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Space Elevator Update
TheMadReaper writes "The 2005 edition of the Space Exploration Conference in Albuquerque, NM came to a conclusion earlier this week. A large fraction of the conference was devoted to the Space Elevator. Surprisingly, there hasn't been much news coverage of this conference, perhaps because it doesn't have Space Elevator in its name. The most interesting fact I got from the conference is that money is really starting to exist in the space elevator world mainly thanks to the work of Dr. Bradley Edwards at ISR and at Carbon Designs, Inc. The strong nanotube talk was also more promising than last year."
Operating costs estimated at 100 kg/lb, ready in 15 years at most optimistic.
Kilograms per pound? What is that?
Now I know, anything is possible with technology. Science fiction of the 50's is science reality of today. But let's stop the conversation of "is it possible" with that. The question of if the Space Elevator CAN be made seems irrelevant to me.
When it comes to this whole Space Elevator business, the relevant question in my opinion is "would we WANT to make something like that?" To me, it's a novelty idea and nothing more. If people want to get serious about space travel, we need to invest more into the building of in-orbit construction yards (IMHO). Once we get the infrastructure in space to produce the vehicles, we'll find that occasional trips to the "Drydock" from Earth to supply it with raw materials will be far more practical than some 21,700+ mile long elevator reaching into the sky.
-Vendal Thornheart
As long as youre wearing a spacesuit theres no reason why you couldn't base jump off to escape... ...Or for the fainter of heart - atmospheric bungee jumping!
Man what a rush.
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beware he who would deny you access to information, for in his mind he dreams himself your master
Forgive my ignorance, MEMS and Nanotech has fascinated me for a while, but I don't know enough of the math behind them to tell if this is true. My grandfather, rest his soul, once told me of something called the Sailor's Rope Rule, which effectively says that the weight a rope can support is diminished by its length. Thus, a 500 lb. rope might support 500 lbs when there's less than a foot or so in length between the pully and the weight, but might only support 250 lbs when there is a good 100 ft. or so... The actual support degradation of course depends upon the width of the rope and the material the rope is made of.
So what I'm wondering is, does the same apply to the weight supported by nanotubes and other molecular chains. I figure it has to be less of a degradation due to the ionic bonds involved, but it would seem to me that, unless some Quantum rule is involved dealing with extremely small-scale weight supporting chains, that they might never overcome this problem due to the sheer thinness of the tubes, chains, etc. It might be extremely strong material, but if it's width is only a few atoms wide, wouldn't this material be, at least in single lengths, more or less useless by the time it got to a respectable length? This is, of course, excluding bundles, which make the most sense, I'm really just curious if the same rule applies to nanotubes as applies to rope.
I recall Arthur Clarke pitching the initial concept for a Space Elevator some time back, and revisited the idea in 3001 : The Final Odyssey - in which he depicted planet Earth having a fully functional ( four actually ) space elevator system; which facilitated a subset of human civilisation living in low earth orbits in reduced gravity - thus invoking presumed benefits of doing so.
Anywho. He spoke a couple years ago, subsequent to 3001's release on how at the time of writing, such a feat was nigh on impossible at this stage - as the materials to construct the 'elevator' were yet to be developed. Until now. The carbon molecule Buckminsterfullerene ( C60 ), also known as 'Fullerene', is supposedly strong enough to actually make such a concept a reality - which is in part the reason the space elevator was hurled back into the limelight of late.
I think its a fascinating idea - which until we develop propulsion systems beyond the primative scope of the 1,000+ year old firecracker concept, certainly seems a more elegant way for the species to venture into Space more regulary. Or, at the very least, be the catalyst for what could perhaps become the initial stepping stones to establishing a permanent presence in space which will hopefully later lead to space initiated launches.
Something I never heared anybody about: Where does the kinetic energy come from that the cargo gains when ascending into orbit? Somehow the cargo needs to gain a huge amount of kinetic energy, because the top of the elevator moves several km/s faster then the bottom. If nothing compensates for this energy, the counter weight would gradually slow down and deorbit, so there must be some kind of propulsion in the counterweight, pushing it prograde whenever cargo ascends and pushing retrograde when cargo descends. Anybody got more info on this?
