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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Previous Space Elevator Coverage (Score:5, Informative)
Previous Articles:
Space Elevators: Low Cost Ticket to GEO? [slashdot.org]
More on Space Elevators [slashdot.org]
Going Up? [slashdot.org]
Calling the Space Elevator [slashdot.org]
Space Elevator May Become Reality [slashdot.org] - The Linked Study(PDF) [usra.edu] Was fascinating.
Space Elevator Could Cost Less Than You Thought [slashdot.org]
Stepping Closer To The Space Elevator [slashdot.org]
I want to walk into an elevator some day and see two buttons - "G" and "O". (Ground and Orbit)
NASA *is* funding this already (Score:5, Informative)
NASA already is funding this kind of research. They have already invested $600,000 into Seattle-based company High Lift Systems [highliftsystems.com], according to a BBC article. [bbc.co.uk]
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!
Re:dangerous?? (Score:5, Informative)
I seem to recall that the base of these things would be on large platforms anchored in the middle of the ocean, so if they did collapse, they would just fall harmlessly over water.
Re:why not construct this (Score:2, Informative)
Well, to put it simply, he's not a complete and utter moron! Please, don't compare this space elevator lunacy with JFK. JFK proposed a difficult but doable task that was definitely within the nations technical capability. The space elevator is only feesible in the minds of those who have read TOO MUCH Heinlein.
Read Kim Stanley Robinson (Score:2, Informative)
Space elevators are part of the story, and the sabotage of a space elevator on Mars results in catastrophe. I recall that the sabotage involved the cable being detached from the space station end. The space station flew off into space, and the cable fell back to ground, wrapping itself around the planet's equator.
Re:dangerous?? (Score:5, Informative)
http://www.highliftsystems.com/convertedToHTML/
Re:dangerous?? (Score:3, Informative)
More links to NASA's space elevator project (Score:3, Informative)
Re:why not construct this (Score:2, Informative)
This was *not* a unique and uninformed view, rather it was typical of large swathes of the scientific establishment. Don't fall into that trap. Remember, when an eminent scientist says something is possible, (s)he's almost always right. When this same person says something is impossible, (s)he's almost always wrong.
Re:Weight of the elevator? (Score:3, Informative)
This is also why a break on the planetside isn't the disaster most people think it would be; the part below the break falls to the earth, probably at not too great a speed, and the part above the break floats out into space.
A break above the satellite is worse, but there are ways of helping that too. One interesting, albiet possibly controversial idea, and bear in mind I'm just thinking of this right now, is to deliberately set up explosives/chemicals to cut the elevator at certain intervals, so if a break does occur, you cut an equivalent amount of the cable off the other end so the body of the cable and the satellite are still salvagable.
Also, since you can lift so much, any manned vehicle can be made safe as long as the explosion doesn't occur onboard (obviously); there's enough weight available to make a vehicle that can land safely on the Earth. (Look at the pods for the Apollo missions; it doesn't take too much to splash-down safely, compared to what it takes to get that high in the first place.)
Re:Climbers - problem (Score:3, Informative)
So the first climber will take up a single strand to the top(or some such), doubling the capability of the cable. The next climber will take two strands up - doubling it again. And so on.
The study also has "sample" designs of a climber in it.
Re:why not construct this (Score:3, Informative)
Heinlein had space elevators?
**Thinks**
Tunnel in the Sky : Transdimensional Gates
Rocket Ship Galileo : Rockets
Methuselah's Children : Rockets (I believe)
Red Planet : Rockets
Between Planets : Rockets
Rolling Stones : Rockets
Star Beast : Spaceships (I believe)
Citizen of the Galaxy : Spaceships
Moon is a Harsh Mistress : Magnetic Powered "Slings"
Friday : Spaceships
Orphans of the Sky : Spaceships
Podkayne of Mars : Rockets
Starman Jones : Spaceships and Rockets
Starship Troopers : Rockets and Spaceships
A note on the classification. I call anything that is propelled by throwing a mass backwards a "rocket", while any ship capable of intersteller transport that doesn't have its propulsion system explained is a "starship". And yes, this is all from memory (other then the book titles, which I googled for), so I have probably screwed up a few. Specifics that I remember include "the Rolling Stones", which was atomic rockets, "Friday" which was starships powered by a device developed by a lone inventor in his basement, and "Moon is a Harsh Mistress", which had magnetic "slings", to lift orbital material into space (it also probably had rockets, but I don't remember.) Some of Heinlein's later works *might* have had space elevators, but he seems to be a fan mostly of atomic rockets.
Clarke used the space elevator in "The Fountains of Paradise", as well as "3001". I believe someone said that Ben Bova used space elevators in the "Mars" series. In the first Uplift Trilogy book, humans had created space elevators, which were made obsolete by the arrival of the Galactics - but still impressed them anyways (David Brin). A few other later authors had used the idea as well. IIRC, a Russian scientist proposed the idea first, under the name of "Sky Hook", Clarke picked up the idea for the Fountains of Paradise, which placed it on an island similiar to Sri Lanke, and other SF authors stole the idea from these two.
Damn, just think about the social skills I would have had if I didn't spend my teens reading SF.
Re:dangerous?? (Score:2, Informative)
You see engineers actually design and test things using a fairly detailed methodology.... they rarely say stuff... "I dont really think that can happen cause it doesnt seem to likely"... Thats why we go to school for four years.
