The Space Elevator 735
| The Space Elevator -- A revolutionary Earth-to-space transportation system. | |
| author | Bradley C. Edwards and Eric A. Westling |
| pages | 280 |
| publisher | Spageo Inc. |
| rating | 9 out of 10 |
| reviewer | James Yonan |
| ISBN | 0972604502 |
| summary | A compelling argument, backed up with a great deal of quantitative analysis on both scientific and economic grounds, that a space elevator is near-term-feasible. |
As a child in the late 60s and early 70s, some of my earliest memories are TV images of the moon shots, the sense of excitement and adventure, and confident assertions by adults that this was only the beginning, that progress was indeed unstoppable, and that it was a near certainty that by the time I was old enough to ask a girl out on a date, the question "would you like a ride in my spaceship" would be greeted not with derision, but with awe. Of course the sad reality is that none of this has come to pass. Space has remained dangerous, expensive, and inaccessible to all except the rare test pilot, scientist, or those for whom capitalism has been unusually kind. Luckily, there are some promising new ideas in space transportation that could represent the breakthrough we have been waiting for in the years since walking on the moon became passé.
In their new book The Space Elevator, Bradley C. Edwards and Eric A. Westling present a compelling argument, backed up with a great deal of quantitative analysis on both scientific and economic grounds, that a space elevator is near-term-feasible. The authors argue that carbon nanotube fibers are both strong and light enough that a 100,000 km elevator, constructed of a 2m wide carbon nanotube "ribbon," could be constructed in 10 years for a cost of US $6 billion, and be capable of lifting a 13-ton payload to geosynchronous orbit once every few days. If feasible, it would present a stunning breakthrough in space accessibility, and likely usher in a new age of space development and exploration.
Edwards writes in the forward:
One day, a few years ago, I read a statement that the space elevator couldn't be done, and I set out to find out why. From there, things got very interesting and resulted in a research proposal being submitted to NASA. The proposal was funded and resulted in, first a six-month study and then a two year study. The core of this manuscript started out as the technical report from the six month investigation I conducted for NASA under the NASA Institute for Advanced Concepts (NIAC) program.
Edwards and Westling begin the book with some history. Until recently, it was thought that alternatives to chemical rockets as a means to reaching LEO (low Earth orbit) were, at least for the foreseeable future, the stuff of science fiction. The idea of a space elevator, foreseen as early as 1903 by the brilliant Russian science speculator Konstantin Tsiolkovsky, foresaw a tower to geosynchronous orbit and beyond.
He was the first to identify the concept that the part of the tower beyond geosynchronous orbit would have an outward "force" due to Earth's rotation that would support the portion of the tower below geosynchronous altitude.
Essentially a space elevator is a geosynchronous satellite with an unusually high aspect ratio. So high, in fact, that even though the satellite is in orbit over a fixed point on the Earth's surface, the lower portion of the satellite actually touches the surface of the Earth. The key, of course, to making this concept workable is to find a material that has the tensile strength to withstand the extreme forces that such a tower or cable would be subjected to. Though a space elevator would need to reach 35,785 km to geosynchronous orbit, since gravity drops off as the square of our distance from Earth, we can collapse the 35,785 km down to its equivalent height as if it were all in 1g, giving 4940 km. This magic number represents the self-support height that a space elevator cable would need to exceed. The self-support height is the maximum length of material, formed into a cable, that can support its own weight in a 1g gravity field before breaking, and can be calculated by dividing tensile strength by density.
It turns out that a steel cable has a self-support length of 54 km, graphite whiskers (fibers) 1050 km, and carbon nanotubes 10,204 km. This last figure is an important result that shows that carbon nanotubes are significantly stronger than would be needed to build a space elevator. The difference between the 4940 km minimum self-support length and the carbon nanotube self-support length of 10,204 km all translates into significant payloads that could be lifted into space using this technology.
So if the space elevator is feasible right now for only US$6 billion (less than half of NASA's annual budget), why aren't we building one ASAP and preparing to retire the shuttles? The answer is that carbon nanotube technology is so new (invented in 1991) that we haven't yet created the infrastructure for mass production. In fact, the authors admit that we haven't even created a nanotube in the lab that demonstrates the requisite strength. While carbon nanotubes have a theoretical tensile strength of 300 GPa (billion newtons per square meter), strengths of only 11.2 to 64.3 GPa have been experimentally measured thus far. Edwards and Westling have heavily based their thesis on nanotubes reaching a tensile strength of 130 GPa in mass-produced volume, so they are to some extent reaching for the future here. Clearly they are counting on a kind of Moore's law to kick in, where the efficiency to cost curve of nanotube production improves exponentially as breakthroughs are made, then asymptotically slows as the theoretical upper bound is approached.
