I’ve been reading about this subject but I find it difficult to understand because of the large amount of opinions out there about how it would work and why we aren’t building it right now if our actual technology is enough to do it, also because it would be a way to get rid of greenhouse gases apart from the different applications to our plans to space exploration.
In: Engineering
There really aren’t many different opinions on how it would work, the principle is fairly simple and commonly understood.
The reason why wer aren’t building one is that it we don’t really ave the tech, especially the material science to do so. We are also missing the demand to make it economically feasible, but that is a minor concern.
And while a space elevator would do away with the need for a lot of rocket fuel being burned and rockets do burn a lot of rocket fuel, not all rocket fuels produce greenhouses gasses and the overall percentage of greenhouses gasses created by burning rocket fuel is negligible.
To expand on the above:
Rockets go to orbit by burning rocket fuel. Due to the tyranny of the rocket equation most of the fuel you start with ends up doing little more than lifting up other rocket fuel. You have to burn fuel to transport fuel.
A lot of rocket fuel is burned just to go up so that the rocket can do its main job of accelerating to orbital speed in a place where there is less air resistance. This is all very uneconomically.
Having to carry all that fuel around is uneconomically.
If we could produce the energy here on earth to lift up accelerate the rocket it would work much better, but that has issues. (Not that people have entirely giving up on Jules Verne style space guns and beamed energy just yet.)
Another way would be to have the rocke climb a long tower instead.
It takes a lot less energy to send a payload up an elevator to the top of a building that to shoot the same payload to that height with a rocket and the difference gets bigger and bigger the higher you go.
The problem with that is that we can’t build buildings tall enough and that even if we could build a tower 100 km tall, that reaches space, stepping of the tower at the top would not mean you are in orbit.
Orbit means going fast sideways, not just being high up. You would still need to somehow speed up to what would be more than 20 times the speed of sound down here when you reached the top.
However there is an altitude much, much higher up at 35786 km above the ground where the orbital speed is the same as the speed of the ground beneath.
If you could build a tower that tall, you could just step of the top and be in orbit.
But if we can’t build a tower 100 km high to the edge of space we certainly can’t build one 35,786 km high up to geostationary orbit.
What we might be able to do is build a satellite or put a captured asteroid in orbit there and suspend a rope from that down to earth.
The physics for that would work in theory. We would need to also suspend a rope a bit higher up to have a counterweight at an even higher altitude.
A vessel could climb this rope or cable to the top and then go from there.
To reach a different orbit or even another planet from geostationary orbit would be much much easier if you didn’t have to expand all the rocket fuel to get there in first place.
It would make putting stuff into orbit much much cheaper than it is now, but it would require a huge upfront cost to build a space elevator like that in the first place. So the economies would only make sense if we need to put a lot more stuff into orbit than we do now. However SpaceX has shown that demand will likely come if the price keeps dropping.
There are some people who dear a catastrophe if the cable should break, but that is not really a big concern.
A real concern is the fact that we don’t have a material to make the cable from. The materials we do have would simply rip apart under their own weight.
There is some idea that we could use some new materials made of differently arranged carbon atoms, but we don’t have that stuff yet at the scale necessary and it isn’t sure that it would work the way we want if we did.
We could help somewhat, by making a cable that is not uniform width, but tapers at the end to be able to support its own weight, but there are practical limits to that too.
However other than that the science is sound and if we needed to build a space elevator on for example Mars we could do it with the technology we have today. (we might need to move the moons out of the way).
As to the greenhouse gas emission. Rocket fuel can be really nasty stuff but some other fuel we use ends up just producing water, which is technically a greenhouse gas, but not a big concern. In any case we don’t send nearly enough rockets into space right now to matter much in the grand scheme of things and having access to satellites for navigation, communication, mapping and weather forecasting ends up saving us emissions elsewhere, so rocketry is not a huge concern, even if a single rocket ends up emitting quite a lot of emissions. There just aren’t that many of them.
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