Uses of Bulk Nano Materials (was beanstalks)

Dear Ian Stirling and Henry Spencer:
wrote:

in
area
region
without
any
of
Kevlar is not impervious to ozone, gets screwed up by UV, loses some of its desirable properties in the cold, shrinks and expands with temperature (a lot more than nano-tubes). Kevlar is not a solution, but an extension of the problem. It is at least, non-conductive, and the ozone and UV can chew on a coating for a while.
David A. Smith
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In sci.space.policy "N:dlzc D:aol T:com \(dlzc\)" <N: dlzc1 D:cox T: snipped-for-privacy@nospam.com> wrote:

Kevlar was just an example, picked out of the air, of a current material that would be suitable from a strength point of view. There are quite a few others that may be suitable, if the conductivity of nanotube stuff is found to be a problem.
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Ian Stirling wrote:

This is the key.
So much of this argument on Beanstalks is "Picked Out Of The Air".
We have had functining free electron lasers to push the cargo up the stalk and other fantastic things "Picked Out Of The Air"
We need to hold these discussions in :
Sci.Fiction.Materials and Sci.Fiction.Space.Policy or Sci.Fiction.Astro
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You are mistaking ill-educated proponents for serious barriers to progress.
Kevlar is not unacceptable as the atmospheric space elevator portion; it has a finite lifetime exposed to air and sun, but a finite lifetime is normal in civil engineering. I have walked across many a bridge made with key components that will fail faster than the kevlar in a space elevator atmospheric segment would. The only requirement to use it safely is for one to be able to replace or repair faster than it is damaged by age and environment, and that it be economical to do so.
Free electron lasers are an overspecification on the part of some proponents. Laser power beaming, in the generic sense, coupled with tuned photovoltaic panels which have their peak efficiency at the laser wavelength, has been tested extensively in the lab and somewhat in the field. It is under active consideration for space to space and ground to space power transfer applications. Protestations that it is not going to work are a mark of lack of education in space power technology.
Free Electron Lasers are but one way to generate coherent laser light. Diode lasers and other laser technologies exist and work just fine for the specified technological requirements. FELs are felt by some enthusiasts to be the wave of the future in lasers, in terms fo efficiency primarily. But they are not necessary. Existing diode lasers, or for that matter even gas electrical discharge lasers such as He-Ne or CO2 lasers, would be able to provide the throughput on the elevator. Diode lasers would be the most energy efficient method that is off the shelf.
There is a lot of potential for far future tethers and space elevators which is based in hypothetical advances in technology. Nearterm space elevators are practical, with existing technology for everything but the length of the CNT fibers we can grow today and to some degree the difficulty in bonding them at joint sections. The latter can be finessed, with greater fabrication expense and joint cost and mass; the former cannot, but test lab maximum fiber lengths are growing steadily, and there is no reason to think we cannot commercially fabricate a few years after labs succeed.
-george william herbert snipped-for-privacy@retro.com
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Nonotechnology and "Space Beanstalks" attract psuedo science and pseudo engineers like a candle flame attracts a moth.
While the light of the candle flame is a wonderful desired product, the swarm of moths (psyedo science/engineers) degrades the appreciation of the wonderful candle flame product immensely.
While *some* good can come out of a discussion like this, it also creates headaches from the incessant buzzing of buzzwords and slightly completed thoughts.
There is little real stuff here from space sciences to appreciate.
Reminds me of the "X-Files" phenomena - where so many believed that the program wasn't fiction first, entertainment second and (pseudo)science last.
George William Herbert wrote:

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It is correct that a lot of non-engineers / non-scientists are attracted to it.
It is not correct that just because a lot of non-engineers and non-scientists are attracted, that there is no good serious science and engineering being done on the problem of building space elevators.
There *is* lots of real stuff here from space science and engineering; not a majority of postings or posters, by any means, but it's a real topic, with real fully qualified physicists and engineers working on it.
That doesn't mean that they have it right yet. But it is a real topic. It's perfectly reasonable to call an enthusiast on an inaccurate representation of the state of the art. It's also perfectly reasonable to address *serious* and properly researched criticism at the actual experts, and publish it etc. People who call themselves scientists (or, worse, justifyably are) and make half assed, unjustified and unresearched criticism and claim it's scientifically valid criticism, are being unethical.
Engineering ethics specifically prohibits doing that. There isn't a canon of ethics for physicists per se, but that doesn't make it right for them to do it.
-george william herbert snipped-for-privacy@retro.com
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George William Herbert wrote:

