Use of 20km tall "space elevator"?

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billyswong
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Use of 20km tall "space elevator"?

Postby billyswong » Wed Aug 19, 2015 12:26 pm UTC

A company showed a plan of building a "space elevator" that's 20km tall.
http://news.nationalpost.com/news/canada/five-things-about-canadas-space-elevator-and-what-you-might-pass-while-going-to-the-top
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The company said it will cut down rocket cost. But is that true?

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Re: Use of 20km tall "space elevator"?

Postby Izawwlgood » Wed Aug 19, 2015 12:31 pm UTC

Pfffffffft, dat company name.

My guess is could marginally cut down on rocket costs, but I wager the majority of rocket fuel is spent getting up to orbital speed, not climbing 20km. I also wager launching rockets from this platform would be very very very dangerous.
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Re: Use of 20km tall "space elevator"?

Postby speising » Wed Aug 19, 2015 12:34 pm UTC

What stands out to me:
- so basically everybody can patent their pipe dreams now
- 20km vs. "space"
- "geostationary orbit, where satellites fly, which is around 25,406 kilometres up."
- "The elevator is designed to withstand the force of a Category 5 hurricane" - oh, really?
"designed" like i "designed" race cars in school? how do they expect to build a 20km tower with known materials?
i guess avoiding the most dense part of the atmosphere would be nice, but i'd really like to see a business calculation for that thing, which has to be able to launch a rocket from the top.

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Re: Use of 20km tall "space elevator"?

Postby Izawwlgood » Wed Aug 19, 2015 12:39 pm UTC

Wait, it's a TOWER? Not like, a thing suspended by a bunch of balloons?

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Re: Use of 20km tall "space elevator"?

Postby SDK » Wed Aug 19, 2015 1:28 pm UTC

This article talks a bit more about the fine details.

"It would be made of stacked rings of Kevlar cells inflated with hydrogen or helium to an extremely high pressure."

I take that to mean that the balloons will help to support the weight of the entire tower. Sounds... difficult... but maybe... possible? Not much atmosphere 20 km up to support the upper section though if that's the plan. Apparently the tower keeps itself upright and avoids bending using gyroscopes. Should be interesting to see if this goes anywhere. In that same article they talk about building a 1.5 km tall prototype in the next 5 years. It also talks about their desire to collaborate with engineering companies who have worked on tall towers in the past, which leads me to believe that they haven't ironed out the technical details of their design. I guess we'll see.
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Re: Use of 20km tall "space elevator"?

Postby speising » Wed Aug 19, 2015 1:55 pm UTC

oh yes, ignite a rocket thruster on top of a stack of hydrogen balloons. nice idea.

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Re: Use of 20km tall "space elevator"?

Postby Whizbang » Wed Aug 19, 2015 2:05 pm UTC

speising wrote:oh yes, ignite a rocket thruster on top of a stack of hydrogen balloons. nice idea.


That's a feature, not a bug. It gives the rockets a little boost.

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Re: Use of 20km tall "space elevator"?

Postby Chen » Wed Aug 19, 2015 2:32 pm UTC

Probably wouldn't be a lot of oxygen at 20km up to actually ignite the hydrogen.

Also its not clear if its a tower supported by balloon like structurs or if the whole thing is just a bunch of balloon like cells.

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Re: Use of 20km tall "space elevator"?

Postby Tyndmyr » Wed Aug 19, 2015 7:02 pm UTC

SDK wrote:This article talks a bit more about the fine details.

"It would be made of stacked rings of Kevlar cells inflated with hydrogen or helium to an extremely high pressure."

I take that to mean that the balloons will help to support the weight of the entire tower. Sounds... difficult... but maybe... possible? Not much atmosphere 20 km up to support the upper section though if that's the plan. Apparently the tower keeps itself upright and avoids bending using gyroscopes. Should be interesting to see if this goes anywhere. In that same article they talk about building a 1.5 km tall prototype in the next 5 years. It also talks about their desire to collaborate with engineering companies who have worked on tall towers in the past, which leads me to believe that they haven't ironed out the technical details of their design. I guess we'll see.


I scratched out better superstructures on napkins as a child.

Just saying kevlar doesn't mean you can ignore the stupid amount of stresses involved here.

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Re: Use of 20km tall "space elevator"?

Postby brenok » Wed Aug 19, 2015 8:23 pm UTC

Tyndmyr wrote:
Just saying kevlar doesn't mean you can ignore the stupid amount of stresses involved here.

Yes, he used the wrong buzzword. Definitely should have said Carbon Nanotubes

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Re: Use of 20km tall "space elevator"?

Postby SDK » Wed Aug 19, 2015 9:18 pm UTC

Tyndmyr wrote:Just saying kevlar doesn't mean you can ignore the stupid amount of stresses involved here.


Okay. Can I say balloons and gyroscopes to ignore them instead? If you can successfully break the building into pieces, with each piece being supported more-or-less independently, then no particular piece is under stupid stress.
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Re: Use of 20km tall "space elevator"?

Postby Qaanol » Thu Aug 20, 2015 4:04 am UTC

Guys guys guys, I think we’re all overlooking the real problem with this design.

Once they start actually building the tower, then all of a sudden people will be scattered across the entire world and speak all sorts of mutually-unintelligible languages.

I mean, can you imagine?
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Re: Use of 20km tall "space elevator"?

Postby Zamfir » Thu Aug 20, 2015 7:37 am UTC

Okay. Can I say balloons and gyroscopes to ignore them instead? If you can successfully break the building into pieces, with each piece being supported more-or-less independently, then no particular piece is under stupid stress.

In that case, why build a tower at all? Just keep the top balloon with a tether, or even do without the tether. Firing a rocket from a balloon is not completely crazy, it has been done on a small scale.

Though the balloons do get very, very large if you want to lift a large mass to the stratosphere.

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Re: Use of 20km tall "space elevator"?

Postby billyswong » Thu Aug 20, 2015 12:27 pm UTC

Qaanol wrote:Guys guys guys, I think we’re all overlooking the real problem with this design.

Once they start actually building the tower, then all of a sudden people will be scattered across the entire world and speak all sorts of mutually-unintelligible languages.

I mean, can you imagine?

So, English will be extinct in one day? That's horrible!

Luckily my mother tongue is Cantonese. We will rebuild in Chinese characters this time :P

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Re: Use of 20km tall "space elevator"?

Postby Whizbang » Thu Aug 20, 2015 12:39 pm UTC

Zamfir wrote:
Okay. Can I say balloons and gyroscopes to ignore them instead? If you can successfully break the building into pieces, with each piece being supported more-or-less independently, then no particular piece is under stupid stress.