The surviving fragments of an orbital tether would not have the requisite mass to produce the sort of wave disturbances you postulate. Actually, from most accounts, the worst health hazard resulting from a broken orbital tether would be small fragments of nanotube floating about in the atmosphere, eventually drifting to ground level and getting lodged in the lungs (as it turns out, carbon nanotubes are about the same size as asbestos fibers...perfect for getting lodged in the lungs).
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~ |rip/\/\aster /\/\onkey
A space elevator, or beanstalk, has two big problems for construction: 1) materials that are strong enough, and 2) getting it to stay up.
The first we're getting close to being able to handle. The second is just a matter of having a counterweight that balances the 22,500 miles of cable from the equator (more on that later) to the top. Without the counterweight, the ground end drags it down.
That means that we really need to build this sucker from the middle out: extend equal masses out and in (or up and down, if you prefer) from geosynchronous orbit. That's a very expensive proposition. Whether it's cheaper to ship carbon for nanotubes up or go and fetch some carbonaceous asteroids down to our orbit I'll leave as an exercise for the reader.
A poster above was concerned about the terrorist target of something like this. The one consolation in this one is that you can't build it on US or European soil: it needs to be at the equator. At least one SF author (I forget which) posited an elevator whose ground-level terminus was an upside-down Y to two islands straddling the equator some hundreds of miles apart. Not the silliest thing I've ever read, but I'm not sure it makes much sense. Tethering one end down will be tricky enough.
So it won't be Imperialist America that's building it... but that's not to say it won't have protestors. It'll cast a shadow pretty much across the entire planet. It will likely change weather patterns in the region.
It will create the most valuable real estate in the world.
It's going to end up in some place where technology and resources are accessible: Brazil, Equador, Congo, Somalia, The Maldives, Indonesia, Malaysia, or some Pacific Island are all candidates, my money is on a spot just south of Singapore -- there's enough high-tech industrial nations close enough to justify it there. Brazil is my second guess.
And who knows, maybe we'll find Saddam building WMDs up there. (obligatory Funny whoring)
Design for Use, not Construction!
Edwards and Westling quote a figure of 8000 objects being tracked by U.S. Space Command. There are about 100,000 additional objects with diameters between 1 and 10 cm to worry about. The worst altitude is LEO at 500 to 1700 km. These numbers would suggest an impact on average every 250 days or so.
The solution is two-fold. You build the ribbon wider in this region, which reduces the chances of a catastrophic hit. Second, you go ahead and track ALL such objects and give the ribbon a small wiggle to avoid them. This is, apparently, feasible. It's an engineering challenge, not a show-stopper.
Professor of Astronomy, Author of Spider Star & Star Dragon (Tor)
I once read a short SF story about a terrorist attack on a station on a space elevator. Some people escaped and eventually managed to get down to the ground using some 'Angel Wings' - devices you stand on that 'ride' one of the cables.
"If you're stuck high and above, you might have the space shuttle come and rescue you."
No.
At altitudes the shuttle can reach, the relative velocity between the shuttle and the elevator would be too great for a transfer.
Also, the shuttle can reach a few hundred kilometers. Not sure specifically what the limit is, but it's under a thousand kilometers. A space elevator has to go all the way up to geosynchronous orbit, which is 35786 km. You're out of reach for most of the journey.
It wouldn't be that hard (relative to the cost of the project anyway) to have an escape pod in elevator cars that have to carry humans. That could carry passangers back to earth, as they'd be in free fall for the most part.
I rarely criticize things I don't care about.