Now assuming that we can economically mass produce carbon nanotube ribbon at a strength of 130 GPa, what's next? Here Edwards and Westling present a well-researched plan for turning the raw material of the carbon nanotube into a functioning space elevator within 10 years. An initial kind of bootstrap cable would be lifted into LEO on board several trips of the space shuttle. This cable would be constructed of carbon nanotubes arranged in parallel with a reinforcing cross-connect adhesive, so that if a nanotube was severed, the remaining tubes would take up the load. The cross sectional dimensions of the cable would be highly asymmetrical, 1 micron in thickness, 13.5 to 35.5 centimeters in width, hence the cable is referred to as a "ribbon". After some assembly in LEO, the initial ribbon and deployment mechanism would be integrated into a spacecraft and sent to geosynchronous orbit, where it would deploy by basically unwinding the spool of ribbon towards Earth, while the spacecraft-spool assembly itself is boosted higher to maintain the total system in geosynchronous orbit. Once a few km of ribbon is unspooled, gravity gradient forces will kick in, ensuring a stable vertical orientation as deployment proceeds. Eventually the end of the ribbon would reach Earth where it would be anchored to a mobile sea-platform, located near the equator, which would have the capability to move the lower end of the cable to dodge known space-junk and electrical storms.
This prototype space elevator will be relatively weak and vulnerable to damage from meteoroids and uncharted space junk, so it will be essential to quickly strengthen the ribbon by widening it. Edwards and Westling's plan calls for "climbers" (electric-powered vehicles that climb the ribbon using a mechanical traction drive) to immediately ascend the ribbon, splicing additional carbon nanotube material onto the existing ribbon, then permanently parking at the far end of the ribbon to add to the elevator's counterweight mass. After 230 iterations of this process, the ribbon will be complete, 2m wide and capable of lifting 20 tons of climber + payload.
Getting a 100,000 km space elevator into position and insuring its survival is a daunting engineering challenge, and much of the book is dedicated to answering what-if scenarios and attempting to prove to the skeptical mind that such an ambitious undertaking is feasible. To this end, each space elevator subsystem is analyzed at length and competing solutions are evaluated for cost and efficiency.
For example three different methods for supplying electrical power to the climbers are evaluated:
- run power up the cable,
- beam power via microwave, and
- beam power via laser.
Answer: use a laser.
An optimal shape (i.e. taper profile) for the ribbon is proposed, so that the part of the ribbon in the atmosphere is narrow to minimize wind-loading forces and the section between 500km and 1700km is widened and slightly curved to maximize survivability from meteoroid or space junk impacts. The destructive effects of wind, lightning, atomic oxygen, debris impacts, radiation damage, and ribbon oscillations are considered and solutions are presented. The conclusion: none of these adverse effects are show-stoppers.
Some basic FAQs are presented and answered, such as where does the energy come from to accelerate a climbing payload on the ribbon to orbital velocity. Answer: from the rotational inertia of the planet. If we shipped a whole continent into space, our days would get a bit longer.
After a comprehensive technical and engineering analysis of the space elevator concept, the authors move on to the economics of the concept and present a sort of skeletal business plan for "Space Elevator, Inc." They present many interesting uses for the space elevator including energy applications that could significantly improve the environment and reduce the combustion of fossil fuels. If the space elevator succeeded in reducing launch costs below $100/kg, large orbiting photovoltaic arrays might be built in space that would collect power and beam it to Earth via microwaves. These ideas are far from new (such an apparatus was patented in the early 1970s), but the reduced launch costs of the space elevator make them far more feasible.
The authors take a detour in explaining some promising results on the nuclear fusion front. Progress on the reduced-radiation IEF concept (Inertial Electrostatic Fusion) for fusion reactors would be accelerated by 3HE mining on the moon, which the space elevator would make feasible.
The rationale for building the ribbon up to 100,000 km is examined. The major advantage of such a tall ribbon is that the centripetal acceleration of the ribbon tip is substantial enough that payloads could be flung to Venus, Mars, or the asteroid belt with little additional energy expenditure. This, the authors argue, would bring down the cost of robotic planetary probes to the point where individual universities could afford their own space programs.
