this post was submitted on 23 Sep 2024
91 points (97.9% liked)
Futurology
1854 readers
152 users here now
founded 1 year ago
MODERATORS
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
IF fully reusable spacecraft ever becomes reality, then a space elevator ON EARTH would probably never be needed.
On the moon, probably. On Mars, maybe. But Earth, a fully reusable rocket, combined with in space assembly just makes a lot more sense.
Especially long term when we actually start gathering raw materials in space. We'll eventually only need to send people , and complex things like microprocessors into space, and the rest can just be made up there.
The benefit of a space elevator is that the fuel is supplied by the ground and does not need to be carried as part of the payload. Remember in the rocket equation, most of the fuel is used for carrying just the mass of the fuel itself. A space elevator eliminates the rocket equation for lifting mass into orbit, and would be much more efficient than any rocket, reusable or not
There are major disadvantages as well.
You have a limited number of locations, which limits the rate of payloads. You can deploy them at the equator, so you'd have to transport things to the lifting pad beforehand, which would primarily need to be transported by sea.
We don't have a way to power the lifter, you can use microwaves or lasers, but that generates a lot of heat, which would be difficult to dissipate at high altitudes.
We also don't have a way to actually build one, but we do have a way to build reusable rockets (the details aren't complete, but several companies are well on their way to building them.)
By the time we'd be able to build a real space elevator, we'd probably already have asteroid mining, and in space constructions and manufacturing. So we're really only sending small, highly technical, or human payloads up, at which point a space elevator isn't really needed.
On top of all that, a fully reusable rocket powered by fuel that can be synthetically created, would be just as environmentally sustainable (assuming any ozone or ionosphere issues don't become an issue.)
I'm all for working on it if it becomes possible, but it's likely a technology that would be obsolete by the time it's possible.
Okay
I mean, it's more of an economic question then an engineering one, if we're assuming ahead of time that it's possible. If we could build an Earth space elevator for the volumetric price of water, you bet we'd be sending one up regardless of how cheap SpaceX launches are.
That's probably never going to happen, but energy prices and expected investment returns could all change quite a lot in the indefinite future, and a space elevator with regenerative breaking is always going to use less energy than anything else.
Actually, microprocessors would be easier to make in a natural hard vacuum, as would things like magnesium or solar cells. In the long term I'd expect the limiting factors will be elements, and general demand to send things to inhospitable places in the first place. Maybe energy if fusion turns out to be way harder than we expected, and we still want to hang out on Pluto or Titan.
Even reusable rockets use a tremendous amount of fuel. Falcon 9 burns 700,000 gallons per second.
Untrue, that's many times over the 25,000 gallons of kerosene they keep on board. That's still a lot of gas, but not 700,000 gallons, not by a long shot. If it burned that much per second it wouldn't even produce enough thrust to carry its own fuel payload
My bad for trusting Google top result.
395,700 kg fuel first stage. Burn time 162 seconds.
https://en.m.wikipedia.org/wiki/Falcon_9#:~:text=The%20rocket%20has%20two%20stages,rocket%2C%20carrying%20143%20into%20orbit.
The 39,000 gallons of LOX in the Falcon 9 doesn't make itself.
To inject a source, there's 395,700 kg total propellant on the first stage, and a burn time of 162 seconds. That gives about 2,442.6 kg/second, and assuming it's fuel balanced it comes out to something like 700 liters of RP-1 per second. Could OP have been using thousands of gallons instead, by accident?
It's still a lot, though, while a space elevator is just a really tall elevator, or alternatively an EV that goes up and down.