you have a lot of questions in here. You really should only ask one at a time on StackExchange. I think there's also a large number of misconceptions exposed here (e.g. comparing the ISS's manuevering fuel usage to the fuel usage of trying to support a megastructure against gravity, and the design goals of a space elevator in the first place) so you should do much much more research.

The "classic" space elevator design has its center of gravity in geosynchronous orbit (either by extending quite a bit beyond this orbit, or having a counterweight, or both) so that it doesn't need constant boosts to stay in orbit. It would be very difficult to have an elevator that needs boosts from chemical rockets beat the efficiency of just using those chemical rockets to launch things into orbit.

"(especially since I expect this structure won't need to burn as much as rockets)": It would need to burn as much as a rocket of the same mass hovering over the pad. And more to power the pumps, since your proposal of using the vacuum to pump the propellant against gravity just doesn't work, for the same reason the atmosphere doesn't just blow off into space. And unless the end of the elevator is whipping around the Earth once every hour and a half, it's nowhere near LEO. LEO is a set of orbits, not a range of altitudes.

All other considerations (and there are a lot) aside, this tower will be useless as a launcher because its tip (at LEO) will not be in orbit. It's just a tall building. Release something from it...the something falls.

I'd hoped to avoid the economics of the problem; two out of four of you went for that anyway, so I'll try to answer as best I can. Propellant is by no means the most expensive aspect of launching rockets; it's not cheap, granted, but the bigger cost by far is building new rockets each time you want to launch one (hence also engineers' salaries). It wouldn't be using rockets (as I said) in the stratosphere, and would be supported with balloons. The stages in the mesosphere would (as I said) be pulled taut hopefully by the stages above it. Once in space proper, we don't need all that much

propellant to stay in orbit (the ISS being a notable example; it burns 7mt of propellant a year to stay in orbit whereas an Ariane 5 will burn through that in just under 2 seconds). Having a fuel line to space also might not be such a bad idea for refueling larger starships. The elevator would, I predict, be able to carry 4 Ariane 5 sized payloads to LEO every day; far outstripping what we're capable of launching with rockets currently; but yes, we would need to burn some fuel to keep it in LEO. To try and quickly answer the other two questions; I diverted largely from the original

Tsiolkovsky design by quite a wide margin; I felt having something dangling all the way out at geostationary orbit was highly impractical and probably not possible to build without at least a space elevator going from the ground to a lower orbit. Also, if we're sending things along a cable to move through space, they'd take months to get anywhere, so it's also impractical for that reason. As for the other comment picking me up on the comparison to the ISS; the ISS does also use fuel to keep itself in orbit and is quite a large structure in it's own right; why was that a poor comparison?

"...utilising the Venturi effect generated by the vacuum of space...". Can you elaborate?

AJN, I suppose it would use the negative pressure created by space's vacuum to draw the fluid along the fuel lines like a Venturi pump would.

Vacuum doesn't have negative pressure, it has zero pressure. That won't draw propellant upward any more than it strips the atmosphere away. And propellant is a small fraction of the launch costs of rockets, but rockets don't sit there thrusting continuously 24/7. And while the very lowest part of the elevator might be able to use air-breathing engines, most of it will have to use rocket engines, and since they won't be in orbit, they will need as much propellant as they'd use making a rocket of the same mass hover over the pad.

Christopher James Huff - No, using the term 'negative pressure' is appropriate in this context; it does generate negative pressure within the pipe itself which leads to the Venturi effect. The Venturi effect relies on a pressure differential between atmospheric pressure and the pressure of space; you righty observed that space has 0 pressure, therefore the negative pressure created in the pipe leads via Bernoulli's principle to an increased rate of fluid flow within it. We're not much closer to the question(s), but we're getting there. You're miles off (literally) on jet engines also.

Christopher James Huff - Also, on this 24/7 thrusting business, you clearly didn't read my original post carefully enough, but to reiterate: the section in the mesosphere will be pulled relatively taut by the section in space allowing the rocket engines on the mesosphere section to provide merely adaptive and corrective thrust to the winds of the mesosphere (hopefully!). In any case, it'll not use as much propellant as a rocket; not close really considering it's capacity for taking payloads to space; also, again, propellant isn't actually that big a deal!

@SamCottle it is a nice idea you have, but I think that you do not understand the difference from being in orbit and space. Having an elevator going up 400km is very different from being in LEO and flying around Earth at 28000km/h. The ISS only stays up because it is going to fast that it "falls" around Earth. That is known as an orbit. An elevator attached to the space station would need to have the top also going at that speed otherwise it will just fall down.

There is no venturi effect here. The only way to get propellant up that high is to actively pump it. And the only thing to pull the elevator taught is the rocket engines holding it up. That's a lot more than "adaptive and corrective thrust", and the engines will only provide it while you feed them that propellant. You are essentially running a long chain of rocket boosters full-time. Yes, the propellant is a big deal.

