Fibre for space elevator

[Cassel]

This should work?

https://www.scmp.com/news/china/society/article/2170193/china-has-strongest-fibre-can-haul-160-elephants-and-space

[kerbiloid]

Spoiler

 

 

[Scotius]

Hmm. 1,5 gram of carbon to get 1 centimeter of cable - of which we need 30 000 kilometers. Likely more, for safety and redundance reasons. Do we even have that much carbon available for processing? And how such big demand would influence other branches of industry, which use lots of carbon for many important products?

Luckily we have those... https://en.wikipedia.org/wiki/C-type_asteroid

A bit far away, though

[magnemoe]

33 minutes ago, Scotius said:

Hmm. 1,5 gram of carbon to get 1 centimeter of cable - of which we need 30 000 kilometers. Likely more, for safety and redundance reasons. Do we even have that much carbon available for processing? And how such big demand would influence other branches of industry, which use lots of carbon for many important products?

Luckily we have those... https://en.wikipedia.org/wiki/C-type_asteroid

A bit far away, though

1.5 ton for an km, so 45.000 ton one downside is that the elevator also has to hold this weight, you would also need more of it as you need an counterweight so over 100.000 ton. Still its an shipload or two. Now getting it into orbit would take 1000 launches with the BFR so yes an asteroid makes some sense here. 
More an problem producing kiloton rater than milligram of carbon nanotubes. 

[KSK]

3 hours ago, Scotius said:

Hmm. 1,5 gram of carbon to get 1 centimeter of cable - of which we need 30 000 kilometers. Likely more, for safety and redundance reasons. Do we even have that much carbon available for processing? And how such big demand would influence other branches of industry, which use lots of carbon for many important products?

Luckily we have those... https://en.wikipedia.org/wiki/C-type_asteroid

A bit far away, though

We have plenty of carbon for processing. We use millions of tons of impure carbon slurry per year to make paper, cardboard and such like materials. Japan alone gets through around 10 million tons per year. Why Japan? First easy to read site that I came across.

Granted, wood pulp is nowhere near pure carbon but using @magnemoe's 100,000 ton figure, I'm pretty confident that we have enough carbon and some to spare.  Turning that carbon into space elevator grade fibre and launching that fibre to orbit, is somewhat more challenging.

[Cassel]

3 hours ago, Scotius said:

Hmm. 1,5 gram of carbon to get 1 centimeter of cable - of which we need 30 000 kilometers. Likely more, for safety and redundance reasons. Do we even have that much carbon available for processing? And how such big demand would influence other branches of industry, which use lots of carbon for many important products?

Luckily we have those... https://en.wikipedia.org/wiki/C-type_asteroid

A bit far away, though

1cm³ weights 1.6g and can hold 800 tons?

So 160kg for 1km cable (cross-section 1cm) and this cable should hold 800t if I am not mistaken.
What gives me 800 tons of 1cm cross-section is 5000km long cable and it can hold itself.

For 30,000km long elevator cable you need 6 cables (1cm cross section) and all would weight 4800t?

Edited October 29, 2018 by Cassel

[kerbiloid]

Any material is strong because its atoms pull each other together.

The atom pull each each other by electromagnetic forces.

So, any thread is a chain of atom-sized electromagnetic retranslators.

Better find a way to move the objects with the electromagnetic forces directly.

[Scotius]

I thought about it too. Iron atoms inside carbon nanotubes? How much iron\magnetic material we would need for an elevator to gain "traction" with electromagnetic field?

[Gargamel]

15 hours ago, Scotius said:

Do we even have that much carbon available for processing?

Well, If we can efficiently harvest it out of the air, that solves global warming too. 

3 hours ago, Scotius said:

I thought about it too. Iron atoms inside carbon nanotubes? How much iron\magnetic material we would need for an elevator to gain "traction" with electromagnetic field?

Now you're adding a significant amount of mass to the tubes...

[cubinator]

3 hours ago, Scotius said:

I thought about it too. Iron atoms inside carbon nanotubes? How much iron\magnetic material we would need for an elevator to gain "traction" with electromagnetic field?

What if you put an electric current through the cable?

Also:

Quote

laser cannons

 

[YNM]

The minimum tensile strength that would satisfy LRFD standards is around 98 GPa. I'm using this paper for the self-loading weight reference (including the assumed carbon nanotube density of 1300 kg/m³), and using LRFD standards that have a multiplier of 1.4 x (Dead Load), with a further capacity reduction of 0.9 as is seen on steel tension members (albeit for non-cable forms, I haven't found LRFD standard for steel cables/wires).

The calculation above only calculates the weight of the cable itself (dead load). If we use a live load of 60,000 kg (lift + 45 ton payload), with said minimum strength, then the cable needs to have a diameter of 3.2 m. (LRFD standards for this load combination uses 1.2 x (Dead Load) + 1.6 x (Live Load - lifts, payloads etc).) The cable needs to be about 150,000 km long (look at the paper on how it's going to introduce the self-straightening).

And yes, this calculation hasn't counted in wind loading and other serviceability standards (like deformation and aging).

There are a few more concerns that I have, however :

- Carbon nanotubes seems to be very... brittle (doesn't have any ductility at the end of the stress-strain behavior), so most likely there will be additional reduction in capacity to satisfy the standard.

