We do not have any known materials which are anywhere near strong enough on the macro scale for a space elevator on Earth. If we did, we would still need to launch it into space using conventional rockets in the first place, which would cost trillions of dollars at current launch prices and require solving a bunch of new issues (if it's launched in segments, how do you join them together at full strength in space? if it isn't, how do you coordinate ten thousand rockets to launch into orbit simultaneously - and where do you launch them all from?) Once it's in space, you have the issue that it necessarily will need to be above the equator, which every satellite in space crosses twice per orbit - and there's no good way to make a structure as large as a space elevator try to dodge things, so it also needs to be strong enough that it can handle impacts from space debris or derelict satellites at orbital velocities without weakening to the point that it breaks.

And then of course you need to supply power to anything climbing it - which is an immense amount of energy required to climb 30,000+ miles vertically - and there's no practical way of sending that energy up the cable itself (you could do it with superconductors, but the power requirements for cooling thirty thousand miles of superconducting cable is more than many nations consume). One option is to use microwaves to beam power to the climber, but this is currently only theoretical, and raises further materials science issues with the microwaves heating up the cable along its length.

Finally, having a space elevator is a massive hazard to the Earth in general. If most structures on Earth fail, the damage is limited to a small area where the structure stands. If a space elevator ever fails for any reason, it would wrap around the equator as it fell, releasing the equivalent of two Hiroshima bomb every mile along the equator as its kinetic energy is rapidly converted into heat. It's not quite as bad as the asteroid that wiped out the dinosaurs, but it would still be enough to significantly alter the climate and wipe out at least half a billion people from the impact alone. It's not a project that should be undertaken lightly.

I am not sure what assumptions you are making in your last paragraph, but I think you are off by enough orders of magnitude to assume you pulled those numbers out of thin air (at best)

> equivalent of two Hiroshima bomb every mile along the equator as its kinetic energy is rapidly converted into heat.

Little boy was 15 kilotons of TNT (63 TJ). Kinetic energy is 1/2 mv^2.

So you are claiming that the mass of a mile of the cable is such that mv^2 = 126e12 J

At equator the planet rotates at 463.8 m/s so you are assuming that the bottom mile of the cable weighs 585.5e6 kg? Ok, you're completely off base here.

Maybe let's look at a higher segment (at geosync orbit). Velocity there is 3.1e3 m/s. You are assuming a mile of that cable weighs 13e6kg. But on the way down it will both ablate (lowering mass) and slow down (lowering velocity), so you are assuming an even more insane higher number.

For comparison, a mile of one inch thick steel cable is ONLY 4e3 kg. Sure, space elevator needs something stronger, but even more so, lighter.

Yeah, you are just off by MANY orders of magnitude, and that claim was likely pulled out of nowhere

A space elevator needs to be far thicker than one inch at high altitude. Even assuming the absolute minimum diameter to safely lift a 2-ton capsule of about half an inch at the bottom (which means the cable will break when the first piece of space debris encounters it), any current material - the best currently available is Kevlar - needs to be about 800 feet wide at geostationary orbit before tapering down again. This would weigh about 130 million tons per mile. Of course, the cable tapers to the ends, so I averaged over the whole length to reach that figure. Also, energy that goes into ablation doesn't just disappear - it dissipates into the atmosphere as heat, which means it contributes to the overall energy from the impact. And in falling it does not slow down, but rather speeds up - descending from geostationary orbit will accelerate something to about 10e3 m/s, further increasing the energy.

I mentioned that... But it needs to be light. The quoted weights are unrealistic for ANY material

> descending from geostationary orbit will accelerate something to about 10e3 m/s, further increasing the energy.

In vacuum, yes, but we have air...resistance

Air resistance is only a factor up to forty miles or so; most of that acceleration happens in the preceding twenty thousand miles. And again, air resistance just means more energy dissipation in the form of a blast wave.

and you said "as it hits ground" which means it WILL go through atmosphere and decelerate...

It actually doesn’t need to be exactly on the equator but just approximately, so it can move around a little bit to dodge things.

That last paragraph doesn’t make sense though.

There are currently insurmountable materials science limitations, and even the materials that come close are not currently possible to manufacture at scale, or even assemble (one carbon nanotubes does not necessarily have the same properties of many carbon nanotubes) at scale into structures which will withstand the structural stresses. I believe this is not necessarily true for other celestial objects besides the earth

For example, Pluto and Charon is a pair that sometimes comes up; a space elevator connecting Pluto to Charon would very possibly just about be within our current civilisation's capabilities, if for some reason we cared to build one enough to sink the Earth's economic output into it. They're tidally locked. (https://en.wikipedia.org/wiki/Space_elevator has its section on "Extraterrestrial elevators".)

A space elevator for our own moon would be far more interesting to me. It could be built with known materials.

Is that true? I thought getting a 28 day period on the moon is beyond the orbit of the moon itself.

I meant for going from the Moon surface to an orbit around the Moon, not reaching Earth.

Yeah I looked up the moon proposals and fundamentally they have to go to L1/L2 points and they are not stationary on the surface or have to pivot around the poles. A tether that was lunostationary is impossible since it would have to cut through the earth

The anchor point on the moon will be fixed. It's the counter weight at L1/L2 that will drift and will need some (small, according to Wikipedia) correction.

No. Stop and think about it. The moon rotates every 28 days with respect to L1/L2.

I try! :-D

Isn't the moon tidally locked and that's why we never see the "far side" of the moon?

And the lagrange points are between us and the moon?

If so, I don't understand why the anchor on the moon can't be fixed.

For what it's worth, I think you're right, although it's been a very long time since I did any mechanics. The tidal locking isn't completely perfect, so the elevator would probably have to be basically a spool of rope rather than an anchor; and the Moon's axis of rotation precesses every 18 years ish per https://en.wikipedia.org/wiki/Cassini%27s_laws, so again there would need to be quite a lot of flex in the elevator; but I don't see why it couldn't be done.

I could be wrong but I remember reading somewhere that mars is doable with reinforced nylon cables

Ok downvotes but I looked it up on a not-necessarily-authoritative source it's estimated that a zylon cable would have a taper ratio of 13, with a mass of ~1k tons.

Earth space elevator is supposed to be grounded somewhere on equator, the orbital point is on the geostationary orbit and further away there is a counterbalance.

There are currently no plausible way to avoid collisions of such a structure with satellites which are below the geostationary orbit. Sooner or later each passive satellite will hit the elevator, and active satellites will have to actively avoid collisions for the whole time they are on the orbit. Any collision would likely disintegrate the satellite and bring serious damage to the elevator - easily enough to break the elevator; after all we're talking about colossal kinetic energy in collision.

Even if nanotubes would be used and could work by themselves - I'm optimistic on that - the inherent conflict between space elevator and the rest of cosmonautics currently is enough to prevent this idea from working.