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Space Elevator Prototype Climbs MIT Building
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!
I bet Spiderman is just a tad bit jealous...
Are we going to start measuring stuff in MIT building heights now?
This sounds nice. Also why just a space lift. could it also be used to scale other objects that we may not want to risk human life on?
I heard the real purpose of the test was to place a police car on the roof.
http://liftport.com/progress/index.php?blog=9&cat= 28
Lifter Success!
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.!
if those MIT kids can measure a bridge in Smoots (Smoot was a student), they can measure make the Green building a larger unit..... try and stop em....
How tall is that... in Smoots?
WikiPedia entry on the Smoot, if you have no clue what I am talking about.
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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.
Environmentally Harmful: birds could run into it and die. Doesn't anyone consider birds?
sigs, as if you care.
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.
--
Power to the Peaceful
Just like the thing described....
then try this link for those of you who don't know what a "space elevator" is (and insist on hanging around here). It is a faq on a study done on the concept. More info is also on the site.
For Pete's sake... I'm going to get real mad if the guys on the 19th floor keep misusing our R&D technology just to fetch their morning "coffee and donuts"...
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It's a good idea in theory, but there's the small problem of someone has to go to the top of the building/object to anchor the ribbon in the first place. So once they work around that, it should be fine.
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.
60000 miles = 316,800,000 feet.
316,800,000 feet / 29 feet per minute = 20.77 years
I fail to see how climbing a 290 foot ribbon, on battery power, is even relevant to building a space elevator. It's realy just someone's fun little robotics engineering project. The amount of energy needed to climb all the way to space is so huge that either a highly energy dense storage medium not yet available, wireless power transmission, or transmitting power on the ribbons themselves if that turns out to be possible, are the only viable options to power a space elevator. Other than that, the lifter is a simple engineering project that could be built today.
what sig?
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?
"" How about taking the safety labels off everything, and let the stupidity-problem solve itself? """
They're making this sound like it's a step towards achieving their goal, but really what they did today wasn't a stretch of the imagination like the final goal is.
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.
No: if it was just the cable, it would need to be twice the lenght of geo-sync orbit. The thing is, there will be a massive satellite at the end. Presumably, in fact, the satellite could be designed to be a launching-off point for interplanetary flight (via building the ship in orbit, instead of having to lift it off the surface). Its pretty easy to show that with a sufficiently massive satellite, the cable can be basically an arbitrary length (or more accurately, an arbitrary length longer than geo-sync orbit).
"Stumble before you crawl"
60000 miles = 316,800,000 feet.
316,800,000 feet / 29 feet per minute = 20.77 years
And the first automobile didn't break the sound barrier either - though we now have an experimental model that has, and consumer-grade vehicles routinely cruise FAR faster than those early manufacturers considered.
Ditto trains. Ditto planes. Ditto ships.
Also: As you get farther up you can go faster for a given horsepower. Once you cross synchronous orbit (or when you go back down) you GAIN energy from going farther, and the limit (if you don't want to keep it as velocity) is how fast you can store or dump it.
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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
I've seen strengths of 65-120 GPa listed for the minimum required strength for a space elevator cable. Spider silk is around 1.3 Gpa, so it's not even close to being as strong as what's needed.
Spider silk is about as strong as Nylon, both of which are many times as strong as steel for the same weight.
Progress is progress, I agree. My concern, however offtopic, is the following question: What kind of conductivity is a 60,000mi carbon nanotube antenna going to have? No one seems to know for certain what kind of geomagnetic effect such a large antenna would have during solar storms. Worst case, catastrophic climate change...Best case, dazzling aurora.
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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
Power will be beamed to the lifters by a medium intensity near-infrared laser. It would not be a good idea to stand infront of such a laser, but it won't hurt you to run your hand through it or even to walk (or fly) quickly through it. The lifters will carry an array of photovoltaic cells keyed to the wavelength of the laser, making a surprisingly efficient power transfer. The adaptive optics (for aiming and mitigating atmospheric distortion) and lasers themselves are in the demonstration stages (for other projects).
mspeten@liftport.com
You're right. The material we need has not been made yet. This is a barrier that can be broken. 105 years ago, heavier than air flight was impossible. Today, space flight is possible. 50 years ago, 1 kilobyte was huge (and on punch cards. Today 1 gigabyte is small. We sometimes sound over zealous (I'll be the second to admit), but this is just a technical problem to solve. Better minds than mine are working on it right now.
mspeten@liftport.com
It's 60 miles to the beginning of space, and approximately 20,000 miles to geosynchronous orbit. The anchor for the space elevator needs to be at 3x geosynchronous orbit or approximately 60,000 miles out. They had that number right, but your comment emphasizes the Herculean nature of the task.
Ben Hocking
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In 1980 (79?) I did a Co-op block at Comsat, the US part of Intelsat, responsible for the first telecommunications satelites. Because these were first described by Arthur Clarke in a science fiction story, he was given the 'first' share of stock in the company and began a long and friendly relationship with the people there. Fast forward to my tenure, where I was working with the 'resident genius' in my department (I don't know what his actual title was, but essentially he had no formal assignments other than to come up with amazing things) using some god-awful quasi-language based on fortran (it was supposed to be really good at matrix calculations and I was writing a program to calculate solar cell array degradation over the life of a satelite. It was my first introduction to dealing with something billed as 'amazing' that almost, but not quite, did what you needed it to do. But I digress from this digression...). I would frequently see him pouring over calculations and eventually asked him what he was doing. "Calculating the tensile strength needed to make a space cable." Then followed a lengthy discussion of what we now call a space elevator. I asked if Comsat was planning to build one. It turns out Arthur Clarke had asked him to do the calculations for a book he was currently writing. I assume his genesis of the idea led to it being called the Clarke point.
I never actually read the book, as, although I always find Clarke's ideas interesting, his writing just grates on my nerves.
FWIW