In that case, why build a tower at all? Just keep the top balloon with a tether, or even do without the tether. Firing a rocket from a balloon is not completely crazy, it has been done on a small scale.

Though the balloons do get very, very large if you want to lift a large mass to the stratosphere.

Because you'd want some way for the supplies and rockets and whatnot to get to your platform, and back down.

Qaanol wrote:Guys guys guys, I think we’re all overlooking the real problem with this design.

Once they start actually building the tower, then all of a sudden people will be scattered across the entire world and speak all sorts of mutually-unintelligible languages.

I mean, can you imagine?

Confound it! Those humans are at it again!

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Re: Use of 20km tall "space elevator"?

Postby sevenperforce » Thu Aug 20, 2015 1:24 pm UTC

So yeah, it's not a tower at all, just a tethered balloon. Which we hope will somehow stay rigid enough to remain usable.

I love this quote:

"Quine has already built a seven-metre-high scale model, which he unveiled in 2009 at York University in Toronto, where he is an associate professor."

That's about as silly as saying that a paper airplane folded out of a single sheet of paper constitutes a "scale model" of a SSTO hybrid scramrocket spacecraft.

And this is funny too: "The design includes gyroscopes to control the tower's movement and actively stabilize it during major storms." I assume they mean gyrostabilizers, because gyroscopes won't do squat without retrorockets or some sort of active control system.

Qaanol wrote:Guys guys guys, I think we’re all overlooking the real problem with this design.

Once they start actually building the tower, then all of a sudden people will be scattered across the entire world and speak all sorts of mutually-unintelligible languages.

I mean, can you imagine?

This has all the wins.

In any case "stabilized with gyroscopesstabilizers is SUPER handwavy. The forces we're dealing with are just plain stupid. A traditional space elevator has a very low cross-section under high terminal tension and thus has very little susceptibility to drag, but this has a high cross-section and no terminal tension, so the cumulative effect of wind will be astronomical. Gyrostabilization is not magic; a gyroscope resists change to its angular momentum by transferring the torque vector to a perpendicular plane. In other words, get the right combination of winds, and this tower is going to twist itself open like a can of biscuits.

Maybe, however, we're wrong and the tower is actually a hybrid between a rigid superstructure and lifting cells, such that every point of the tower is under an allowable tension. That might work a bit better. Removing the capacity for free flexing is both a blessing and a curse.

I wonder if his estimate of energy savings is on point. Launching from 20 km up does not significantly decrease terminal energy requirements, but it does reduce drag considerably as well as dramatically reducing gravity drag, which should result in some noticeable savings.

And I'm not sure exactly what's being patented here. This isn't a new idea.

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Re: Use of 20km tall "space elevator"?

Postby Whizbang » Thu Aug 20, 2015 2:29 pm UTC

sevenperforce wrote:This isn't a new idea.


Hehe. They said "Space shaft".

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Re: Use of 20km tall "space elevator"?

Postby Tyndmyr » Thu Aug 20, 2015 2:34 pm UTC

SDK wrote:
Tyndmyr wrote:Just saying kevlar doesn't mean you can ignore the stupid amount of stresses involved here.


Okay. Can I say balloons and gyroscopes to ignore them instead? If you can successfully break the building into pieces, with each piece being supported more-or-less independently, then no particular piece is under stupid stress.


Heh, I like the sarcasm.

But yeah, gyroscopes are great, but don't solve your stress problem. A balloon of that size is going to catch some wind. Merely stationkeeping a length of this balloon chain would require gobs and gobs of thrust. So, even before we start looking at other effects, either you're relying on crazy good tensile strength to keep the balloon together, or you're relying on an implausible amount of active stabilization. Oh, looks like seven's already on this.

I am concerned that this person is a professor. Hopefully not of physics. *googles* Oh. Goddammit. He is.

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Re: Use of 20km tall "space elevator"?

Postby Qaanol » Thu Aug 20, 2015 2:39 pm UTC

Whizbang wrote:
sevenperforce wrote:This isn't a new idea.


Hehe. They said "Space shaft".

I withdraw my objection, let us erect this immediately. It is a stroke of genius.
Last edited by Qaanol on Mon Aug 24, 2015 6:10 am UTC, edited 1 time in total.
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Re: Use of 20km tall "space elevator"?

Postby SDK » Thu Aug 20, 2015 4:05 pm UTC

Tyndmyr wrote:But yeah, gyroscopes are great, but don't solve your stress problem. A balloon of that size is going to catch some wind.

Yeah, that's the thing I wasn't considering. Seems like a plausible way to have a super structure support itself, breaking it up into pieces, but wind will have to be dealt with for the entire tower as one regardless of your setup.
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Re: Use of 20km tall "space elevator"?

Postby sevenperforce » Thu Aug 20, 2015 4:35 pm UTC

The only way I could see to avoid the wind shear issue would be to have a linked network of parallel vertical shafts, each as long as could be easily stabilized from internal rigidity alone. Thus, each segment of the tower has the freedom to rotate independently. Advantageously, this rotation could serve as a power source, effectively making the space tower into a massively gigantic wind turbine.

Ideally, you'd have three vertical shaft segments connected at a central hub. Each segment would have an airfoil cross-section and be independently orientable. Thus, by rotating the three segments to a particular place and angling them appropriately, virtually any desired drag/lift vector could be produced. Contra-rotation of adjacent segments would result in zero net torque on the overall superstructure.

It would make the climb up a bit messier and increase complexity by many orders of magnitude, but you'd be well on the way to solving the stability problem.

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Re: Use of 20km tall "space elevator"?

Postby Tyndmyr » Thu Aug 20, 2015 7:45 pm UTC

I have no idea why you need a shaft to begin with.

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Re: Use of 20km tall "space elevator"?

Postby sevenperforce » Thu Aug 20, 2015 8:08 pm UTC

It's a materials integrity issue. 20 km is on the order of the breaking length of high-grade metals, so in order to have a decent safety factor you would need to use very expensive and exotic materials if you were going to just do a single tether from ground to balloon. In contrast, if you stack the cells on top of each other and they are all individually supporting their own weight, then there is only a minimal compressive/tensile load in the vertical axis.

But oh how unstable in every other axis.

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Re: Use of 20km tall "space elevator"?

Postby Tyndmyr » Thu Aug 20, 2015 8:17 pm UTC

Still no need for a shaft.

Hell, a series of blimps, each with a tether down to the next tier, would be more practical. You're still splitting up the cable handling, avoiding ridiculous tensile strength requirements, and making winch requirements way easier.

