Space Elevator Conference Prompts Lofty Questions

itwbennett writes "Even the most ardent enthusiasts gathered at the annual Space Elevator Conference on Friday don't expect it to be built anytime soon, but that doesn't stop them from dreaming, planning, and trying to solve some of the more vexing problems. One of the trickiest questions is who's going to pay for the operational costs when an elevator is eventually built. 'It's been nine years we've been looking for someone' to study that, said Bryan Laubscher, one of the leading space elevator enthusiasts and principle at Odysseus Technologies, a company working on high-strength materials."

Comments

Or build a skyhook

[MichaelSmith]

It needs to be strong but nanotubes aren't required. You make a cable about 1000 km long. It has fittings on both ends which vehicles can attach themselves to. It orbits slightly more than 500 km above the ground and rotates its its axis horizontal and at 90 degrees to its orbit. The length and orbital altitude and chosen so that when one end almost reaches the ground it has a low velocity, while the other end is above escape velocity. You use it to exchange mass between the surface of the Earth and a trajectory which will take you to other planets. A dead mass can be sent down to Earth and a vehicle carrying passengers and supplies can be sent the other way.

Re:Or build a skyhook

[strack]

thats a stupid idea. the sheer drag as it plows through the atmosphere repeatedly means itll last only a few orbits, if that. even if the speed was low, the drag would still be large enough to bring it down quickly. and anything you sling into orbit is gonna pull the entire thing down, so your gonna need the same, probably more, thrust to bring it back to that 500km orbit than youd spend just blasting a rocket with that payload on the same trajectory.

Re:Or build a skyhook

[0123456]

thats a stupid idea. the sheer drag as it plows through the atmosphere repeatedly means itll last only a few orbits, if that.

I'm not entirely convinced. If you rotate it at the correct speed it could have zero velocity relative to Earth at the bottom of the swing and you could pick the orbit so that it picked up payloads in thin air (of course getting the payloads onto something that's rotating like that would be tricky).

Re:Or build a skyhook

[physicsphairy]

Well, one idea is that you catch random orbiting junk at the other end, replenishing the lost momentum. In any case, efficiency isn't particularly important. The major limitation on getting things into space right now is construction, launch logistics, etc. If we could somehow be continuously sending things into space, it would be well-worth having to send two or three times the fuel along with.

Re:Or build a skyhook

[KonoWatakushi]

Sadly, since a skyhook is not attached to the earth, it misses one of the key advantages of a space elevator: the earth itself supplying the necessary angular momentum. For an elevator, only potential energy must be supplied, and that rapidly gets cheaper the further up you go. Past geo-synchronous orbit it is entirely free, but velocity still increases linearly with height. (Keep in mind that the kinetic energy is proportional to the square of the velocity; paying for that energy directly is very expensive.)

With a skyhook, not only must you pay for the initial velocity, you can't arbitrarily choose the final delta-v, so there is still a considerable amount of energy that needs to be supplied, compounded with the extra fuel that must be carried to do so. Not to mention the continual input of energy to overcome atmospheric drag and maintain height. (If the up/down traffic isn't balanced, this is even more expensive, so you also need to consider the cost of moving that mass through space in the first place.) It would probably still be an improvement, but it would be complicated and could never hope to match the exceptionally low costs made possible by an elevator.

In terms of practicality, it may not require such exotic materials, but it would be that much more costly to orbit (and impart angular momentum to) such an enormous mass.

Re:Or build a skyhook

[MichaelSmith]

Say you use it to send mass to the moon. For every 1000kg of food, fuel and people you send up, you send down 1100kg of lunar rock. This shifts the the centre of gravity of the rotating tether to a higher altitude every time two payloads are exchanged. Each end of the tether drops down to 10 or 20 km altitude, and at a low speed. Its motion relative to the ground would be mostly vertical. The amount of energy lost on each rotation would be fairly small and could be offset by importing rock from places outside our gravity well.

Putting the whole structure in orbit and spinning it up would certainly be expensive, but it might be possible to build it on the moon and send it down the gravity well.

