Slashdot Mirror
Thoughts on the Space Elevator
Keith Curtis writes to tell us that Glenn Reynolds, of Instapundit fame, has posted his thoughts on why NASA should be building a space elevator instead or their current plans. Keith has also posted his throughts from an engineer's perspective (although admittadly still not a rocket scientist). "The challenges are many, but it has been a viable option since carbon nanotubes, structures so strong that one the width of a human hair could lift a car, were invented. A space elevator could be between 10 and 2000 times cheaper than conventional technology and will force NASA to change just about everything they do. Hopefully one day that bureaucracy will wake up and realize it."
Sigh. Ya know, we could build a structure to space with todays (hell, 20+ year old) technology if we wanted. The Launch Loop concept was published 20 years ago and is viable today. It costs less than a space elevator is predicted to cost and, unlike the space elevator, can be built from the ground up instead of from orbit down. So yeah, please stop saying stuff like: once we have strong carbon nanotube fibres we'll have a space elevator two weeks later. It doesn't work like that. The majority of studies that remain to be done to make the Launch Loop a reality are much the same as the many studies that still need to be done to make the space elevator a reality. Someone has got to finance those studies and unless you can get PhD students to do it on government funding that means you've got to pour money into a hole that might never fill up.
How we know is more important than what we know.
The August issue of IEEE Spectrum also had a story about the space elevator. This article is available online here. Not knowing much about the space elevator, I found this article very informative.
"But, I don't remember ever hearing that we actually have the technology to produce enough carbon nanotube material to actually build a prototype device of some sort let alone a cable spanning to LEO."
A space elevator must extend to geosynchronous orbit, 36000 km up.
I rarely criticize things I don't care about.
The LiftPort Group of companies working towards a space-elevator are making a great deal of progress. Slashdot reported on the faa approval of their high altitude tests, for example. See here and here for more LiftPort specific information. Check here and here here for several reports concerning the viability of the elevator -- be sure to check the NIAC pdf. Blaise Gassend has a great collection of information. Finally, though carbon nanotubes are still in their infancy (its been a little around ten years since they were discovered) - their theoretical tensile strengths are perfect for application in a space elevator construction. This recent development spells a rosy future, and many innovations yet to come.
http://en.wikipedia.org/wiki/Pixie_dust
It already exists. Just not for what you are thinking about using it for. IBM owns the patent on Pixie Dust. Although I can't see that they care about it anymore now that they sold thier hard drive division.
It's not that easy, the space elevator is supposed to work because it has (will have) a counterweight on geosynchronous orbit that keeps the elevator in place. The space elevator is more like a string tied to a balloon than a wooden stick.
A space elevator will be made of carbon fiber nanotubes correct?? What would be the effect on a hurricane hitting the elevator? Can the string be realed in from one end?? Would it be more prudent to build this in a place far away from a coastline??
negliable if built correctly. The local winds wouldn't have enough kinetic force to move the cable much.
"There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy."
Liftport is testing weak ribbons. The sort of ribbons they want simply do not exist. It's unobtanium.
I don't know why I have to post this information on each space elevator thread (you'd think people would have gotten it down by now), but here we go again. The strongest measured SWNTs thusfar are just over 60GPa; most were lower. Most space elevator designs call for >100GPa; probably the cheapest and most thought out plan, by Dr. Bradley Edwards (of Liftport fame), calls for >120 GPa.
It gets worse. That's the strength for individual tubes. Bundles are 100GPa ribbon come true.
If you need links, I'll gladly provide them; I just don't want to have to post this every few days. We don't have a space-elevator cable material, and won't any time to, so everyone who says that we should just build a space elevator instead of a new launch vehicle might as well be clamoring for pixie dust.
Also, I can kill you with my brain.
Liftport is testing weak ribbons. The sort of ribbons they want simply do not exist. It's unobtanium.
If you read our literature (blog, press release, articles - heck you can write and ask) you'd discover we're not testing ribbons at all.
