7 ms·

TIL it's estimated that over 48 tons of meteors hit the atmosphere every day. Regarding actual space elevators though, while they're not sci-fi to the extent o

TIL it's estimated that over 48 tons of meteors hit the atmosphere every day. Regarding actual space elevators though, while they're not sci-fi to the extent of something like FTL travel - ie. they're technically not physically impossible - they're still pretty firmly in the realm of sci-fi. We don't have anything close to a cable that could sustain its own weight, let alone that of whatever is being elevated. Plus, how do you stabilize the cable and lifter in the atmosphere? A space elevator on the moon is much more feasible: less gravity, slow rotation, no atmosphere, less dangerous debris. But it's also much less useful.

lnsru 1y ago
Space elevator was the perfect application for carbon nanotubes according my professor few decades ago. I wish humanity could unite for such project and enter space exploration phase. But I feel it will stay sci-fi forever.
- tiagod 1y ago
  Thing is, you're going to invest massive amounts of R&D in something that might be impossible, when you could invest in actually building stuff in space so you only need to shoot humans out there.
  - floxy 1y ago
    Instead of massive amounts of R&D, why not small amounts for the next 100 years? Seems like this is something a tech bro could bequeath to humanity, Nobel style. A $250 million fund that pay out $10 million per year in grants. And maybe some larger chunks when the board of directors sees a good opportunity to do larger scale trials.
    - tiagod 1y ago
      I'm pretty sure we've invested way more than $250m in carbon nanotubes.
Yizahi 1y ago
The problem with space elevator is not only the lack of material today, but also the fact that such elevator is an ultimate and very fragile weapons platform, you basically get stones up the well and then drop them on the enemy. Meaning that any authoritarian country would destroy it even before it is ever built. And sturdy enough space elevator after it's break at any high point would start falling down on the planes in a loop, eventually flattening everything in its path when higher portions reach supersonic speeds. So unfortunately there is low chance it will be built, unless we sort out stuff on the planet first.
- pbmonster 1y ago
  I don't see it. Why worry about a weaponized space elevator when stealth bombers, cruise missiles and ICBMs exist? If the power building the space elevator wants to bomb you, you're going to get bombed.
  - tsimionescu 1y ago
    The bigger problem I think is the elevator itself. Cutting it and letting it fall would be far more destructive than any weapon ever fired or even conceived.
    - pbmonster 1y ago
      Probably no easy task. Snipping off just the first few kilometers is not catastrophically destructive yet, and cutting it down further up would require multistage rocket designs, sophisticated steering/targeting and potentially significant yield (you'd need to cut unobtainium, after all...). If you can build a space elevator, you can defend against those. You better thoroughly inspect what cargo you put on the elevator itself, of course.
      - tsimionescu 1y ago
        Only if the material is way over provisioned. In general, the higher the intrinsic structural load is on a material, the easier it will be to destroy. So, to defend from these attacks, you not only need a cable that can support its own weight, plus the weight of the desired payload, plus some small-is extra tolerance. Instead, you probably need a cable that can support, say, twice its own weight plus four-five times the payload. Not to mention, now you don't only need excellent strength along the cable, but also across from it, and extreme heat resistance too (all of the strength is irrelevant if it's enough to coat some part of the cable in thermite and ignite it)
pbmonster 1y ago