I suppose I could file copyright claims for this, but I'd feel incredibly dirty basing an IP claim around balloons tied together.

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Re: Use of 20km tall "space elevator"?

Postby sevenperforce » Thu Aug 20, 2015 8:29 pm UTC

Tyndmyr wrote:Still no need for a shaft.

Hell, a series of blimps, each with a tether down to the next tier, would be more practical. You're still splitting up the cable handling, avoiding ridiculous tensile strength requirements, and making winch requirements way easier.

The structure needs to be semi-rigid, though, or the tethers will end up accumulating the same total amount of tension as if all the buoyancy was solely on top (though it will at least be evenly distributed rather than concentrating at the center). The admittedly useful part of the "Thoth" design is that the superstructure is neither solely under compressive load nor solely under tensile load and thus has neither compressive nor tensile failure modes.

I suppose I could file copyright claims for this, but I'd feel incredibly dirty basing an IP claim around balloons tied together.

Don't you mean patent claims? ;)

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Re: Use of 20km tall "space elevator"?

Postby Tyndmyr » Thu Aug 20, 2015 8:46 pm UTC

sevenperforce wrote:
Tyndmyr wrote:Still no need for a shaft.

Hell, a series of blimps, each with a tether down to the next tier, would be more practical. You're still splitting up the cable handling, avoiding ridiculous tensile strength requirements, and making winch requirements way easier.

The structure needs to be semi-rigid, though, or the tethers will end up accumulating the same total amount of tension as if all the buoyancy was solely on top (though it will at least be evenly distributed rather than concentrating at the center). The admittedly useful part of the "Thoth" design is that the superstructure is neither solely under compressive load nor solely under tensile load and thus has neither compressive nor tensile failure modes.


Nah. If you're doin' blimps, you're doing active station keeping, which pretty much has to happen anyway, so the drag on the whole system isn't cumulative. Each tether would need to be strong enough to handle the one blimp, plus some cushion for bouncing around or whatever. I'm pretty sure such a system still wouldn't be anything like cost effective, but at least it wouldn't self destruct.

Using mixed compressive and tensile loads doesn't free you from failure modes...sometimes it gives you more flexibility in design, but if the whole damned thing is inflated with helium, the base *has* to have tensile strengths of at least as much as the net lifting power of everything above it. Plus whatever wind is involved. Can't imagine what would hold that.

I suppose I could file copyright claims for this, but I'd feel incredibly dirty basing an IP claim around balloons tied together.

Don't you mean patent claims? ;)


I suppose so, though I view the whole lot as filthy with excessive claims, so it's a moot point. =)

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Re: Use of 20km tall "space elevator"?

Postby sevenperforce » Thu Aug 20, 2015 9:14 pm UTC

Tyndmyr wrote:If you're doin' blimps, you're doing active station keeping, which pretty much has to happen anyway, so the drag on the whole system isn't cumulative. Each tether would need to be strong enough to handle the one blimp, plus some cushion for bouncing around or whatever.

Well, the drag is one issue, but I'm talking about tensile load in the vertical axis, because that's the real problem here.

If you're going to daisy-chain blimps together with tethers, then you will end up with a cumulative tensile load. That's because blimps are not naturally stable; they have a wide range in which they will float up and float down based on changing temperature, wind conditions, and so forth. Since you don't want higher blimps to drift down below lower blimps (particularly if you're going to have cargo climbing up this whole blasted assembly), you have to have constant tension from bottom to top. Moreover, this needs to have excess tension in order to account for the weight of whatever is climbing it.

Using mixed compressive and tensile loads doesn't free you from failure modes...sometimes it gives you more flexibility in design, but if the whole damned thing is inflated with helium, the base *has* to have tensile strengths of at least as much as the net lifting power of everything above it.

That's not quite what the design is. Rather, the design comprises stacked cells which are each individually inflated with lifting gas. The cells have roughly neutral buoyancy so that they can rest on top of each other in rigid compression/tension but with only a very minimal effective weight. I'm presuming that the top of the tower has excess negative buoyancy in order to hold the tower in relative tension, but the rigidity of the frame can take care of accommodating increased weight from climbing loads. Thus, the base will only have to support minimal tension.

The end result is the same as a single tethered balloon except that the "tether" is both rigid and capable of supporting its own weight, and cargo can be carried up with its weight distributed downward.

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Re: Use of 20km tall "space elevator"?

Postby Tyndmyr » Thu Aug 20, 2015 9:45 pm UTC

sevenperforce wrote:If you're going to daisy-chain blimps together with tethers, then you will end up with a cumulative tensile load. That's because blimps are not naturally stable; they have a wide range in which they will float up and float down based on changing temperature, wind conditions, and so forth. Since you don't want higher blimps to drift down below lower blimps (particularly if you're going to have cargo climbing up this whole blasted assembly), you have to have constant tension from bottom to top. Moreover, this needs to have excess tension in order to account for the weight of whatever is climbing it.


Well, you do need *some* tension, but it need not be extremely high. Tethering a blimp on a fairly lengthy bit of cable is pretty typical. You want *some* positive tension at each tier, and yeah, that's cumulative, but you'll still mostly want lifting force balancing cable(and load).

Actual loads climbing, depending on the size, might introduce additional interesting variables, but the lift system might not even be the tether. For wear and tear, you probably wouldn't particularly want it to be.

Still, probably needlessly complex vs just lifting with a single balloon, since each individual balloon would have to be capable of supporting the whole load anyway. So...one bigass balloon(which is, by itself, usually not worth it for big rockets, due to excessive required size) is way, way easier.

I think the actual economics would require a pretty stupid amount of traffic even to be a net win over existing shuttle launches, simply due to the costs of construction and maint.

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Re: Use of 20km tall "space elevator"?

Postby drachefly » Mon Aug 24, 2015 3:40 pm UTC

For the lateral forces, it might help to have similarly bouyant guy wires. That should spread the stress out. Of course, now you're multiplying the cost and the footprint.

And I'm still not sure what 20 km up is supposed to get you. The PE change to LEO is something like 10% of the KE you need to get. Reducing the 10% by 20% or so is going to save on rocket fuel costs by, oh, 2%. Only now you need to launch from that thing.

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Re: Use of 20km tall "space elevator"?

Postby sevenperforce » Tue Aug 25, 2015 3:59 pm UTC

drachefly wrote:For the lateral forces, it might help to have similarly bouyant guy wires. That should spread the stress out. Of course, now you're multiplying the cost and the footprint.

