4 ms·

So, the article said they need a material 100x stronger than steel. I'm not strong on materials science, so can anyone tell me: why not use 100 steel cables?

So, the article said they need a material 100x stronger than steel. I'm not strong on materials science, so can anyone tell me: why not use 100 steel cables? I was imagining assembling the cables into a rope-like structure. After all, rope is an excellent example of how you take relatively weak fibres and assemble them into something much stronger.

fizx 12y ago
It would weigh 100x as much. The key limitation is not collapsing under its own weight.
- roberthahn 12y ago
  That sounds like only part of the answer. Wouldn't increasing the mass of the counterweight keep it from collapsing?
  - function_seven 12y ago
    Yeah, but then you're back where you started. If you multiply the number of strands/fibers/cables, and you also multiply the anchoring mass to counteract that, you're probably still faced with having a tension greater than the material can resist.
    - roberthahn 12y ago
      Right, that makes sense now. Thanks!
  - wwosik 12y ago
    It's the cable breaking, not just falling down.
ColinDabritz 12y ago
Weight. 100 steel cables weigh 100 times as much as one 100x stronger steel cable (requiring 1000 steel cables to hold up, etc). One of the primary challenges with the elevator is holding the cable up.
cbhl 12y ago
If I recall correctly, they want tensile strength, which is measured as force per unit area. The problem with using 100 steel cables is that they have 100x the mass, which means the force per unit area is the same. Hence the need for a new material.
- roberthahn 12y ago
  Oh, I see! Thanks for the explanation.
dalacv 12y ago
Or even more obvious, why not use Superman's hair?
- Zikes 12y ago
  That's just silly. I mean, how would you cut it from his head?
  - kapilvt 12y ago
    kryptonite scissors ofc :-)
ufmace 12y ago
One of the core challenges with the space elevator concept is that they need a cable that can reach from the earth's surface to somewhere beyond geostationary orbit, with exactly how far depending on how they want to arrange the counterweight. The midpoint of that cable will have to support the weight of all of the cable that's below it, and that's around 10-15k miles of cable. So we need a material out of which you can make a 15k mile long cable that can hang free, supporting its own weight. Making it thicker doesn't help, because then you just add more weight that you'll have to support. We need a better material that has this level of strength when manufactured at scale.
- mrfusion 12y ago
  Has anyone looked into the idea of tapering the cables? It would seem like at the bottom on the cable they wouldn't have to support as much weight as at the middle? So could you make them thin at the bottom to save weight and then gradually make them thicker at higher altitudes?
  - cdash 12y ago
    It has been looked at and the figures used might even include tapering. One thing is sure though, even with tapering it is not possible today for a earth space elevator.

fizx 12y ago

It would weigh 100x as much. The key limitation is not collapsing under its own weight.

roberthahn 12y ago
That sounds like only part of the answer. Wouldn't increasing the mass of the counterweight keep it from collapsing?
- function_seven 12y ago
  Yeah, but then you're back where you started. If you multiply the number of strands/fibers/cables, and you also multiply the anchoring mass to counteract that, you're probably still faced with having a tension greater than the material can resist.
  - roberthahn 12y ago
    Right, that makes sense now. Thanks!
- wwosik 12y ago
  It's the cable breaking, not just falling down.

ColinDabritz 12y ago

Weight. 100 steel cables weigh 100 times as much as one 100x stronger steel cable (requiring 1000 steel cables to hold up, etc). One of the primary challenges with the elevator is holding the cable up.

cbhl 12y ago

If I recall correctly, they want tensile strength, which is measured as force per unit area. The problem with using 100 steel cables is that they have 100x the mass, which means the force per unit area is the same. Hence the need for a new material.

roberthahn 12y ago
Oh, I see! Thanks for the explanation.

dalacv 12y ago

Or even more obvious, why not use Superman's hair?

Zikes 12y ago
That's just silly. I mean, how would you cut it from his head?
- kapilvt 12y ago
  kryptonite scissors ofc :-)

ufmace 12y ago

One of the core challenges with the space elevator concept is that they need a cable that can reach from the earth's surface to somewhere beyond geostationary orbit, with exactly how far depending on how they want to arrange the counterweight. The midpoint of that cable will have to support the weight of all of the cable that's below it, and that's around 10-15k miles of cable. So we need a material out of which you can make a 15k mile long cable that can hang free, supporting its own weight. Making it thicker doesn't help, because then you just add more weight that you'll have to support. We need a better material that has this level of strength when manufactured at scale.

mrfusion 12y ago
Has anyone looked into the idea of tapering the cables? It would seem like at the bottom on the cable they wouldn't have to support as much weight as at the middle? So could you make them thin at the bottom to save weight and then gradually make them thicker at higher altitudes?
- cdash 12y ago
  It has been looked at and the figures used might even include tapering. One thing is sure though, even with tapering it is not possible today for a earth space elevator.