Look the longest Nanotube is about 2 mm. (I've seen them and know the student making them.) Nanotube fibers are made but they are tough to do. The amount of MWNT (the easy stuff!) made in the US is small. There is no way to make a massive amount of the stuff. Certainly not the amount needed for an 'elevator'. Now let's consider the minor factoid that you will have to drop something heavier than you are lifting. (Or at least of similar mass.) I have single word that this space elevator project does not consider - physics
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Something that has puzzled me, but I am sure someone has brought up in scientific discussions, is orbital wobble. Will this cause the earth to wobble during orbit? You can take a 5 pound ball, and spin it on a flat surface and observe it, now try taping a .5 lb weight on a 6 inch string to it, and spin it fast enough to get the weight to fly out horizontaly. I wonder if the earth will have the same effect.
-William
God is everything science has yet to explain.
Two main points are:
Geostationary orbit is a long way up.
We don't know yet if carbon nanotubes have the strength require to be able to handle their own mass over such a distance - or half it if you have an asteroid keeping station at the other end.
Call back when we have the technology to bridge from Singapore to Mexico City in a single span - we'll be a small fraction of the way there.
I see this whole concept as just being another aspect of people getting too influenced by Biblical sound bites - they want to build a tower of Bable for the sake of it, while similar ludrous schemes for launch like building a mass driver circling the equator would be orders of magnitude cheaper. Keep your religeon and your science seperate guys. People would argue this came from SF, from people that have heard of geostationary orbit but don't have a clue, but it gets rooted in our heads from Sunday School and the Bable story.
I saw your presentation at Norwescon this year, and I was interested and impressed. My only really negative comment is that it seemed a little too much like a presentation by a .com trying desperately to convince people that you really had a viable business model.
I was really hoping for a sober engineering discussion that talked frankly about the problems and possible solutions. I thought your climbing robot was the most interesting part of the discussion. But when the 'vision' guy took over that to explain how you all had a chance in hell of making money on all this, I stopped being interested.
I think your company has a chance of succeeding actually. And your ideas about leveraging the technologies you create along the way in order to fund further R&D is are excellent. But talk that's all pretty powerpoint slides and slick presentation really turns me off. I'm not a businessman, and I don't think most of the people there were. I'm an engineer. Details and plain-talk matter to us.
As for stupid comments on Slashdot... I sometimes wish there were a '-1 counterfactual' rating, but it would get abused horribly to moderate down valid opinions people disagreed with. So the best you can do is to post truth and hope the moderators notice. Really, trying hard to control public perception of your company is going to backfire. It's just best to let people see what's going on and let them decide for themselves.
Need a Python, C++, Unix, Linux develop
It seems likely that the estimates of 12 years are a little optimistic for something of this scale, but I would certainly like to be wrong on that count. However, if we spend 5 billion dollars on this and we end up developing the technology to cheaply produce super-strong cables out of carbon nanotubes, I say it is money well spent, even if there is no space elevator.
If it works, a space elevator is THE best way to get things in and out of orbit. Also, I am sure you realize it, but your bridge analogy is specious at best. Building long bridges and tall elevators are not comprable projects.
My guess is that the next elevator behind you would stop and you would somehow board it, then the one above would be jettisoned off the ribbon in some way. This seems like a contingency they'll have to plan for. I wish I had thought of asking that question at NorWesCon last weekend. The Liftport folks gave a presentation and took a lot of questions. The trip up will take 7 days. They plan to send up one elevator per day, so 6 elevators at a time will be on the ribbon. Once the elevator gets to the orbital station, it will be kept there as raw material for large structures such as solar power satellites. They aren't going to have elevators climb back down.
Presumably people will have to return to Earth in a re-entry craft that will have been hauled up the ribbon. Wish I had thought to ask about that too. Re-entry from geostationary orbit would probably be simpler than from low orbit, because from low orbit you have to lose about 17,000 mph velocity. From geostationary maybe you could spiral down at a gentler rate.
...would be to cable a suspension bridge with this stuff, and use that as a bellwether for issues with the real deal. It'd look kind of odd, because the carbon ribbon would be thread-thin compared with the normal steel cables.