It is probably correct that these types of discussions flitting around the flame of nanotechnology and "beastalks" are very devoid of much good progressive discussion.
There is no doubt that there is HIGH VOLUME of discussion and HIGH HEAT of pseudo discussins.
But that doesn't make this a good use of anybody's time.
However, there are always people who need to fill time, and this kind of discussion certainly consumes time if one attempts to follow all of it.
I am not so stupid as to claim that there isn't good science or engineering being done somewhere on these topics.
But, for the most part, for the reasons given, these discussions are of little value.
For example, you reach many false conculsions about what is in my mind, and you experess those false conclusions. The reply is then effectively a waste of time because of the false conclusions you drew.
You are nicely demonstrating my point of WASTE OF TIME.
And Goodbye ...
I won't waste more of my time on useless pseudo science/engineering roundabouts.

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Funny, I am sure you said that before.
Earl Colby Pottinger
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jbuch wrote:

You might say that it's really a complex interweaving multi-faceted discussion between numerous different parties. Making it necessary to follow the different discussions and to be careful to not confuse them with each other and address claims made by one person in a response to another person. Nor, of course, to intermingle them together and judge their validity or lack thereof collectively rather than individually. This can be challenging, and is a non-trivial task, but it is not impossible.
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Dear Ian Stirling:
wrote:

current
total
a
contacting
strength.
billions
its
(a
of
chew
The issues of zero thermal expansion, non conductivity, resistance to ozone (and monatomic oxygen), and light is a null set of members. Purportedly carbon nanotubes can be made non-conductive. Whether this can be done in bulk...
Personally, I'd like to see a magnetically-powered cannon stretch west-to-east across the USA, and launch payload into space from an end elevated 4km into the air. Evacuate the tube, and "blow" compressed gas in the direction the payload would head... but no 3g limit upon striking the atmosphere I'm afraid.
David A. Smith
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In sci.space.policy "N:dlzc D:aol T:com \(dlzc\)" <N: dlzc1 D:cox T: snipped-for-privacy@nospam.com> wrote:

Why zero thermal expansion? And the bottom 100Km/miles could be almost trivially replaced anyway, it's of negligable mass compared to the rest, and one car could easily take it up, lower a new one, and unhook the old one.
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Dear Ian Stirling:
wrote: ...

material
ozone
Purportedly
in
The stranding exposed to the Sun will get longer, and the other side get shorter. This will increase internal stresses, as the cool side will carry the majority of the load.
As areas warm, the entire tether will grow longer, and the object tensioning the cables will move away from the Earth and retrograde. The as it cools, the tensioning object will be drawn in, and precess. A few tens of feet, but the loading on the tethers will have to be adjusted dynamically, to keep the loading the same. Making it dynamic will allow you to reel in or play out tether to compensate for "global" heating and cooling.

As long as you have a lot of redundancy, yes. The support car must not need the replaced cable to stay up, and the balance of the cables above must be able to support n+1 below.
David A. Smith
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In sci.space.policy "N:dlzc D:aol T:com \(dlzc\)" <N: dlzc1 D:cox T: snipped-for-privacy@nospam.com> wrote:

The cables being talked about are microscopically thin. There is essentially no temperature gradient.

