Japanese 2050 Space Elevator project (Obayashi Corporation)

Archibald said:
I will stop this conversation right here before being rude... :rolleyes:
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Please, feel free to vent - as a blunt German, I have no problems whatsoever with anyone being rude to me, as long as that someone doesn't have any problems with me retaliating with some German industrial strength rudeness in return :D .
 
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martinbayer said:
Please, feel free to vent - as a blunt German, I have no problems whatsoever with anyone being rude to me, as long as that someone doesn't have any problems with me retaliating with some German industrial strength rudeness in return
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in the Space projects section? Really ?

OK. mods will surely end up cleaning up the OT content, but surely we can behave ourselves better than giving them this type of extra work.
 
Today, phys.org has a story

"New Strategy To Obtain Carbon Nanotube Fibers With Higher Dynamics Strength."

The claim is 14 GPa

That good enough?
 
publiusr said:
Today, phys.org has a story

"New Strategy To Obtain Carbon Nanotube Fibers With Higher Dynamics Strength."

The claim is 14 GPa

That good enough?
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Maybe? IIRC 10GPa was the minimum yield strength to run a tether to orbit at all. 14GPa would give a low-but-reasonable safety margin.
 
Scott Kenny said:
Maybe? IIRC 10GPa was the minimum yield strength to run a tether to orbit at all. 14GPa would give a low-but-reasonable safety margin.
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Hi,
I had thought that I had seen values of 40 to 50 GPa being required, but I don't know what that fully represents.

Unfortunately, in looking through alot of readily available information on space elevators a lot of discussion appears to be centered around the tensile stress requirements imposed on the cable as it extends from the ground to orbit. However, that is only one partof the loads that the cable will experience, especially when you consider things like wind forces and wind shear over the enter length of the cable that exists within the atmosphere. In addition to that the cable would also have to withing lightning strikes, impact loads (rain, sleet, birds, debris, etc), contact wear and tear from the "elevator car" moving up and down the cable, thermal stresses and olther such things.

And finally, any "thickening/reinforcing" of a cable to account for things like this and/or the need to provide a relatively constant cross section of the cable to ensure that the "car" will maintain a suitable amount of connection to the cable as it moves up and down the tether (as oposed to allowing for an extreme tapering of the cable over its length) then the total weight of the cable will need to increase further driving up the required design tensile strength of the cable.

Also, just for comparison when discussing factors of safety, according to this article a typical elevator operating in a building on Earth would potentially have a factor of safety of "12" in comparison to the fully loaded weight of the elevator car (ie its mass times 1 G), which helps account for the fact that the elevator cable in this situation will see more than 1 G as the elevator car accelerates and decelerates in use, plus wear and tear, margins and other such stuff.

Similarly, according to this document for launching appliances and embarkation ladders on modern ocean going ships will have a factor of safety of 4.5 on davits and winch structural members, and 6 on "falls, suspension chains, links and blocks". As such, a facrtor of safety of 1.4 would potentially be very low for something like a space elevator tether which could potentially cause a large amount of dmae if it were to break somewehere along its length aloowing its lower part to fall to the ground.
 
PFJN said:
Similarly, according to this document for launching appliances and embarkation ladders on modern ocean going ships will have a factor of safety of 4.5 on davits and winch structural members, and 6 on "falls, suspension chains, links and blocks". As such, a facrtor of safety of 1.4 would potentially be very low for something like a space elevator tether which could potentially cause a large amount of dmae if it were to break somewehere along its length aloowing its lower part to fall to the ground.
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Yes, the failure mode of an elevator is ugly. It's probably going to need shearing charges built in at 100km and in a lot of places between there and the surface as well.

Thing to remember about safety factors is the relative masses involved. On the davits etc, the mass of the cables is a small fraction of the mass the cables are supporting, so you need a pretty huge safety factor to account for the large mass getting accelerated.