And finally, a working space elevator can be used to manufacture new space elevators at a much lower cost than the initial implementation. The authors suggest that the first significant commercial application of the space elevator might simply be in making additional space elevators and selling them to commercial clients. In this manner, elevators with payload capacities up to 200 tons could be deployed using wider ribbons, making possible a large-scale human presence at geosynchronous orbit and bringing the kind of commercial activities that would go along with that, such as tourism.
The book ends with a flight of fancy of sorts into a future where space elevators have become commonplace. Space elevators around Mars create an efficient Earth-Mars transportation network. Elevators on the moons of Jupiter throw spacecraft down into Jupiter's turbulent upper atmosphere to scoop up 3HE and ship it back to Earth in decade-long space convoys where it will power the latest and greatest IEF fusion power-plants.
While The Space Elevator goes a long way towards convincing skeptics of the feasibility of the general idea, the big question marks that remain in my mind are:
- Will carbon nanotubes really reach the 130 GPa level in cost-effective mass production that will be required for elevator construction?
- Much of the elevator deployment plans depend on the flawless execution of robotic mechanisms controlled remotely from Earth, including the trip from LEO to geostationary orbit, the deployment down to Earth, and the subsequent strengthening of the ribbon by robotic climbers that splice additional nanotube material onto the existing ribbon. As we learned with the Hubble Space Telescope, it is essential to have astronaut access for unexpected but critical repair missions. But much of the space elevator deployment will take place above LEO, out of access of human shuttle missions. What do we do if there is a glitch during deployment that requires an astronaut repair? We will need to seriously address such contingencies, lest we get saddled with a stuck elevator that could become the mother of all space junk.
- Have there been any successful tether missions to date in space? While the answer appears to be yes, I would have liked to learn more about them.
Doubts aside, this is a compelling work that will likely become both a manifesto and bible for the space elevator movement, presenting a convincing argument that the space elevator is our best chance yet to bring Moore's law economies to space. It is an engaging read and I highly recommend it.
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Climbers - problem (Score:3, Interesting)
Re:why not construct this (Score:2, Interesting)
Anyway, everyone knows that the real reason that NASA got so much money was to beat the Commies. It WAS military spending.
Do they cover what happens (Score:3, Interesting)
* = and it invairably seems to be a 'him', I think women are just genetically smarter that way.
Another good reason to reach for this (Score:5, Interesting)
Obviously this isn't a short-term, instantaneous fix, but this is exactly the sort of project that something like the United States should undertake to help maintain its lead in the economy, if it is interested in maintaining it. The economic advantage of having the only working space elevator (even if it was only until we could build another for someone else, assuming optimistically we wouldn't build ourselves a few backups first) in the world would be absolutely incredible.
Considering the price, it's complete foolishness not to pursue this, even if common sense says the opposite. And the best news of all is that carbon nanotube research is interesting enough on other, more commonly-sensible grounds, that it's going to continue anyhow.
Another thing that should be emphasized is "Suppose China gets there first." Personally, I'd love to see a space race over this issue. It would be one hell of a lot more productive over the long term then the moon race was!
One possible practical application? (Score:3, Interesting)
Getting rid of our garbage -- do you know how much cleaner cities could be if we could just send garbage to the sun???
Re:The obvious question (Score:4, Interesting)
Keep in mind that (it seems to me) the portion of the cable above the break will float up rather than falling down; the tether is as anchored to the Earth as it is suspended in space. Furthermore, it seems that this station will necessarily be situated in the middle of deep blue nowhere (because of air traffic control considerations), so whether we're talking about Ecuador or the Outback, the cable crashing slowly down is probably only a financial disaster.
I think the main problem would be security. This cable would be a monument to humanity, and hence a prime target for terrorists.
What I want to know is: (Score:4, Interesting)
Why (Score:4, Interesting)
I guess any space technology improvement is a good one, but does it really need to be so brute-force-ish? Whatever happened to the NASA of old that created the shuttle?
They say that the next generation of space craft is still many years off, but I bet money could dramatically reduce the time frame (money always fixes problems like this - yay capitalism!)
I think it is good to at least gaze into the future of possibilities and while this certainly would make for cheap satellite launches, etc.. I am skeptical at how safe it would be to send humans up or back on it..
Say it comes to a grinding halt 1/2 way up. What on earth do you send to rescue the people off it this time?
