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Re: Engineering Newsletter

Timothy replies to Kevin:

>Okay, Okay, I think we've all heard enough of this argument.  Neither of 
>you is going to change the other's mind.  If all we can do is figure out 
>how to send a one-way mission, then I think we can assume that it will 
>never be used until someone comes up with a valid reason to send so many 
>people off on a no-return mission.  What's a good reason?  Why, one that 
>would attract enough qualified (intelectually and psychologically) 
>volunteers of course.  I think we all agree that it would be a good 
>_idea_ to have a return flight, The question, is whether it is possible 
>or not.  i think it is,  A one-way mission would only be sent in the 
>direst of planetary emergencies (sun going nova, hostile aliens etc.)

You shouldn't say that neither one is changing their mind. I'm certainly not
argueing to enforce my ideas on those of Kelly, I'm trying to figure out why
we do so fundamentally disagree. Now after a few letters, I think it is
getting clearer were our differences are.
If you don't like to read these discussions that's fine, but I sometimes
have the idea that discussions are too easely stopped, so that in the end
both (or more) members still disagree and that means that the whole
discussion was done for nothing.

><as an aside, if we knew the sun was going nova, could we use that to 
>boost colony (ship/worlds) to other systems?>

Probably not, the Sun would have grown too large before you could use its
nova. I think the increase of the Sun's radiation will not be that significant.

>Impractical and expensive, yes, but there are no tech dificulties.  you 
>would not be "creating" the energy, but only re-directing a tiny fraction 
>of the sun's output.  I would say it thusly "you would be using 1/3600 of 
>the suns total output for a period of 2 years" After that, the energy 
>could be used right here in Sol System for any other project that was 

I'm sorry, I'm not sure how I got to the numbers but what I wrote between
braces is totally wrong, you would need about 1/(1E8) part of the Sun's
total output.
Meaning a solar panel with a 1000 kilometre radius near Earth.

>As to anti-matter and large energy requirements -- I think it would be 
>far more useful to figure out how we can send the most mass for the least 

That would always be anti-matter or a beam that is very tight.

>Tim, i have a question for you regarding anti-matter,  how do you intend 
>to direct the "exhaust"?  as I see it, anti-hydrogen would combine with 
>normal hydrogen (scooped?) and this would result in a burst of Gamma rays 
>in _all_ directions.  how will you harness the momentum of these photons?
>assuming you can make and store the anti-hydrogen, how many Kg of 
>anti-matter would you need to get to the target star?  do we carry the 
>return trip fuel with us? or try to make it from the target? if we are 
>going to make it, what percentage of energy can be turned into 
>anti-matter? (and you can't assum 100% eff. either, or then I can assume 
>100% eff. solar arrays and microwave converters ;) ) and where does the 
>energy come from if you intend to make it?

I haven't a complete oversight, but can tell you what I have in mind:

1. Matter is injected by matter, so that the photons collide with normal
matter. This matter is heated and will escape at the place of the lowest
pressure, the backside. This anti-matter engine needs more matter than
(I think in this case the comparison is big with chemical or fusion engines)

2. When an electron and anti-electron collide from almost rest, then 2
photons of 511 KeV (2400 nm) are formed, so this means that photons of
resonable equally wavelength are created. So that would allow some kind of
mirror to reflect them to the back. To be honest sometimes there are 3 or
more photons formed with a total energy of 1022 KeV but all have different
Now the problem is how to get only (anti)electrons and no protons or other
bigger particles. I haven't an aswer to that, so for now this method will
not work.

You also ask how efficient it will be, that is hard for me to estimate, but
like most engines it has to be efficient otherwise it will melt away. This
seems like an easy way out, but I think it is true. So what it is important
that the products of the antimatter reaction are all discarded and not
absorbed in the engine. If the end-products are controlable this may not be
too hard.

>(one idea for storage of anti-matter, start with anti-hydrogen,made from 
>slamming high-speed protons into a stationary target, and use fusion to work 
>your way up to anti-iron  does anti-matter give energy when it fuses 
>with anti matter? i think it must. when you have a quantity of anti-iron, 
>magnetize it and your storage problems are solved.  many of these 
>technologies probably won't be avail until 2250 AD  :(  )

You could see anti-matter just as ordinary matter. All physic laws that are
valid for matter do hold for anti-matter. Thus fusion would work.
In fact Hydrogen is also a metal, it just has a very low melting point, I
don't know however what its magnetic properties are.
Also all materials have magnetic properties, though most don't have such a
strong and autonomic fields as iron. So all materials will be attracted to
or repelled from a magnetic field only some much more than others.

>I thought you said you didn't know what Kansas was like.  ;)
>(for information, it is totally flat, totally farming, and totally boring)

I had some feeling about what it should be like...

>One of the implicit assumptions I'm going to use is that some form of 
>self-replicating machinery is possible.  not nano-tech, and not 
>self-directed either.  I'm assuming that a robot can be made that can 
>make a copy of itself given: premade circuit board (pentium level 
>motherboard with cameras and wireless modems) and ready made ores.  that is, 
>some other machine refines the ores and gives our robot "ingots" of 
>aluminum or silicon or whatever else it needs.  
>The robot needs to do the following autonomuos tasks:

I like the idea about such robots, especially because you could design them
to build habitat units, or is that too difficult?

>1) shape metal into any shape (most NC millers can do this today)

What does NC mean?

>2) make a 1 meter by 1 meter solar cell from a solid ingot of silicon and 
>proper doping materials (they work in vacumn, so much bulky equipment 
>won't be needed

Even if needed (because of dust attracted and distributed by the
ore-extracters) these vacuum pumps should not be that bulky.

>these would then be able to first, turn out many copies of themselves, 
>and then secondly, they could begin turning out the hectares of solar 
>panels needed for the maser transmitters. the same system would work in 
>Sol, as would work in TC 

That would mean roughly 1E8 hectares, or about 3 hectares per second if you
want to do it in 10 years :|
The 1E7 masers would need to be build by robots too! This may need more
complicate fabricating processes than solarcels.

How much work can one robot unit do? Say 1m^2/second.
So that means about 3E4 robots are needed.
How long would one robot need to replicate itself? Say 3 days.
Using exponetial growth: 2^T=3E4 --> T=173 --> 3*T=519 days needed to make
3E4 robots.

If I use these numbers your plan could succeed. But are they realistic? 3
hectares per second seem so much. (You could really see it grow)

Just a note: Would super conductors be any use to us? In free-space (not
near a Sun) the temperatures are ideal for super conductors.