> A space elevator on the moon is much more feasible: less gravity, slow rotation The slow rotation is a minus, it means you've got to string the tether up to L1 instead of "just" up to geo/luna-stationary orbit. A lunar space elevator needs to be at least 56000 km long, more than 20000 km longer than the one to earth. > But it's also much less useful. Yeah, especially because all the things that make lunar space elevators a little more attainable also make lunar mass drivers a lot more attainable. Why ride in an elevator for a week if you also can just be fired from a cannon?
- pfdietz 1y ago
  A space elevator is kind of like a vertical mass driver, so just build one of those along the surface of the moon with modest acceleration, survivable by passengers. Rotating cables ("rotavators") on the moon seem much more practical than full space elevators. https://en.wikipedia.org/wiki/Momentum_exchange_tether#Rotovator https://en.wikipedia.org/wiki/Momentum_exchange_tether#Rotov...
- tempestn 1y ago
  Ah, good catch. Stand corrected on that one.
adwn 1y ago
Almost all discussions around space elevators focus on the cable itself, how to manufacture and deploy it, and completely forget about the issues that would arise afterwards: 1) How do you attach the climber to the cable without affecting its structural integrity? By squeezing it really hard? A material that's optimized for longitudinal tension strength is probably not very tolerant of lateral compression. 2) How do you provide power to the climber? A regular electric cable can't support its own weight, so either you have to attach it to the climbing cable, or you have to make it from the same material. 3) Is it even worth it? The climber needs to cover a distance of ~36,000 km, so even at 200 km/h it takes 7.5 days from the bottom to geosynchronous orbit. How many climbers and what payload can the cable support at the same time? Refer to issue #1 regarding limits in speed and mass per climber. The throughput in tonnes/day is absolutely abysmal in relation to the immense upfront infrastructure cost per elevator. Compare this to SpaceX's Starship, which is getting closer and closer to fully reusable 100 tonnes to orbit in minutes. Space elevators will stay science fiction forever, not because they're infeasible, but because they're useless.
- seer 1y ago
  If you somehow manage to get magnetic fields involved, so you are not afraid of friction with the cable itself, at 1.3 max apparent acceleration/deceleration (after a turnover) and including earth’s gravity you get 116min to geostationary. If you account for various inefficiencies like taking it slow in the lower atmosphere Ant whatnot, it still should be in the matter of hours. So totally feasible and even comfortable.
  - adwn 1y ago
    > If you somehow manage to get magnetic fields involved, so you are not afraid of friction with the cable itself, at 1.3 max apparent acceleration […] This means that half-way after 58 minutes, the climber is traveling at 0.3 * 9.81 m/s² * 60 * 58 ~= 10.2 km/s ~= 36,720 km/h (!!!) relative to the cable. A tiny imperfection or wobble is going to make the climber crash into the cable, destroying both. A climber with a mass of 10 tonnes requires 10^4 kg * 1.3 * 9.81 m/s² ~= 127.5 kN of force to accelerate at 1.3 g. At the ~56 minute mark, the climber reaches a speed of ~9,888 m/s. This means it requires a power output of 127.5 kN * 9888 m/s = 1.26 GW (!!!) to achieve this acceleration, plus overhead for the power electronics and transmission. Even at a voltage of 1 kV, that's around 1,500,000 A (!!!) of current that you have to transmit and invert. If you have a way to reliably transfer that amount of power without touching the cable which is moving at 10 km/s relative speed, or with touching but without immediately melting the cable or the collector, let me know :-) > So totally feasible lol no
lloeki 1y ago
Well if it's contingent to having massive amounts of unobtainium and subject to unsolvable engineering reality check conundrums then it's just as unlikely as an Alcubierre drive which "only" needs exotic matter that allows negative energy.
