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15 Oct 12
1 edit
Hmm with a youngs modulus of 293 GPa you have about 29% of the strength of a single CNT so you're not there yet.
But it's a step in the right direction.
Have a look at this for more details on space elevator feasibility...
http://www.spaceward.org/elevator-feasibility
16 Oct 12
Originally posted by googlefudgeWow, they really thought that through!
Hmm with a youngs modulus of 293 GPa you have about 29% of the strength of a single CNT so you're not there yet.
But it's a step in the right direction.
Have a look at this for more details on space elevator feasibility...
http://www.spaceward.org/elevator-feasibility
18 Oct 12
1 edit
Originally posted by twhiteheadIt makes more sense to use some kind of kinetic energy mechanism to transmit
A space elevator is such a good idea that it is well worth thinking through (and building as soon as is feasible).
heat energy of a vessel travelling down by laser to another vessel travelling up.
Even an 80% loss would make it worthwhile. Then we could use the kinetic energy
of asteroids. I don't think I need to tell you how much that could be worth...
18 Oct 12
Originally posted by Thequ1ckYes, I think you do. How much energy would you get from an asteroid and how would you go about harvesting it?
Then we could use the kinetic energy
of asteroids. I don't think I need to tell you how much that could be worth...
Are you talking about on a tether? If so, you need to get the asteroid to the same velocity as the tether first and that would probably take more energy than you eventually get out of it.
18 Oct 12
8 edits
Originally posted by Metal BrainRemember that, unlike a steel lighting rod, carbon readily burns in air when it is heated.
Carbon isn't a bad conductor of electricity. Lightning would destroy it.
But there are many ways to work around that such as covering the surface of the cable with a thin layer of non-combustible material.
Remember that may modern airliners have carbon and resin composite skins which are often struck by lighting with very little damage as a result.
But one problem they may have not considered properly is the occasional piece of space-rock or space junk colliding with the cable in space thus cutting it -what the hell would they do about that? - I think this would be the main safety problem.
Even the inevitable collisions with tiny bits of space dust would gradually damage the cable -have they even thought about that?
Also, the ions such as very high speed protons in the solar wind would have a slow corrosive effect on the carbon in the space cable as they would inevitably collide with the cable at high speed -have they even considered that?
There would also be the issue of how to stop terrorists from flying aircraft or missiles into the cable.
Perhaps there may even be the possibility of an aircraft flying into the cable by accident?
I have also thought of the possibility of a freak ice storm covering the lower part of the cable with such a massive weight of ice that the whole lot would be pulled crushing down.
In short, I think there would be so many things that could go disastrously wrong with a space elevator that, also taking account of the frightful massive initial capital costs, I think it definitely would not be worth building for a very long time. There are less risky and, in the short term, cheaper alternatives. A space elevator may pay for itself in the very long run but would not be worth building until technology and science comes up with ways of adequately protecting the cable and I don't see how that could happen for a very long time.
18 Oct 12
2 edits
Originally posted by twhiteheadI dunno. Gotta be some kind of material that absorbs heat and emits light out there though.
Yes, I think you do. How much energy would you get from an asteroid and how would you go about harvesting it?
Are you talking about on a tether? If so, you need to get the asteroid to the same velocity as the tether first and that would probably take more energy than you eventually get out of it.
My guess would be Sodium acetate.
'Sodium acetate is also used in consumer heating pads or hand warmers and is also used in hot ice. Sodium acetate trihydrate crystals melt at 54°C,[5] (to 58°C [6]) dissolving in their water of crystallization. When they are heated to around 100°C, and subsequently allowed to cool, the aqueous solution becomes supersaturated. This solution is capable of cooling to room temperature without forming crystals. By clicking on a metal disc in the heating pad, a nucleation centre is formed which causes the solution to crystallize into solid sodium acetate trihydrate again. The bond-forming process of crystallization is exothermic.[7][8][9] The latent heat of fusion is about 264–289 kJ/kg.[6] Unlike some other types of heat packs that depend on irreversible chemical reactions, sodium acetate heat packs can be easily recharged by placing in boiling water for a few minutes until all crystals are dissolved; they can be reused many times.'
http://en.wikipedia.org/wiki/Sodium_acetate
18 Oct 12
Originally posted by humyIf you follow the link you will find that yes, they not only thought about it, but factored replacement of the whole cable every few years into the equation.
Even the inevitable collisions with tiny bits of space dust would gradually damage the cable -have they even thought about that?
There would also be the issue of how to stop terrorists from flying aircraft or missiles into the cable.
Would this be harder or easier than say flying a plane into the shuttle launch facilities? Which would do more actual damage?
Perhaps there may even be the possibility of an aircraft flying into the cable by accident?
This problem presumably exists with all tall structures. Again, which would cost more in terms of lives and money, a plane hitting a sky scraper or a plane hitting the space elevator? Many airports are in and around cities, the space elevator could be placed in an area with a large no-fly zone around it.
In short, I think there would be so many things that could go disastrously wrong with a space elevator that, also taking account of the frightful massive initial capital costs, I think it definitely would not be worth building for a very long time.
What are these costs? How do they compare to other risky ventures such as the space shuttle?
A space elevator may pay for itself in the very long run but would not be worth building until technology and science comes up with ways of adequately protecting the cable and I don't see how that could happen for a very long time.
Simply having multiple cables in a weave of some sort easily takes care of most of your protection issues - except possibly a large aircraft impact.
18 Oct 12
Originally posted by humyAircraft are not grounded or close to the ground. Lightning would still destroy it, especially from the ionosphere. Carbon is a dumb idea.
Remember that, unlike a steel lighting rod, carbon readily burns in air when it is heated.
But there are many ways to work around that such as covering the surface of the cable with a thin layer of non-combustible material.
