Space elevators a fantastic idea that maybe someday could be reality?

[Nibb31]

Why is everone going on about the price? Carbon nano-tubes are pricey-atm. They might be cheaper than wool in 120 years-if they are as good as we think they will be, people will work out ways to make more for less. Besides, 80 or so miles is a long way-but we've layed fibre optic cables longer than that across the sea-floor. as for who would use that-space station construction anyone? Or even, moonbases? Building one is impractical now-but if you could get every module into space for almost free? These things are usefull.

Or carbon nanotubes might turn out being super expensive. And it's not 80 miles, it's 22400 miles (x2 for the counterweight). That's a damn heavy spool of fiber, whatever the material you use.

Why "almost free" ? Do you know how much energy would be required to power multi-ton climbers at high speeds over such huge distances ? or how much it would cost to build the damn thing ? How can you anticipate launch prices so far in the future ?

And if we had those sorts of advanced materials, why couldn't we use them to build reusable SSTO rockets instead, which would decrease launch costs, increase flexibility, and make a space elevator less competitive.

But honestly, Skylon's probably going to be the answer-cheaper than an elevator and you still get about 200 uses out of each one. And that's predicted to be ready by 2020 or so.

No it won't.

[randomness5555]

Well it's nice to see the forums being so optimistic

By almost free, I mean this compared to the price of a rocket, and i'm not counting the cost of actually building the thing-just the price per launch. Besides, run some metal teeth along the length of the cable and you can just have one line with cogs on the elevator to go up/down. As for the cost, I hardly think the tubes (IF that is what is used-atm it seems to be the best candidate) are going to get more expensive to make. Carbon is not a rare element, and if they look like they are going to be as good as predicted, a lot of companies are going to want to make them.

Also, 'No it won't' is not a counter argument. Skylon's recently recived extra funding after they proved that the engine design works, so it's still dead on track to meet predictions.

As for the lack of demand argument, I say this-you build it and people will find ways to use it, and money is not the point anyway. Space travel has NEVER been profitable-apart from for the companies that build the rockets themselves. But give them an SSTO that could be used to build say, an orbital refinery that can make products you can only make or can make better in 0-G and you start to see a use for it. Also, think of the MILITARY use eh? Think about how much money they would pay to build orbital weapons-rods from the gods anyone? Starting to see my point?

Edited July 9, 2014 by randomness5555
Spelling error

[SargeRho]

Actually, the only reason there is a space industry is because space is profitable for certain things like telecommunications.

[Z-Man]

Do you know how much energy would be required to power multi-ton climbers at high speeds over such huge distances ?

About 50 megajoules per kg for the whole trip (speed cancels out, naturally; I estimated by calculating the amount of energy required to get the mass up to 10km/s.), that are about 14 kwh. Production costs for that are in the 1$ range today. So several thousand for a multi-ton climber, ignoring that you may be able to reclaim a large portion of the energy on the way down.

And earlier:

Do you have any idea how much a 36000km spool of graphene or carbon nanotube wire weighs?

A single carbon nanotube? About half a gram, tops. You don't need that many of them for the boostrap construction. A million should suffice fine.

Lesson: when using "do you have any idea how much..." as an argument, make sure the answer actually supports your side. Yes, everything else is still a big problem. Will the tether be strong enough? Can we actually produce a suitable material at reasonable cost? How do we get the energy to the climber? Etc. But raw energy cost and tether weight are not.

[shynung]

Besides, run some metal teeth along the length of the cable and you can just have one line with cogs on the elevator to go up/down.

Going to GEO still requires a lot of energy, whether using rack-and-pinion gears, rope-and-pulleys, or anything else usable as energy source, and all that has to be carried (or transmitted) to the climbers. The energy required would need a major power station somewhere nearby to provide all that power.

One of my favorite solutions to that would be installing rocket engines on the climbers themselves; but then again, why need the elevator if the climber can practically fly itself to space?

Also, 'No it won't' is not a counter argument. Skylon's recently recived extra funding after they proved that the engine design works, so it's still dead on track to meet predictions.

As for the lack of demand argument, I say this-you build it and people will find ways to use it, and money is not the point anyway. Space travel has NEVER been profitable-apart from for the companies that build the rockets themselves. But give them an SSTO that could be used to build say, an orbital refinery that can make products you can only make or can make better in 0-G and you start to see a use for it. Also, think of the MILITARY use eh? Think about how much money they would pay to build orbital weapons-rods from the gods anyone? Starting to see my point?

There's a whole heap of arguments on why that might not be the case here.

Edited July 9, 2014 by shynung
grammatical blunder

[Kryten]

Space travel has NEVER been profitable-apart from for the companies that build the rockets themselves.

