Posted on 06/25/2004 2:21:35 PM PDT by Junior
WASHINGTON - President Bush (news - web sites) wants to return to the moon and put a man on Mars. But scientist Bradley C. Edwards has an idea that's really out of this world: an elevator that climbs 62,000 miles into space.
Edwards thinks an initial version could be operating in 15 years, a year earlier than Bush's 2020 timetable for a return to the moon. He pegs the cost at $10 billion, a pittance compared with other space endeavors.
"It's not new physics — nothing new has to be discovered, nothing new has to be invented from scratch," he says. "If there are delays in budget or delays in whatever, it could stretch, but 15 years is a realistic estimate for when we could have one up."
Edwards is not just some guy with an idea. He's head of the space elevator project at the Institute for Scientific Research in Fairmont, W.Va. NASA (news - web sites) already has given it more than $500,000 to study the idea, and Congress has earmarked $2.5 million more.
"A lot of people at NASA are excited about the idea," said Robert Casanova, director of the NASA Institute of Advanced Concepts in Atlanta.
Edwards believes a space elevator offers a cheaper, safer form of space travel that eventually could be used to carry explorers to the planets.
Edwards' elevator would climb on a cable made of nanotubes — tiny bundles of carbon atoms many times stronger than steel. The cable would be about three feet wide and thinner than a piece of paper, but capable of supporting a payload up to 13 tons.
The cable would be attached to a platform on the equator, off the Pacific coast of South America where winds are calm, weather is good and commercial airplane flights are few. The platform would be mobile so the cable could be moved to get out of the path of orbiting satellites.
David Brin, a science-fiction writer who formerly taught physics at San Diego State University, believes the concept is solid but doubts such an elevator could be operating by 2019.
"I have no doubt that our great-grandchildren will routinely use space elevators," he said. "But it will take another generation to gather the technologies needed."
Edwards' institute is holding a third annual conference on space elevators in Washington starting Monday. A keynote speaker at the three-day meeting will be John Mankins, NASA's manager of human and robotics technology. Organizers say it will discuss technical challenges and solutions and the economic feasibility of the elevator proposal.
The space elevator is not a new idea. A Russian scientist, Konstantin Tsiolkovsky, envisioned it a century ago. And Arthur C. Clarke's novel "The Foundations of Paradise," published in 1979, talks of a space elevator 24,000 miles high, and permanent colonies on the moon, Mercury and Mars.
The difference now, Edwards said, is "we have a material that we can use to actually build it."
He envisions launching sections of cable into space on rockets. A "climber" — his version of an elevator car — would then be attached to the cable and used to add more lengths of cable until eventually it stretches down to the Earth. A counterweight would be attached to the end in space.
Edwards likens the design to "spinning a ball on a string around your head." The string is the cable and the ball on the end is a counterweight. The Earth's rotation would keep the cable taut.
The elevator would be powered by photo cells that convert light into electricity. A laser attached to the platform could be aimed at the elevator to deliver the light, Edwards said.
Edwards said he probably needs about two more years of development on the carbon nanotubes to obtain the strength needed. After that, he believes work on the project can begin.
"The major obstacle is probably just politics or funding and those two are the same thing," he said. "The technical, I don't think that's really an issue anymore."
That's my biggest question. But when I think of the mass of the thread, half of which is extending above the orbiting center of gravity, even a strong wind at the bottom might be analogous to trying to turn a supertanker around by squiring the bow with a water hose. It's all in the numbers.
That's the height where you could just step out the door and hover right there because you would be naturally moving at the orbital speed for that altitude. But if you keep going up you would reach a point where if you let go of the handrail you would have escape velocity and would leave earth's gravity well.
They were talking about making the base 50 kilometers high. If it is a solid structure, it would be the only part of the elevator inside the atmosphere. Would wind affect the base? Like the wind affects pyramids and mountains. A little erosion noticeable after 1000 years. Would they even feel a vibration up in the cable?
Wow, I wish I hadn't missed this conversation.
Man, there's been some incredible process in this field since I heard about it 9 months ago! 20 cm CNTs!!! Thats incredible!! I thought they were still measured in microns! I heard that they theoretically only needed to have 2-3 cm lengths in order to be able to put the tubes in some kind of glue and still have the strength. Although continous strands are ideal. And we may indeed get them.
And just recently I read about tapered ones that can be built pretty far away from the equator. Thats great! That alleviates most of the political problems with building it near the galapagos. So where exactly do we want it then? I guess a rather poetic place would be cape canaveral, although it might be possible to put it anywhere in the contiguous 48. I guess you get bonus points in the atmosphere if you do it at a higher altitude.
Does anybody know why they want a 50km base tower? That seems unnecessary to me. You might as well just build it on the ground.
I don't see any kind of weather as a problem since you are going to want a pretty high tension even at the base. (I never did understand those pictures of it being moored at some kind of flimsy movable oil rig looking thing. I figure the base itself is going to be one serious piece of civil engineering.) And the atmosphere is only like 62 miles thick if you go by the "astronaut" definition. So its not a significant length of the cable. Does anybody know about the answer to the question of it shorting out the atmosphere?
