```Timothy re: Kelly
Subject   : Plasma mirror

>>What I meant with no turning, was that it just had to reflect the beam
>>STRAIGHT back. To do that is has a very precise orientation: the
>>incoming beam. The mirror does not have to track a moving object, that
>>is the task of the Earth beaming station. If Earth beams it to the
>>Asimov, then it also aims to the mirror. because the Asimov and the
>>retro-mirror are always lined up.
>
>That wouldn't work, but eiather way.  Straight back is still a direction
>to aim at, and it couldn't do it.

Is it really that hard to keep the mirror straight? And still, if the beam
deviates, the Asimov can still follow it (too a certain amount) by
redirecting its own mirror.
Doesn't this problem arise also on the Asimov itself, it too uses a big
mirror to accelerate, if its mirror is a bit offside, it is out of the beam
in seconds. If you move 1E8 metres in one second, only minute angles are
needed to be off the "road" 1E4 metres or so.

>We have no real idea whats in interstellar space, but is fair to expect a
>few comets, asteroids ect; and I don't think we can plan on everything in
>our way getting neatly blown out of the way.

If there are indeed so many rocks that we have to worry, then we certainly
should make use of them. How big do you think the chances are that any of
these lumps comes even near the Asimov?

>NO!  A retro reflecter mirror wil not work unless the retro-mirror is much
>bigger.
>-If its the same size and the retro mirror is straight in frount of the
> ship.
> It will be in the shaddow of the ships drag mirror.  So it won't 'see'
> any of the beam to reflect.
>-Even if its not in the line of sight.  Being the same size as the drag
> mirror on the ship.  It can't reflect anymore energy back to the drag
> mirror,
> than the mirror gets directly from earth.  So It wouldn't be able to
> decelerate the ship.

These two remarks mean that you haven't understood how I planned to make
that retro-mirror!
It was constructed of two mirrors at a right angle to each other... (See
previous letters)

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

>>             )
>> -------------)
>>            //)
>>          (--------| Plasma
>>          (--------| Plasma
>>            \\)
>> ------------)
>>            )
>>
>> ( are the small mirror at the Earth side of the Asimov
>> ) are the big mirror at TC side of the Asimov
>> -- / \ Light rays
>
>Pretty much it.  Imagine the ship as a hollow pipe with a plasma in the
>inside of the pipe and in frount of it.  (The ship surrounds the plasma,
>not the other way round.)  The microwaves are reflected back and inward by
>the forward main ring sial, toward the rear ring sail (drag sail) which
>reflects it forward inside the open area of the ship toward the plasma.
>It heats and is reflected off the plasma backward.

And then after it has reflected backward? The ship needs to absorb or better
to reflect the photons in the direction of TC. If it reflects straight back,
then it enters the plasma pipe, that must mean trouble.
Please tell me what happens after the (first) reflection on the plasma.

>> Indeed, that's what I'm saying. If a system is only 10% or even 0.1%
>> efficient, then for example a fusion system that uses a 1:1000 ship:fuel
>> ratio as well.
>
>As well what?  Efficency is not nessisary for a system to be usable, but a
>ship that needs to carry a thousand times its weight in fuel simply can't
>be built.

letter.)

>You've never suggested how you think such amounts of anti-matter could be
>made.  Or how we could build such engines.  Or store such amounts of
>antimater.  2050 is to close for us to overcome all those problems on that
>scale.

That means fusion is also out of the question! I've heard that the first
commercial fusion power plant would be there at 2050. From there it is still
a big step to scaling up such a power plant about 1E8 times.
And if fusion isn't our source for the beaming station what is? A
mirror-array to collect the energy of the Sun would be too large or too
difficult to construct.

The current electricity capacity of the world is about 3E12 Watt. So all
what we have now should be scaled up 1E6 times!

Finally we come to the conclusion that doing this in 2050 is completly out
of the question. Even going to Alpha Centauri isn't possible, simply because
we there isn't a power-source by then that can do the trick.

>>How to store the anti-matter? Just like normal matter, create anti-atoms
>>and anti-solids. Finally charge it and suspend it in electro/magnetic
>>bottles. OK, it sounds easy, but it seems to be possible.
>
>In theory, but its a big jump from theoretically possible to usable.

You are right. But the only experiment done with moving an object by laser
light involved a mass of about a milligram. So that would mean that any
lightsailing technique is not much more than theory too.
What I mean is that probably none of the existing and almost-ready-to-use
techniques could bring us to TC.

>We went around on that question a lot a few months ago.  Yes you have to
>bring the crews back.  No one would fund a suicide run without a desparte
>need, and we don't have one.

Staying there isn't necessary suicide! Going back may be a bigger risk.
(On that question I didn't vote for a 2-way trip)

>> I think that we have to assume that this minimum is possible, otherwise
>> no system is possible unless we "invent" anti-gravity, or if we use a
>> ship that has much less mass (which is almost impossible).
>> So it would be better if one the rules of the SD "discussion" was that a
>> minimum (unknown?) power source of 1E18 watt is available in 2040.
>
>Or limit the discussion to systems and power levels that seem likely.

Lower power levels mean not going to TC! Lower levels mean a much longer
trip, and we agreed that wasn't our goal.

>> Increasing efficiency or affordability make any design more probable and
>> feasable. If for example the space shuttle had AI and nanotech. it would
>> probably much more saver, reliable and cheaper.
>
>True, but since we havn't figured out a near lightspeed ship thats more
>than marginaly plausible, trying to cut costs on it doesn't mater.  All
>that would do would be to make a nonfunctional system cheaper.

It makes a lot of difference if one needs 1000 Watt or 1000*1000 Watt. For
the first a simple petrol-generator will do, but for de latter you need
almost a complete power-plant.

>> If one makes such a big ship, a lot of things may go wrong and endanger
>> the trip. The more complex the ship, the more probable that the trip
>> isn't completed. NanoAI will decrease that probability significantly.
>
>But of course, Nano are about the most complex and unrepairable systems
>we've even theorized making.

Maybe unrepairable, but there will be many of them, so one or two less
doesn't matter. The strength of nano is not only their tinyness, but also
their vastness (for small price? and weight). The goal will be that they
become selfreproducive in a (hopefully) controlled way.

>The odds of finding lifeforms and planets are how to judge. Certainly
>we're only taking about a handful of stars within search range.  But it
>seems likely all of them could have planets, and we have no idea how picky
>life is about where it can form.  In Sol, earths a yes, Mars is a maybe
>(please send unbroken lab gear) Venus I'd bet strongly against.  As for
>the rest and their moons... ??
>
>One thing we can be sure of, none of the planets out there will be
>habitable. Earth wouldn't be habitable to us if we hadn't evolved here.

Why wouldn't they be habitable? It would be possible that there are already
other forms of life there. (Not necessary intelligent)

In any event a handfull of starsystems should keep us busy for a couple
decades.  Obviously past 2100 all the systems were discussing will seem
archaic, and our physics quite naive.

Probably the next century would keep us busy only by "colonizing" moon and
mars. And maybe some nice asteroids for their low gravity.

>> I've done some calculations, these show there is not that much profit
>> (in energy) when one compares prelaunching with take-all-with-you (from
>> now on  TAWY).
>
>So?  It would make a critical difference in the fuel mass ratio of the
>ship.

So, energy stays about the same, or even better it doesn't have to be
produced it (the hydrogen) only has to be collected.
Why would making a big lump of Hydrogen be so difficult? It doesn't all have
to be launched from Earth (asteroids or moons?)

Timothy

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