Care to explain how SES made £500 million profit last year?

[PakledHostage]

And earlier:

A single carbon nanotube? About half a gram, tops. You don't need that many of them for the boostrap construction. A million should suffice fine.

Lesson: when using "do you have any idea how much..." as an argument, make sure the answer actually supports your side. Yes, everything else is still a big problem. Will the tether be strong enough? Can we actually produce a suitable material at reasonable cost? How do we get the energy to the climber? Etc. But raw energy cost and tether weight are not.

Perhaps "do you have any idea how much" isn't a solid argument against the possibility that a space elevator will ever be built, but "you don't need that many of them for the boostrap construction" is equally naive. Maybe you can explain how you envision that bootstrapping process to occur, or how you can be so certain of the strength of a material that hasn't been invented yet? You can't criticise Nibb31 for making a vague argument and then proceed to make one yourself.

Edited July 9, 2014 by PakledHostage
Fixed formatting and added a phrase.

[Seret]

Also, 'No it won't' is not a counter argument. Skylon's recently recived extra funding after they proved that the engine design works, so it's still dead on track to meet predictions.

Skylon grew out of an earlier project called HOTOL, which has been getting kicked around since the 80s. Considering they don't even have prototype engines yet (and the engines are the easy bit) expecting a flying Skylon in six years is a bit of an eyebrow-raiser.

[Z-Man]

The energy required would need a major power station somewhere nearby to provide all that power.

Number checking again. One climber, 10t, 10m/s eats up 1 MW while under full gravity. That's about what a medium-large train uses (peak power, of course, as opposed to continuous), so not all that much. No need to plonk down a nuclear power plant, though you probably do want a couple of gas turbines nearby.

PakledHostage: A million tubes gets you a ribbon a couple of cm wide easily. If a space elevator is possible at all, a climber should scale down to be usable with that. It'll be small, of course, but it would not need to be big. It just needs to carry up more ribbon and mass for the counterweight above. Ideally, it would "stitch" the new ribbon up to the one already in place to make it wider and wider, but if that's not possible (it probably isn't), you can first pull up many smaller tethers and then finally use multiple climbers in unison to pull up the real tether to use later. If it is possible to build a small elevator (big if), there is very little reason to assume you can't use it to build a bigger elevator.

[Mr Shifty]

I'm curious how nanotubes are theorized to work for this. They have a density of about 1.3 g/cm³ and a theoretical tensile strength of 100GPa or so. If we supposed a space elevator has to be 36,000 km long, then how does the math work out? The mass of the cable is A*h*d, where A is the cross sectional area, h is the height of the cable, and d is the density. The mass that the cable can support under tension is t*A/g, where t is tensile strength and g is gravitational acceleration. Since A appears in both equations, you can cancel it out, and you get that the mass of the cable, m=(d*g*h/t)*m_h, where m_h is the mass that it can hold. Run the numbers for nanotubes and you'll see that for any cross-sectional area, the cable weighs about 500 times more than it can hold. Even grant the wikipedia's assertion that the cable only has to support about 5,000km of its own weight at sea level, and you're still off by two orders of magnitude.

[Nibb31]

Also, 'No it won't' is not a counter argument. Skylon's recently recived extra funding after they proved that the engine design works, so it's still dead on track to meet predictions.

The counter argument has been covered amply elsewhere in the forum several times. If you want to discuss Skylon, then please go ahead and reply to this post:

http://forum.kerbalspaceprogram.com/threads/84583-Space-economies-and-economics?p=1241640&viewfull=1#post1241640

[Z-Man]

m=(d*g*h/t)*m_h

That formula appears to be correct. An important number to extract from this is L₀ = t/(d*h); if h = L₀, then m = m_h. When I plug in your numbers into google's calulator, I get this:

L₀ = 5000 km

So a 5000 km cable can just about support its own weight, just what Wikipedia claims is needed. You probably got your units wrong somewhere. Densities in g/cm^3 always confuse me, I know that much.

Additionally, you can make the cable even longer by making it thinner at the bottom; the diameter will grow with e^(h/L₀) (it's more complicated for the actual case where you want to go up to GEO, but similar enough. Edit: actually, it is just as simple. Just plug in the effective height in for h instead of the true distance to solid ground.). Nasty exponential! That means that a small difference in tensile strength of a factor 2 can mean the difference between "feasible" and "absolutely impossible". We we don't know the properties of longer, woven fabrics of carbon nanotubes yet (or, for that matter, how to produce them), so it's too early to tell which side they fall on.

Edited July 9, 2014 by Z-Man

[Mr Shifty]

You probably got your units wrong somewhere.

Ah yes, you're right. I'm pretty sure I forgot a m->km conversion somewhere.