I'm not sure how the force vectors would work out for the construction of buoyant guy wires. Will they be pulling up at the top, or down, or what? I can't help but think that the wind forces tugging on them would make the tower even less stable.

And I'm still not sure what 20 km up is supposed to get you. The PE change to LEO is something like 10% of the KE you need to get. Reducing the 10% by 20% or so is going to save on rocket fuel costs by, oh, 2%. Only now you need to launch from that thing.

Oh, it's worse than that. At an altitude of 100 miles, potential energy is 1.6 MJ/kg while kinetic energy is 30.5 MJ/kg; the gravitational potential energy is less than 5% of the total energy cost. And 20 km isn't quite 20% of that. The potential energy savings of a launch from 20 km is just 0.62% of total energy cost.

The advantage of a high-altitude launch, as previously discussed here, lies in lower gravity drag, lower aerodynamic drag, and a lower required thrust-to-weight ratio. The first two are only minor advantages (gravity drag and aerodynamic drag only cost about about 1.2 km/s of delta-v), but the third element is bigger. Ground launch is completely dependent on sickeningly high thrust to enable vertical takeoff, but high thrust typically means low exhaust velocity and low efficiency.

If you can launch horizontally at a high altitude with low drag, then you can use higher-efficiency, lower-thrust rocket engines or even hybrid scramjet/rocket engines. You can afford to lose some altitude at first, because even a very modest lift-to-drag ratio will rapidly level your flight and you can get up to speed at your leisure while rapidly recovering the lost altitude. Well, not at your leisure per se, but more gradually than in a vertical launch arrangement.

The Space Shuttle main engines delivered a combined thrust of 570 tonnes force, while the external tank, orbiter, and 863 tonnes of fuel carried by the external tank total just under 1000 tonnes. That's a thrust-to-weight ratio of less than 0.6, not nearly enough for unassisted vertical takeoff. Yet the 4.46 km/s exhaust velocity of the high-efficiency liquid rocket SSMEs means that the unboosted Space Shuttle still packs 8.9 km/s of delta-v, just about enough to reach LEO.

The orbiter lift-to-drag ratio on landing approach was about 4.5; with the external tank, that would have probably dropped to 2.25. But an L/D ratio of 2.25 is enough to hold 1000 tonnes of weight aloft with only 444 tonnes thrust, allowing the SSMEs at full throttle to keep the shuttle aloft in aerodynamic flight with the opportunity to increase speed and altitude, particularly as more fuel is expended to lower vehicle mass. So even though there's no significant savings in terms of delta-v, launching from a platform could have allowed the Space Shuttle (or a similarly-designed spaceplane) to forgo the solid rocket boosters and function as a true SSTO vehicle.

Even more savings would be possible with a hybrid scramjet/rocket engine. Using a scramjet engine with the option of liquid oxidizer injection (really an air-breathing rocket engine similar to the SABRE proposed for the Skylon spaceplane), your launch vehicle could blast off the platform "runway" under liquid rocket power and enter a shallow dive to reach scramjet speeds as rapidly as possible. At Mach 5 or so, scramjet mode would kick in and dominate, leveling out and taking your vehicle back up to altitude and to a velocity of around 4-7 km/s. At that point, oxidizer injection would resume, returning the engine to pure rocket mode and boosting the rest of the way to orbit.

The primary advantage of SSTO is reusability. In order to decrease spacecraft volume to maximize this advantage, such a vehicle would likely use kerosene like the Merlin 1D or liquid methane like the proposed SpaceX Raptor, despite their lower impulses of 3.05 and 3.56 km/s, respectively, since both fuels take up substantially less volume than the liquid hydrogen of the SSMEs.

Worst-case scenario, where you use kerosene fuel and the scramjet must be boosted all the way to Mach 7 and then can only take you to 4 km/s before full-rocket operation is required, your spaceplane will need a total fuel mass ratio of 7.1:1. Best-case scenario, where you use liquid methane fuel and the scramjet can begin functioning as a ramjet as early as Mach 4 and can take you all the way to 7 km/s before the rocket takes over again, your spaceplane will only need a fuel mass ratio of 1.5:1. In the former case, SSTO remains challenging but definitely doable; in the latter case SSTO becomes trivial. By comparison, a fully-loaded Boeing 747 has a mass of 448 tonnes and carries 189 tonnes of jet fuel for an effective "fuel mass ratio" of 0.73:1, so you could say by way of comparison that the latter-case SSTO would need "only about twice as much fuel as a 747".

Of course, unless you have a way of landing on top of the platform, you've got to factor in the need to hoist your spaceplane up to the top every single time you launch. Still probably cheaper than the alternative, though.

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Re: Use of 20km tall "space elevator"?

Postby drachefly » Tue Aug 25, 2015 4:24 pm UTC

sevenperforce wrote:
drachefly wrote:For the lateral forces, it might help to have similarly bouyant guy wires. That should spread the stress out. Of course, now you're multiplying the cost and the footprint.

I'm not sure how the force vectors would work out for the construction of buoyant guy wires. Will they be pulling up at the top, or down, or what? I can't help but think that the wind forces tugging on them would make the tower even less stable.


Up? What do you think I think guy wires are?

Each is a cable stretched from a distant point on the ground to some point on the tower. If the tower deviates from straight up, then the one up-wind will gain tension and the one down-wind will lose tension. This helps keep the tower pointed straight up. You can lead multiple wires to different heights on the tower.

Also, each cable produces additional down-wind drag when the wind blows crosswise, so that isn't great. But if it would make things worse, then the tower itself is hopeless long before.

Since tension is usually much stronger than compressing something not-so-dense, maybe you can do it with regular wires supported by occasional balloons, rather than the scheme used for the compressively-loaded tower. That would minimize drag.

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Re: Use of 20km tall "space elevator"?

Postby sevenperforce » Tue Aug 25, 2015 5:10 pm UTC

Breaking length for high-grade metal is on the order of 20 km. If your guy wires are slanted to around 45 degrees, then they're going to be at least 41% longer than the height of the tower at their attachment point, meaning they'll be well over breaking length.

The reason I asked about what the vector was is that you suggested "buoyant guy wires". If you're talking about just holding the wire aloft with evenly-spaced balloons along its length, then you're still going to have strength issues (though thankfully not quite so significant) but drag is going to be astronomical. Changes in air temperature and pressure will cause changes in buoyancy, necessitating some built-in slack in the guy wires...but if you have slack in the guy wires, then what are they there for? Putting enough slack in the guy wires to allow them to remain stable will negate any stabilizing effects.

The advantage of the single-column vertical tower is that it's designed with neutral buoyancy so as to avoid significant compressive load. But drag isn't going away.