Re:Or build a skyhook

[OeLeWaPpErKe]

Or how about this simple way of doing things :

Orbits come in many sizes. Orbits close to geostationary orbits have the following properties :
if you are slightly closer to earth, you will fall down (slowly)
if you are at the exact right spot, you will stay there
if you are slightly further away from earth, you are in effect on an escape trajectory, you will gain height (slowly)

So here's an idea. Since this cable has to withstand umpteen giganewtons of tension anyway, place the top of the elevator too high. Therefore the cable will have to pull on the satellite to keep it in a stable orbit. Since a giganewton more or less doesn't really matter, let's add a giganewton. Then we can attach payloads of up to 100 tons to the wire without causing the satellite to fall down to earth.

Where does the energy come from ? It uses the rotation of the earth to pull satellites into orbit, so conservation of energy is effected by slowing down the earth for every satellite going up.

Also the whole point of a space elevator is that we don't need to carry fuel to put fuel into orbit. When the US launches the space shuttle, 50% of the fuel in the rocket is used up to give the rocket 1 meter elevation. Electricity is available everywhere if you've got millions to spend on hugely expensive solar panels (and millions would be *very* cheap for satellites). Rockets have 0.4% efficiency because most fuel is used to have a little fuel available higher up. With a space elevator at 50% efficiency, launch energy costs would go down a factor of 120 ...

And let's not forget that a space elevator would make space-based solar power a braindead endeavour, so it would probably pay thousandfold for it's energy expenditures anyway. An operational space elevator would be even better than working fusion power.

But imho a better and easier option would be to get a working fabrication facility operational on the moon. Your mother can knit a working space elevator for the moon together easily, and her grandson is probably operating a catapult capable of launching satellites into earth orbit from the moon surface near some people he doesn't like. So another easy option would be to simply fabricate satellites on the moon. It would have the additional advantages of massive free amounts of solar power, easily mineral stores you wouldn't believe, and you can easily get to the rest of the solar system in addition to earth orbit (which would still require a relatively big rocket starting from earth geostationary orbit).

Re:Elevator to nowhere

[wmbetts]

Fine then! When it's built you can't ride it!

The major issues and such

[JoshuaZ]

Anyone interested in this issue should read the NIAC report http://www.spaceelevator.com/docs/521Edwards.pdf which discusses the issues in detail and the technical problems. Space elevators would make space travel much cheaper. But the technical issues are immense. The NIAC report carefully outlines the major issues and how they might be handled. We would need to make extremely high quality carbon nanotubes at an immense scale. We also would need to put into space a structure orders of magnitude larger than anything we've put in space. Indeed, a space elevator would be one of the largest physical structures ever made by humans. And the engineering hurdles, such as the problems of wind in the lower atmosphere, are massive. But there's nothing about the idea that is physically impossible. The primary issues are issues of scale. And the issues are being worked on. Right now, there's a lot of work on making carbon nanotubes of high quality in a large scale. Since such nanotubes would have many different applications there's a lot of funding for that and that will likely be extremely beneficial to humanity well before it scales up to anything near that needed for a space elevator. Since the nanotube manufacturing is the primary technical hurdle, this is a good thing. I doubt we will see a space elevator in my lifetime, but maybe my children, or their children, will see it. And on that thing ribbon, space travel will finally become as cheap as so many have envisioned it.

Re:Elevator to nowhere

[The Pirou]

Lots of things have sounded stupid by outsiders as demonstrated by the vilification of Galileo by geo-centrists. Should he have let them stop him?

By getting together and starting broader dialogue about the idea of creating a viable mechanism for transit these people are at least working on the 'pseudo-code' for the problem. Whether this particular idea should fail or not, the solutions presented have the potential to act as a fulcrum for broader scientific discovery. Scientific revolutions don't happen by deciding not to attempt to pursue something because it sounds silly given your current understanding of the world around you.

Re:$18B

[Anonymous Coward]

That number is way lowballed. What, are they thinking the price of the nanotube cable is comparable to the market price of carbon?

Anyone dumb enough to pay to build a space elevator this early in the game will lose their money.

Seriously, it's an elevator from the ground to one point in geosynchronous orbit. A payload released at almost any other altitude will need reaction mass to establish a stable orbit, most of which will be expended in the direction of the cable and thus wear it down. (The exceptions are payloads released near geosynchronous orbit which will establish elliptical or parabolic orbits.) Finally, other satellites and debris at lower orbits especially, will impact the cable, both damaging it and setting up waves which will need to be safely dissipated somehow. A paint chip at 500 miles up is going to hit at around 17k miles/hr. and will have plenty of kinetic energy that needs to go somewhere.

