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Report: Space Elevators Are Feasible
Daniel_Stuckey writes "It's the scourge of futurists everywhere: The space elevator can't seem to shake its image as something that's just ridiculous, laughed off as the stuff of sci-fi novels and overactive imaginations. But there are plenty of scientists who take the idea quite seriously, and they're trying to buck that perception. To that end, a diverse group of experts at the behest of the International Academy of Astronautics completed an impressively thorough study this month on whether building a space elevator is doable. Their resulting report, 'Space Elevators: An Assessment of the Technological Feasibility and the Way Forward,' found that, in a nutshell, such a contraption is both totally feasible and a really smart idea. And they laid out a 300-page roadmap detailing how to make it happen."
For anyone interested in the concept of the space elevator, The Fountains of Paradise (1979 Novel) by Arthur C. Clarke, is a must-read!
It's a very well-written novel that focuses on many of the technical aspects of building a space elevator.
Yeah, the plastic they use for retail packaging should be strong enough.
“He’s not deformed, he’s just drunk!”
As bigjarom mentioned, what's holding us back right now from cheap lift via skyhook is that we haven't quite gotten our carbon nanotube strength up high enough. It's theoretically quite possible.
After that, it's just a question of how do we get enough materials and probably some sort of ribbon* making facility into GEO to actually do the laying. One idea I have is that rather than having to ship all materials to GEO, only to drop it towards the earth, you have a descending constructor that you supply. Though the orbital mechanics of resupplying it can get quite hairy...
*Modern design philosophies has the cable being more of a flat ribbon than circular.
I don't read AC A human right
It's the scourge of futurists everywhere: The space elevator can't seem to shake its image as something that's just ridiculous, laughed off as the stuff of sci-fi novels and overactive imaginations.
I've first heard of space elevators decades ago, and not once have I read or heard anyone saying it's a ridiculous or laughable idea. All I've heard is that it'd be a really great, smart and economical way to access space, if only a strong and light material could be found to prevent the cable from being several miles across in diameter at the base and collapse under its own weight. Where did the story's submitter get that from?
"A door is what a dog is perpetually on the wrong side of" - Ogden Nash
One of the things I don't see discussed much is the potential failure modes for such a system.
My wife is a physical oceanographer, and one of the failure modes for instruments deployed on cables from a ship is a 'wuzzle' -- a large tangle of steel cable. Given the nature of the stuff, a length of cable that fits nicely in a spool on deck can twist itself into a knot larger than the ship.
So one thing I'd like to know is what are the potential hazards a couple thousand miles of elevator cable falling to the Earth's surface? Could we end up with tangles miles in diameter?
I think a space elevator is a great idea if it's feasible, provided that in the criteria for "feasible" we include being prepared for the conceivable ways the project could fail.
Post may contain irony: discontinue use if experiencing mood swings, nausea or elevated blood pressure.
Or, just read the linked report by a team of ACTUAL scientists instead of a SCIENCE FICTION story written 35 years ago.
You can't, unless you want to pay for it.
"First they came for the slanderers and i said nothing."
i say let's get fusion right first, then invest in SETI programs, then make contact with another intelligent force, then see how they approached the space elevator problem. Then we can apply alien civilization best practices to leap-frog the current space elevator timeline.
In the above book, a Martian space elevator fails (more specifically, is induced to fail by the deliberate application of high explosives.) The result is highly destructive. The Martian equator is no longer an imaginary line, but rather a prominent physical feature.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
SETI as fun as it is seems pretty pointless to me, at least in its current form. I doubt any advanced civilization would use radio communications for more than 200 years. IMO we would be better off looking for other signs, such as Dyson Spheres.
Problem is that plastic's extremely porous and fragile until it gets to its actual destination. And since the Elevator is effectively always in transit....
I believe the plastic in question is the kind of plastic that semi-permanently entombs your purchase in a chrysalis so touch that you need a diamond tipped super electro buzzsaw or a weapons grade baloneyum industrial laser to burn through it.
BestBuy packaging - toughest stuff known to man.