An illustration of The rocket fan's point, courtesy of XKCD: space is not high, space is fast. If your elevator isn't traveling as fast as an object in LEO, it is not in LEO, no matter what its altitude!

Back to the economics then. It takes about 40kg of xenon gas per year as I understand it to propel a 2000kg satellite travelling in LEO to 3.5 km/s. i think I did mention repeatedly that the stages in space would be pulling the stages in the mesosphere taut and, hence, would be travelling faster than the planet's rotation. Is that what's confusing people here? I don't think, at any point, I suggested that the structure's portion anchored in LEO would be travelling at the same speed as the planet. How would that work? If we suspended a rope between two cars, one car would have to be moving

faster than the other for it be the "pulled taut"! In any case, propellant is still a relative non-issue since (with an elevator) we don't need to put in nearly as much effort in getting propellant to space as with we do with rockets (even if we have to pump it up there); not because rockets use so much fuel, but because they're hard and expensive to build.

Uh...you can stretch a rope taut between two cars that aren't moving at all, and unless they're circling each other, they have to move at the same speed or the rope will break. A space elevator is moving with respect to the Earth only because the Earth it's attached to is rotating, for a 400 km long elevator the top is basically stationary with respect to the base. You just have a tower supported by rocket propulsion, no part of it is anywhere close to being in orbit.

If your tower is 400 km tall (ISS altitude) and it's built on the equator its tip will be moving 1780 km/h in round numbers (about 100 km/h faster than the surface of the Earfh). ISS orbital speed is 28,000 km/h in round numbers. Your tower is useless as an orbital launcher.

Christopher James Huff - It's analogy, I wouldn't stretch it to breaking point (and, here, you can crucially learn also that the pun was intentional). I don't really know how else to come back at this without saying something like: more like you'd have a 400km tower, the top part of which is in orbit, kept there by rockets, and I said that from the beginning.

And once again, the top of a 400 km tower is not in orbit. It is practically stationary with respect to Earth's surface, and will take as much thrust to hold up as it would take to hover a rocket of the same mass 400 meters above its launch pad.

Really try to picture what's in my mind. I hate having to allude the clear reality that you haven't fully read/understood the initial post, but here we are. The sections extending from the Karman line to LEO are SEGMENTED into 10km sections each stretching pipe and cable; the underlying assumption (rejoining usefully on the initial question) was that some sort of pipe would be capable of pumping fuel up there. I don't quite know what that is yet. Hence I asked. But yes, granted, it would need to be slack up in space (to some extent) such that the kevlar (or whatever we're making the cable

out of) doesn't break. As for being stationary with respect to Earth's surface, I don't know what I've said in my previous answers; I've re-read them a few times; but you seem to be labouring under the impression that I'M under the impression that i'd be hovering this tower (for whatever reason) above its base; why do you think that?

The most efficient dynamic for the machine to adopt, of course, is for it to burn enough propellant to keep each stage of it supported above the atmosphere WHILE also propelling it forward to keep the sections in the mesosphere taut; therefore it'd be constantly using some propellant (as I mentioned; which pails into insignificance considering the reusability advantages of space elevator technology) to keep it orbiting around the Earth. I don't know how much more sophistry I need to put up with; I DO KNOW satellites remain in orbit for a while WITHOUT propellant. the interstitial physics ain't

all that challenging (for MOST people).

@SamCottle okay, lets say we have a fuel pipe going up to 400 km being held up by rocket engines. Assuming that the bottom is attached to the ground and the top is going at a speed of 28000 km/h so that it is in orbit, then you have a fundamental issue. Since the top of the fuel pipe is going around Earth, and the bottom is still attached, the rope (fuel pipe) will warp around Earth.

It doesn't matter how you segment things, it doesn't matter how you pump things. You can't be moving at 7 km/s with respect to the ground at 400 km altitude, circling the planet every 90 minutes, while maintaining a continuous pipeline to the ground.

Well, you can if you submit to burning propellant. You might not be travelling on quite an elliptical trajectory as you would in what would be considered 'orbit' in the strictest sense; you'd be travelling in straight lines away from the planet's surface, then allowing the planet to pull again on the tether, then pulsing the engines again to maintain corrective thrust. Again, it's not important if they WERE to be firing all the time (for the reasons I've mentioned); they wouldn't be; they'd still be providing a significant cost-benefit advantages over rocket launches

Also, we're still in the exact part of the problem I most wanted to get away from. I'm fairly happy in my mind that (whatever amount of propellant this thing uses) it provides cost-benefit advantages over rockets. To clarify; it will be travelling faster than the planet's speed of rotation, because it needs to pull sections in the atmosphere taut; it will not be travelling so fast such that it wraps itself around the equator.

I was mostly interested in whether or not it's possible to get LOX and liquid hydrogen to orbit at all using such a device.