Commercially, this is useless, even if you could build it easily and cheaply. It's an engineering nightmare, and no amount of focus on the easy parts of the design -- and the material is the easy part -- will change that.

Re:Elevator to nowhere

[Baloroth]

Do you know anything about space elevators? Seriously. They're a great idea. Practically speaking, they are also very difficult, but if we could build one, the cost of traveling to orbit would become relatively speaking extremely cheap (technically, the energy requirements would stay the same. But the delta-v required would become as low as we please, making very cheap and low-power sources effective). Long term, unless we find a much better way to get to space, they are very likely to be built.

I agree that that is a very stupid question. Obviously, whoever uses it would pay for its use. Aka, commercial companies, NASA, military, etc. Since lots of people want to put stuff into space, lots of people could fund its operation .Probably it would be run by a company or government who would charge for its use (preferably, there would be at least two to introduce competition). That part is relatively easy. Its construction, on the other hand, is quite a problem. Financially and technically. However, it is a very good idea. Keep in mind, 150 years ago space travel on rockets was also just an idea in a few peoples minds. Turns out it isn't such a bad idea after all.

Plus, having an actual stairway to heaven would be pretty awesome...

Please Mod Parent Up

[Anonymous Coward]

Launch Loops are indeed far more interesting and practical. Can anyone here explain why space elevators seem to be the more popular idea among the two?

Re:Please Mod Parent Up

[Rei]

A couple hundred miles of maglev track versus tens of thousands of miles of unobtanium cable exposed to micrometeorites, space debris, undamped oscillations, etc. Hmm, which is more realistic...

And I have no clue what you mean by "80 mile high bridge", except to assume that you've grossly understood how a Lofstrom loop works.

The key issues are:

1) A Lofstrom loop requires no unobtanium. It may well be *physically impossible* to create the material needed for a space elevator on Earth, let alone economically practical. After all, the strongest *invididual SWNTs* measured thusfar were barely over 60GPa at the density of graphite, when you need a *bulk cable* that's ideally over 100GPa at graphite densities, preferably over 120.

2) A Lofstrom loop transmits power (the primary lift cost from both systems) at about 50% efficiency. A space elevator beams power at a couple percent efficiency. Hence a Lofstrom loop costs an order of magnitude less to operate.

So we're back to the start. Why a space elevator, apart from the fact that everyone knows of it through sci-fi? Wait, I think I answered my own question.

Re:Please Mod Parent Up

[mosb1000]

A space elevator is essentially a static structure, it does not require any power to stay in place. As such, it is more like a building than a machine. It's much less complex, which means quality control would be much simpler/possible. There are many questions about how you would build a launch loop too. The only real question about a space elevator is the material. They think single walled carbon nanotubes could be strong enough to do the trick. That means the technology is more likely to pan out in the long run. And if you could build it, it could be much cheaper to operate and much simpler to build than a launch loop.

So, in short, the space elevator gets more attention because it is a more compelling proposition, and seems more likely to succeed.

Re:Please Mod Parent Up

[Darfeld]

What about the fact that Space elevator allow easy atmospheric re-entry and the launch loop does not?

Re:Please Mod Parent Up

[evanbd]

I think you underestimate the control problems inherent to very long, very flexible structures that need to move to avoid debris. It's a lot more like a machine than it looks at first glance.

Substantial Progress being made

[mbone]

One of the interesting things about this conference (which I attended) is that nanoscience researchers on Friday reported substantial improvements in the ability to make carbon nanotubes. They can now "grow" 1 cm nanotube mats, which can be spun into fibers. This is a substantial improvement from even 1 year ago.

I still think that a terrestrial space elevator is a decade out, but this year has convinced me that it is coming much faster than a lot of people think.

Re:Substantial Progress being made

[AGMW]

I still think that a terrestrial space elevator is a decade out, but this year has convinced me that it is coming much faster than a lot of people think.

If we actually return to the moon, might a space elevator be more practical there? Could we do that now?
What about Mars ... how close are we to using a SE there?