Severed Cables
If a cable is severed the lower segment will fall back to Earth while the upper portion floats outward. The worst case would be if the countermass breaks off the far end of the cable and the entire 91,000 km of cable falls back to Earth.
Depending on the location of the break, the epoxy used, the dynamics of the fall, etc. the cable will re-enter the Earth's atmosphere at a velocity sufficient to heat the cable above several hundred degrees Celsius (figure 10.9.1). If the cable is designed properly, the epoxy in the cable composite will disintegrate at this temperature. This means the cable above a certain point will re-enter Earth's atmosphere in small segments or carbon nanotube / epoxy dust. About 3000 kg of 2 square millimeter crosssection cable (20 ton capacity) may fall to Earth intact and east of the anchor. Detailed simulations will be required to determine the possible sizes of segments that will survive and the health risks associated with carbon nanotube and epoxy dust. In terms of the mass of dust and debris that will be deposited, we can compare what will happen to what naturally happens now. Each year 10,000 tons of dust accrete onto Earth from space, the additional 750 tons of the first cable will increase that year's infall by 7.5%. A larger 1000-ton capacity cable would have a mass of 30,000 tons or roughly equivalent to 3 years of normal global dust accretion. Further investigations are required to determine the environmental impact of depositing this much dust along the Earth's equator.
Re:why not construct this (Score:2, Informative)
Are you quite finished masturbing yet?
Maybe you should provide some proof with your claims of having "the most advanced nation in the world with the highest quality of living". You also have more people that are suffering and homeless, and whatnot, than some other countries.
The only thing advanced about the USA is its military.
Re:dangerous?? (Score:2, Informative)
It is the case. I double-checked for my own sanity (though I suspected I was correct), and the moon is moving further away from Earth, though I misreported the rate- its orbit lengthens by 3.8 centimeters a year, not a foot.
What if a big enough asteroid or piece of space junk plowed into it, driving it lower into it's orbit or even into the atmosphere?
This would depend highly on the trajectory of the asteroid or meteroid prior to impact, its mass and velocity, etc. Possible results could include...
Then again, these are just guesses. I'm not a physicist. I'm also not an astronomer, but I seem to recall hearing that most meteroids skid across the atmosphere rather than plunging straight down, which would make the first two cases the bigger likelihoods in my opinion.
Also, when you talk about something "sufficiently large", you could be talking about something REALLY big, too...something we'd have time to look out for. The LEO end of the elevator would have a pretty good "bird's eye view" of the larger objects flying on an intersect course. If things got bad, but we saw them coming, we could save "collapse" of the elevator by just letting go of the ribbon on Earth's end, shooting the LEO end off into space.
Those are just a few crackpot possibilities.
Re:dangerous?? (Score:3, Informative)
If it falls, it breaks up and burns up in the atmosphere, or flies off into space. Wastes a lot of money, but causes no significant danger or environmental damage.
I dont know about you guys, but the whole concept seems flawed from the start. How about maintenance? What if the payload falls? I dont want to live anywhere near this thing...
It only seems flawed because you're not used to it. If you hadn't grown up watching rocket launches, you would think that throwing people into space via the force of huge chemical explosions was a flawed idea too. (it sounds like something Wily Coyote would try, doesn't it?)
Re:dangerous?? (Score:1, Informative)
Different circumstances; that elevator used a metal cable (possible due to the lower gravity), and was falling through an almost nonexistent atmosphere, hence it was able to wrap and do damage. A nanotube ribbon would be designed to break apart in the thick Earth air while descending in case of a ribbon failure.
Re:I would think that this would depend on one thi (Score:3, Informative)
It'd be a meter wide, a few tens of thousands of kilometers long, and a micron thick. That's 10^-6 meters. It probably wouldn't fall so much as flutter.
The idea of a carbon nanotube ribbon space elevator has been on
Link to online version of the book manuscript (Score:3, Informative)
nice analysis !!
Re:Perhaps the book covers it... (Score:3, Informative)
The thing is, all the space elevator concepts I've seen have put the crawler in physical contact with the cable. There are limits on maximum speed imposed by the mechanical strength of all the other components--not just the cable. Realistically, I would expect an acceleration relative to the cable of maybe a tenth of a gee for the first and last three minutes of the trip.
That results in a cruising speed of over six hundred kilometers per hour (better than 400 mph in the United States) and climbs the cable in a little less than four days. If the maximum acceleration were limited to 0.01 g, the acceleration phase would last a full half hour--but the whole trip would be lengthened by only about three percent.
If the vehicle actually were to accelerate (at 0.1 g) for the entire journey, at the halfway point the top speed would be a hellish 25000 km/h--a little hard on your crawler wheels and bearings, even though the trip would only be four hours long.
That said, if the cable had a 20 ton breaking tension (estimated), I probably wouldn't ever put more than a two or three ton load on it. I could jerk a crawler through a five gee mishap and not have to worry. (Actually, one wonders how much the nanotubes can stretch longitudinally before failing. Can we get away with large transient loads that get soaked up by the cable stretching?) For the first few years, I'd want most of the payloads going up to be more nanotubes, leading ultimately to several parallel ribbons--and crawler tracks.