Re: Engineering Newsletter

[Kevin C Houston <hous0042@maroon.tc.umn.edu>]

On Sun, 14 Jan 1996, Timothy van der Linden wrote:

> 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 
> 
> 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.

Oh, you two can go on argueing if you want to, don't let me stop you.  I 
just thought that the ground had been covered many times before in finest 
detail.  I did not realize that you were still confused as to what Kelly 
meant.  i suppose that's my own fault for thinking that all members of 
this group speak english with perfect understanding (typical american 
attitude i know, but at least I can admit my mistake)  I'm just glad this 
dicussion isn't taking place in Dutch or Polish


> >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 
> >desired.
> 
> 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.


and a lot smaller if you could put in orbit at mercury's distance.

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

i don't agree, that's true only if you want to do it in a man's 
lifetime.  if you are willing to accept a lower speed, then you can do 
the trip with a _lot_ less energy.

> > >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
> antimatter.
> (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
> wavelengths.
> 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.

I meant by eff. Question, "what will the eff. of energy to antimatter 
conversion be?"  or How many kilowatts does it take to make a gram of 
anti-matter? 

> 
> >(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

only if you put it under a hellish pressure.

> 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.
> 

Actually, if we could get any respectable solid at all, like Li maybe, 
then we could give it an electricall charge and keep it suspended that way

> >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?

no, I think that would be possible.

> 
> >1) shape metal into any shape (most NC millers can do this today)
> 
> What does NC mean?
> 

Numerically Controlled,  old fashioned term for computer controlled

> >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.

Tim, i think you have a little problem here. 2^173= 1.19 E+52 robots  =8^O

In fact, I'm having trouble following where some of your numbers come from.
assuming that your 1000 Km radius solar array is correct,  I get

(1000 * 1000)^2 *PI() = 3.14 E+12 m^2 of solar cells

i think your estimate of solar cell production is way too liberal,
I say 1 m^2/day is more likely.

so now we need 8.6 E08 robots to do the job in ten years

I think your three day replication estimate is good.

using exponential growth, I get 2^T=8.6 E08  T=29 days 3 * T =89 days

thats if we start with one robot.  I think we would probably start with a 
1000. if we let reproduction continue for 100 days ( nice round number) 
we'd have 8.59 E09 robots, and at the lesuirely rate of 1 m^2/day, we 
could build the entire solar array in 365 days.  100 robots could work on 
each maser transmitter, and all of them could be built in a month.  we'd 
still have plenty of robots left over to build habitats, mine fusion 
fuel, or whatever other job we needed done.  with that many pentium level 
processers, the resultant computer power would be staggering!


Now, as Kelly says, when you get this many "Grunts", the job of the top 
boss becomes more and more difficult.  but with several layers of "middle 
managment" computers, I think it would be doable ( although, maybe not at 
the speed I was reffering to


> 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.

yeah, I think we are going to need that technology in many areas.  
Computer circuitry, accelerator coils, fusion containment coils  anywhere 
you have a lot of energy, and no way to remove the heat.


Kevin