Science advances one funeral at a time- Max Planck
If the break is below the half-way point it will go up if the break is above the half-way point it would come down.
Also the process that seems to most likely for construction would be to deploy from the mid point of the cable and then spool in both directions at once. This way the overall forces remain in balance.
Also everything I have read about planned space elevators has it based in the middle of an ocean. This allows some movement if necessary to avoid something large in space but also gives some safety in the event of a failure. If the cable broke below the mid point controlled explosions all the way along the cable would reduce most of the damage with the a large % of the resultant bits burning up in the atmosphere or landing in the ocean. It would probably be much worse for things in orbit than things on the ground.
Taking space elevators to their logical conclusion though would see them being the bases of super towers that reach into space. The cables end up being the foundation supports of the tower.
And the desire of anyone with the ability or funds to do it to go to space regularly enough to need it. When I think back to being a kid and how space felt like the future, it makes me sad that typically it seems like no one besides researchers gives a shit anymore. I used to watch Star Trek and knew it wouldn't happen in my lifetime but it felt like that was the eventual goal and the direction we were heading in. Now I see it as the fantasy it is, because without some compelling financial gain in taking trips up there for anything besides tourism for the super-rich, I think we are going to stay stuck on this rock.
Or, just read the linked report by a team of ACTUAL scientists instead of a SCIENCE FICTION story written 35 years ago BY AN ACTUAL SCIENTIST.
FTFY.
Clarke had 256 pages and apparently conveyed the general ideas. Paying for 300 pages seems like a stupid thing to do if you want a general idea.
If they cannot communicate how it is feasible in an elevator speech, I don't expect to learn much in the manifesto.
3 pages has sufficed to explain the Higgs (excluding cartoons); I expect to understand the space elevator, in big boy words, in 2 or less. Anything else is hiding something, or so poorly written it cannot be trusted.
Superfluous vocabulary is ostensibly a plausible alternative, however a great many potential readers may find themselves sidetracked by such unnecessary verbosity. As such, I have expectations of a concise manner of thought conveyance as would be warranted by the writers. Vis a vis- said writer probabilistically desires their audience foremost not fall immediately into slumber.
My kingdom for mod points. This is sad but true. If we do ever leave it will be to mine unobtanium like in the movie Avatar, not to further mankind in general.
Picard tries to explain to Ralph Offenhouse from the 20th century that there would be no need for his law firm any longer: "A lot has changed in three hundred years. People are no longer obsessed with the accumulation of 'things'. We have eliminated hunger, want, the need for possessions." (TNG: "The Neutral Zone") - http://en.memory-alpha.org/wik...
Well you might also remember that Clark predicted FTL drive in your rush to find a pedestal tall enough.
And maybe you should actually READ the study before dismissing it because it has too many big words.?
Oh, wait, this is Slashdot, we don't do that, do we.
Sig Battery depleted. Reverting to safe mode.
Connected to a platform in space, the mass of the platform is to spin with the Earth's rotation. Centrifugal force is actually pulling on the elevator 'cable'.
$5 / month hosted VPS on linux = awesome!
Financial gain may be the most likely reason for advancement now, but it won't take more than another 50 to 100 years for it to become a necessity due to any combination of pollution, population, warfare, and resource depletion. Humans have always been really crappy at innovating unless we absolutely have to. When we aren't faced with some kind of crisis, we tend to get really good at perfecting known technologies and ideas, but that's about it.
So yeah, space exploration is pretty much out of the question as long as people (both investors and consumers) are more interested in mobile phone games and reality TV. As soon as shit hits the fan again -- and it will -- we'll see another big leap in advancement.
The super-rich are not the only potential market, people of modest means engage in tourism as well. All the super-rich are doing is helping to pay for the necessary r&d and initial infrastructure. Costs will come down with improved technology and greater experience. Even **IF** tourism was the only potential space industry there would still be a potential market of millions of travelers. Its just a matter of time as costs work their way down the willingness-to-pay curve.
That said, I do not believe the commercial utility of space is limited to tourism. And whether we are dealing with tourism, scientific research or industrial application there will be a point where getting the resources locally will make more economic sense than lifting the resources from earth. That will open up even more commercialization of space.