tsimionescu 1y ago
While a space elevator doesn't contradict any fundamental limits of physics, that doesn't mean it's actually possible to build one. There is no reason to be certain that it's actually possible to create a material that has the required characteristics in terms of tensile strength to support it's own weight, plus the weight of the elevator, plus the weight of all the additional cabling. It also has to endure the huge temperature differences that it will experience along its length and from day to night and from season to season. This is especially true considering that you don't need something that barely holds - you need something that you know will hold up to many times more weight than it needs to, so that it can be safe: the potential energy such a thing would store would be enough to dig into hundreds of meters of rock all around the world, if it ever crashed. So, you have to ensure there is no realistic chance of it ever crashing. It also has to be highly non-fragile in other ways, so that a madman with a bomb or a freak collision with an airplane or a meteor (especially likely in the thin upper layers of the atmosphere) won't bring it all down. This combination of properties may well be completely impossible to actually achieve in a material. Even if there is no obvious basic law of physics that it would break, that doesn't mean that it wouldn't break other, harder to touch, derived laws.
- Jolter 1y ago
  A terrorist attack on a space elevator happens to figure in the first episode of the TV series Foundation. https://foundation.fandom.com/wiki/Bombing_of_the_Star_Bridge https://foundation.fandom.com/wiki/Bombing_of_the_Star_Bridg... It’s about as devastating as you would expect.
  - lproven 1y ago
    That's odd. The first episode was the only one I watched and I don't remember that bit. It might have grabbed me. A terrorist attack on a space elevator is a pivotal plot point in Blue Mars by Kim Stanley Robinson, which IMHO is a better work in basically every way than Asimov's magnum opus.
    - Metacelsus 1y ago
metalman 1y ago
thing is we do have materials strong enough, because as it turns out the issue with strength is in flaws between indivual molecules in any given material, not so much the type of material, and very small amples with perfect molecular bonds are plenty strong, but getting consistent perfect molecular bonds is the challenge, and if this can be done, other technologys ,such as vacume ballons will be possible, such as flying citys to go with the space rlevators
zoomzoom 1y ago
There are designs for untethered structures in orbit that could function with current technology, e.g. https://en.wikipedia.org/wiki/Skyhook_(structure) https://en.wikipedia.org/wiki/Skyhook_(structure)
fijiaarone 1y ago
Have you ever tried to balance a string on its end? It gets harder, the longer the string is. There aren’t any other physics than that.
- hermitcrab 1y ago
  I think most plans envisage a large mass (such as a captured asteroid) in geostationary orbit to anchor the top of the elevator cable.
- LorenPechtel 1y ago
  Tension, not compression. Doesn't matter how floppy it is.
JumpCrisscross 1y ago
> while they're not sci-fi to the extent of something like FTL travel - ie. they're technically not physically impossible On Earth. Zylon or M5 [1] could build an elevator on Mars. Kevlar on the Moon. To drive this home, it’s estimated we could build a lunar space elevator for less than what Bechtel fleeced NASA for a mobile SLS launcher [2][3]. [1] https://en.wikipedia.org/wiki/M5_fiber https://en.wikipedia.org/wiki/M5_fiber [2] https://opsjournal.org/DocumentLibrary/Uploads/The_Lunar_Space_Elevator_a_Near_Term_Mea%20(1).pdf https://opsjournal.org/DocumentLibrary/Uploads/The_Lunar_Spa... [3] https://oig.nasa.gov/wp-content/uploads/2024/02/IG-22-012.pdf https://oig.nasa.gov/wp-content/uploads/2024/02/IG-22-012.pd...

