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Space Elevator Prototype Climbs MIT Building
Posted by
timothy
on Tue Nov 16, 2004 11:41 PM
from the no-place-for-lecter-to-hide dept.
from the no-place-for-lecter-to-hide dept.
Jackie O writes "According to an employee blog on the Liftport Group website, their prototype robot for the Space Elevator has just successfully climbed a 260-foot building (in a driving snowstorm, no less) at MIT. Now all they have to get it to do is climb over 60 thousand miles into space, carrying things. Good luck there." Update: 11/17 05:17 GMT by T : Liftport has posted some photos from the ascent, too. Thanks!
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Oh great, (Score:5, Funny)
how many smoots in a green building? (Score:4, Funny)
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Re:how many smoots in a green building? (Score:5, Informative)
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Re:Oh great, (Score:5, Funny)
1 foot = 0.00344 MIT Green Buildings (MITGB's)
One Mile = 18.2 MITGB's
1 kilometer = 11.3 MITGB's
Space Shuttle orbit = 3,186 MITGB's
Space Elevator Tether Point = 1,092,400 MITGB's
Looks like they've got a little bit of scaling up to do.
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When? (Score:5, Insightful)
Re:When? (Score:5, Funny)
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Re:Maybe not a good idea? (Score:5, Informative)
An EXTREMELY strong tether is fixed to a large mass far out in orbit, this mass along with the earth's rotation hold the tether very taut and allows for smaller masses to scale up it. Much like if you tied a small weight to a string and whirled it around your head, imagine a small robot climbing the string...thats the idea of a space elevator.
The issue with the idea of a space elevator currently is the technology that would go into the tether. It is believed that many strands of carbon nano tubes, those tiny super strong tubes grown/created long and attached together, would be able to withstand the stress.
Next the tether would not be round like a rope, but flat like a belt. Being flat, it would be much harder to get twisted if sufficient force is applied to each end, pulling the ends apart.
So that is the general idea the theory behind space elevators...I am sure I left some details out and all, but here is a decent link if you want to learn more. http://www.space.com/businesstechnology/technolog
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Good technical summary (Score:5, Informative)
I did a lot of calculations about this a few years back; here are some results that might interest you. Here's the apparent strength of gravity as you go up the elevator, allowing for both the earth's rotation and the 1/r field:
Apparent gravity table 0km 9.8m/s
350km 9.0m/s
700km 8.0m/s
1200km 7.0m/s
1750km 6.0m/s
2500km 5.0m/s
3400km 4.0m/s
7500km 2.0m/s
10500km 1.0m/s
18500km 0.5m/s
Weightlessness comes at the Clarke point, of course, 35950 km up. Above that, there is a centrifugal effect, and the earth appears to be 'above' you---but you would have to be nearly 200,000 km up before the apparent gravity reaches -1.0 m/s. In practice, no one would build it out that far; you just want to go far enough to keep the center of gravity at the Clarke point, plus a bit more to put the lower end of the elevator in tension. A big mass just slightly above synchronous orbit is probably the way to go.
Midway Station, the lowest point where you go into an elliptical orbit instead of hitting the ground if you jump off, is 23450 km up, and has a tiny apparent gravity of 0.29 m/s. The total energy cost from ground to the Clarke point is just over 13 kW-hr per kg lifted, which means $100 a ticket at today's energy prices, minus savings for energy generated by the 'down' cars, plus (rather large) financing charges on the capital investment.
Next come strength-of-materials considerations. We need a material with the highest possible (breaking strength)/(density), which is a tough sell, because Kevlar, good piano wire, and nearly everything else has essentially the same optimum value for this parameter. They all have breaking strengths of a 'few' billion Pa, and a density of a 'few' thousand kg/m, where 'few' is the same number in both cases. The strongest high-tensile materials are the heaviest, by and large. Exotic materials like spun sapphire or diamond do better on the micron scale, and buckytubes get close to the theoretical limit (the strength of the chemical bonds themselves). In principle, such materials should be anywhere from 40 to 120 times stronger than the optimal value above, which I shall call '1x piano wire'. But Griffith theory teaches us that the length of the 'critical' crack (one that releases enough energy to drive its own spontaneous propagation) goes down as 1/(stress). So even if exotic materials can be machined in gigaton lots, we may find that they are unusable at the huge stresses we need. The first woodpecker that comes along may bring the whole thing down if the critical crack is a few microns long.
But let's assume we can cope with this issue, if necessary with nanobot inspectors checking for micro-cracks, or simply a sheath of unstressed material around the structural members. The tension is essentially zero at the bottom: if we wanted we could leave the cable hanging loose a foot from the ground. (We want some tension there, of course, when we build an actual elevator, or the dynamic oscillations will kill us.) At the Clarke point, where the stress is largest, the stress depends on the weight of the tower below, which depends on the strength of the material. It's like rocketry, ironically enough: the 'fuel' for the upper stages is 'payload' cost for the lower ones. In this case, of course, it's upside-down: we have to keep the lower part of the tower as light as we dare, so that the upper part doesn't have to be exponentially heavy. And a high-tensile steel tower, like a rocket powered by Wisconsin butter (happy now, Senator Proxmire?), just doesn't have enough juice.