Nanotube bending radius (Score:2, Interesting)
Chip H.
no free ride (Score:1, Interesting)
Re:dangerous?? (Score:1, Interesting)
Re:NASA *is* funding this already (Score:5, Interesting)
Because . . . ?
I must confess that intuitively,
Oh. Your intuition. I guess we should give up on this right now.
Can you just imagine the harmonics on this thing when the jetstream plucks it (or whatever).
I don't have to imagine. I have computers. I can model the questions. Obviously, I personally haven't, but the people writing this book have. While I have not read this exact book, the atmospheric effects have not been neglected in the other treatments I have read have not, and they aren't much of a problem.
They are certainly more intelligent then your analysis. Talking about harmonics in this situation is a crock of shit. The exact "resonance frequency" depends on the tension, but over tens of thousands of kilometers you're talking something that is a vanishing fraction of a Hz! At that point "resonant frequency" is meaningless, you're just talking about tension propogating.
Given the failure of human intuition to handle large numbers, which you see routinely on Slashdot, I gotta say I'm much more inclined to believe a well-researched book then your intuition, or mine either for that matter.
Re:Do they cover what happens (Score:1, Interesting)
you americans: always with the terrorism! After the space shuttle exploded the first headlines i saw on CNN were "Shuttle Explodes: Possible Terrorist Attack?"
What's even more depressing is that your terrorist fever is inspiring excuses for moronic behavior around the world: Here in Canada the law now defines a terrorist as, among other things, somebody who voices political dissent in the vicinity of visiting diplomats and leaders (Bill C-36.) Thanks a lot. Ariel Sharon is suddenly killing palestinians publicly instead of covertly, because he can call it his own "war on terror." Bleh.
Less lightning? (Score:3, Interesting)
Assuming that the current theories on how lightning is created are accurate, I wonder if the localized decrease in lightning would have any environment effects.
Re:'Because We Can' good enough reason? (Score:1, Interesting)
"What if it falls down?"
Obviously the big one. The answer is "not much". The structure is very lightweight (if you're picky about physics, very low mass), and with suce a realitively enormous surface area, it'll be akin to dropping a gigantic plastic grocery bag (except a similar structure made of plastic would have much higher mass)- it may not even impact the ground for a while, instead being blown about by the high winds in the upper atmosphere. When it finally does touch down, it may not even have the force to break through a glass window since it'll still be drifting down like an oversized feather. And if it somehow manages to pick up any decent speed, the atmosphere once again becomes our protector, heating it up and causing it to burn up like most any other piece of matter falling from space.
"What about the terrorists?"
Forget about them. Since having it fall doesn't cause that much physical damage, it's a poor target from that standpoint. However, the real impact would be psychological- but not for long. If these structures proliferate quickly, then nobody's going to give that big a hoot if one of them falls- the others are still there and lifting away, it could probably be replaced in days if the paperwork could be pushed through fast enough: "Terrorists blew up Space Elevator #152 today. Officials say that they'll have the replacement up and running within a week, but call for added security measures. Chinese controlled elevators have continued to operate normally, and their government has said it does not consider terrorist actifity a long-term threat to its space plans."
"What if it affects the Earth's rotation?"
Really now. Maybe if we lifted enough material to form a habitable ring around the planet, we might see it slow by a few seconds, but this is a rather farfetched possibility. If it really does get to be a problem, start seeding the planet with asteroid dust on calculated trajectories to speed things back up.
"What if God gets angry?"
Well, the Tower of Babel evidently miffed Him a bit, but we seem to be doing a fine job [cnn.com] of reducing language to an incomprehensible gibberish already. I say take the chance, and if the first three attempts (has to be three or you won't get anywhere statistically close to a good sample) are all smited by heavenly bolts, we should reconsider the endevor.
In conclusion, I really don't see the risks to be that serious, but the rewards to be substantial- including what would possibly be the greatest reward of all- being able to go outside before sunup or after sundown, look up at the night sky, and see the still-lit tops of the elevators, and know that we took a dream, and made it reality. You can haggle business costs all you want, but an inspiring sight? That's priceless.
Re:'Because We Can' good enough reason? (Score:1, Interesting)
Generally playing devil's advocate involves formulating an actual, real, plausable scenario contrary to what's being proposed.
Sure, they have done a very good job of explaining away the disaster scenarios that they have come up with, BUT, this cannot solve all possible problems and would be terrible to assume that they can do so. Why? Because, nothing like this has EVER been done before. We only really learn from our mistakes, and why? Because until we make mistakes, we usually fail to see them for mistakes.