Remember that may modern airliners have carbon and resin composite skins which are often struck by lighting with very little damage as a ...[text shortened]... of adequately protecting the cable and I don't see how that could happen for a very long time.
18 Oct 12
9 edits
Originally posted by twhitehead
If you follow the link you will find that yes, they not only thought about it, but factored replacement of the whole cable every few years into the equation.
[b]There would also be the issue of how to stop terrorists from flying aircraft or missiles into the cable.
Would this be harder or easier than say flying a plane into the shuttle launch faci easily takes care of most of your protection issues - except possibly a large aircraft impact.[/b]
Would this be harder or easier than say flying a plane into the shuttle launch facilities?
No, but it may do more costly damage that would be much harder to repair and take longer to repair. Replacing and repositioning such a cable way up in outer space would surely be extremely costly compared with repairing a mess on the surface of the Earth where we have much easier access!
http://en.wikipedia.org/wiki/Space_elevator_economics#Cost_estimates_for_a_space_elevator
“....the fixed costs would be US$6 to 12 billion, for construction;[7] and one-way designs (such as Edwards'😉 will add to the cost of the elevators ...”
( this is probably an optimistic estimate since most major engineering projects of this sort tend to go over budget )
http://en.wikipedia.org/wiki/Space_Shuttle
“...Building Space Shuttle Endeavour cost about US$1.7 billion. One Space Shuttle launch costs around $450 million ...”
so, on the bases of the above figures, I would imagine that it would cost much less to repair the damage done by an aircraft flying into a shuttle launch facility than into a space elevator cable by perhaps, very roughly, one order of magnitude. If you have figures for estimated costs that falsify this then I would like to see them.
Also, the taller something is, the more attractive as a target it may appear to be to a deranged terrorist mind; and you cannot get much taller than this!
Once this gets built, it would become a massive symbol and be the priority target in the minds of many terrorists.
OK, having said all that, I concede that the risk of terrorist attack can be made insignificant simply by keeping a permanent military presence around the cable so terrorism shouldn't be the main consideration. But the question of a possible terrorist attack would be a very trivial side point compared to what I clearly have said would be the main risk which would clearly not be a terrorist attack but would be, as I said “... the occasional piece of space-rock or space junk colliding with the cable in space thus cutting it -what the hell would they do about that? - I think this would be the main safety problem.
Even the inevitable collisions with tiny bits of space dust would gradually damage the cable -have they even thought about that? ...”(my previous comment)
With such a massive length of cable in space all the way up just past geostationary orbit would mean it surely wouldn't be particularly unlikely for something to collide with it. Would you disagree?
Simply having multiple cables in a weave of some sort easily takes care of most of your protection issues
wouldn't having multiple cables rather than one massively increase costs? Having to do that would make the alternatives look even more attractive from purely the cost point of view.
Personally I think one ( not sure which one ) of the laser propulsion alternatives would be the most attractive option:
http://en.wikipedia.org/wiki/Laser_propulsion
The technology needs a lot of costly development before it becomes practical but, once developed, it would offer significant advantages over both using rocket power ( which is very energy inefficient because, unlike with laser propulsion, most of the energy is used just lifting the fuel ) and using a space elevator ( which requires a massive space cable and a massive space counterweight ) .
18 Oct 12
1 edit
Originally posted by humyYou are probably right, but I think your argument is still flawed. If we follow your argument then we shouldn't have the space shuttle either because it is too expensive a target for terrorists. We should only have launch vehicles valued at under 1 million dollars each.
If you have figures for estimated costs that falsify this then I would like to see them.
Remember that we have lost two shuttles including crew. (The loss of the crew was possibly as big a blow to the space program as the financial loss.)
So we had two > 1 billion dollar projects that failed during normal operation without even a terrorist attack - yet we didn't give up. I don't think risk of failure and high cost is a good enough reason to give up. It is a matter of evaluating that risk and judging just how great a risk it really is.
With such a massive length of cable in space all the way up just past geostationary orbit would mean it surely wouldn't be particularly unlikely for something to collide with it. Would you disagree?
No, I think you are probably right, and this is an issue that all space tethers must deal with even ones that are not space elevators.
wouldn't having multiple cables rather than one massively increase costs?
I don't know the exact costs. What I do know is that the problem you mention has been thought about and the costs you quote earlier probably include this.
http://en.wikipedia.org/wiki/Space_elevator_safety#Meteoroids_and_micrometeorites
However, most space elevator designs call for the use of multiple parallel cables separated from each other by struts, with sufficient margin of safety that severing just one or two strands still allows the surviving strands to hold the elevator's entire weight while repairs are performed.
19 Oct 12
1 edit
Originally posted by twhiteheadI did not say we should not have a space elevator because of the terrorist threat.
You are probably right, but I think your argument is still flawed. If we follow your argument then we shouldn't have the space shuttle either because it is too expensive a target for terrorists. We should only have launch vehicles valued at under 1 million dollars each.
Remember that we have lost two shuttles including crew. (The loss of the crew was pos viving strands to hold the elevator's entire weight while repairs are performed. [/quote]
That was not my argument.
"...the risk of terrorist attack can be made insignificant simply by keeping a permanent military presence around the cable so terrorism shouldn't be the main consideration...." (my previous quote)
19 Oct 12
Originally posted by humyMy apologies then.
I did not say we should not have a space elevator because of the terrorist threat.
That was not my argument.
I agree that it is a risk, but one that we should guard against rather than cancel the project over.
I still think the space elevator is one of the best ideas out there and that it should be built as soon as we have strong enough materials at an affordable price. Of course the question is what an affordable price is. Some of the articles I have read suggest that it could be done as a profitable business (whereas most other space programs have been government sponsored).