Re:Delusional mental patients

[Lanteran]

Did you miss the last few decades there, buddy?

Re:A virus!?

[Anonymous Coward]

A few years ago I contracted a virus called linux. It gave me Open Sores.

FYP

We should use our old rockets first

[iamacat]

Our lack of progress in space exploration has more to do with losing the will than limitations of technology. We could have launched a mission to Alpha Centauri by now if we pursued project Orion with modern advances to material science and optimized computer control of propulsion. If we are not doing that, who is to say we will build a space elevator even if the technology is feasible?

Re:We should use our old rockets first

[loufoque]

The reason we're not doing is that nuclear scares people.
Nuclear power plants are being closed and replaced by burning more oil as we speak.

Re:Anytime soon

[hedwards]

Projects like this are frequently as interesting, if not more so, for the byproducts that have to be developed in order to make it work.

Chemical bond strength vs Gravitational strength

[John.P.Jones]

I was thinking about how the energy of chemical rockets is just barely sufficient (given fuel mass) to make chemical rockets that can escape Earth's gravity well. I'm not sure of the exact headroom but my understanding is that it is fairly tight. From what I have read on the strength of nanotubes, they too are theoretically just strong enough to barely make a space elevator a possibility (if we could manage to weave them into a macro-fiber without significant losses.) If this turns out to be the case I wonder if there is a connection between these two methods and the strength of chemical bonds to overcome the gravitational potential of our planet. Need it be so that these two very different ways of utilizing bond strength achieve a similar maximum gravitational field that they can overcome? And even more speculatively could the fact that the gravitational field of the Earth is near this value be important in the suitability of it to life?

Re:A virus!?

[nmb3000]

Unfortunately not but it's nice that a scam alert site comes up first.

Google indexes Slashdot comments, but will not pay any attention to links they contain. All URLs inside comments include the rel="nofollow" attribute, excluding them from participating in search engine ranking.

Re:panax

[PwnzerDragoon]

Shit, we lost another one. I keep telling them to be more careful where they drop those ropes.

Re:Elevator to nowhere

[dvice_null]

"The aeroplane will never fly."

— Lord Haldane, Minister of War, Britain, 1907 (yes, 1907).

"No flying machine will ever fly from New York to Paris ... [because] no known motor can run at the requisite speed for four days without stopping."

— Orville Wright, c. 1908.

"The whole procedure [of shooting rockets into space] . . . presents difficulties of so fundamental a nature, that we are forced to dismiss the notion as essentially impracticable"

— Sir Richard van der Riet Wooley, British astronomer, reviewing P.E. Cleator's 'Rockets Through Space,' in Nature, 14 March 1936

Re:Elevator to nowhere

[Osgeld]

yea thanks I dont get my future vision from made up bullshit in a special effects house, the age of sifi actually having a real influence on tech is gone, sifi has gotten even more outlandish with its bullshit, and tech has cought up to the point where some dev at apple thinking that compressed music in a large archive is the way of the future, is long gone.

so enjoy your movies past of futures that will never be, I personally will be doing the best I can with what is available

I like Launch Loops myself.

[Soralin]

http://en.wikipedia.org/wiki/Launch_loop Launch loops are basically a big cable, supported magnetically in a vacuum sheath, and accelerated up to high speeds (14km/s+), it could be set up as a 2000km long track along the ground, about 80km up. Since it's moving faster than escape velocity, it would appear to move away from the ground, since the ground is curving away from it faster than it's moving. so it would just need to be tethered to put it into a nice flat path, and could be magnetically looped around and sent back the other way at the end stations. A craft to be launched could just produce a magnetic field, and it would be pulled along at 3g or so, and could let go when it got up to it's desired speed, with a small rocket to circularize it's orbit at higher than 80km, if it's not headed off at escape velocity.

It solves a number of issues that are problems for a space elevator, like how to get something to climb up a tether, or get power to it, which can be done relatively easily for a launch loop, since it could just pull power off the grid whenever it's convenient, and store it in the motion of the cable itself. And it doesn't need any new materials, or really strong ones or anything like that. Not to mention, being much faster to get to orbit, but still suitable for acceleration-sensitive cargo, such as humans. And it can launch quite a bit more material/time then a space elevator can, at a cheaper price. Mainly limited just by the amount of electrical power it has available, and at high power levels, by the need for the cable to cool down between launches.