Have you read it? Let me know if it's any good. To me, it just looks like a scam to get people's money.
No money involved, they give it away for free if you know where to look:
http://www.virginiaedition.com/media/spaceelevators.pdf
Archived here:
http://www8.zippyshare.com/v/72888832/file.html
http://www.sendspace.com/file/16c8xj
http://wikisend.com/download/118300/spaceelevators.pdf
If engineered correctly, the total force applied at ground level could be "up" rather then "down".
I almost feel bad whooshing someone with a 5 digit ID. Almost.
Yeah, if you want a materials strength nightmare, forget about the elevator cable.
Think about a foundation strong enough to withstand the pressures of a 100-200 mile high tower pressing down.
Why don't you think about familiarizing yourself with the concepts behind the space elevator? There won't be anything like that. The end of the cable "floats" in the receptacle. It hangs from its anchor asteroid.
Oh wait! Lemme get my unobtainium!
Why don't you instead get a quick education in the topic we're discussing before you flap your yap?
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
Someone found a free copy of the report. Enjoy.
"First they came for the slanderers and i said nothing."
Here's a link to the actual report, so enjoy.
"First they came for the slanderers and i said nothing."
Using the elevator for transfer of goods - will work but the goods will get a huge dose of radiation
Using it for transfer of organic matter (i.e. humans) above LEO is not feasible due to the speed/shielding needed
The worst part of Van Allen belt is about 19000km wide and starts at around 7000km high. Apollo moon missions passed trough it at roughly 15km/s, spending roughly 2*21 minutes in it.
The astronauts received roughly 1rem of radiation through 3 layers of thick aluminum radiation shielding.
That is 1/5 of the yearly the limit in US for people working with radiation.
At reasonable speed (~200m/s) the elevator would take ~26h to pass through the belt, meaning it would need at least 75x more radiation shielding than Apollo did and that the lift would need 15m thick aluminum honeycomb walls (using 70's technology).
Even with todays technology the shielding will be way too bulky/heavy for elevators to be viable alternative to rockets for above LEO human transfer.
Probably because it's best modelled as a lot of little chunks each with different gravitational force on them and forces from the elements above and below - and that's not trivial if the thing has a break in it somewhere.
The simplest mode of failure is if the thing is under a huge amount of tension and somebody cuts it off at the base - as in at least one movie. In that case the entire thing flies off into a high orbit (for the counterweight, trailing the ribbon behind it) or escapes entirely. Having a huge amount of tension make sense in keeping it straight, but of course constraints of reality would get in the way if we finally have a real material that comes close to having the right properties for an Earth based space elevator.
And the desire of anyone with the ability or funds to do it to go to space regularly enough to need it.
It's like proposing to the East India Company to build a modern mammoth tanker. They would not understand why anyone would want to transport such quantities of material across the ocean. You can't really blame people for not having a clear vision of the future though.
When I think back to being a kid and how space felt like the future, it makes me sad that typically it seems like no one besides researchers gives a shit anymore. I used to watch Star Trek and knew it wouldn't happen in my lifetime but it felt like that was the eventual goal and the direction we were heading in. Now I see it as the fantasy it is, because without some compelling financial gain in taking trips up there for anything besides tourism for the super-rich, I think we are going to stay stuck on this rock.
I disagree.
Firstly, we have some exciting missions to planetoids. Pluto and Ceres are about to be visited (spacecraft is already on its way).
Secondly, the ISS is a great success of global cooperation. And now it is being supplied by commercial parties, at lower cost than ever. And the fact that it's up there (it's huge in comparison to anything else we've put in space) is a sign we're moving forward.
And then the Chinese are breathing down the necks of Western space agencies, and catching up quickly. Thereby ensuring that we don't get lazy.
And finally, I really believe that this idiotic Mars One program can be a success. The global budget for advertising is simply insane, and if they would only capture 1% of the advertising money, they can totally build a Mars mission. It needs to gain popularity, but in this modern age, that is not rocket science.
