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Re: Engineering Newsletter

Timothy re : Kelly
Subject    : Plasma mirror

>Reasonably flat, and optically flat are very different!  Optically focused
>over light-years is even more different.

OK, I give up... I hoped that this this unflatness would not be too big.
But If you can't make a mirror that is flat enough than you can't make a
curved mirror that is curved enough. So a curved mirror would spread the
light just as much as a flat mirror. So this means that ANY mirror that
works over a larger distance is out of the question!

>Again, you can't use a 2 part retro mirror since the drag mirror on the ship
>has to be much smaller.

No, because the two parts of the retro-mirror could have been place further
apart (but makes the construction not easier).

              Beam that missed the mirror
         /      ||  \
     A /        ||    \ B        Two mirrors A and B at a perpendicular angle
     /__________________\        but at some distance from each other
 / ||           ||       || \
   ||           ||       ||
   ||           ||       ||
   ||           /\       /\
   \/          Beams from Earth
Beam to Earth

   XX The Asimov
The mirrors are connected in some rigid way!

>>I assume that the plasma is replenished all the time. So at the same time
>>that the plasma is replenished inside the plasma-pipe, there are also coming
>>reflected photons from the TC side. Doesn't that create a problem?
>Can't think of any.  It actually should help.

After rethinking it, I see what you mean.
The only thing I'm not sure about is what the physics of plasma reflection
are. We may reflect radio-waves to the ionosphere everyday but how does it
work? And does it work in the Asimov also?
I don't know how big the plasma-tube is going to be but at certain
radiation-densities materials get blown up, so you don't even need to ionize
the molecules yourself to create a plasma.

>Its not the weight, its the mass fraction.  You could scale up the craft, but
>not increase the fraction of its total that is fuel or cargo (well not by
>much).  Given the speeds and time we're talking about, you can't go with a
>ship with lower accell.

Yes, I understood that. But do the engines take the most of the weight? Or
in other words, what percentage of the ship (without fuel) is reserved for
the engine? If that percentage is small it may be possible to scale up the
engines a bit. But indeed there is a limit, only where is that limit?
Ideally the weight of the engine grows slower than its power: Make an engine
twice as big doubles the power, but the weight increases with the squareroot
of 2.

> > >Also of course if the energy to accelerate the fuel doesn't need to be
> > >carried in the ship, the ship can get by on less fuel.
> > 
> > Yes, but that would involve a beaming technique.
>No, I was talking about my fuel launcher idea, not a beamed power system.

Probably launching is even more difficult than beaming.

>>How much push did you have in mind? There is already much research going on.
>>Already a few seconds of "controlled" fusion are possible. Development isn't
>>possible yet, because not enough is known about the plasma flows that are
>Actually there is very little research going on.  Several areas considered
>more promising than magnetic confinment have no funding due to competition
>with established programs.  In the U.S. each new model car turned out
>receaves more R&D funding than all of fusion. Given the abundant conventional
>fuel sources, alternate energy suplies get little interest.

Here in the Europe (also in the Netherlands) there are several institutes
busy. Most of the research is in a very early stage. Spending more money may
help a bit but not that much as you would hope. Some things just can't go
any faster.
Besides that, it is not fair to assume that money alone can change research
that fast, otherwise antimatter may become a possibility too.

>I don't beleave G.M. has any launcher program?

You're right, after some research and your forwarded letter, I figured it
was the X-33 that I had in mind, and GM should be Lockheed Martin Skunk
Works, McDonnell Douglas Aerospace and Rockwell International Corp.

>>Wasn't there an experiment with a solarsail last month?
>Not that I know of.

I will try finding some info, if I know more I'll let you know.

>10 whole planets to build what in?  They would have no place to live in other
>than their ship.  No resources to suvive in the ship for more than a few
>decades (and we have no ability to do better than that).  How are they going
>to survive?  What do you mean by having them "stay there and try to make a
>living"?  What is there for them to do that would pay for their keep and
>supply flights?

My guess was that they would construct a pre-fab habitat and from there they
would expand. Being on a planet gives you much more resources and savety
than a spaceship. Not all planets will be equal favourable, but a solid
planet the size of Earth will be better than a spaceship after the main
habitats are equipped.

> > If we aren't planning on staying there, why go there? If it's just to
> > investigate it may be better to send unmanned probes. (That would be 
> > a task for AI)
>Your expecting a lot out of A.I.s.  Humans will probably be more adaptable
>for some time.  Also no one would fund a A.I. exploration flight.  Tax payers
>want to see humans explorer, and lose all interest in programs without human

To see? There won't be a live television show with interactive
conversations. By the time Earth gets the first message of landing, the crew
is already on their way back. Also would you pay money now to see a
spectacular show that happens in 30 years?
And indeed I am expecting a lot of AI, humans may be more adaptable for a
while, but have lots of limitations that "machines" don't have.

>> So TC is out?
>Seems like.

So where to and when is our new goal? Until now only fusion may bring us out
of the solar system within reasonable time. Even if you use a beam, the
fusion is necessary to maintain the beam.

>No, most deseases don't interact with our genetic structure (only viruses do)
>the rest (molds, bacteria, fungus, etc..) just use us as chemical food or
>fertalizer. Here we evelved defenses against those deseases, but on an alien
>ecosphere the counterparts could be radically invulnerable to our defence
>techneques, and we'ld have no time to evolve new ones. 
>Then again alergies, even to things we've been exposed to for centuries, can
>kill sometimes us in minuttes.

Is there any hope for us? Our best hope was to find a living planet, full of
life and oxigen. Now it seems that it is better to find a barren planet with
no life at all.
Do we indeed have not enough time to develop a anti-bodies against these
diseases? We indeed should be very careful, but that doesn't mean that after
we have found most anti-bodies we can live there.

>I ment near earth comet cores.  Their are a few thousand of them charted, and
>are easyier to get to than Mars.

Comet cores? I'm not sure anymore what you mean, what kind of orbit do they
have? Elliptical or (near) circular? And do they turn around the Sun or the
Earth? How big are they?

>More precisely the low G would deteriorate your system.  Short term you
>couldn't handel 1 G.  Long term you die from cardiovascular, bone, and immune
>system deterioration.

Oh, I didn't know that it was that serious. But I assume we can adapt to a
thirth of Earth's gravity or is that still to little?

>Sorry, I thought it was clearer.  Is this preferable?

Unfortunately not, the problem was not the double > but the three (>> )
characters added, that makes that all lines are broken off and one word is
shown on the next line. If the you add only one > (no spaces) this word-wrap
happens less often.
Probably Steve has "trouble" with everyone because he use lines of 60
characters or so.

>A, I the only one who remembers to CC Dave Levin on the address list?

I've never received a (personal) notice from Dave, he just left me (us?) in
the dark and I always had to hear from some others that they had made
contact with him. The least he could have done was send a (general) note
telling he had no time for the SD-project anymore.
In fact the only message I got from him was the one of December 17th.
So in short, I'm a disappointed by Dave's performance.