Got time? Spend some of it coding or testing
There's no way a space elevator can be built with any kind of materials we know about today. Not even close. It's a fun idea to think about, but expect to see it built about the same time we invent warp drives and start learning new things from our Vulcan neighbors. Here are just a few thoughts of why off the top of my head, but there are easily hundreds of reasons more.
Move a wire through a magnetic field, and what happens? A current is induced in the wire, proportional to the change in the magnetic field (or, equivalently, the motion of the wire in a uniform magnetic field). Well, a space elevator is definitely moving, and the magnetic field it moves through is definitely not uniform. These currents would easily be enough to vaporize a steel structure like this. Ok, you say, make it out of something entirely non-conductive (i.e., non-metal). Out of what, rubber? Carbon nanotubes are very conductive, as you CS people should know. Try to build it out of something like diamond and it isn't strong enough. And you have to get something nearly entirely non-conductive, too, a high resistance won't work. If you don't know why, ask your oven, it knows. No known material ends up doing a good job at this.
The minimum energy curve from the ground to orbit isn't a straight line because of the Earth's rotation. The elevator couldn't be straight, or anywhere near straight. Consider that at the Earth's surface, we move around at a "horizontal" speed of about 1047 mph (1685 kph) (4000 mi * 2 * pi / 24 hours), at a geosynchronous orbit we're at 6860 mph (11040 kph). That means to move on a straight line you need to be changing your horizontal speed by a few thousand miles an hour! I.e., you'd need a force pushing sideways on your elevator and tower to keep it straight, but unless you want to put rockets on the sides of it, there's nothing you can do to add that kind of force, so you need to make it curved, like an Archimedean spiral, in fact. But, with it shaped like that, you've got a very tall curved structure, and gravity is still pulling it straight down. So it turns out you need to make it out of a much stronger material than you would for a straight tower on a non-rotating Earth.
Any object when heated is going to expand, which is a non-trivial effect even for small objects. Look at concrete bridges, even small ones, for example. Periodically there are gaps in them an inch or so wide, to allow for thermal expansion of the bridge, if those gaps weren't there, the bridge would break. Bridges even only on the order of tens of meters long need these. A space elevator obviously couldn't have gaps, and will be on the order of thousands of kilometers! This means there will be *significant* changes in where the top of the elevator is, which means you need a significant change in the angular momentum at the top of the tower to keep it from collapsing. Of course, that's only if the tower is straight, if it's spiral-shaped, like a real one would need to be, you've got a much more serious problem, because the shape of your spiral just changed! You've got even more of a problem when you consider that the temperatures along different points of the structure will be different, and will be constantly changing, particularly the points near the top--what's the temperature of an object in space in darkness vs. direct sunlight!? And then there's the problem that this will cause the strength of the material the elevator is made up of to change, too! So you end up with an elevator that's longer than it was a minute ago, weaker than it was a minute ago, and no longer the same shape, trying to do the same job!
But that's not all, you also have to consider that deformations only propagate along the structure at the speed of sound in the material. This isn't an issue in a small structure, but one that's 100,000 km high, it's a serious issue! When part of the structure expands or contracts the whole thing won't move instantly! There will be serious waves of compression and expansion propagating through it. The structure will *bend* because it can't move out of its way fast enough for its expansion.
MIT's Blaise Gassend has a space elevator simulation available, which produces some rather neat animations of what happens when a space elevator breaks. It might be good as the basis for a more elaborate project.
GPL'd source code
There oughta be a law against stupidity. I mean, seriously, what forces people like yourself to post when they clearly don't know anything about the subject? May be you are so stupid as to not realise it?
40 mm single-wall nanotubes were made in 2004 (photo of 40mm SWNT here). The tensile strength of nanotube composites has been measured and was (Ray Baughman's group at University of Texas) as high as 600J/g (compared with Kevlar fibres at 27-33J/g).
I hate incompetent morons, who speak as if they are on the same level with people who know something. Please, don't ever break into a discussion unless you have something truly valuable to contribute and you double- and triple-checked it. Thanks.
Future Wiki -- If you don't think about the future, you cannot have one.