```Kelly re: Timothy
Subject   : Plasma mirror

>>  >>>> I don't think refocussing is necessary, the mirror itself can
>>  >>>> be just a flat mirror so the reflected beam is nothing
>>  >>>> different than the beam from Earth.
>>  >>
>>  >>>That would mean the catcher sail on the ship would be the same size
as the
>>  >>>reflector mirror.  That would mean it would get more push forward
from the
>>  >>>direct beam from earth, than push back from the reflected beam from
the
>>  >>>mirror.
>>  >
>>  >>Hmm, yes, but there seems to have a similar problem with
>>  >>the plasma mirror.
>>  >
>>  >Not really, Since the ring sail & catcher mirror are in the same place
>>  >(attached to the ship) the ring sail would be getting the same energy
(no
>>  >energy drop due to r^2 losses.)
>>
>>  But would the beam from Earth not strike the ring sail?
>>  If not, please could you make an (ASCII)drawing, because then I don't
>>  understand how where the ring-sail and catcher mirror and the plasma are
>>  located.

Yes, the beam strikes the ring sail, and is reflected backward (Sol ward) and
inward toward a small catcher mirror.  The beam is then reflected forward
from the catcher mirror to the plasma mirror.  Net fore-aft thrust is nil
until after it reflects off the plasma mirror.

>>
>>  I don't use a ring-sail AND a catcher mirror, during deceleration, I
have
>>  only one flat mirror directed to TC on the ship and a retro-mirror that
is
>>  not coupled to the ship.

A|----\
O-----------/

O           Earth

----------- Beam from Earth

\
/           Retro-mirror

----        Beam from TC (Beam from Earth reflected by the retro-mirror)

A|          Asimov with a flat mirror

>>  >> This design makes the total mirror about 3 times bigger.
>>  >>The beam from Earth should be directed mainly on mirror B
>>  >> so that the beam to the Earth (or from TC) is reflected
>>  >>mainly from A. The final result is that there are two beams
>>  >> next to each other, one is going up the other is
>>  >>going down.
>>
>>
>>  It overcomes the problem you mentioned: tracking.
>>  The only thing the Asimov has to do is move about 1000 kilometers to the
>>  left after it has uncoupled the retro-mirror. The result is that the
mirror
>>  and the Asimov will move in the same direction during deceleration.

You still haven't dealt with the problems of a drop mirror.
- Given that the point of the exercise is that the mirror and ship will
accelerate apart until they are moving apart at nearly light speed.  They
will be getting very far apart, and the "Retro-mirror" will need to aim to
track the decelerating ship.  By having the ships flat reflector mirror the
size of the full power mirrors you eliminate the retro-mirror needs to focus,
but not to keep aiming at the retreating ship.
extra forward thrust from the earth beam on the back of the ship.  (I don't
by the ship running on a tiny beam that just fits in the sail.  The ship will
need to maneuver, and the transmitters couldn't hope to generate that much
accuracy.)
- The energy retuning to ship will drop off like a rock as the distance
between ship and retro or drop mirror increases.  Given that the mirror will
not be that smooth (it will probably be rippling) the beam will be diverging
- Need for active control systems on drop mirror.

- Need for structural stiffening on drop mirror.

==============================================================================

Kelly re: Timothy
Subject   : nanoAI

>>  >>We have ideas, the biggest problem is the enormous amounts
>>  >>of fuel that are needed. Lets say we use a
>>  >>take-all-fuel-with-you system. For matter&anti-matter fuel
>>  >> the ratio fuel:ship would be about 20:1 for small ships 1E4 >1E5 kg
this
>>  >may be acceptable but for ships 1E8 or 1E9 kg
>>  >>its a completely different story.
>>  >
>>  >Your taking hundreds of tons of antimatter!  That is a staggering
amount to
>>  >manufacture, or even hold on to!
>>
>>  My assumptions are that making anti-matter in 50 years will be about 50%
>>  efficient. Of course I can't be sure of this, but why wouldn't it?
>>  (Rethorical question)
>>  Besides this efficiency, I wonder why you are so blaffed by these
numbers.
>>  These numbers are just the sum of the energy needed during 1 or 2 years
of
>>  acceleration.
>>  If we build a maser beaming station, a similar amount of energy is
needed.
>>  The only thing you do when transferring energy to anti-matter is making
it a
>>  bit more permanent. It probably is the easiest way to store such amounts
of
>>  energy.
>>
>>  So the moral is, anti-matter is merely an amount of energy that is
easier to
>>  keep in storage.

