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The Space Elevator
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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Good Lord - the amount of Muzak one would have to listen to on the trip to the moon should be enough to stop a project like this in its tracks!
The whole space elevator thing is a conspiracy being run by The Illuminati. They plan to run wires up within the elevator shaft providing an unparalleled antenna for their mind control rays. At the top they are going to have a lounge and war room from which they can watch their world and plan our lives.
Call me paranoid all you want, but it's about time the trut... oh just a sec, there's someone at my door...
Trolling is a art,
Why does Bush not say that his goal for America is to construct this during this decade? (similar to JFK, etc)
This time in our history will be looked back at for terrorism, war, and world diplomatic struggles. Why not unite and construct something of this magnitude to unite us all? I am sure the terrorist strikes will stop themselves if the US gains a reputation for a R&D and science nation instead of a warring and military nation. If the U.S. put a 6 month hold on current military spending on new aircraft/ships/etc they could afford this construction 10 times over.
[I can picture a world without war, without hate. I can picture us attacking that world, because they'd never expect it]
If it falls, blame it on an oil-rich nation and invade. Duh.
NASA already is funding this kind of research. They have already invested $600,000 into Seattle-based company High Lift Systems, according to a BBC article.
Sounds to me the right thing to do -- invest in other companies to do the ground work, and see if it really is viable. If not they go bust -- Oh well. If it goes well, then great!
they plan on anchoring it off the coast of australia (or apparently thats a good spot for it) (i dont know why)
and also apparently due to the forces acting on it if it did "fall" or break it would go flying off into space instead of collapsing on earth
keep in mind how fast the earth is spinning! if you spin a basketball with a straw attached to it and the straw gets unstuck from the basketball...where will the straw go? It sure wont collapse onto the ball.
[I can picture a world without war, without hate. I can picture us attacking that world, because they'd never expect it]
The good reason to reach for this which can't be emphasized enough in the current environment is that for a relatively modest investment, the impact on the economy would be enormous (and good). Compared to other proposals to jumpstart the economy, this one has incredible bang for the buck.
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!
I totally believe that Space Elevators are feasible in the near term. However, my concern is with whether we should. Is there a compelling enough reason that outweighs the risks involved to actually go and build one of these?
What risks you may ask?
Well, sure, shuttles are quite expensive to launch and are not flawless by any means. But what was lost recently? 7 lives, a bit of research and a relatively moderate chunk of change.
Ever thought about the effect of a disaster with one of these elevators? Use your imagination. Now remember that you have to use your imagination to even allow the concept of these being built so you can't just write off the possible effects of a catastrophe just because it's unlikely or far fetched...the whole idea is so if the idea becomes reality, well, likely so do many of the possible disasters that could come along with it.
Ever heard of the plan to build a dam across the mouth of James Bay, separating it from Hudson's bay? It was fully engineered and can be done...thank GOD nobody with more cash than sense has decided to back this idea.
Neato factor just doesn't cut it for me, I need real reasons that outweight the risks.
No Comment.
Okay, okay, you're saying, that's obvious. However we could look at another scenario to see how such things are possible:
Say we're sitting in 1983 or so, and we're saying, boy, it would be nice if all universities could have supercomputers and massive 10GB storage arrays to do computational exercises. Looking back 20 years, we know that's basically possible. The desktops of today were the supercomputers of yesterday.
So, let's figure out how to spread the cost. How can we incorporate carbon nanotubes into equipment that everyone needs/wants to use? Does it mean integrating it into automotive equipment? Consumer electronics? Clothing? What?
What would be the killer business/consumer application for carbon nanotubes?
If we assume that cost is a function of production size and research money, the best way to up both is to provide a market that's not pie-in-the-sky (forgive the pun). We can have cheap nanotubes in 10 years, but it seems that the best way to do that is to make nanotubes common everywhere, not by utilitizing the NASA budget (which is going to be under heavy scrutiny after the latest disaster).
-- Bird in the Bush: The Renewable Energy Blog http://www.birdinthebush.org
One can't help but be reminded of the biblical Tower of Babel (a proposed tower that would reach heaven) -- you'll remember that God put the ax to that project by mixing up the languages spoken by the various participants.
:)
Now, if NASA is involved, will the mixup be metric versus imperial measurement?
who's moderating the meta-moderators?
But couple of issues.
50,000 miles is a long way for a mechanical crawler. Escpecially one that amounts to a 20 tonne capacity elevator and it could never exert more than the load limit in terms of force.. IE if 20 tonnes is the theoretical maximum for the 130 rated nano tubes then lifting 20 tonnes at say a 9.8 mps (1G) acceleration would be roughly 40 tonnes of force on the cable meaning a broken cable. Thus you would likely be lifting 18 tonnes and having low acceleration loads, you also could not exceed that load when decelerating. Hitting the gas or breaks to hard could lead to exceeding the cables strength. I am wondering if a lighter system with more leeway to zip up and down the cable would not allow for easier and more timely transfer of mass.
for example:
If you can accelerate/decelerate at 1g with a 20 tonne vehicle (40 tonnes of force ) then you can accelerate at 4g's with a 10 tonne vehicle ( also 40 tonnes of force ). This means you can go ~4 times as fast which is a very significant difference when dealing with long transit distances. So a 20 day round trip by the 20 tonne could be accopmlished in 5 days by the ten tonne and would allow for 4 trips in the same time. Even if the 10 tonne only had 30% of the cargo capactiy it lifts more in the same amount of time over the long haul. You get that benifit whatever the units of acceleation are be it G or more likely in fractional G acceleration loads. And the smaller the rates we are dealing with the larger the impact is of relatively small increases.
Don't get me wrong, the idea is great but the margin of error here sounds awfully thin esepcially considering the key material hasn't reached its theoretical proving point in a LAB much less in a mass production environment. Once they do that I say full steam ahead. But until then its a bit premature to start tossing out headlines reading "Space elevator for just 6 billion "
perhaps if it read
"Space elevator for just 6 billion IF IF IF IF IF IF IF IF IF"
I don't ask you to be me. I only ask you not expect me to be you.