The only feasible stationary tethered space platform would probably be a hybrid design. Wind speed reaches its maximum between 5 and 7 miles altitude, so you'd want a compressive design below and a buoyant design above with a tensile tether connecting the two across the region of highest wind shear.

The first mile could be a freestanding compressive tower, transitioning to a second mile of traditionally-guyed compressive mast topped by about 2.5 miles of neutral-buoyancy tower. Current materials strengths can easily manage a tensile tether of around four miles long. Once you were above the highest-velocity winds, you'd resume neutral-buoyancy tower for another four miles, terminating in a positive-buoyancy platform which provides constant but modest (at least compared to a single tethered balloon) tension on the tether:

hybrid platform.png
hybrid platform.png (8.07 KiB) Viewed 5550 times


Good luck climbing that cable.

Advantageously, the entire neutral-buoyancy-tower portion could be equipped with (or even composed of) vertical-axis wind turbines, allowing massive power generation capacities. It would be more than enough to constantly electrolize water to replenish the lost lifting gas, provide motive power to the climber assembly going up the tower, and generate massive amounts of energy to the surrounding region as well.

Catastrophic failure of the tether would not result in significant damage to the surroundings, as the positive buoyancy of the top half would carry it free and the near-neutral-buoyancy lower tower portion has an extremely low terminal velocity. I'm a little worried about the guyed mast portion, though.

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Re: Use of 20km tall "space elevator"?

Postby drachefly » Thu Aug 27, 2015 3:44 pm UTC

If the drag on the guy wires is a problem, then the drag on the tower is a much, much worse problem.

The guy wires may be 40% longer, but they can be far, far thinner, so the total drag will be lower than the drag on the tower.

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Re: Use of 20km tall "space elevator"?

Postby sevenperforce » Thu Aug 27, 2015 4:37 pm UTC

drachefly wrote:If the drag on the guy wires is a problem, then the drag on the tower is a much, much worse problem.

The guy wires may be 40% longer, but they can be far, far thinner, so the total drag will be lower than the drag on the tower.

The problem with guy wires isn't drag; it's that they will not be able to hold up their own mass against gravity. The tower doesn't have that problem because it is near neutrally buoyant. But making neutrally buoyant guy wires would increase their cross-section to the point that the drag on the guy wires would be an order of magnitude greater than the drag on the tower.

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Re: Use of 20km tall "space elevator"?

Postby Chen » Thu Aug 27, 2015 5:23 pm UTC

In case people hadn't actually found it, it's US Patent 9085897. Can find it at: http://www.uspto.gov/web/patents/patog/ ... atent.html

I read through a bit but my comp here at work won't load the images, so I'm having a hard time following a lot of the description. That and the math is pretty badly formatted when just looking at the text version. I assume the actual PDF version would be easier to read.

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Re: Use of 20km tall "space elevator"?

Postby SDK » Thu Aug 27, 2015 8:44 pm UTC

Anyone who knows more about gyroscopes than me want to comment on the following paragraph (from the patent)?

9085897 wrote:The presence of a gyroscopic stabilization system will cause an oscillation L, which is beneficial to control as it provides efficient energy storage of time-varying torques 782; oscillations may be damped by pneumatic damping so as to vary the pressure cell pressures at the elevator core structure harmonic frequencies so as to dampen oscillations actively. The energy that may be extracted by damping is given as the product of rate of change of pressure and sum of the compartment volumes. The control system typically acts on the first six harmonic bending moments of the elevator core structure 12 or until the structural bending modes have a wavelength in the vertical axis of length that is shorter than that of the length of the pressure compartments or a small multiple of that length. The first three moments for control are illustrated in FIG. 4A, FIG. 4B and FIG. 4C respectively. The damping effect may be achieved actively using a high pressure line-and-vent network system and passively by allowing support gas to vent from pressure cell to pressure cell along a connecting line network.


A lot of words in this patent. Some weight calculations too. I just skimmed it, but it's basically as we theorized as far as I can tell. One line in there though, "The space elevator tower can be further scaled to provide direct access to altitudes above 200 km" has me wondering how balloons are going to help you once you're that far out of Earth's atmosphere.

Here's the whole thing, spoilered below, for those too lazy to look up the patent themselves. Images (and full patent following).

Spoiler:
Abstract

A freestanding space elevator tower for launching payloads, tourism, observation, scientific research and communications. The space elevator tower has a segmented elevator core structure, each segment being formed of at least one pneumatically pressurized cell. The pressure cells may be filled with air or another gas. Elevator cars may ascend or descend on the outer surface of the elevator core structure or in a shaft on the interior of the elevator core structure. A payload may be launched from a pod or deck at the upper end of the space elevator tower. The space elevator tower is stabilized by gyroscopic and active control machinery. The space elevator tower maintains a desired pressure level through gas compressor machinery. Methods of constructing the space elevator are also disclosed.

Claims

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The invention claimed is:

1. A space elevator tower for location on a planetary surface, the space elevator tower comprising: a pneumatically pressurized structure formed from flexible sheet material, said pneumatically pressurized structure divided into a plurality of segments along a length of the space elevator tower, each of said plurality of segments containing a plurality of cells defining a core, and a plurality of stabilization devices distributed along the length of the space elevator tower; wherein the plurality of cells are pressurized with a gas to support the pneumatically pressurized structure; and wherein said plurality of stabilization devices is configured to provide active stabilization of the space elevator tower using a harmonic control strategy.

2. The space elevator tower as claimed in claim 1, wherein the space elevator tower includes a main pod at a top of the tower for accommodating personnel or equipment.

3. The space elevator tower of claim 2, further comprising a payload launch system.

4. The space elevator tower as claimed in claim 1, wherein each of said plurality of cells are cylindrical, and said core is defined by a plurality of the cylindrical cells arranged in a circle, said core having a diameter greater than the diameter of each individual cylindrical cell.

5. The space elevator tower as claimed in claim 1, wherein the plurality of cells are arranged in a circle to form the core.

6. The space elevator tower as claimed in claim 1, wherein, for each of said plurality of segments, the plurality of cells are cylindrical and have substantially the same diameter.

7. The space elevator tower as claimed in claim 1, wherein the plurality of cells are located between inner and outer walls, the outer wall defining an exterior surface of the space elevator tower and the inner wall defining the core.

8. The space elevator tower as claimed in claim 1, including at least one elevator mounted for movement in the core of the tower.

9. The space elevator tower as claimed in claim 1, including at least one elevator mounted for movement on an exterior surface of the tower.