Sure, the massive budgets of the golden days of the space race are over. It's all a bit more sensible now. Until the entertainment industry steps in!
the desire of anyone with the ability or funds to do it to go to space
Not only the desire to go, but some destinations ("space" is not a place) are necessary, too. I would expect that the main use of this device would be for freight, not people. For a start the safety requirements are much less stringent (apart from if it collapses on top of people) and therefore the implementation costs would be less.
There's also the little matter of geography. A space elevator would have to be built on or near to the equator. At present none of the equatorial countries have the will, means or need to build one. In the past the imperial powers have created global infrastructure, but there are no more imperial powers and there is not sufficient political stability for others to want to risk 10's or 100's of trillions of <insert name of preferred currency here> in some tropical location outside of their control.
politicians are like babies' nappies: they should both be changed regularly and for the same reasons
I've seen proposals that talk about using a ribbon that is only just barely larger than is needed to support itself for the initial strand. Send it up in a conventional rocket (at the time this was discussed, they talked about using a Saturn V or possibly even the Space Shuttle; these days a Falcon 9 Heavy would probably be enough or even more-than) to geosync and have it unspool in both directions from there. Grab the lowered end as it reaches earth. Then, send up a small climber, carrying another, possibly even smaller strand of ribbon. Join it to the first one. Now you have a stronger ribbon. Repeat (potentially with increasingly large builder-climbers) until you have a strong enough ribbon for whatever you want to do (send up people, or ISS modules, or other satellites, or parts for a Project Orion-style nuclear pulse rocket to be constructed in space... you get the idea).
I don't know how feasible all the steps there are, but it's worth considering as an alternative to sending up the entire thing all at once.
There's no place I could be, since I've found Serenity...
I've always liked the idea of space elevators, but I've also been bothered by a problem that I've never seen addressed, "micrometeoroid erosion". Sure, you can build one. But how long is it going to last, with nothing to protect the main cable/strands/shaft/whatever-you-want-to-call-it from a near-endless --though admittedly low-rate-- series of impacts by speedy dust particles?
It was also, sadly, complete bullshit ("sadly" because it's one of the worst research failures in the series, which is otherwise fairly good hard sci-fi). The material he envisioned making the cable out of was not only wildly impractical, it was apparently chosen explicitly because of several characteristics it exhibited that are exactly opposite of what would be desirable. You need a material with an extremely low mass per unit length. You do not need a highly durable material, certainly not on the scale of diamond hardness. You also want a ribbon, not a true cable. That gives the climber more surface area to grip for a given amount of mass per unit length.
The result would be more akin to a silk scarf a few feet wide (at the base, several times that at geosync) and many thousands of miles long slowly falling to earth. Some, possibly much, would be burned up in the atmosphere. Some more would flutter to the ground, buffeted by the winds but no more harmful than if some airplane unspooled a bunch of tissue paper in the high atmosphere and then let it go. Some places it might tangle and fall to the ground in a knot, but even then it would have a fairly low terminal velocity and relatively low mass. You might destroy a building or two in the worst case; you would not wreck the entire circumference of the planet
The very concept of building the ribbon out of anything that could contain the energy needed to produce a "kilometres-wide path of destruction" without harmlessly burning up in the atmosphere is as idiotic as it is unrealistic.
There's no place I could be, since I've found Serenity...
Ocean, actually. We have rather a lot of it, especially around the equator.
Sigh. This whole "the cable could fall and kill us all!" bullshit has been debunked again and again, but still people keep pulling it out of their asses like they have any idea what the fuck they're talking about. Do at least a little research before spouting your mouth off, OK? For starters, ribbon, not cable. Think silk scarf, not suspension bridge.
Oh, and as for the idea that where you built it would matter for people living "in the cable fall direction"... you really don't get the scale of this thing, do you? The Earth's circumference is less than 25000 miles. The distance to geostationary orbit - which is the shortest such a ribbon could be, realistically it would be about twice that - is more than 22000 miles. If it *did* fall, and somehow survived re-entry and came down in one continuous piece, it would probably wrap around the equator. But that wouldn't happen, because any material which could survive such a fall would be completely impractical for use as ribbon material in the first place!