Your "devil's advocate" scenario is "What if it falls?" As the review states (and as you mention), the authors of the book do address this question. They address it with actual scientific analysis of the problem and its effects. You say that we have never done anything like this before? Anything like what? Sending stuff to space? Done. Sending tethered stuff to space? (According to the review) Done. Building carbon nanotubes? Done. Building long, strong carbon nanotubes? Theoretical, but testable in the lab before putting it into production. Dropping big, heavy stuff from space? Done. What else could go wrong? The beauty (and the point) of the system is that it's very simple and very cheap. Seriously, what could possibly happen other than the thing falling? Can you think of anything? I can't.
It's just food for thought man, open up a bit.
I do think the idea is way cool, I just want to make sure that that is enough to warrant building it.
I like a good discussion as much as anyone, but let's stick to the facts rather than fear-mongering. When the discussion is over, we have a choice: either do it or not. You are right that we learn from mistakes, so let's make some. At least we're going somewhere, rather than sitting in a hole, paralyzed by theoretical fears.
Was the Atomic Bomb worth building? Debatable yes but millions of deaths would have been avoided if it hadn't been
I'm not really sure what this has to do with anything. The atomic bomb was engineered as a weapon. If we're talking about engineering a space elevator as a weapon, that's a different discussion. Besides, where did you get those numbers? About the only thing I can find on the death count [iadfw.net] puts the totals at 200,000 in Hiroshima and 140,000 in Nagasaki. Even with deaths possibly attributed to radiation poisoning in the US and Japan, you're still quite a ways from "millions." Besides, how many lives have possibly been saved by the medical and industrial applications of nuclear technology, directly descended from the Manhattan Project?
In conclusion, feel free to play devil's advocate, but throw some real facts in there. The point of a discussion is to separate the good ideas from the bad ones. From a scientific standpoint, this point addresses your question. What more is there to do other than try it?
OK, someone explain to me... (Score:5, Interesting)
If I had several billion dollars, I would be a complete idiot NOT to sink my money into such a venture. Of course,
For the mega-rich, the income potential and (maybe more importantly) the "my name in human history" potential of this SHOULD be irresistible. Plus, I'm a firm believer in free-enterprise. Let companies do it for a profit and it will be safer, quicker, and more efficiently run than any government project.
Re:Earth - another ringed planet (Score:3, Interesting)
Once the first is complete, second and third and more will be much cheaper to produce. We could have a Space Elevator in every city.
As for debris, once we have nanotechnology we'll easily be able to both identify (and collect) particles of the smallest size that could damage ships; and also we'd be able to harden the ships to withstand greater damage (they would even be self-healing, so if a rock would punch a hole through it, the ship would just create a temporary "tunnel" through itself for the rock and avoid a collision completely).
Re:Plot. (Score:2, Interesting)
"And they said, Go to, let us build us a city and a tower, whose top may reach unto heaven..." --Genesis 11:4
Re:One possible practical application? (Score:3, Interesting)
Actually, our nuclear waste is the most useful waste we have, from a recycling perspective. Where else are you going to get transuranics to power RTGs for future spacecraft, or daughter radionuclides for portable heat sources when you want to melt your way through the Europan ice cap?
Re:NASA *is* funding this already (Score:2, Interesting)
Because . . . ?
Because they can't make the string. The 6 billion, from what I got out of the review, is assuming we can make it. Now, I have no doubts that we'll eventually be able to make the string, but we can't make any today, or probably this year or even (Speculation here) this decade. So, that's why.
Now, as to getting it done the second it is feasable, I say we should, and will. Any company that can do it (and is forward thinking) will make a massive profit off of it.
Carbon Nanoscrolls (Score:2, Interesting)
Science Daily [sciencedaily.com]is reporting today that UCLA chemists have found a new method for producing Carbon Nanoscrolls. It appears to be a cheaper alternative to Nanotubes. Edit: I see a previous AC poster mentioned this briefly. Well, this expands on it a bit.
UCLA chemists report in the Feb. 28 issue of Science a room-temperature chemical method for producing a new form of carbon called carbon nanoscrolls. Nanoscrolls are closely related to the much touted carbon nanotubes but have significant advantages over them, said Lisa Viculis and Julia Mack, the lead authors of the Science article and graduate students in the laboratory of Richard B. Kaner, UCLA professor of chemistry and biochemistry.