10. The space elevator tower as claimed in claim 8 or 9, wherein each said at least one elevator includes motor driven drive wheels, for frictional contact with an elevator guide and support.

11. The space elevator tower as claimed in claim 1, wherein each elevator is provided with at least one of an electromagnetic drive, a cable support, and a drive.

12. The space elevator tower of claim 1, further comprising a brace structure.

13. The space elevator tower of claim 1, further comprising an anchorage extending into the ground beneath the space elevator tower.

14. The space elevator tower of claim 1, further comprising a plurality of pods distributed at a plurality of heights along the pneumatically pressurized structure.

15. The space elevator tower of claim 1, further comprising a plurality of platforms distributed at a plurality of heights along the elevator tower structure.

16. The space elevator tower of claim 3, wherein the payload launch system comprises a static launch tube located in the main pod.

17. The space elevator tower of claim 3, wherein the payload launch system comprises at least one rotating launch device.

18. The space elevator tower of claim 1, wherein the gas is air.

19. The space elevator tower claim 1, wherein the gas is not.

20. The space elevator tower of claim 1, wherein the gas is hydrogen.

21. The space elevator tower of claim 1, wherein the gas is helium.

22. The space elevator tower claim 1, wherein walls of the plurality of cells consist of a material with high mass-to-tensile strength properties.

23. The space elevator tower of claim 1, wherein the flexible sheet material comprises boron.

24. The space elevator tower of claim 1, wherein the flexible sheet material comprises a Kevlar polyethylene composite.

25. The space elevator tower of claim 1, wherein the plurality of stabilization devices further comprise gyroscopic wheels.

26. The space elevator tower of claim 1, wherein the plurality of stabilization devices further comprise gas compressor machinery.

27. The space elevator tower of claim 1, further comprising gas compressor machinery located on the ground.
--------------------------------------------------------------------------------

Description

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FIELD

This invention relates to space elevators, and more particularly to a freestanding space elevator tower.

BACKGROUND

In order to access space or near space, payloads must gain significant potential and kinetic energy. Traditionally, regions above 50 km in altitude can only be accessed using rocketry, where mass is expelled at high velocity in order to achieve thrust in the opposite direction. This process is extremely inefficient as rockets must counter the gravitational force during the flight by carrying mass in the form of propellant and must overcome atmospheric drag. In contrast, if a payload is hauled to space or near space along an elevator system, the work done is significantly less as no expulsion mass must be carried to do work against gravity, and lower ascent speeds in the lower atmosphere can virtually eliminate atmospheric drag. Elevator cars' motion may also be powered remotely by electrical or inductive means, eliminating the need to carry any fuel.

It has previously been proposed, most famously by Arthur C. Clarke in his 1978 novel, The Fountains of Paradise, that a space elevator could be constructed using a cable and counter-balanced mass system. For Earth's gravity and spin rate, such a solution requires a cable of at least 35,000 km in length and a counter balance mass similar to a small asteroid. Such a system could be constructed by launching the cable into space or manufacturing it in situ and lowering it into contact with Earth. However, the technological obstacles that must be overcome, including the construction of a cable with suitable strength characteristics or the in-space construction of the apparatus, have not been realized since the concept was popularized by Clarke. Known materials are simply not strong enough to enable the construction of a cable of that length that would even be capable of supporting its own weight.

SUMMARY

The present invention is a self-supporting space elevator tower for the delivery of payloads to at least one platform or pod above the surface of the Earth for the purposes of space launch. The space elevator tower may also be used to deliver equipment, personnel and other objects or people to at least one platform or pod above the surface of the Earth for the purpose of scientific research, communications and tourism. While the described space elevator tower can provide access to lower altitude regions, the space elevator tower can also be scaled to access altitudes above, for example, 15 km, the typical ceiling altitude for commercial aviation. The space elevator tower can be further scaled to provide direct access to altitudes above 200 km and with the gravitation potential of Low Earth Orbit (LEO).

Although ascending to an altitude significantly below 35,000 km will not place a payload in Earth orbit, a platform or pod supported by the space elevator tower has significant advantages over a surface-based launch platform. While surface-based rockets must be designed to overcome atmospheric air resistance, launch from a high-altitude platform has no such requirement, and, consequently, existing space equipment such as an orbital transfer stage or conventional upper stage can be used to insert payloads directly into Earth orbit. Ideally, payloads should be raised to the highest feasible altitude before launching in order to maximize the energy advantages; however, the energy advantages for space flight are readily leveraged above 5 km.

A platform or pod supported by the space elevator tower also has significant advantages over orbiting satellite platforms. Geographically fixed, but providing access to regions of space closer to the surface than geostationary orbit, elevator platforms provide the ideal means to communicate over a wide area and to conduct remote sensing and tourism activities. As a tourist destination, the elevator platforms provide stations located at fixed attitudes from the surface for observation. The elevator platforms provide the means to safely access a region of space with a view extending hundreds of kilometers.

The space elevator tower may also provide a near-surface observation platform with oversight over a fixed geographical area. Such platforms can be used for observation, remote sensing and communications. Small systems may be mobile and delivered to sites for temporary applications for example to provide temporary communications towers typically between 25 m and 150 m. Used with an elevator component equipment may be accessed and maintained during operation. Used without an elevator component, equipment may be installed only during the construction of the apparatus.

The invention provides in one aspect, a freestanding space elevator tower, comprising a segmented elevator core structure. More specifically, in accordance with one aspect of the present invention, there is provided a space elevator tower for location on a planetary surface, the space elevator tower comprising a pneumatically pressurized structure that is at least partially formed from flexible sheet material and is at least partially supported by internal gas pressure, the space elevator tower including a main pod at the top thereof, providing at least one of: a launch device for launching objects from the main pod, and a platform for at least one person or for communications; and remote sensing equipment.

The tower can include at least one stabilization device attached to the pneumatically pressurized structure to provide at least partial active stabilization.

The invention provides in another aspect, an elevator core structure for a space elevator, the elevator core structure comprising a series of core segments, the core segments comprising at least one or more pneumatically pressurized pressure cells.

The invention provides in another aspect, a core segment for an elevator core structure in a space elevator tower, the core segment comprising at least one pneumatically pressurized pressure cell.

The invention provides in another aspect a method for the active control of the elevator structure comprising an apparatus that adjusts pneumatically and by other means the attitude of the core structure in order to null external forces, eliminate structural bending moments and maintain the core structure over it's footprint.

The invention provides in another aspect, a method of constructing an elevator core structure for a space elevator tower, the method comprising: a) extruding core segments from a fluid core material; b) embedding pods containing control and stabilization machinery in the core segments as they are extruded; and, c) raising the pods, preferably using a roller system and pneumatics.

