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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."
In the interest of promoting more enlightened discussion, a lot of good information concerning space elevators can be found here.
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~ |rip/\/\aster /\/\onkey
How about creating a simulator for a space elevator? It would be great to mess around with values to see how possible this thing really is. The closest thing to a simulator I've seen is this but its sadly lacking.
http://spaceelevator.sourceforge.net, anyone?
Actually, if you have heavy objects impacting the Earth's surface, it's sort of preferrable to have them hit land, not water. Dust clouds and solid ejecta are unpleasant for the locals, but tsunamis are unpleasant for people who live thousands of miles away.
They aren't going to be attaching an asteriod to the other end. Its much simpler to just make the cable 60,000km then it is to move an asteriod nearby GEO and make a 36,000km cable.
Aside from which, manufacturing spacecraft is perhaps one of the most industrially complex things we do. Trying to replicate that in a place more remote, and with far more environmental challenges than, say, Antarctica, would have gargantuan capital costs dwarfing the elevator. In fact, the only way you could probably get the infrastructure up there would be an elevator or something equivalently cheap.
Any sufficiently advanced technology is indistinguishable from a rigged demo
--Andy Finkel (J. Klass?)
Humans could and would travel on such an elevator. It would probably be much safer than sitting on top of a bomb that is a rocket, and much, much cheaper. It wouldn't be the most pleasant ride, but there's no reason it couldn't or shouldn't be done.
Professor of Astronomy, Author of Spider Star & Star Dragon (Tor)
>Jeez, try to imagine the havoc if the cable comes loose
>from its orbital anchor. Thousands of miles of pure splat!
That's why you don't build it as a cable. You build it as a ribbon, with lots of surface area. If the ribbon snaps, portions high up in the atmosphere will burn up upon reentry. The portions of the cable that don't burn will flutter to the ground - think tickertape parades.
"A 40,000mm bridge is a 40m bridge. That's less than 120 feet. People have built multiple KM bridges long before now, the new Millau bridge in france is 2.5 KM in length."
Is it made out of carbon nanotubles or anything with the strength it would take for a Space Elevator?
No, so it's not in the same class structurally.
Even for Slashdot, your post is uninformed.
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).
The biggest obstacle to space travel is the cost of escaping the earth's gravity well. Space elevators offer a possible solution to this problem, assuming you can develop the materials to build a stable and reliable cable or ribbon. Building a huge construction platform in orbit is utterly worthless if it still costs thousands of dollars a pound to haul raw materials up to that platform, as it does today with chemical rockets. You'll have gained absolutely nothing. Space travel will still every bit as prohibitively expensive as it is right now.
In contrast, the cost of hauling materials up a space elevator involves the amortized cost of the elevator itself, plus whatever electrical energy it takes to run the mechanism that pulls the platform into orbit. Over time, the cost could drop to a few dollars per pound, making it cheaper to haul material into orbit than it is to fly it across the continental United States. That would truly open up space travel to the masses, and enable us to construct gigantic structures in orbit, plus haul up the fuel or reaction mass to move those structures anywhere in the solar system. That would include places like the asteroid belt and the Oort cloud, where there are resources we could harvest that would enable either additional construction in space, or that could be hauled back to earth and down to the surface via the space elevator for terrestrial use.
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.
Building an infrastructure buys you nothing if you can't supply it with raw materials. If we continue to rely upon chemical rockets for access to space, it will never become inexpensive enough to support the kind of construction and development you're advocating. It would cost trillions to build and supply a space drydock capable of building even modest craft. We've already spent close to $150 billion just constructing the International Space Scrapyard, and it doesn't even build anything - it just sits there. Supplying the tiny crew with food, air, water and fuel costs hundreds of millions a year. If you think a space elevator is impractical, that's nothing compared with trying to build anything substantial in space using chemical rockets to haul up the materials and components from the surface of the earth.
Your objections are very leaky.
It is a single point of failure. If any one of the millions of potential problems with a space cable turns out to be a show-stopper, the whole investment is lost.
It's possible to "prove" the space shuttle can't fly based on the number of parts and the failure rate in those parts. Yet it flies. It isn't like we've spent a fraction of the GNP on it. This argument comes down to "I don't think it will work because it seems complicated." It's actually much simpler than riding a bomb into space which is what astronauts currently do.
The benefits are small. The energy needed to shift a payload from the bottom to the top remains the same with or without the structure. The amount of money and energy spent on building the structure needs to be recovered in improved efficiency, and that seems unlikely.
This is just wrong. The benefits are huge! This would reduce cost to orbit by orders of magnitude. When you put material into space, you're not paying for the energy. It actually doesn't take all that much energy to put something into space. The calculation is easy. It's about 60 million Joules per kg (1/2 mv^2 with v=escape velocity). You can take a day to lift (which is 86400 seconds). That gives you about 700 J/s (which is the same as 700 Watts). It's the same energy you need to run 7 100 Watt light bulbs for 24 hours.
All of the investment is up front. There is no incremental benefit to this - the elevator does not become useful until it's complete. Any return on investment (including to governments in the form of kudos or re-election benefit) is delayed until long after completion of the project.
This objection is correct, but trivial. Edwards and Westling, the only ones who have done a realistic design study, put the cost at around $10 billion. That's less than the NASA budget for 1 year. That's much less than building a successor to the shuttle. That's factors of several less than the defunct superconducting supercolidor, and similarly less than the space station. Heck, Bill Gates could in theory build it for fun. Given the international nature of the problem, issues about security, the need for some additional bits of engineering/research, it is a government project. But not an outrageously expensive one.