Regarding satellites and space debris, people talk about oscillating it to avoid the big stuff, but that implies some active rocketry, which means big tanks somewhere along it. I think having 3 or 4 seperate strands would be useful for redundancy (although they would vary in distance as they get farther from earth I guess). But Rightwhale has a point that most stuff is just going to make little spots when it hits.
Also, how do cars pass each other going up and down? Changeover stations? The best way would to have an up path and a down path, if possible.
One last thing, I think it would probably be good to only send people out on the elevator beyond the geosynchronous point in very important situations. You don't want to have a space station with thousands of people on it that will go sailing off to the heliopause if somebody snaps the cable high up on it. Restrict elevator usage beyond that point to non-manned use for slingshots. Also you want to rig all the cars with your classic capsular lifeboats. Hm, and maybe also some explosive charges along the length so that you can get all of the pieces to fall in a small area if it snaps, instead of wrapping around like red mars (although it would be more like newspaper falling in our case) Also, you want to have an explosive set just above the geosynchronous station, or whatever, so that if somebody breaks it right before the station, it won't go sailing to the heliopause with the anchor.
I just saw a thing on the space elevator on headline news! It was great! Of course, we freepers aren't supposed to like headline news. So just pretend it was on fox. Or something.
I don't know if this thing can or can't be built, but if there is a shot at it I think a lot of science could be learned by trying. Some more long tether experiments in orbit ought to be done soon. Supposedly this elevator construction would begin in orbit by unreeling the first segments toward the ground and toward the deep space anchor point and then adding segments until it reaches the ground and the deep anchor.
It is totally doable with blimps spaced every mile in elevation so that if one link fails the next link is secured. Blimp Cable Blimp Cable Blimp Cable Blimp Cable Blimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp CableBlimp Cable
Would the elevator actually conduct current, or is the voltage there for other reasons and current won't come down no matter what.
Perhaps something horizontal could be tried first; a Los Angeles to Hawaii bridge maybe.
FIJAGH!
If we can erect a building so tall that it reaches the edge of space, we hardly need an "elevator" to go much higher. A catapult on the roof would suffice for getting a payload into orbit.
I'd think it would be constanly sinking an awful lot of DC to ground. The advantage would probably be an absence of lightning for a large circle surrounding the tower.
Yes, the analogy they use is to suspension bridges. First you shoot a string across your chasm, then you pull climbers with successively larger strings across it, until you get a size you like, and keep it.
The first strand would probably be on the scale of microns in diameter. you'd need to have some good skills in winding up string, Super bright LEDs and micro-sized radar, so that you can find your little micron strand floating to the ground. I think you could launch it on a single heavy lift rocket.
Hm, I didn't think about letting a string out upwardly for the anchor. You'd probably need the anchor to be reeled outward from your geosynch station. You might have a second launch with the anchor and far out string attached that docks with the string going back to earth. You can let out the anchor slowly as you get more laser powered climbers coming up from the ground, so that you keep its cg slightly past geo.
Hm, if we do a non-equatorial elevator, then the tapered ribbon is going to be flung down toward the equator asymptotically. The geosynch station would probably make a bump down in the shape with its increased mass. Anyway, the point is that the geosynch station wouldn't really be above the equator. Which means if you don't allow people out beyond the geosynch point, as I suggest, then you are going to be launching people out of a wierd orbit the aren't you?
That is where the distinction between geosynch and geostationary comes in handy. An elevator anchored off the equatorial plane would settle down to a kind of asymptotic line once it is built.
Yes, but if the main station is at the geosynchronous point and pretty much all manned flights get off the elevator here, then you are actually only about 40% of the way up the length of the elevator. So lets say you build it at 30 degrees north latitude (as I understand, that would be doable on earth) then at 40% down, with a concave curve, you're over about 5 degrees north latitude. I'm getting all this from sketching out a model to scale.
So, if your elevator ride ends at the geosynchronous station, then you're orbit is going to have a declination of 5 degrees right?
Does anybody know what the exact theoretical maximum latitude on earth a tapered space elevator could be built at?
I remember somebody asked something about whether CNTs conducted electricity or not. Depending on the chirality (the angle at which the graphene was rolled up) it can be semi-conductive, or really conductive, it can also be superconductive at low temperatures. But I have no idea how it would conduct as an actual ribbon. One good thing is that it will burn up at like 3000K I believe. So if it ever starts to short out the atmosphere, it would burn up before it destroyed the world's weather.
No one will get off at geosynch altitude. The point is to achieve escape velocity, which would require travelling out far enough to where you can just let go and will have the energy leave earth's gravity well immediately.
check this out: http://www.mit.edu/people/gassend/spaceelevator/non-equatorial/
note that the picture in his drawing assumes no counterweight, so the thing just stretches way out there. Hm, one advantage of not doing any counterweight at all is that you get a longer string and don't have to rocket up any mass to serve as a counterweight. If you timed it right, and didn't mind taking the elevator car with you, you could just maglev right off the end of the thing and put your self in a hohmann transfer orbit couldn't you?
The entire elevator in his basic non-equatorial elevator remains north of the equator, and is held there by tension on the base station.
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