The invention provides in another aspect, a method of constructing an elevator core structure for a space elevator tower, the method comprising: a) raising a core segment with a climbing construction elevator that grips the outer surface of the existing elevator core structure; b) sliding the core segment on top of the existing elevator core structure on a horizontal track on the climbing construction elevator; and, c) actively adjusting the centre of mass of the existing elevator core structure to maintain the elevator core structure over its footprint.

Further aspects and advantages of the invention will appear from the following description taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the following drawings, in which:

FIG. 1 is an isometric view of one embodiment of a space elevator tower;

FIG. 2A is an isometric view of a second embodiment of the space elevator tower;

FIG. 2B is a third embodiment of the space elevator tower;

FIG. 2C is a fourth embodiment of the space elevator tower;

FIG. 2D is a fifth embodiment of the space elevator tower;

FIG. 2E is a sixth embodiment of the space elevator tower;

FIG. 3A is an isometric view showing one embodiment of the structural components of a core segment;

FIG. 3B is an isometric and cutaway view of one embodiment of the structural and mechanical components of a core segment;

FIG. 4 is a schematic diagram showing active stabilization control of the elevator core structure;

FIG. 5A is an isometric view showing an alternative embodiment of the structural components of a core segment;

FIG. 5B is an isometric view showing an alternative embodiment of the structural components of a core segment with an interior elevator shaft;

FIG. 5C is an isometric view showing an alternative embodiment of the structural components of a core segment, and also showing an embodiment of an elevator car;

FIG. 6A is an isometric view showing an embodiment of a payload launch system;

FIG. 6B is an isometric view showing an alternative embodiment of a payload launch system;

FIG. 7A is an isometric view showing a method of constructing an elevator core structure;

FIG. 7B is an isometric view showing an alternative method of constructing an elevator core structure;

FIG. 8 is an isometric view showing an alternative application of the elevator core structure; and

FIG. 9 is an isometric view showing an embodiment of an elevator car and also illustrating a method of gripping the core structure.

DETAILED DESCRIPTION

FIG. 1 illustrates a segmented space elevator tower 10 built in accordance with a first embodiment of the present invention. Specifically, the space elevator tower 10 has an upper end 11 and a lower end or main tower portion 13. The lower end 13 comprises an elevator core structure 12 having a plurality of core segments 14 stacked end-to-end along the length of the elevator core structure 12. The upper end 11 of the space elevator tower 10 comprises a main pod 16 and a platform 18. The main pod 16 and the platform 18 are supported by the elevator core structure 12.

The elevator core structure 12 has mechanical and structural supports (not shown) for ascending and descending elevator cars (not shown). The elevator cars may be used to transport equipment, payloads, personnel, tourists or other loads to the main pod 16 and platform 18, or to any point along the length of the elevator core structure 12. In one embodiment, an elevator car may ascend the space elevator tower 10 on the exterior surface of the elevator core structure 12 on tracks (not shown) or by a device that grips the outside of the elevator core structure 12. In alternative embodiments, the elevator cars may ascend and descend the space elevator tower through a shaft located on the interior of the elevator core structure 12. Since the elevator cars may remain in contact with the elevator core structure during the entire ascent or descent, the mechanism for elevating and lowering the elevator cars may be provided by frictional contact, at least one winch mechanism located along the length of the elevator core structure, or by inductive means or by any other suitable means. The elevator cars may be self-powered, or may derive their power pneumatically, electrically, magnetically or inductively from the elevator core. In some embodiments, the elevator cars may use more than one mechanism during an ascent or descent.

Stations and other buildings and structures may be provided inside the core segments 14 along the elevator core structure 12 at convenient locations for disembarkation of passengers and cargo. Given the mass restrictions, these structures will be of lightweight design and may include pressurized zones with airlock access from elevator cars in order to provide accommodation and amenities.

Please note that the two-digit numbers corresponding to parts of the space elevator tower 10 are included, as the last two digits of a three digit reference, wherever a generic reference is made to a component of the various embodiments of the space elevator tower.

FIGS. 2A-2E illustrate examples of alternate embodiments of the space elevator tower. Similar components of the space elevator tower are similarly numbered.

FIG. 2A illustrates an alternative embodiment of the space elevator tower 110 having an upper end 111 and a lower end, or main tower portion, 113. The lower end 113 comprises an elevator core structure 112 having a plurality of core segments 114 stacked end-to-end along the length of the elevator core structure 112. The elevator core structure 112 supports a main pod 116 and a platform 118 at the upper end 111 of the space elevator tower 110. The core segments 114 are arranged in a four-square configuration with an open lattice brace structure 120. Each four-square configuration of the core segments may support a deck 122 at convenient locations for disembarkation of passengers and cargo, and the deck 122 can form part of the structure maintaining the relative locations of core segments 114.

FIG. 2B illustrates an alternative embodiment of the space elevator tower 210 having an upper end 211 and a lower end, or main tower portion, 213. The lower end 213 comprises an the elevator core structure 212 having a plurality of core segments 214 stacked end-to-end along the length of the elevator core structure 212. The elevator core structure 212 supports a main pod 216 and a platform 218 at the upper end of the space elevator tower 210. The core segments 214 are arranged in a tapered four-square configuration with an open lattice brace structure 220. Each tapered four-square configuration of the core segments may support a pod 224 at convenient locations for disembarkation of passengers and cargo. The pods 224 can act as way-stations, to provide amenities, and for storage to house stabilization mechanisms and, as in FIG. 2A, can form part of the structure maintaining the relative locations of the core segments 214.

FIG. 2C illustrates an alternative embodiment of the space elevator tower 310 having an upper end 311 and a lower end, or main tower portion, 313. The lower end 313 comprises an elevator core structure 312 having a plurality of core segments 314 stacked end-to-end along the length of the elevator core structure 312. The elevator core structure 312 supports a main pod 316 and a platform 318 at the upper end 311 of the space elevator tower 310. The core segments 314 are supported with an external open lattice brace structure 320; while this is only shown for two opposite sides of the tower 310, this brace structure 320 would be provided all around the tower 310, and in plan view may show, for example, four, six, or eight structures 320 arranged radially around the tower 310. A series of pods 324 are distributed along the length of the elevator core structure 312, such that there may be a pod 324 between each pair of neighboring core segments 314. In this specific embodiment, the pods 324 have the same diameter as the core segments 314. The space elevator tower 310 shown in FIG. 2C has an anchorage 326 at the base of the elevator core structure 312 that extends into the ground beneath the space elevator tower 310 to provide greater stability to the space elevator tower 310, and it will be understood that such an anchorage 326 can be provided for any of the embodiments shown.