Professor of Astronomy, Author of Spider Star & Star Dragon (Tor)
Well, if you're below geosynchronous orbit, but more than a few kilometers above the surface, things are going to get hot when you re-enter the atmosphere. You'd want the heat shield.
If you're at geosynchronous orbit, you'll stay there, and you won't need the heat shield.
If you're above geosynchronous orbit, you'll get flung out into space with a delta vee somewhere between 0 and 3 km/second. Again, you won't need the heat shield.
Well, it's not as if you're at orbital velocity at low altitudes, but there is a nontrivial amount of energy you've accumulated.
For instance, a 80kg person who is 100km up the space elevator has accumulated ~80MJ of potential energy; this is a nontrivial amount of energy that will be dissipated as heat over a very short period-- the vast majority of it in a couple minutes.
I don't know the appropriate constants offhand (surface area of a person, etc) to calculate temperature under these thermal loads, but i can throw out a few numbers:
80MJ = 19 megacalories-- enough to raise the temperature of 190 kilograms of water by 100 degrees celsius.
80MJ = enough to run 450 standard home 1500W space heaters for the 2 minutes of heating.
So clearly, thermal considerations do matter for jumping from 100km.
I used to hang out on their forum a while back. One solution that was proposed was to "maypole" the tether when it enters the atmosphere - i.e., have it split and have a number of anchor points.
Edwards already had discussed several issues: one, the potential site, has almost no thunderstorms. Also, depending on the type of CNTs that you use, many are very resistive, and would not be the easiest route to the ground, but the most difficult. A risk factor, however, would be water streaming down the tether making a more conductive path.
sed "s/SJW.*$/... never mind. I was about to say something stupid, and also, I'm a troglodyte./Ig"
I didn't mean to imply that I'd found some magical way around the 2nd law. What I meant was that all existing launch systems recover 0% of the energy expended to send objects into space, whereas the space elevator has the potential to recover at least some of the energy spent to send mass into space. All physical devices will have inefficiencies, but those inefficiencies will diminish as technology improves.
As for the current re-entry method, it's the cheap way of slowing down without using fuel, it doesn't have to happen but it is a carefully calculated risk.
True, it's the best we have at the moment. What I'm saying is that it is (a) dangerous and (b) wastes energy by shedding it as heat instead of reclaiming that energy for the next launch.
I'm not a practising materials scientist anymore, but from what I've read of carbon nanotubes they have a possible potential to be strong enough someday - but since we don't know how much it's going to cost us per unit volume to make the stuff or how much we'll need it is way to early to make up numbers from nowhere.
That's true, but it doesn't mean that we shouldn't invest in some relatively cheap studies of what carbon nanotubes could do when we finally get them working. In addition, I sincerely doubt that economics of carbon nanotubes will be a large problem because there are a huge variety of applications for nanotubes that don't involve spaceflight at all. Economies of scale and all that. Plus, the whole point of a space elevator is that the costs associated with each launch are miniscule- it's only the initial construction that is expensive. A large initial investment will prove less expensive over the long haul than continuously wasting energy by sending small payloads into orbit and then wasting all their orbital energy in re-entry.
It's hype - and from the way people in the west have been brought up it strikes a Biblical chord.
I agree that the people who think an elevator can be up and running within 15 years are probably overoptimistic to the point that you could call it "hype", but I've honestly never seen anyone besides you compare the space elevator to a biblical story. Most of the discussions I've had with colleagues regarding the space elevator, and most of the articles I've read about it have been concerned with the technical challenges involved and the incomparable riches it could provide to the human race if we ever manage to construct one. It's an engineering project, albeit an ambitious one, which is fundamentally no different from, say, the moon shot.
If we are going to ship millions of tonnes into space it could either be an elevator or infrastructure to get stuff from places that are not in such a deep gravity well.
Mining near earth asteroids is definitely a good way to jumpstart the human presence in the solar system, but it doesn't address the fact that some things need to be taken into space from the surface of the Earth. For instance: people, any technology that requires large factories to be constructed (such as computers), and food (at least until greenhouses can be constructed in orbit). In addition, mining near earth asteroids may be a way to reduce the amount of mass that needs to be lifted into orbit for a space elevator. If we can manage to capture an asteroid of the right size and put it into GEO to act as a counterweight, the cable length can be shortened considerably, from 143,000km to 36,000km.
The Space Tethers will be built far sooner and are really much better. These can toss you into space fast so you don't fry in the radiation belts, recycle the energy from payloads going down into payloads going up, and be built with materials we have today.
Look the longest Nanotube is about 2 mm. (I've seen them and know the student making them.)
e nt_progress
A couple of millimeters was the record in 2003. As of September 2004, the longest was 4 centimeters. What will the record be for 2005? 2006? 2010? 2020?
Wikipedia also states the following:
http://en.wikipedia.org/wiki/Carbon_nanotube#Curr
In 2004 Alan Windle's group of scientists at the Cambridge-MIT Institute developed a way to make carbon nanotube fiber continuously at the speed of several centimetres per second just as nanotubes are produced. One thread of carbon nanotubes was more than 100 metres long. The resulting fibers are electrically conductive and as strong as ordinary textile threads.
Granted, these continuously-spun variants don't have the required strength yet, but I think it's still a little early to call all of this outright stupid.