimov.  A square sheet of the necessary size could almost eclipse 
Saturn if it could be place next to is.

By the way.  The retro mirror is 10,000km wide (not in radius) so a + or - 
1000km  to hit isn't too bad.  This gives us a 12,000km wide beam from Sol 
with 30%  of the beam immediately lost to space.

Calculation for this is pi  * 1E4^2 / pi * 1.2E4^2 = .69.  1 - .69 = .30 * 
100 = 30%

The retro-mirror is responsible for keeping the beam steady in the direction 
to Sol (beaming straight down the the Sol beam in fact).  The Asimov just 
has to find the retro-mirror's beam.  It is understood that the beam from 
Sol will cause some overall losses in the system since it will be hitting 
the back of the Asimov's sail.  These losses could get up to 2% given that 
the sail is 1000km wide and the Sol side beam is 10,000km wide.  Oh, and I'm 
assuming that the retro-beam is + or - 10km dead on the Asimov sail.

Since I'm we're talking about system efficiencies.  I wonder if it would be 
better to skip masers and use  visible light reflecting sails.   LISTEN UP. 
 THIS IS IMPORTANT.  We know that our masers waste 90% of their power just 
to transmit (right?).  If we were using solar panels like on the Hubble, 
then that is another 90% lost.  Already our 1E18 W needed to accelerate the 
Asimov is up to 1E20.  This gets worse as we transmit across interstellar 
distances through refocusing array's and retro-mirrors before ever getting 
to the Asimov which will have a none too pretty reflective sail itself. 
 This could easily put our starting power bill at 1E21.

IDEA!  Why not skip converting the sunlight and just gather it directly into 
lasers using these huge mirror apparatuses that I'm proposing.  The arrays 
aroundSol would need to be heavy to keep from getting blown away, but that's 
okay.  In fact, for weight, each could have a robot service station complete 
with many a megaton of equipment and raw materials just to keep it going. 
 It would take a while to this array set up, but then we are figuring on 
unbelievable automation.

SOMETHING ELSE IMPORTANT.  I was up late last night reading old newsletters, 
trying to come up with ideas and see what kind of breakthroughs we needed. 
 As of this time, I hold next to no hope for humanity going to the stars 
without automotive breakthroughs that would revolutionize industry by put 
the blue collar guy almost completely out of the construction business.

I know it seems a stretch but the alternative is to have equally improbable 
breakthroughs in physics and who knows what other tech.  Come to think of 
it, we are already depending on some real breakthroughs just to get certain 
pieces of the ship working like the superpowerful ion drive.  This is not as 
spectacular as autonomous robots but just as necessary for exploration of 
TC.  And since we're talking about how to get to TC, I really think that 
light sail propulsion is our best bet.  That prospect makes me shudder since 
we don't know how much damage interstellar matter will do to do the sails 
(not to mention the hab section).  But this seems to me that this Argosy 
that I'm trying to get into shape is what we are going to be stuck with 
(until we find something better).

Quote from ST:NG.  Picard:  "things are impossible only until they are not."

 About the retro-mirror design.  What do you guys think?  I proposed this 
retro-mirror configuration (as a refocusing station idea) when I first 
joined the discussion group in January, but I don't remember what you guys 
thought about it.  Please respond because if this won't work, I don't know 
what will.  My brain has been very focused on the Starship propulsion 
question and I am out of ideas that could make the Argosy class ship fly. 
 At least for now.