lnsru 1y ago

Space elevator was the perfect application for carbon nanotubes according my professor few decades ago. I wish humanity could unite for such project and enter space exploration phase. But I feel it will stay sci-fi forever.

tiagod 1y ago
Thing is, you're going to invest massive amounts of R&D in something that might be impossible, when you could invest in actually building stuff in space so you only need to shoot humans out there.
- floxy 1y ago
  Instead of massive amounts of R&D, why not small amounts for the next 100 years? Seems like this is something a tech bro could bequeath to humanity, Nobel style. A $250 million fund that pay out $10 million per year in grants. And maybe some larger chunks when the board of directors sees a good opportunity to do larger scale trials.
  - tiagod 1y ago
    I'm pretty sure we've invested way more than $250m in carbon nanotubes.

Yizahi 1y ago

The problem with space elevator is not only the lack of material today, but also the fact that such elevator is an ultimate and very fragile weapons platform, you basically get stones up the well and then drop them on the enemy. Meaning that any authoritarian country would destroy it even before it is ever built. And sturdy enough space elevator after it's break at any high point would start falling down on the planes in a loop, eventually flattening everything in its path when higher portions reach supersonic speeds. So unfortunately there is low chance it will be built, unless we sort out stuff on the planet first.

pbmonster 1y ago
I don't see it. Why worry about a weaponized space elevator when stealth bombers, cruise missiles and ICBMs exist? If the power building the space elevator wants to bomb you, you're going to get bombed.
- tsimionescu 1y ago
  The bigger problem I think is the elevator itself. Cutting it and letting it fall would be far more destructive than any weapon ever fired or even conceived.
  - pbmonster 1y ago
    Probably no easy task. Snipping off just the first few kilometers is not catastrophically destructive yet, and cutting it down further up would require multistage rocket designs, sophisticated steering/targeting and potentially significant yield (you'd need to cut unobtainium, after all...). If you can build a space elevator, you can defend against those. You better thoroughly inspect what cargo you put on the elevator itself, of course.
    - tsimionescu 1y ago
      Only if the material is way over provisioned. In general, the higher the intrinsic structural load is on a material, the easier it will be to destroy. So, to defend from these attacks, you not only need a cable that can support its own weight, plus the weight of the desired payload, plus some small-is extra tolerance. Instead, you probably need a cable that can support, say, twice its own weight plus four-five times the payload. Not to mention, now you don't only need excellent strength along the cable, but also across from it, and extreme heat resistance too (all of the strength is irrelevant if it's enough to coat some part of the cable in thermite and ignite it)

pbmonster 1y ago

> A space elevator on the moon is much more feasible: less gravity, slow rotation The slow rotation is a minus, it means you've got to string the tether up to L1 instead of "just" up to geo/luna-stationary orbit. A lunar space elevator needs to be at least 56000 km long, more than 20000 km longer than the one to earth. > But it's also much less useful. Yeah, especially because all the things that make lunar space elevators a little more attainable also make lunar mass drivers a lot more attainable. Why ride in an elevator for a week if you also can just be fired from a cannon?

pfdietz 1y ago
A space elevator is kind of like a vertical mass driver, so just build one of those along the surface of the moon with modest acceleration, survivable by passengers. Rotating cables ("rotavators") on the moon seem much more practical than full space elevators. https://en.wikipedia.org/wiki/Momentum_exchange_tether#Rotovator https://en.wikipedia.org/wiki/Momentum_exchange_tether#Rotov...
tempestn 1y ago
Ah, good catch. Stand corrected on that one.

adwn 1y ago

Almost all discussions around space elevators focus on the cable itself, how to manufacture and deploy it, and completely forget about the issues that would arise afterwards: 1) How do you attach the climber to the cable without affecting its structural integrity? By squeezing it really hard? A material that's optimized for longitudinal tension strength is probably not very tolerant of lateral compression. 2) How do you provide power to the climber? A regular electric cable can't support its own weight, so either you have to attach it to the climbing cable, or you have to make it from the same material. 3) Is it even worth it? The climber needs to cover a distance of ~36,000 km, so even at 200 km/h it takes 7.5 days from the bottom to geosynchronous orbit. How many climbers and what payload can the cable support at the same time? Refer to issue #1 regarding limits in speed and mass per climber. The throughput in tonnes/day is absolutely abysmal in relation to the immense upfront infrastructure cost per elevator. Compare this to SpaceX's Starship, which is getting closer and closer to fully reusable 100 tonnes to orbit in minutes. Space elevators will stay science fiction forever, not because they're infeasible, but because they're useless.

seer 1y ago
If you somehow manage to get magnetic fields involved, so you are not afraid of friction with the cable itself, at 1.3 max apparent acceleration/deceleration (after a turnover) and including earth’s gravity you get 116min to geostationary. If you account for various inefficiencies like taking it slow in the lower atmosphere Ant whatnot, it still should be in the matter of hours. So totally feasible and even comfortable.
- adwn 1y ago
  > If you somehow manage to get magnetic fields involved, so you are not afraid of friction with the cable itself, at 1.3 max apparent acceleration […] This means that half-way after 58 minutes, the climber is traveling at 0.3 * 9.81 m/s² * 60 * 58 ~= 10.2 km/s ~= 36,720 km/h (!!!) relative to the cable. A tiny imperfection or wobble is going to make the climber crash into the cable, destroying both. A climber with a mass of 10 tonnes requires 10^4 kg * 1.3 * 9.81 m/s² ~= 127.5 kN of force to accelerate at 1.3 g. At the ~56 minute mark, the climber reaches a speed of ~9,888 m/s. This means it requires a power output of 127.5 kN * 9888 m/s = 1.26 GW (!!!) to achieve this acceleration, plus overhead for the power electronics and transmission. Even at a voltage of 1 kV, that's around 1,500,000 A (!!!) of current that you have to transmit and invert. If you have a way to reliably transfer that amount of power without touching the cable which is moving at 10 km/s relative speed, or with touching but without immediately melting the cable or the collector, let me know :-) > So totally feasible lol no

lloeki 1y ago

Well if it's contingent to having massive amounts of unobtainium and subject to unsolvable engineering reality check conundrums then it's just as unlikely as an Alcubierre drive which "only" needs exotic matter that allows negative energy.