There's no place I could be, since I've found Serenity...
Protective polymer coating, topped up every time the car passes over it?
A counterweight always seemed kind of silly compared to just extending the ribbon as far in the other direction. That way you can also "build" the elevator by unspooling cable in both directions from GEO. You also get the ability to use the upper portion as a launch platform for interplanetary travel (at the end of the ribbon, you'd be experiencing a strong acceleration *away* from earth, just let go at the right time for the direction you want to travel).
Laser-delivered power is one good option. There are a few others, and you might want to supplement it with power collection on the "roof" of the climber (either to collect solar energy directly, or to collect beamed power from a midpoint station) as ground-based lasers would become inefficient above a certain point.
There's no place I could be, since I've found Serenity...
I believe the plastic in question is the kind of plastic that semi-permanently entombs your purchase in a chrysalis so touch that you need a diamond tipped super electro buzzsaw or a weapons grade baloneyum industrial laser to burn through it.
I bought one of those, but I can't open the package it's in.
Perhaps it hasn't been addressed much, but from what I've seen part of the 'protection' is that you would be more or less continously extruding new cable(on the order of a couple miles a day!), so as time goes by the cable WOULD be refreshed.
Besides that, if you're sensible you're going to orient your ribbon so it's the narrow end that's facing most probable impacts, highly limiting it's cross section. Then you have to factor in that this material will be the strongest material used in space to date; it should be quite resistant to those effects.
I don't read AC A human right
I'm not sure Star Trek should be considered in the same sentence as talk of viable space exploration the future.
Utopian thinking is nice but it's an ideal not a potential reality.
Main problem I foresee is what happens when someone presses all the buttons.
Now that would be a good use for the term 'bootstrapping'.
I am not really here right now.
what it'll take it for China to start weaponising space, "for their own defence" and then funding will immediately be made available to get other countries weapons system up there.
Why else did the US go to the Moon - it was because there was a chance the Russians might have found a way to put missiles on there of course, all dressed up as exploration and "good of mankind".
So c'mon China - we're bored of terrorists, we need a new 'enemy' to spend vast sums defending against! you guys are the only ones with enough cash to do anything.
Sigh... your numbers are wrong, your science is wrong, and your concept is questionable.
Let's start with the basics: GEO is 35,768 KM from the equator. You need twice that much, at most, ribbon (not cable. Cable is dramatically less feasible and stupid besides). No idea where you got 100,000 KM from...
Now, about that ribbon. It's a few feet (maybe around one meter) wide at the base, where tension is low. It's several times that at GEO, where tension is highest. It's got a thickness comparable to paper and a mass per unit length even lower. The part that falls, in the event of a catastrophe, will mostly burn up in the atmosphere, the rest will drift back to earth with a very low terminal velocity. It might kill a few unlucky people who happen to have a tangle of it fall on their heads; it's *not* going to "impact the surface" "with dramatic consequences".
But, to consider the meat of your proposal. First of all, you understand that the thing is under tension along its whole length, right? The primary limitation on our ability to build one is finding material of sufficient tensile strength. The middle (at GEO) will be under particularly bad tension; we *think* we can make materials strong enough to be feasible for that. You want to turn this thing into a *network* (implying interconnections)? Where do you plan to obtain the additional tensile strength for the extra mass hanging off the tensioned parts, pray tell? Oh, you can (and probably would) put multiple cables next to each other, allowing climbers to pass one another and providing redundancy, but each one would basically be its own space elevator that happens to be next to a few others. A single attack, if big enough, could still take them all out... but so it goes.
There's no place I could be, since I've found Serenity...
So, in order to prevent the whole thing from crashing down, there has to be a safety margin of extra ribbon above GEO, meaning some extra tension in the wire, even at ground level. That barge can't be too light-weight, or else it'll turn into a space-barge...
how do we get enough materials and probably some sort of ribbon* making facility into GEO to actually do the laying.