Only major downside would be that it isn't statically stable, there would have to be dynamic control of the rotor at the end stations, given that it's all just supported and directed magnetically. And it would need to remain powered to keep it from eventually collapsing.

Re:Elevator to nowhere

[sunspot42]

The Shuttle program and the ISS alone have cost us north of $200 billion.

With a space elevator, you could conceivably haul the components to build something as large as the ISS into orbit in just a month, for less than the cost of a single Shuttle launch.

Given that the cost differential between launching on chemical rockets and hauling cargo up on a space elevator is THOUSANDS of dollars a kilogram, you can pretty much guarantee that a space elevator will turn a profit. It'll cost around $200-$300 a kilogram to haul payload into orbit with a space elevator, compared to $4,000 and up - way up - with rockets. The operators of a space elevator could charge $3,500 a kg and pretty much monopolize the entire launch business, pocketing $3,000 a kg with each payload.

At least until somebody else builds a space elevator...

JSEA

[mattr]

The Japan Space Elevator Association (http://www.jsea.jp in Japanese) in addition to covering technical and engineering also considers business and legal issues. And here is a video from JSETEC 2011 shot in Fujinomiya City, Shizuoka Prefecture on August 7 showing a climber built by Takane Matsumoto of Team Aquarius. Certainly it's cool that something like his climber exists! I don't know how high it went but I think they were going for 600m altitude. Anyway I expect these groups would welcome anybody who wanted to investigate building a loop instead.

The major nitpick

[dbIII]

Space elevators would make space travel much cheaper. But the technical issues are immense.

We can't honestly say the first part without having a bit more of a clue about the second.

Are they for real with those questions?

[roman_mir]

So the questions are: can you have 6 climbers on a ribbon instead of 3?

Seriously, those are the questions? So I guess they have a ribbon that allows 1 climber already then?

How about REAL questions:

1. What is the maximum carbon fiber ribbon length can you even make with current technologies? What is the longest length of ribbon that can be made that will support its own weight with current tech?

2. What is the climate and weather going to do to the ribbon? Rain? Thunderstorm? Tornado? Hail? Even all the Sun light? A meteor strike? Lightning? Static electricity?

3. Can you pull the ribbon into space in case something serious is taking place near the planet's surface, like a huge storm?

4. What about fire, will this thing burn? What if a fire starts while climber is on its way, half way through?

5. Will there be a way to evacuate from the climber with parachutes or rockets or whatever in case of emergency?

6. How do you make the ribbon stay in one place above the ground anyway?

Can they can answer those questions above before talking about having simultaneous 6 climbers instead of 3? Because they have to answer those questions before they can even do 1.

Re:Does a space rope have the same physics?

[LBU.Zorro]

Sigh.

The whole point of a space elevator is that the centre of mass of the cable is at geosynch orbit (well slightly past it). There is no need to continuously thrust to hold the cable up because the rotational speed of the planet will fling away the cable.

The reason that the cable stays up is the gravity drops off by the square of the distance but distance travelled by the cable per hour at any height increases. The period of rotation is always 24 hours (give or take some lean) but the circumference described is greater as the height increases.

What this means is that at geosynchronous orbit the force downward due to gravity (at that distance from earth) exactly matches the centripetal forces from orbiting the planet (or more accurately attempting to fly off in a straight line but the gravity of the planet curving that line).
Below geosynchronous orbit if you are orbiting the earth once a day you're doomed to crash into the planet without active energy input (the rate of curvature is higher than your speed thus you'll hit), above geosynchronous orbit if you're still orbiting the earth once a day you're doomed to escape the planets' gravity altogether and go flying off as you spiral out. This is why low orbit satellites orbit so quickly and high orbit satellites orbit so slowly, the relative strengths of gravity at the different orbits, plus the distance travelled to complete an orbit dictate the speeds.