Easier?  The ship would still need to carry something like its own weight in
matter anti-mater.  A mass of thousands to millions of tons.  Forward was
hoping optimistically we'd be able to routinely generate and store milligrams
to grams of antimatter.

>>
>>  >People are mentally much more adaptable and reliable than any current
>>  >Nano/A.I. systems.
>>
>>  You can't compare adaptability and reliable to CURRENT systems. That
would
>>  be the same as to say that current engines would not work for our
project
>>  and thus that it was not possible.

True, but since no current A.I. system works very well, and no nano-tech
systems work at all, I'd have a very hard time expecting them to be developed
to that degree of reliability in 50 years.  Its out there with the "we
discover warp drive possibilities".  Sooner or later we'll do them, or
something like them; but they don't fit within LITs "no radical new tech"
parameters

>>  From this I can conclude that I have a more optimistic view about
nanotech
>>  and AI, then you do.
>>  Of course nanotech and AI are now in an early stage, but if 50 years
ago,
>>  you had said what computers of today would be like, then they had
laughed at
>>  you also.

50 years ago we had production computers.  Only a handful, and their
capacities were trivial be current standards; but thats farther than
Nano/A.I. systems, and no current computer or automation system could attempt
anything on the scale of what you are suggesting

>>  >>That is something completely different discussion: Why do we
>>  >>want to go there anyway. I was having a discussion with Nick
>>  >>Tosh about that, until his connection broke down. I can tell
>>  >>you, that I don't know why we want to go there so soon
>>  >>anyway.
>>  >>If you have an answer I'd like to know...
>>  >
>>  >As I remember the idea of LIT was to see if we could think of some way
we
>>  >could build a starship in 2050 with probable technology of the day.
Tau C
>>  >was selected as a target to focus the groups attention on.
>>
>>  I know that, but I thought it was interesting to figure out why we want
to
>>  go there. Is it just to have pissed on the ground there? Or is it
because we
>>  want to colonize it? Or is it for scientific reasons? Or maybe all of
them?
>>  All these things me be reasonable at first but, if you think a bit
further,
>>  they make not much sense anymore...

True.  The LIT project assumed a big (blank check) push to go to Tau, but no
reason or goal was given, and the group has never been able to agree on one.
Thats a pretty big hole in the discussion, but since we also can't figure
out how to get there in the first place its kind of a mute point.

One thing I was considering was what we can do.  My Explorer design could
certainly be able to carry enough fusion fuel to decelerate from 1/10th C.
Marshal Savage mention something like a 20 to 1 fuel to ship mass ration to
do that.  I'd like to check that, but for the moment will assume its true.
Obviously trying to do that at 2/10ths C would take 20 squared (400) ship
masses of fuel.  So thats out, but at even those speeds drag is a serious
factor.  Savages book mentions that at near light speed the (one atom per
cubic centimeter) inter-stellar Medium could cause up to 37 milligrams of
drag pressure per square centimeter of frontal area.  I'd like to work up the
numbers for various interstellar densities and ship speeds; but it seems
likely that some kind of magnetic or electrostatic, scoop or parachute could
give us a big amount of breaking force.

If we stay with a .1 to .2 C top speed ship we might be able to get a
practical mission to some of the nearer stars.  Not Tau C, but Alpha Centuri,
Barnard's, Rigil Kent (Rigel kent A is a G2 yellow Main star at 4.4 LY, B is
a K6 orange-main at 4.4).  A .2 C ship could get there in a usable period of
time.  A version of my Explorer Fusion design could get there and back.  If
you have some reason of wanting to go there regularly.  The first ship could
assemble automated fuel launchers in the target systems.  That would allow
lighter ships to make the same run at higher speeds without carrying heavy
fuel loads.  (Assuming they trusted the fuel launcher at the receiving system

I suppose launching construction/survey flights might be practical (i.e
someone might be willing to pay for them.) if they could be kept down to that
length of time, and the public had an interests in the stars similar to the
Apollo days.  But what do we do there that would interest people that much?
Science seems a pretty thin reason.  Colonies can be built in this solar
system just as well as another.

Apollo was run for the international prestige (specifically vs the Soviets).
I can't see anyone coming up to threaten a specific group that much by 2050;
but even without that the project might attract enough enthusiasm among a
major country to fund it.  (My experience on International space projects
makes me discount them out of hand.)

So I guess what we want to do there is a question that we'd need to resolve.
More specifically why we'ld feel we needed to do it then?  If you willing to
wait another half century.  You could expect to have relyable equipment based
on physics unknown to us now.  (Matter conversion?  Time space distortion?
Such things have been seriously proposed.)

Kelly

```