On an orbital elevator, however, that's inverted. How much does 36,000km of tether mass? What % of the tether mass is one of those trains? I'd be surprised if the trains and cargo exceed 1% of the tether mass. Crud, I'd be surprised if the trains exceeded 0.01% of tether mass!

As a side note, I've read a long time ago that the max speed of a train going up the beanstalk is only 200-300kph even in vacuum due to vibrational limits, so there's not much additional load inflicted by the trains accelerating and decelerating. Remember, we're talking probably 2000 tons of train going up and coming down, times 5 trains on the beanstalk each direction, and having at least 4 tracks going all the way up. Why 5 trains each direction? So that one train leaves each day. What's in the train going up? People, food, water, parts for whatever spacecraft are getting assembled up top, probably some air. What's in the train going down? People, refined metals from asteroids, trash, and possibly organic waste (sewage) to use for fertilizer. You'd generally try to keep the upload and download roughly equal in mass, but it's not absolutely necessary. Makes powering the trains easier, though.

So despite having 10,000 tons of trains going up the beanstalk and another 10,000 tons going down, the 4 sets of tracks alone are going to weigh in the neighborhood of 20 million tons (70kg/m). Not the tethers. The tracks the trains use. The tethers will need to support that much weight.
 
martinbayer said:
I'd love to see that turned into a vertical version of Bullet Train!
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That speed basically is already. Yes, I know the Shinkansen is a bit faster.

The catch is that the Shinkansen is pretty lightly loaded as trains go, passengers are not a very dense cargo compared to water, let alone metal.

Means that the bottom of the Elevator is basically a mid-sized train station. 4 tracks, plus a yard that's probably 4 more tracks on each side.

Guess I should say why 4 tracks, 2 each direction: so that if/when one gets damaged you can reroute traffic around the damaged section and run a repair train up to fix it. There's even rail switches between the up and down tracks, since there's only one train per day you can adjust up and down speeds to let the two trains cross to tracks out of the way without having to stop unless something is VERY wrong.
 
Flyby rotorvator/skyhooks don't have to be as long--and if backspun--perhaps re-entry heating lessoned?
 
Scott Kenny said:
That speed basically is already. Yes, I know the Shinkansen is a bit faster.

The catch is that the Shinkansen is pretty lightly loaded as trains go, passengers are not a very dense cargo compared to water, let alone metal.

Means that the bottom of the Elevator is basically a mid-sized train station. 4 tracks, plus a yard that's probably 4 more tracks on each side.

Guess I should say why 4 tracks, 2 each direction: so that if/when one gets damaged you can reroute traffic around the damaged section and run a repair train up to fix it. There's even rail switches between the up and down tracks, since there's only one train per day you can adjust up and down speeds to let the two trains cross to tracks out of the way without having to stop unless something is VERY wrong.
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Never mind - I watched Bullet Train on a recent travel leg and found it to be a delightful blood soaked contemporary fun diversion - no more, no less :)...
 
martinbayer said:
Never mind - I watched Bullet Train on a recent travel leg and found it to be a delightful blood soaked contemporary fun diversion - no more, no less :)...
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Oh, that movie.

Man, I completely missed the reference... mea culpa!
 
Uniting heaven and earth is a terrible idea... Can you imagine the bullwhip effect caused by an earthquake on such a long cable?

Can you imagine the impact on terrestrial facilities when the cable came loose and fell?

A cake for terrorists... Imagine the publicity: kidnappings, bomb threats, nerve gas attacks... All the bad stuff of commercial aviation in space at popular prices.
 
Justo Miranda said:
Uniting heaven and earth is a terrible idea... Can you imagine the bullwhip effect caused by an earthquake on such a long cable?
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Most earthquake displacements are measured in inches.

Justo Miranda said:
Can you imagine the impact on terrestrial facilities when the cable came loose and fell?
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That's why there are multiple shearing charges inside the beanstalk, along with a nice clear spot for the cable to land to the east of the installation.