What we are doing is testing lifter technology. Sending a bot up and down in a reliable fashion is one of those easy-until-you-really-think-about-it deals. A whole lotta picky engineering needs to be ironed out to make those work in a reliable fashion.
Display some adaptability.
Actually, the design for one of the ribbons was so thin and wide that the wind resistance alone meant that it fell at about the speed of a cardboard box.
See http://www.elevator2010.org/site/primer.html and http://www.liftport.com/faq2.php#science2 for starters, Google for more.
What really makes sense is an infrastructure that makes getting people and payloads in particular to and from space cheap and reliable, even ordinary. The only chance for that right now is a space elevator.
You have a 3% chance of death flying on a space shuttle. That's an incredibly poor record, and incredibly expensive.
Lose Weight and Feel Great with Isagenix
Hmm, I wonder what happened to my post. It's like my second paragraph is all messed up (and my other paragraphs missing). It was supposed to read something like:
It gets worse. That's the strength for individual tubes. Bundles are around 20GPa currently. They're limited by VdW and pi bonding. It gets worse still, however, because the best bulk fabric isn't as good as individual bundles, and are only (5-10) GPa. And even that's not ready for mass manufacture. Notice how many orders of magnitude this is off from what is needed.
Can it be improved? Yes, but not that much. Individual tubes can be made more consistant, and potentially have higher tensile strength (although probably not the earlier theoretical predictions) by tube type selection and refined production methods, but there clearly are major limits on this, and even those things will likely take decades of research before we can approach what their limits are.
Bundles can be improved by longer tubes, but again, they're not going to be stronger than the tubes themselves - only weaker. Getting long tubes (which will strengthen how tightly the tubes end up adhering to each other overall) in a mass-producable method is not going well. The way tubes today are assembled, be it CVD, electric arc, etc, is that the tube is extruded from a gathering sphere of condensing carbon, and it seems to be limited in its capability to grow. Short tubes can be merged, but that makes getting good tensile strength even harder. Instead of the problematic method of using long tubes to maintain bundle strength, you can do pressure-induced intertube bonding (trade sp2 bonds for sp3), but that'll weaken your tube tensile strengths.
In short, both problems, incredibly difficult or even potentially intractable by themselves, help defeat each other. Even with the best of luck and most dilligent research programs, with current tube-strength measurements there's not much hope for a realistic strength fiber any time in the forseable future, if it is even physically possible at all.
Also, I can kill you with my brain.
Since the Moon rotates only once every 29 days or so, the cable would need to be so long that it would hit the Earth, in theory.
Also, in any location other than directly toward Earth or directly opposed to Earth (on the far side of the Moon), Earth's gravity would distort the elevator.
There is a way to place a space elevator on the near side of the Moon, by using the Earth's gravity to counterweight the "top" of the cable, rather than using centrifugal force.
This type of elevator has several advantages:
- It is much shorter than it would otherwise need to be, meaning it uses much less material in its construction, and the material does not need to be as strong as for a longer, non-Earth's-gravity-counterweighted cable.
- The cable goes through L1, one of the Earth-Moon Lagrange points, which is a node on the Interplanetary Superhighway.
- Material mined on the Moon can be lifted "up" the elevator, through the Earth-Moon Lagrange point, then lifted "down" the cable toward the Earth, and deposited directly into Earth orbit.
This last advantage is particularly, uh, advantageous, because such orbits are highly elliptical, and could even intersect the Earth or its atmosphere, which would allow material (e.g., the He3 that you mentioned) to be shipped from the Moon to the Earth without using any rockets at all!The only parts of the Moon that are in constant sunlight are perhaps a very few locations at the poles, which are useless vis a vis a Lunar Space Elevator (although this article proposes a non-vertical Lunar Space Elevator terminating at the Lunar South Pole that could be used to lift water (believed to be located there) into Earth orbit).(Note, however, that it's still longer than the Earth's Space Elevator.)
In fact, such an elevator's cable could be made out of Kevlar!
Search Google for more info.
Those who sacrifice security to condemn liberty deserve to repeat history or something. - Benjamin Santayana