5 ms·
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 lau
by skykooler 4y ago
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.
- dmitrygr 4y agoI 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
- skykooler 4y agoA 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.
- dmitrygr 4y agoI 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
- skykooler 4y agoAir 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.
- dmitrygr 4y agoand you said "as it hits ground" which means it WILL go through atmosphere and decelerate...
- jrpt 4y agoIt 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.