tsimionescu 1y ago

While a space elevator doesn't contradict any fundamental limits of physics, that doesn't mean it's actually possible to build one. There is no reason to be certain that it's actually possible to create a material that has the required characteristics in terms of tensile strength to support it's own weight, plus the weight of the elevator, plus the weight of all the additional cabling. It also has to endure the huge temperature differences that it will experience along its length and from day to night and from season to season. This is especially true considering that you don't need something that barely holds - you need something that you know will hold up to many times more weight than it needs to, so that it can be safe: the potential energy such a thing would store would be enough to dig into hundreds of meters of rock all around the world, if it ever crashed. So, you have to ensure there is no realistic chance of it ever crashing. It also has to be highly non-fragile in other ways, so that a madman with a bomb or a freak collision with an airplane or a meteor (especially likely in the thin upper layers of the atmosphere) won't bring it all down. This combination of properties may well be completely impossible to actually achieve in a material. Even if there is no obvious basic law of physics that it would break, that doesn't mean that it wouldn't break other, harder to touch, derived laws.

Jolter 1y ago
A terrorist attack on a space elevator happens to figure in the first episode of the TV series Foundation. https://foundation.fandom.com/wiki/Bombing_of_the_Star_Bridge https://foundation.fandom.com/wiki/Bombing_of_the_Star_Bridg... It’s about as devastating as you would expect.
- lproven 1y ago
  That's odd. The first episode was the only one I watched and I don't remember that bit. It might have grabbed me. A terrorist attack on a space elevator is a pivotal plot point in Blue Mars by Kim Stanley Robinson, which IMHO is a better work in basically every way than Asimov's magnum opus.
  - Metacelsus 1y ago

metalman 1y ago

thing is we do have materials strong enough, because as it turns out the issue with strength is in flaws between indivual molecules in any given material, not so much the type of material, and very small amples with perfect molecular bonds are plenty strong, but getting consistent perfect molecular bonds is the challenge, and if this can be done, other technologys ,such as vacume ballons will be possible, such as flying citys to go with the space rlevators

zoomzoom 1y ago

There are designs for untethered structures in orbit that could function with current technology, e.g. https://en.wikipedia.org/wiki/Skyhook_(structure) https://en.wikipedia.org/wiki/Skyhook_(structure)

fijiaarone 1y ago

Have you ever tried to balance a string on its end? It gets harder, the longer the string is. There aren’t any other physics than that.

hermitcrab 1y ago
I think most plans envisage a large mass (such as a captured asteroid) in geostationary orbit to anchor the top of the elevator cable.
LorenPechtel 1y ago
Tension, not compression. Doesn't matter how floppy it is.

JumpCrisscross 1y ago

> while they're not sci-fi to the extent of something like FTL travel - ie. they're technically not physically impossible On Earth. Zylon or M5 [1] could build an elevator on Mars. Kevlar on the Moon. To drive this home, it’s estimated we could build a lunar space elevator for less than what Bechtel fleeced NASA for a mobile SLS launcher [2][3]. [1] https://en.wikipedia.org/wiki/M5_fiber https://en.wikipedia.org/wiki/M5_fiber [2] https://opsjournal.org/DocumentLibrary/Uploads/The_Lunar_Space_Elevator_a_Near_Term_Mea%20(1).pdf https://opsjournal.org/DocumentLibrary/Uploads/The_Lunar_Spa... [3] https://oig.nasa.gov/wp-content/uploads/2024/02/IG-22-012.pdf https://oig.nasa.gov/wp-content/uploads/2024/02/IG-22-012.pd...