There's no way this will get built with materials launched from Earth, it will have to use resources mined in space. Just the segment from terra to GEO will have to be 23 thousand miles long; even just for a single "strand" we don't have a vehicle that can lift anywhere close to that much material. Lifting all the "strands" necessary would take many thousands of launches.
OTOH, once SpaceX gets its reusable boosters working, it will be much cheaper to get up there. That will speed up the development of space-based industries (such as asteroid mining) that would make this project more feasible. It's not inconceivable (barely) that such a project could be undertaken in my lifetime, but I rather doubt it.
In the meantime, a rotating skyhook seems much more viable, especially for the moon.
XML is like violence. If it doesn't solve your problem, you're not using enough of it. --AC
Speed of Light: 299,792,458 m/s (meters per second)
Great Pyramid Grand Gallery: 29.9792458N Latitude
coincidence?
Some drink at the fountain of knowledge. Others just gargle.
Lifting all the "strands" necessary would take many thousands of launches.
Not from what I'm seeing. At least one source says that a 'starter' cable can be had as light as 9 metric tons. Another says 20.
A Falcon Heavy can lift over twice that to orbit, though maybe not all the way to geosync...
After you get the first thread down, you use that thread to lift more mass to increase capacity.
I don't read AC A human right
We have both people worried about space elevator cables crashing to earth if an airplane hits one and people concerned about SETI not picking up incidental radio leakage from alien civilizations on the same story.
Can I get somebody to please express concern about the LHC creating a black hole on Earth so I can go home for the day?
My God, it's Full of Source!
OUTSIDE_IP=$(dig +short my.ip @outsideip.net)
Their estimated price is $500/kg which is a ridiculous price.
Today a falcon 9 can launch 13150kg to LEO for $50million.
The projected elevator can lift 13150kg to LEO for $6.6million.
A nice improvement until you consider that a reusable falcon 9 launch will cost perhaps $500,000.
Which means Space-X with a little luck can reach $38/kg.
It is not hard to imagine that with modest success at re-usability Space-X can drop the cost from $50million to $5million with just a reusable first stage, which would make the Space-X price $380/kg.
That makes space elevators uneconomical before they are even built.
Now a careful reader will note I am arguing GEO vs LEO prices. Once in LEO a ion engines can be used to make the transition to a higher orbit with all of the same efficiencies of an elevator and they already exist.
I fail to see the economics of a technology with a huge up-front cost and that it looks like a much less expensive investment in rocket technology can devastate.
Actually in a design I saw some time ago, the cross section of the ribbon would be more like an arc of a circle. No straight line path of a micrometeorite would be capable of severing the cable.
You post is mostly wrong and stupid.
". It's got a thickness comparable to paper"
What do you base that one? It has to be able to carry an elevator, you know for the space elevator
" will mostly burn up in the atmosphere"
Do you even have a clue what cause things to burn up in the atmosphere?
Why do you ignore the fact that the counter weight is going to fly off, do a figure eight, and the come back to earth?
When something strike the counter weight, it' will have a different angle of momentum and push it out of orbit, which will cause it to swing closer to earth, out of it's orbit and begin wrapping the planet becasue it will be pulled closer by the leash the attaches it to the planet.
I have yet to hear a proposal on how to avoid that from anyone who actually can do the math.
Of course, the idea s to get into space cheaper, but we need more then that. What will we do once we can get into space cheaper? IT won't mkae leaving the solar system that much easier. History has shown that when simple gets easier to get to, the general public and corporations really screw it up.
We have a pretty large problem with space debris right now.