Assuming each wire has to take a thousand tonnes of tension at the bottom (add wires as needed, depending on what you want to send up the tower...), we get a minimum thickness profile like this:
Minimum thickness table Strength/Density 5000km 10000km Midway Clarke Orbit
6 x piano wire r = 16cm
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The real purpose (Score:5, Funny)
more useful blog link... (Score:5, Informative)
Blog entry (Score:4, Informative)
Woohoo! I have to say that the creator of our robotic lifter, David Shoemaker, rocks! The latest incarnation of the lifter faced what was probably its most difficult challenge to date: climb MIT's 290-foot-tall Green building in the middle of driving snow. And the robot succeeded marvelously, despite some problems!
The morning started off cool, but with temperatures dropping. Blaise Gassend and I brought everything for the rooftop anchor station up to the roof and got it assembled. There was a bit of ice rain that started falling (and melting once it landed), but it wasn't too bad. Once the anchor station was assembled, we headed back inside to finish prepping the ribbon and to work on insulating the lifter's battery. When we went back outside, the weather had changed - it was now a very serious snow storm! I decided that we could go ahead with the lifter test, since the wind wasn't too bad, and I thought that snow was at least better than rain.
We had planned on attaching a safety line to the robot to catch it in case the ribbon broke (which we weren't expecting, but we wanted to be extra cautious). Unfortunately, the safety line was a last minuted addition that did not get tested in advance, and of course it was the thing that broke. Partway up the ribbon, the string that was hooked to the safety rope got tangled in the axle of the lifter, and the rope itself was separated from the string. So our safety line turned out to be more of a detriment than a help! And due to the wind, the ribbon got twisted around perhaps 10 whole revolutions, which also slowed the lifter's ascent. But the lifter kept going, and even though it was slower than normal, it made it all the way up to the roof level, reversed course and headed back down (halfway up, the twist in the ribbon unwound itself).
I want to thank Blaise Gassend for his great help in setting things up and preparing part of the ribbon. Look for pictures and perhaps video to be online within the next few days, and perhaps a more detailed description of the event.!
Space elevator practicalities (Score:5, Funny)
As cool as this idea is, there are some problems (especially for the lower altitudes). Some of the problems are more serious than others:
Wind shear: winds at various altitudes can differ widely. Both the cable and anything climbing it will be affected.
Resonance: a cable will tend to vibrate; it will be necessary to dampen the vibration. Usually this is done with strategically placed weights. With an object climbing the cable, however, the resonance will be constantly changing.
No Adspace: There will be no place to put banner ads, so the thing will never be profitable [slashdot.org].
Environmentally Harmful: birds could run into it and die. Doesn't anyone consider birds?
Re:Space elevator practicalities (Score:4, Interesting)
In the Mars series, these points are largely addressed. Wind shear and resonance are handled by thrusters placed every so often along the cable, managed by a supercomputer. Adspace isn't needed - the thing pays for itself because it's a transport mechanism. Mars has no birds.
In addition, he also brings up the issue of terrorism (those same locations that have thrusters also have anti-missile defenses), and the massive destruction the entire thing causes when it comes down, after they break off the counterweight asteroid it's using.
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Re:Space elevator practicalities (Score:5, Funny)
Again with the birds! Birds will fly into just about anything over 5 feet tall - it's called "natural selection".
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Re:Space elevator practicalities (Score:5, Funny)
I consider them to be evil feather-covered lizards. Does that count?
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Re:Space elevator practicalities (Score:5, Funny)
- Terrorism: A space elevator is vulnerable to terrorism at every part of its length. A terrorist can target any section of the elevator, but we have to defend all of it. That's not a winning stragegy -- we have to take the fight to them.
So screw colonizing Mars, we need to occupy it now or the terrorists will win.Parent
stop laughing - prototype - ... (Score:5, Interesting)
I can't help but think about all the political hurdles that'll delay the space elevator more than any technical setbacks. And then I get to thinking about how slow and unromantic a space elevator ascent would be compared to the exciting phallic-rocket launch. Still, the space elevator is about the only way to eventually get launch costs below a dollar per pound; chemical rockets are too energy-wasteful to ever reach that point.
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Re:stop laughing - prototype - ... (Score:5, Funny)
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What's the point exactly? (Score:4, Insightful)
Just a question from a Norwegian (Score:5, Funny)
Or does it mean that it was fairly windy, snowing abit and it totalling a couple of centimeters on the ground and people who had watched to many catastroph-movies lately bandied about in Libraries burning books and being faintly surprised about how little warmth it produced?
I don't see this as very eventful or important. (Score:5, Insightful)
If I claimed that I can jump to the Moon, you'd look at me like I was crazy, because the laws of physics would be completely in opposition to my claim (for example bones would shatter long before you could exert the force to jump even 50 feet). Now if I showed you that I could jump 3 feet, would that really convince you that I'm making progress towards my claim of jumping to the Moon?
To get back to this space elevator idea, climbing 260 feet is no big deal at all using cables that we have today. It's simple work. However, making a cable that is 30,000+ miles and able to support its own weight plus the weight of the payload is impossible with these cables. They'd need a material that doesn't yet exist.
The real hurdle in this project is not making the robot climb the short conventional cables that are readily available, the real hurdle is getting a hold of cables of unbelievable strength made of a substance that doesn't yet exist.
Re:That wouldn't work. (Score:5, Insightful)
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Background Info (Score:5, Informative)
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Re:Thats nice but... (Score:4, Informative)
Google calculator link... [google.com]
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Way too long. (Score:5, Funny)
316,800,000 feet / 29 feet per minute = 20.77 years
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