The cable that is being replaced is in place until the new one is connected. The car can carry 100 miles of cable without too much problem, it's very light. It just rises to the position, hooks the old cable onto the end of the new, and reels out the old one.
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Dear Ian Stirling:
wrote: ...

get
carry
"essentially no" is not "identically no". Kevlar is a horrible conductor of heat. There is a temperature gradient, and there will be differential stress. And as you point out, "kevlar is just an example".
David A. Smith
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<snip>

in
Why a magnetically powered canon? A large good old chemically powered one would work to launch water and fuel. The US had a space canon program in the 60's, but it was canceled. The guy in charge of the space canon program was Dr. Bull After he was sent to jail for supplying arms to S. Africa (he claimed it was under the direction of the CIA) He went free lance and designed Iraq's super gun. I believe UCLA has an under funded program to build a canon to launch payloads using cheap chemical propellants, but I have no references.
Gregg
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Unfortunately, no. There are fundamental limits on the muzzle velocity of plain old chemical guns ("powder guns"), and they aren't terribly high. Tricks like transferring energy to a gas like hydrogen ("light gas guns") can improve the situation, but it's still not good.

Gerald Bull's cannon-launch scheme used a projectile with *four* rocket stages in addition to the gun launch. The rockets did most of the work; four rocket stages will get you into orbit starting from the ground.

Chemical propellants just don't *come* cheaper than LOX plus kerosene, which makes a dandy rocket-fuel combination, costing only a few dollars per kilogram orbited.
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Granted rocket fuel is cheap - but the launch vehicles are not. - I wasn't aware of the muzzle velocity problem. I heard the researcher from UCLA interviewed a couple of years ago and I'm sure he presented the argument for chemical launch canons in the best possible light. (research dollars were at stake) - Do you know any of the economic arguments for electromagnetic rail and canon/ rocket vs. standard launch vehicles for items like fuel, water and robust payloads? I'm just curious.
Gregg
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Correct, but neither are launch vehicles built to be shot from cannons. (If the gun-launch system gets to use new ultra-cheap rockets in its projectiles, it should be compared against an all-rocket system using the same technology.)

The usual approach :-) is to compare your favorite unorthodox launch system -- which is assumed to get a large up-front investment at low or zero interest rates, to have a steady stream of paying payloads waiting for it, to be built and run by a streamlined low-overhead organization, and to encounter no political or regulatory difficulties -- with today's off-the-shelf rockets which have none of those advantages.
The picture tends to look very different, and much less favorable to the unorthodox system, if the same assumptions are used for both technologies. Just the steady stream of paying payloads alone would make an enormous difference to the economic feasibility of new pure-rocket launchers.

In an honest, apples-to-apples comparison, it is hard to justify any sort of gun or catapult launch unless it eliminates at least one rocket stage. Just making the tanks smaller saves almost nothing; reduced complexity, not reduced size, is where real cost savings show up.
That is not easy to do, because even setting aside the SSTO debate, most everyone agrees that you can get to orbit with two (reusable) stages. The gun/catapult has to deliver a lot of velocity to eliminate one of those. Worse, if it gives a rough ride, it may require stronger structures, which hurt stage mass ratio and push you toward *adding* a stage. And the required high muzzle velocity tends to cause serious thermal problems.
The one place where some form of catapult may show to advantage is in supplying a launch assist to a near-SSTO rocket. Guns are probably out of the running for this one, because the strong structures needed for gun projectiles are probably incompatible with near-SSTO rocket performance.
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Henry Spencer wrote:

Not everyone understands that you are talking about a gun projectile filled with rocket propellant. The projectile rendezvous with the rocket, docks with it above the atmosphere, and provides its propellant for the rocket. Solid propellant is not good because it would crack under the stress. Liquid propellant is better but the bottom of the projectile must be strong and massive to survive the enormous pressure of the gas gun. I imagine some kind of reusable sabot having massive bottom.
Orbital sling is easier to make than the long gun and its centrifugal acceleration is smaller than acceleration produced by the gun.
Last, but not least, a reusable, pressure-fed first stage of a rocket launcher looks pretty good. It is simple, cheap, and sturdy enough to survive splashdown.
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There are plenty of human life critical safety installations using kevlar cable with light sheathing from the elements.
Kevlar has a finite lifespan when exposed to such abuses.
So, unfortunately, do steel, aluminum, glass fiber, plastic composites, titanium, glass, etc.
Everything corrodes or ages. We just replace it.
If we cannot do maintenance and repair, then no civil engineering project on the face of the earth is likely to survive much longer.
-george william herbert snipped-for-privacy@retro.com
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