- Does it resist fires and punctures very well ? Does it need sheathing ?

Edited October 30, 2018 by YNM

[kerbiloid]

Spoiler

With such superstrong superstring one can make a trampoline to throw the cargo up.

Or a trebuchet.

 

Edited October 30, 2018 by kerbiloid

[KerikBalm]

They claim that they've made a 70cm long nano tube... this is pretty significant... the military applications may be more important here.

Not to rehash an old thread, but an orbital ring seems more feasible than a space elevator, and would require a minimum tensile strength that is much lower that required by a space elevator... So low that standard kevlar would work just fine...

[YNM]

1 hour ago, KerikBalm said:

an orbital ring seems more feasible than a space elevator

Would they hold tension, bending moment or shear stress ?

EDIT : It seems that they're the same as thin-walled sections.

So, where are you supposed to place them ?

Edited October 30, 2018 by YNM

[KerikBalm]

"Would they hold tension, bending moment or shear stress ?"

The cables to the ring would be under tension, as would the spinning ring

"So, where are you supposed to place them ?"

One of the great things about orbital rings, you could put the ground station's anywhere (provided that they are all in a plane that goes through the center of the Earth

[YNM]

1 hour ago, KerikBalm said:

you could put the ground station's anywhere

No, I mean their orbital height/radius. Different height results in different forces (though it may scale such that it turns out to be a no-variation situation).

Also, how does the ground 'anchors' work ? Do they sling off the orbital section or do they hold up the orbital section ?

1 hour ago, KerikBalm said:

The cables to the ring would be under tension, as would the spinning ring

But not due to axial forces, it's due to 'pressure' almost the same as thin-wall members.

The pressure will be their centrifugal force (so their weight per length as they're orbiting).

[KerikBalm]

yes... so? The ring's in tension because its spun up fast. The cables to the ring stations are just in tension from the weight of the cable hanging down.

The point is you don't need carbon nanotubes for that, its a structure of the same size as the monolithic elevator, and it can be constructed entirely on earth and then deployed. The ride to orbit is much shorter.

[YNM]

1 hour ago, KerikBalm said:

The point is you don't need carbon nanotubes for that

I'd still like to count it though. You know a design they propose ?

Edited October 30, 2018 by YNM

[cubinator]

6 hours ago, KerikBalm said:

Not to rehash an old thread, but an orbital ring seems more feasible than a space elevator, and would require a minimum tensile strength that is much lower that required by a space elevator... So low that standard kevlar would work just fine...

Are we talking a Von Braun-style ring, or a planet-circling ring? Because I think the latter would be easier to build with a space elevator anyway.

[kerbiloid]

Spoiler

GMO beans growing to the sky.

With carbon biofibers.

 

[DerekL1963]

9 hours ago, KerikBalm said:

They claim that they've made a 70cm long nano tube... this is pretty significant... the military applications may be more important here.

If it can be produced in industrial quantities...   There's been any number of "breakthroughs" in this field over the decades that never amounted to anything because (for one reason or another) nobody could figure out how to reliably and repeatably produce in more than microgram quantities. 

[magnemoe]

2 hours ago, cubinator said:

 Are we talking a Von Braun-style ring, or a planet-circling ring? Because I think the latter would be easier to build with a space elevator anyway.

Problem with an planet circling ring with tethers down to the ground is that the ring can not rotate at orbital speed. You can get away with it an theory called active support, have an inner ring spinning far faster than orbital speed who hold the structure up. Problem with this is that happen then some of the magnetic bearings fails or some other fail mode, it would be an train wreck who would be very visible from the moon. 
Pretty sure this has to be far more massive than an space elevator to as it just has to be an long wire.
 

[cubinator]

1 hour ago, magnemoe said:

Problem with an planet circling ring with tethers down to the ground is that the ring can not rotate at orbital speed.
 

You can if it's at GEO altitude. Anyways, you were suggesting more of a regular ring station, like in 2001? That would definitely be feasible with big rockets like BFR.

[kerbiloid]

What looks a little strange in the space lift projects: 

geostationary orbit radius ~=42 000 km
Moon orbit radius ~=384 400 km.

So, Moons is just 9 times farther from the Earth, and the gravity is much less between them.

Why stop at the Earth ring?
An Earth ring by default means the possibility of the First Earth-Moon TerraLunar Cableway Transportation Company.

P.S.
LOP-G may sale transit tickets.

Edited October 30, 2018 by kerbiloid

[Bill Phil]

11 hours ago, cubinator said:

Are we talking a Von Braun-style ring, or a planet-circling ring? Because I think the latter would be easier to build with a space elevator anyway.

Planet circling. It does require less structural strength, but it is an active structure, in that it has moving parts. Most importantly a matter stream travelling at faster than orbital speed that is magnetically deflected so that it stays in place, thus providing "lift" of a sorts. Tether this to ground stations (or use space fountains I guess) and mount accelerators on the ring.

It might be easier to build with a space elevator, but I would argue the orbital ring has at least one advantage. A shorter distance, thus shorter amount of time. The space elevator goes straight through the Van Allen belts, and with a slow elevator passengers could be in the Van Allen belt for weeks. A ring would not. Though this may be a non-issue, depending on a few things.

Regardless, the necessary structural strength exists for a ring, but not for a space elevator.