Space Elevator Prototype Climbs MIT Building 422
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!
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.!
Background Info (Score:5, Informative)
Re:Thats nice but... (Score:4, Informative)
Google calculator link... [google.com]
Maybe not a good idea? (Score:3, Informative)
And the fact that a rope and pully would do the same job faster just occured to me.
I don't know if it is even a good idea in theory. Velocity differences and rotations between the two anchoring points would need to be considered. Even if one was going to try to use a geostationary satellite as one end-point, the mass of the object (rope or ribbon,) connecting the satellite to the earth would be significant, and would drag the satellite crashing back down to the earth. If the satellite was on station further out than the geostationary orbit, and the combined center of mass and the rope/ribbon were at the altitude for a geostationary orbit, the stresses involved would be tremendous, especially when the location of the space elevator would vary, causing the center of mass to vary.
Of course, I'm sure those guys at MIT have already done the calculus to figure those things out, and know how much stress would be present.
Re:Should read 60 miles... (Score:3, Informative)
Re:Just a question from a Norwegian (Score:2, Informative)
Re:Should read 60 miles... (Score:4, Informative)
Photos of the robot! also height=290 feet (Score:4, Informative)
Wow, I wasn't expecting my blog post to get /.'d. I was dead tired from the day of the test, and just wanted to get some info online for anyone who was curious. Sorry for not getting more details or photos up sooner.
BTW, the height of the building our robot climbed is 290 feet, not 260. Not a huge difference, but I wanted to correct the error in the original /. post.
After seeing more than a half-dozen comments on my blog post right after being slashdotted tonight, I got real motivated to get the pictures up ASAP. You can now see pictures of the day at http://www.liftport.com/gallery/MITdemo_2004Nov [liftport.com]
Re:Larry Niven (Score:3, Informative)
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
Re:how many smoots in a green building? (Score:5, Informative)
Re:Should read 60 miles... (Score:1, Informative)
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
Getting power to the lifter. (Score:4, Informative)
Sixty THOUSAND miles into space? (Score:3, Informative)
Bruce
Re:how many smoots in a green building? (Score:3, Informative)
Re:Maybe not a good idea? (Score:4, Informative)
[ Snip ignorance about a space elevator... ]
Young grasshopper, time for research, try Wikipedia's article on space elevators [wikipedia.org] for a starting point. The external links (at the bottom) are good for advanced research.
Short answer: There is nothing, as far as we can tell, which makes a space elevator impossible. Current limiting technology appears to be the size and strength of carbon nanotubes we can create.
Re:Good technical summary (Score:2, Informative)
Incase anyone is wondering about the whole gravity thing, heres are quick primer: force of gravity, F = GmM / r^2, where F is in Newtons, G is a constant, m and M (the two masses) are both in kg and r, the distance between the two bodies, is in metres.
When only considering gravity (no other forces), F = ma, where F is the gravitational force between the two bodies (same for both bodies, just in opposite direction), m is mass and a is acceleration measured in m/s^2. When you chuck F = ma into the original equation, you get ma = GmM/r^2 => a = GmM/r^2 / m => a = GM/r^2. (m/m = 1) Hence, the acceleration you experience due to gravity has nothing to do with your own mass, only that of the earth (and your distance from it). Thats why everything on Earth accelerates downward at about 9.817 m/s^2. Often the symbol 'g' is used to for acceleration due to gravity.
Just thought I mention that because simple gravity can be quite interesting
Picture and Liftport Site (Score:3, Informative)
The Liftport site was
Re:Good technical summary (Score:3, Informative)
I don't think this has to be a dealbreaker. If carbon nanotubes are used, their natural structural unit--one tube--is a nanometer or so in diameter. It takes thousands of strands to get a structure that's anywhere near a micron in size. Bundle those together every so often to prevent propagation of a failure up and down (think ripstop nylon) and voila. They key problem these days is in reliably synthesizing significant lengths of nanotube consistently and reliably. (Not to minimize all the other engineering difficulties, of course....)
Re:Some Trivia about 'Clarke Point' (Score:3, Informative)
Actually, I believe it was an essay or an editorial. It was published in "Wireless World", a British electronics magazine. AFAIK, Clarke patented the geostationary orbit, but his patent expired before anyone had the capacity to put a satellite there.
Arthur Clarke had asked him to do the calculations for a book he was currently writing
The book was "Fountains of Paradise", where a space elevator was built in an island located south of India. That island would be Sri Lanka, except that the Equator doesn't cross Sri Lanka.