The Kruger Dunning explains most post on
At one time I believed that the space elevator was the only way we would ever be able to move into space on an economic basis. All rocket based methods were just too expensive. That was until I read what Elon Musk had to say about it http://www.spacex.com/news/201.... The real reason that space exploration is expensive is that we throw away the spacecraft after a single use not the fuel used to get there. Space elevators are very energy efficient and would have great longevity, however, the practical and economic problems of building a 30,000 mile long cable is vastly larger than the problems of solving reusability of spacecraft. SpaceX is well on the way to solving the reusability problem. They have a practical road map and are executing it in spectacular fashion. They have already tested and proven vertical rocket powered landing technology and on their next Space Station resupply mission they will be testing booster landing leg deployment and engine restart to try and achieve a soft splashdown in the ocean. There last attempt of restart was successful however the descent became unstable and they had to abort. It is believed that the landing legs will provide extra aerodynamic stability allowing for a successful soft splashdown. I believe it is only a matter of a few years until they have a fully reusable system. This innovation will drive down the cost of space travel by a factor of 100. In 10 years the average upper middle class American will be able to afford a vacation in space. Travel to Mars will still be expensive but not unattainable for many.
Or...
Christians
Jews
Communists
White supremacists
Environmentalists
Neo-luddites
Unionists.
And whatever the fuck these guys are.
Science is all about firing a drunk pig out of a cannon just to see what happens.
Then you have to factor in that this material will be the strongest material used in space to date; it should be quite resistant to those effects.
I don't have the numbers handy, but I'm thinking the ribbon material is a couple orders of magnitude at best stronger than conventional materials, while impact energy is MANY orders of magnitude higher than the "strength" in question.
To put it another way, if an impact dumps enough energy to raise several cubic millimeters of material to a five-figure Kelvin temperature, the "material strength" becomes somewhat irrelevant. Vapor/plasma doesn't resist tension very well.
In fact, I'd think that stronger materials would receive more transferred energy from an impactor as it's punching through. You'd just have to count on having enough material left to hold things together.
Correct.
Stronger materials are worse in structure impact scenarios because they transfer nearly all of the energy to the structure. You need flexible materials, a non-rigid design, and break-away failure modes. This all then necessitates a very redundant (and thus large) structure. If your carbon nanotube cable/ribbon takes a high-energy impact, the issue isn't the entire cable/ribbon surviving, it's preventing the energy from transferring to the structure (the anchors and the payload).
I say build it with 3 times as many cables as needed, and install electronic sensors to measure impacts on each cable. When a sensor detects an impact, it can signal to the anchors to cut its cable. Since the cable isn't perfectly solid, the sensor has a good chance of telling the anchors to cut the cable before the energy from the impact reaches the anchor. The cable becomes slack and can't transfer the impact energy to the structure in anywhere near as direct a fashion as if had remained under tension by both anchors. You could incorporate this into the elevator car, too, so it has the option of cutting a cable. You just need to have sensors spaced strategically so you can reliably signal and execute the cut before the energy reaches the structure.
Then read the study
They address micro-meteorites, lightning, induced currents, radiation exposure, and a whole host of other objections. The biggest problem they identify is the obvious one. We don't have any materials to build the tether with yet.
They "project" that such materials will become available in the 2020's, which is good....that's a whole 14 years before nuclear fusion!
Don't worry, China is willing to take risks and try unorthodox ideas to defend themselves against the US, which spends utterly insane amounts on weapons.
True story. A coworker bought a scissors and couldn't get it open without a scissors, but there wasn't a scissors in the office which is why he bought one.
Scissors is an interesting word. Apparently derived from the latin word for chisel => a pair of chisels.
Wikipedia:
The noun "scissors" is treated as a plural noun, and therefore takes a plural verb ("these scissors are"). Alternatively, it is also referred to as "a pair of scissors". In American English, "a pair" is singular and therefore takes a singular verb ("this pair of scissors is"). In British English, "a pair" does not take the singular ("this pair of scissors are"). The word shears is used to describe similar instruments that are larger in size and for heavier cutting. Opinions vary geographically as to the size at which 'scissors' become 'shears', but this is often at between six to eight inches (about 15 to 20 cm) in length.
And yet, Wiktionary says
(countable, plural in form, usually with a plural verb) A tool used for cutting thin material, consisting of two crossing blades attached at a pivot point in such a way that the blades slide across each other when the handles are closed.
Those scissors are sharp. (indicating singular or plural scissors)
That scissors is sharp. (less commonly to indicate singular scissors)
Scissors are used to cut the flowers.
Use a scissors to cut them if you don't have proper shears.
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