The parts of the cable that are above geosynchronous orbit are attempting to escape earth, and the parts of the cable that are below geosynchronous orbit are trying to crash down to earth - the reason the cable stays up is that these are balanced. The entire weight of the cable (less the reduction due to centripetal forces) below geosynch (and adding the tension in the cable necessary to lift a weight) is indeed all passed through the portion of the cable in geosynch orbit (it's actually a huge section as 1 metre from geosynch either way isn't much difference). But the cable isn't a cable, at least not in current designs, it's a ribbon varying in width from thinnest at the ends to widest at geosynch as the loads vary - there are also thickness variations due to expected damage to the cable, ie at certain orbital levels micro-meteorite (and space junk more likely) impacts are very likely so the cable would be made wider to compensate.

Please note that this doesn't allow anything to be pulled up the cable, it is just supporting itself, what you need to do is stick a nice big weight on the end of the cable on earth, like say the base station weighing in at hundreds of tonnes (but not supported by the cable, supported by the earth's surface) and then extend the cable upwards until it has a tension high enough to do something useful. The tension in the base of the cable where it meets the base station will be at least the weight of anything you want to send up the cable (and have more because acceleration increases the force).

The real problem with understanding this is that humans live on such a small height variation and deal with speeds so slow that you cannot easily imagine what happens to gravity over those distances and how much energy is involved in those speeds - if you accept that orbital mechanics isn't the same as you running about on earth it becomes much easier to understand.

No revisions of any laws (other then potentially materials sciences as we don't yet have a material that has a strong enough tensile strength but low enough weight) are required for this to work, all you need to do is understand them.

The 'energy' you use to raise the payload is electrical converted to kinetic converted to gravitational potential. If there happened to be a mountain of a magical material that reached out into space then climbing that mountain would not violate any laws of thermodynamics.

Towers have problems, compressive strength vs weight, mechanical strength of the earths crust, and major issues with stability. Compression is a positive runaway scenario (the tower bends slightly and the weight causes the bend to accelerate), tension has a negative (or neutral I suppose) runaway scenario (the cable bends and the cable tries to straighten out).

Z.

Re:Who's going to pay

[Mindcontrolled]

Yeah, sure. Them there socialists are out to get you. Be afraid, good citizen, be afraid, there's them there socialist boogeymen in your closet! I just stay in my European socialist hellhole and enjoy life. The US were on the road to third-world status when I worked there in the early 2000s - go ahead and slide further in to your banana republic mode, you seem to enjoy it. I just pity the decent guys over there. But hey, if you want to get out - i got two large sofas in the living room - ample space for a couple of refugees.

Re:Elevator to nowhere

[vlm]

"if we could build one"

How about we get to the point where we can build a bridge over a valley somewhere with carbon nanotubes first. Even that is a LONG ways out. Not any of our lifetimes. And that bridge is about 10000X easier to build than a space elevator.

Not really. CF is basically "really weak nanotube". CF doesn't burn too well in a vacuum, and there are not many vandals in space, or at least you can put a guard shack at the base and be done with that issue.

There are "many" CF bridges, at least in the USA. Mostly corrosion proof, you tend to find them up north in "road salt country". I can imagine, within my lifetime, we will no longer use steel rebar in concrete.

The problem with purely CF bridges, is to stop vandals with no more than a hunting knife from collapsing the bridge, or stop a simple vehicle fire from incinerating the bridge, you have to encapsulate the thing in concrete, which of course in freeze/thaw cycles delaminates from the CF, or sticks to the surface of the CF making the CF delaminate, etc.

People get real confused about CF and give it mystical properties it does not have. It has spectacular, record breaking tensile strength, yes. Surface hardness? No, not like diamond, in fact its about as hard as charcoal WRT to dulling cutting blades. Abrasion resistance? No, not like stainless steel, more like the plastic resin its bonded with. High temperature strength? No, not like tool steel, more like the plastic its bonded with. Bullet proof? Yeah about as bullet proof as an equal amount of plastic. It's just about unstretchable, but otherwise you may as well think of it like plastic.

Carbon based bridges are a huge mess, not because carbon based structures suck, but because vandals suck, and gasoline automobiles suck.

Re:Elevator to nowhere

[Arlet]

Space junk is also a problem in GEO, because it tends to concentrate in a narrow useful orbit. The only advantage is that relative velocities are small, so damage from collisions is not as severe. On the other hand, lack of atmospheric drag keeps the junk in orbit for much longer.

https://secure.wikimedia.org/wikipedia/en/wiki/Space_debris#Debris_at_higher_altitudes