h a l f b a k e r yWhy did I think of that?
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So, I was thinking about the space elevator. Presuming it could be made one day, the government or whoever launched it up and tethered it would give out specs to build machinery to climb the cable/thread, and then individual companies would provide their own vehicles to carry up what they want to put
in space, or perhaps some companies would make vehicles and lease the, whatever, you get the idea.
And so people would be sending stuff up like this. It's likely that there will be multiple vehicles going up at any one time. This poses a problem, because if one companie's vehicle fails, and its cargo drops, that cargo will fall and damage all the cargo below it being sent up by other companies.
Private industry will work to form insurance for this problem, but the amount of damages from such accidents would be huge, damaging this specialized machinery (the other vehicles) of multiple different companies and their cargo. It may be more than private industry could do.
So it might be a good idea for the government to provide a public space-elevator insurance program that they would help fund.
Yes, these are the things I think about. I think of one science thing and my brain goes off on tangents. I could even tell you how teleportation machines would spark another death-penalty debate.
List of expendable equatorial cities..
http://en.wikipedia...by_latitude#Equator
[not_morrison_rm, Jul 30 2012]
[link]
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Tangents are awesome. (+) |
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//Tangents// are what the vehicles would fly off at if they broke free of the cable. They wouldn't drop straight up or down. Plus I have a couple questions. Could a space elevator support lots of vehicles at the same time? I've always assumed that there would only be one vehicle travelling up and down and companies could pay for a ride, similar to the space shuttle. Space launch companies already assume lots of risk when launching things. There is no telling when a rocket will explode and take a $500000000 satellite with it. What we really need is insurance for the occasion when aliens attack and destroy the space elevator, causing the tether to wrap itself around the earth several times and destroying a handful of major cities/continents. |
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//the earth several times and destroying a handful of major cities/continents. |
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Presumably it'd be an equatorial moon string, sorry, space elevator. I think there's just a lot of ocean and a few cities eg Nairobi, which no one's going to miss. It might be possible to put an explosive break so it missed Indonesia, as an optional extra. |
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wow, DIYMatt, kind of a lot of inaccuracies you got there for a halfbaker |
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Things that got disconnected from the space elevator would not fly away from it on a tangent. The space elevator is in geosynchronous orbit with the earth (it's space tether is, to be specific). So relative to the earth's surface, it isn't moving, no part of it is. What would happen/have to happen, is the object would also slowly accelerate linearly along the direction of the spin of the earth as it climbed. The higher up you go, the fast the object is moving, but still always geosynchronous. Hopefully, the cable accelerating the object won't slow down the cable over time as more and more objects are transported. If that did happen, then the tether in space would need to be equipped with its own engine to accelerate itself to adjust as it slowed down as more and more stuff was transported. Ideally though, just the gentle tension in the cable would be enough to accelerate the cargo/elevators without moving the tether, if you crawled up slow enough, though I feel like thermodynamically that must be impossible, since the energy to accelerate the loads has to come from somewhere. |
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What is interesting that I realized when you said that is that that also means that the higher you go, the lower the perceived gravity is; stuff will fall a lot slower when you're closer to the top. This is because the objects is moving really fast at that height and closer to geosynch orbit (remember, the goal in the first place is that you go as high as the tether and hit geosynch orbit so that you're in space). I checked this on wikipedia, and yeah, they got some math showing how it can be calculated. |
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And if the counterweight or some of the elevators were destroyed, the cable would not wrap around the earth. Remember, the cable is in geosynch orbit with the earth, it's already moving. The only way to get it to act sort of like you're saying is if you decelerate the cable or some parts of it. Simple strikes and explosions would not cause a catastrophic reeling-in. |
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The tangent fly-off is correct. The way to look at it is in terms of tying a weight on the end of a string and rotating in place, holding the other end of the string. That weight is moving FAST. So, any point along the length of a space elevator is moving faster around the Earth than the Earth's rotation speed. Anything that falls off will fall down and forward, relative to the rotation direction of the Earth. |
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Caveat: the preceding may not be especially significant for the very first few kilometers of cable, near the Earth's surface. |
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you would have to assume that the cable is under
tension, however small. Which means the
counterweight is almost certainly mounted slightly
further out than strictly necessary. This would
imply that the areas above the break would be
dragged further out by the counterweight. Then
you only have to worry about the stuff below the
break. However, a conventional cable above a
thousand km or so is going to burn up in the
atmosphere. There are problems.... the cable is
going to be made out of unobtanium. As we
haven't been able to get hold of any of that, we
don't know if it will burn up or not.... being
completely resistant to friction might be one of
it's properties.... |
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I bunned this after reading the first line. I then went on to
read the rest and discovered that I would have bunned it
anyway. As our friends the British stereotypically say: Good
show, old man! |
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Oh, there is one other thing: I have mentally designed a
mechanical brake that could be applied automatically or,
in the event of complete failure, manually, to arrest the
fall of a car. Assuming a car with a loaded weight of 25,000
kg, application of a caliper-style brake with consumable
shoes constructed of a synthetic rubber/graphite
composite, applied with even pressure to the nanotube
ribbon with a cumulative force of 70,000 kg/cm^2 across a
2m^2 footprint, the fall
of the car at terminal velocity should be arrested within
20-
30 km. My calculations are based on upscaled formula
concerning the braking of freight trains, so there may be
some flaw involving exponential multiplication of forces or
something. Anyway, the key to this method would be to
compose the brake shoes so that they degrade at a rate
sufficient to slow the fall of the car without damaging the
ribbon (also an area where my knowledge is deficient).