Justo Miranda said:
A cake for terrorists... Imagine the publicity: kidnappings, bomb threats, nerve gas attacks... All the bad stuff of commercial aviation in space at popular prices.
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Maybe we should start actively hunting the bastards then...
 
Archibald said:
Kim Stanley Robinson did it, at least for Mars... in his trilogy.
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That's exactly why there's a shearing charge in my plans. A lot of them, actually, one to limit the amount of falling tether and the rest to chop the falling stuff into pieces small enough to burn up.
 
Nice moving goalposts, but the resonant modes are well known. It's also why the trains are limited to 300kph.
 
PFJN said:
Hi,
Although adding things like shearing charges does seem like a good idea it must be kept in mind that any added weight to the system would increase the required tensile strngth of the cable material further above its already extremely high requirements (see for example https://www.isec.org/space-elevator-newsletter-2024-april/#tether )

Regards

Pat
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When you're talking about a 20+ million ton system a couple thousand kg of explosives is a rounding error.
 
This is why I like backspun flyby rotorvators--not as massy, less prone to icing, etc.
 
publiusr said:
This is why I like backspun flyby rotorvators--not as massy, less prone to icing, etc.
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How often can they send a load into orbit? And how much at a time?

Because if you're going to go through the effort to make a beanstalk, make it big enough to DO things!
 
martinbayer said:
Never mind - I watched Bullet Train on a recent travel leg and found it to be a delightful blood soaked contemporary fun diversion - no more, no less :)...
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They should have stayed with the original title: Psychopathic Killers with Good Language Skills on a Train.

I... uh... hated it.
 
Scott Kenny said:
When you're talking about a 20+ million ton system a couple thousand kg of explosives is a rounding error.
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Uh I'll point out that because the cable design is likely to be highly resistant to individual 'strands' being cut the amount of effort and explosive goes up kinda fast. It's a balanced game, likely you'll have "replacement" points along the cable where you can splice in new sections to replace those that are older or damaged but it's not easy to build and there's always the chance of accidental discharge. (That came out wrong :) )

Scott Kenny said:
How often can they send a load into orbit? And how much at a time?

Because if you're going to go through the effort to make a beanstalk, make it big enough to DO things!
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Oh agree but the timing is actually a design issue and a question of how you're doing re-boost. Depends on if you have a high impulse design (say chemical) for re-boost or an more efficient (say SEP) engine. The former can make pickups every time the end is in position the latter might only be able to 'launch' once or twice a day.

I personally don't like rotovators as much as the standard skyhook's but the rotovator is closer to "today's" technology than the latter.

Randy
 
Scott Kenny said:
When you're talking about a 20+ million ton system a couple thousand kg of explosives is a rounding error.
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Hi,
I believe that you may be underestimating some of the issues
For starters the proposed cable material has not only a high tensile strength but also apparently a high shear strength. If I am understanding correctly the shear strength may be on the order of 0.21 to 0.49 TPa. As such, any shearing charges would have to be large enough to apply sufficient force to shear that material.

Secondly there is a question of how many would be needed. From this wiki page on space elevator risks it suggests that if a break occurs below an altitude of 25,000km, while the upper part would likely be carried upward by the now freed counterweight, the lower section (below the break) would fall to Earth. The question then becomes how long of a segment should this lower portion of the tether be broken into by the shearing charges to ensure that they will "burn up" in free fall. As just a very random guess, even if we assume a 10km spacing between shearing charges that would mean that we would need 2500 charges along this lower segement of the cable. Addd to this is the additional weight of the detonation triggering device. If these shear charges are intended to be "wired" to a control station then you will need to add the weights in for all the cables that will be needed to extend over that 25,000km length. Conversely, if the charge detonators are either trigered by radio, or some other signal, then we would need to include the weights of those devices as well.

Where it then gets tricky is that these weights aren't just added "straight to" the other weights, but rather, any increase in the weights that the main tether must carry ends up increasing the loads on that tether, thus leading to a need to further increase the size (and hence weight) of the tether itself.