The Rocket Fan - Just for clarification: the tether connecting the various stations from the Karman line out to LEO will be pulled taut by the end station at LEO. The station at the Karman line will also be generating thrust, but in the opposite direction. Therefore, the Karman station's thrust will be acting against Earth's rotation while the station at LEO will be thrusting with Earth's rotation. This means the section in the mesosphere is (hopefully) pulled taut and that we don't need as much propellant to stay in LEO.

Again, you won't be applying occasional "corrective thrust". Your tower isn't in orbit, it's hovering. Your average thrust needs to be exactly what you need to counter Earth's gravity. Pulsing the engines just means you need bigger engines and higher peak propellant delivery rates, because you'll need more thrust to compensate for them not running full time. No, the equivalent of running a hundred or so launch vehicles 24/7, 365 days a year, on top of all the other stuff required to make the elevator work, will not be competitive with rocket launches.

Also, if something's orbiting at 160-200km up, with some amount of propellant, I'd have said that's in LEO; otherwise, we might have to entirely revise our definitions of what an 'orbit' even is. Again, I'm not that interested in how much propellant we're burning; it'll be less than a rocket's worth of propellant per day (I'm 99% certain) and even if it were, space elevators are reusable tech and provide savings over rockets for THAT reason. I was just about hydrogen and oxygen pipes.

Christopher James Huff- I DIDN'T SAY THAT I WOULD BE!! That was only for the section in the mesosphere!! I can't hold your hand through the original text I posted and I refuse to ad nauseum reiterate things I've already told you.

"it'll be less than a rocket's worth of propellant per day (I'm 99% certain)": a single RS-25 running in vacuum would support a little over 200 t of elevator, including the high-pressure pipes and the propellant inside them, and would consume about 45000 metric tons of propellant per day, 22 times the mass of the entire Shuttle stack.

@SamCottle language pls, there is no reason to shout. We are just trying to figure out what you want this elevator to be. If the top part of it is in LEO, then it will be moving around the planet so then it cannot be attached to the ground because otherwise it will be warping the fuel pipe around the planet. If you want the top of the elevator to be at the same point so that it does not warp a pipeline around Earth, you need to have it hovering with constant thrust

There are 3 options you have for your elevator. The first is to have the top in GEO and a fuel pipe going all the way down to Earth. The second is to have it hovering in a lower altitude (maybe 400km), but it will need constant thrust to keep it up. The third option is that you have the fuel pipe hanging from a space station in LEO, but it cannot touch the ground. The bottom of the pipe would just scratch the upper atmosphere. Similar to a sky hook. What I am understanding is that you want to mix the second and third option which is not possible.

Christopher James Huff - Sources and calculations please.

The Rocket fan - I see where you're coming from, I do. I depart from your way of thinking on this issue of "constant" thrust. To really get an in-depth picture this you'd need a team of people, computer simulations, and more math that (let's face this!) any of us are capable of doing here and now. I maintain that propellant is a relatively unimportant issue and was quite happy from the outset, even IF it ends up being more than a single rocket launch, to stick with this idea in spite of the propellant it uses. My personal opinion is that we need a space elevator for a variety of reasons

, that building one will move us to a new era of space exploration, and that the science we'd learn out the attempt at building one is far more valuable than any amount of money we spend on propellant. Come on dude, this opens up Mars, it opens up the outer solar system, it enables us to do a world of things in space we wouldn't really have considered using rockets alone.

@SamCottle so you want the second option I mentioned. That is fine, but FYI it is not in orbit.

Sure, ok, it's not orbit then. In any case, it's moving around the centre of the planet as opposed to falling back into it; that is, it's suspended using thrusters against gravity and not merely hanging free. I don't know what you call that.

@SamCottle I guess you could call it a suborbit, but is constantly under thrust to push it upwards so that it maintains a stabil altitude. Aka hovering

Yeah, I'll give you that. It's in the grey area between orbital and suborbital.

and so this goes the way of every Great Idea submitted to Space Exploration SE: it has a number of obvious issues, we explain some of them, the poster defends them, etc etc etc. Go do an introductory design on this. Estimate how much it will weigh, how much fuel it will consume, compare that to how much fuel the world actually produces in the first place, and check what will happen to the payloads when they reach the end. Your design's nonsense and people have been very kind pointing it out to you.

"Sources and calculations please.": it's a very straightforward application of the thrust and propellant consumption figures you can get from any number of sources. Start here: en.wikipedia.org/wiki/RS-25

As for what it "opens up", even if it was physically workable, it wouldn't even get you to orbit. You need almost the same delta-v you'd need from the ground to get to a minimal orbit, except now you need to get it with a vehicle you can haul up the elevator, meaning your payload is a tiny fraction of what you load on at the bottom of the elevator. You've got a tremendously expensive megastructure which is constantly burning propellant at a rate we frankly just can't supply, and it doesn't actually get you anywhere.