Still, I think it would work. |
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In order for a space elevator to be stable, either it does have engines at the counterweight, or, more likely, as much mass has to come down as goes up. The most likely approach to this is asteroid capture or similar, and using that to return counterbalancing mass. |
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Every version of it I've heard discussed does use an integral climber (possibly more than one, although that has problems), not different ones from different companies. |
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Space elevators won't tend to burn during re-entry as much as various vehicles, since the lower falling portion is similar in velocity to the atmosphere. That being said, assuming long carbon nanotubes as the structural material, they will burn quite happily, so you're probably only going to have to worry about a couple hundred or so miles of the lower elevator wrapping around the planet. In fact, almost by defenition good structural materials are going to burn at re-entry temperatures. |
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From chemical companies dealing with things that can kill
you with one whiff to power plants to airports societies
have a LOT of experiences dealing with big risk/big
reward scenarios. Insurance and safety regulation can
easily mitigate enough risk to make the space elevator
feasible. |
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Anyone else reminded of Babel when contemplating the space elevator?
We should probably make sure that their are no Nimrods building it or it might get dragged into the sky and we'd all suddenly start speaking the same language... |
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// In order for a space elevator to be stable, either it does have engines at the counterweight, or, more likely, as much mass has to come down as goes up. // I thought the energy came from slowing the rotation of the earth slightly. If the counterweight is set to be slightly larger (or farther away) than necessary for perfect balance so that it is for putting a non-trivial force on its anchor blocks, then a climber weighing much less than that force can climb up without disturbing it too much. As it climbs, the cable will lag slightly, at the location of the climber, looking like a slightly pulled bow string wiht the location of pull sliding up the string. The angle of the cable to the earth's surface and to the counterweight's orbit will be less than 90 degrees, accelerating the climber horizontally, but slowing the earth minutely, and the counterweight slightly. Some time after the climber stops, the cable will straighten out, but it will still be at an angle other than 90 degrees since the counterweight was slowed. This allows energy to be transfered for the earth to the counterweight. Practically, the cable will never be at 90 degrees to the earth's surface unless it sits unused for a very long time or a bunch of mass is carried down the cable. |
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Should this idea not be entitled "Space elevator
public insurance", to avoid confusion with insurance
for elevators in public spaces? |
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//Why does the elevator cable need to be long enough to
"wrap itself around the earth several times?//
22,236 miles is the absolute minimum. Why limit
ourselves? |
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I believe if you've got enough traffic to justify a space elevator, you are going to severly distort the cable over time. Far better to return mass (which shouldn't be a big deal, and could even show a profit, if you're returning high grade asteroid ores). I may be wrong on that one though. Round trips for the climbers also save money in construction costs. |
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As far as efficiency, if nothing else, an elevator allows you to completely avoid lifting fuel, since you can use electric power (beamed, conductive cable, or onboard solar or nuclear). That alone would represent a huge savings. In addition, high strength electric motors and tractions systems are much lighter and much cheaper than equivalent rocket engines. |
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Once the construction costs were recovered a climber is going to be far, far cheaper than a rocket. Construction costs probably push them to similar levels during the amortization period (15-20 years) assuming sufficient volume. |
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Thinking about it, put the insurance office on whatever the space end of the cable is attached to, and make strict "payout only to people who apply in the office in person" policy. |
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Do we need to use the cable to bring things down? I thought getting up was the problem solved. To get down, can't we just point the cargo at the Pacific and give it a push? |
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I don't see why this is too complex a job for the private insurance market, which routinely deals with situations much more complex than this. Also, I'm not sure it's even that much of a risk - elevator technology is pretty good and no one has ever died as a result of their elevator plummeting down an elevator shaft (even when an aeroplane crashed into the Empire State Building the occupants of the elevator which has all its cables severed were OK). |
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The point is to bring it down in a controlled manner, such that you don't lose half of it in atmospheric friction (and a miss doesn't wipe out Maui). |
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//no one has ever died as a result of their elevator plummeting down an elevator shaft |
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Admittedly most people just seem to die of something else, but it seems that when the elevator cable mechanism breaks away from the mountings it generally makes for a very fatal plunge. |
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"On the night of May 22, 1903, in Pittsburgh, PA,..the Pennsylvania Electric Mechanical Institute .....of seventeen passengers was loaded into the elevator on the first floor, bound for the party on floor six. |
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Just as the elevator reached the floor, it suddenly let go and fell six stories, crashing into the elevator pit. The multi-ton elevator cable and assembly came crashing down onto the elevator, crushing the occupants. " |
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and American Woolen Company, December 1946.."...the elevator operator.. heard something break overhead. She jumped out of the elevator just as it let go and crashed three stories down into the elevator pit... the elevator cable, drum and assembly crashed through the roof of the wooden elevator" |
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I'd agree with just throwing stuff back down, unless it would be heklpful to carry it down to help re-accelerate the counterweight to make up for the deceleration on the way up. |
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of course the elevators (the climbing vehicles) themselves would have to climb back down, they'd (probably) be too expensive to just dispose of. Which then makes me wonder, shouldn't the space elevator have two cables, one for up and one for down? |
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Thinking about it...this one cable jobbie is the only elevator/lift. Cos stuff only goes up. All the other elevators/lifts take stuff up and down, so really they should be "elevating and descending machine". |
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