In the paper referenced previously, the authors make use of a unit of measure called the Mega Yuri, which represents the "yield stress (or breaking stress) per unit of density of a material under tension", where 1 Yuri is equal to 1 Pa⋅m3/kg or 1 N⋅m/kg, which is the breaking/yielding force per linear density of the cable under tension. Thus 1 M Yuri would be equal to 1,000,000 Pa m3/kg. Also in that paper it is noted that "a working stress of 38.9 MYuri (89.4 GPa with 2298.5 kg/m3 density) would result in a tether mass of 4,492 tonnes, with a cross-sectional area rising from 7 mm2 at the Earth to 23.7 mm2 at GEO." Whereas, if the value of yeild stress/unit density were have (such as if the weight of the cable per unit mass were doubled) then the mass of the tether "would be 26,608 tonnes, with a cross-sectional area rising from 14.1 mm2 at the Earth to 163 mm2 at GEO." Or in other words a doubling of the notional total weight of the tether while keeping the yield stress constant increases the total weight of the tether by a factor of 5.92 (=26,608/4,492).

As such, if we are adding weights along the length of the tether from the ground level up to a 25,000km height, then we are effectively increasing the "notional density" of that material over that length, and hence we should expect not only an increase in the total weight of the fixed equipment due to the addition of these charges (and detonators etc) but also an increase in the weight of the tether itself, which which will have to get bigger to support this added weight, and the increase will not likely be a simple straight line increase.

Regards

Pat
 
Scott Kenny said:
How often can they send a load into orbit? And how much at a time?

Because if you're going to go through the effort to make a beanstalk, make it big enough to DO things!
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I was thinking of having a space-base floating at sea. It would have lathes, a machine shop, medical facilities, etc.

An asteroid rotorvator would yank this base off the ocean in one go.

It would have SRBs to lessen the loads...have hydrofoils...

Once in space, it can slowly be pushed to its destination.
 
edwest4 said:
They should have stayed with the original title: Psychopathic Killers with Good Language Skills on a Train.

I... uh... hated it.
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De gustibus non est disputandum/certandum. Also, Sandra Annette Bullock, if only for a few precious minutes. Haters gonna hate, I guess...
 
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martinbayer said:
De gustibus non est disputandum/certandum. Also, Sandra Annette Bullock, if only for a few precious minutes. Haters gonna hate, I guess...
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Martin,

I expected better from you. Meum commentum sincerum fuit. Non erat scandalizare.
 
edwest4 said:
I was raised a European. I am concerned that America has warped your German upbringing, especially California.
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I actually consider living in SoCal truly/honestly mind expanding in the best sense (and I haven't even yet tried any mind altering locally legal drugs that would violate my current employer's company policy, because that will have to wait until after retirement), but I'm a stubborn oldish bastard with my core values pretty much set since over 4 decades ago, and I actually always strive to do my best in any situation, so WYSIWYG.
 
martinbayer said:
I actually consider living in SoCal truly/honestly mind expanding in the best sense (and I haven't even yet tried any mind altering locally legal drugs that would violate my current employer's company policy, because that will have to wait until after retirement), but I'm a stubborn oldish bastard with my core values pretty much set since over 4 decades ago, and I actually always strive to do my best in any situation, so WYSIWYG.
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For what it's worth, my core values have no reason to change.
 
My proposal is, to use a hollow string and shoot a magnetic piston inside by compressed air (Helium or H2 might be better suited). The capsule on the outside would be connected by strong magnets to the inside piston. From a certain point onwards, the pressure must be reduced before piston and capsule will crash into the counterweight by the expanding gas volume.

@martinbayer : I'm not so sure about the information quality of the English language. If you ever talked to a patent attorney you will probably learn, that German is much more capable of describing precisely than English. Despite my not so sophisticated English, I have to agree, that it is much easier to learn than French (learned it in school) and probably most other languages.
 

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