FIG. 2D illustrates an alternative embodiment of the space elevator tower 410 having an upper end 411 and a lower end, or main tower portion, 413. The lower end 413 comprises a plurality of core segments 414 stacked end-to-end. The elevator core structure 412 supports a main pod 416 and a platform 418 at the upper end 411 of the space elevator tower 410. The core segments 414 have a variety of diameters such that the core segments 414 are progressively narrower from the base of the elevator core structure 412 to the upper end of the elevator core structure 412.

FIG. 2E illustrates an alternative embodiment of the space elevator tower 510 having an upper end 511 and a lower end, or main tower portion, 513. The lower end 513 comprises a plurality of core segments 514 stacked end-to-end along the length of the elevator core structure 512. The elevator core structure 512 supports a main pod 516 and a platform 518 at the upper end 511 of the space elevator tower 510. A series of pods 524 are distributed along the length of the elevator core structure 512, such that there may be a pod 524 between each pair of adjacent core segments 514. The pods 524 have a larger diameter than the core segments 514, but may have a different diameter. The space elevator tower 510 shown in FIG. 2E has an anchorage 526 that extends into the ground beneath the space elevator tower 510 to provide greater stability for the space elevator tower 510.

FIG. 3A illustrates the structural components of a core segment 614 built in accordance with the present invention. The core segment 614 has a hollow cylindrical shape with a longitudinal axis 630, a wall 632 with a thickness A disposed circumferentially around the longitudinal axis 630, and an inner wall surface 634 and an outer wall surface 636. The core segment 614 has a length B along the longitudinal axis, and has an outer diameter C, and an inner diameter D=(C-2A), which corresponds to the thickness A of the wall 632.

In this embodiment, the wall 632 of the core segment is composed of a plurality of adjacent hollow cylindrical pressure cells 638 having the same length as the core segment 614, having mutually parallel longitudinal axes 640, parallel to the longitudinal axis 630 of the core segment 614, and arranged in a single ring at a constant radial distance E=(D+A)/2 from the longitudinal axis of the core segment.

The pressure cells 638 are hollow and are filled with a pressurized gas. The walls of the pressure cells 638 consist of a material with very high mass-to-tensile strength properties, for example, boron or a Kevlar polyethylene composite at a thickness able to retain the cell pressure with adequate margins and according to engineering practice. The material of the walls is otherwise generally sheet-form and flexible, i.e. by itself it provides no significant strength in compression. The number of pressure cells 638 will be related to the diameters C, D and the wall thickness A (the diameter of each cell 638).

FIG. 3B illustrates the structural and mechanical components of one embodiment of the core segment 614 according to the present invention. It is to be appreciated that the core segment of the present invention is not limited to the following example and that features of the following configuration may be combined to produce further variations of the core segment without departing from the scope of the present invention.

The core segment 614 has a longitudinal axis 630, a wall with a thickness A and an inner wall surface 634 and an outer wall surface 636 positioned circumferentially around the longitudinal axis 630, forming a cylindrical shape with a hollow interior cavity 639. The core segment 614 has a length B along its longitudinal axis 630, an outer diameter C and an inner diameter D.

The wall 632 is composed of a plurality of adjacent hollow cylindrical pressure cells 638 having the same length as the core segment 614, having mutually parallel longitudinal axes 640, parallel to the longitudinal axis 630 of the core segment 614, arranged in a single ring at a constant radial distance E=(D+A)/2 from the longitudinal axis 630 of the core segment.

The core segment 614 has an upper end 650, a midsection 652 and a lower end 654 distributed continuously along the core segment 614. At the upper end 650 of the core segment 614, the hollow interior cavity 639 of the core segment 614 houses a vacuum chamber 656 having an inner diameter D and a depth H. The vacuum chamber 656 is sealed from the midsection 652 by a pressure deck 658 having a diameter D spanning the inner wall 634 of the core segment 614. A gyroscopic wheel 660, coaxial with the core segment 614, having a diameter F smaller than the inner diameter D of the vacuum chamber 656 and having a depth G smaller than the depth H of the vacuum chamber 656 is rotationally suspended in the interior of the vacuum chamber 656. A similar vacuum chamber 656 and gyroscopic wheel 660 are located at the lower end of the core segment 614.

The core segment 614 further comprises a machinery housing 662 located on the pressure deck 658 in the midsection 652 of the interior cavity 639 of the core segment 614. The machinery in the machinery housing 662 includes compressor machinery, gyroscopic machinery, and other control machinery (not shown). The gyroscopic machinery provides the rotational momentum of the gyroscopic wheel 660. The compressor machinery maintains a low pressure condition in the vacuum chamber in order to reduce viscous drag on the gyroscopic wheel 656, maintains the pressure in the pressure cells 638, and redistributes gas as required. Gas and power conduits 664 run through the hollow interior cavity 639 of the core segment 614 to distribute gas, power and interconnect with other segments as required.

Unless the pressure cells 638 are pre-pressurized and in case of leakage, the compressor machinery (not shown) is required to pump gas into the space elevator tower 10. Compressor machinery may be sized by predicting and monitoring pressure cell 638 leak rates with time and also including a margin for space elevator core structure 12 pneumatic control. Alternatively, a high pressure gas line may be utilized to pressurize and control the elevator core structure 12 with compressor machinery and pressure reservoirs mounted on the ground or mounted on only some of the segments 614.

The gyroscopic wheels 660 are heavy spinning wheels or gyroscopes that increase the angular momentum of the elevator's core structure in order to stabilize its orientation in space. Conveniently, the wheels may also be adapted to act as compressors and pressurize the structure. The wheels are spun at high radial velocities in order to ensure that a significant fraction of the structure's angular momentum is stored in their motion. The gyroscopic wheels 660 normally operate continuously while the elevator core structure 12 is in operation and are duplicated throughout the elevator core structure 12 so as to ensure redundancy and downtime for maintenance access. The wheels may alternatively be installed inside the pressure cells 638 so as to induce vortices in the support gas to further enhance the gyroscopic mass.

In a single wheel design, the gyroscopic wheel 660 is orientated to spin with its axis aligned with the elevator core structure 12 such that horizontal forces applied to the elevator core structure 12 are transferred to processional motions in the core. Other gyroscopic systems as are known in the art may also be installed in the space elevator tower 10.

The control machinery may also include active damping systems that enhance the structure's ability to damp oscillations. In one embodiment, the control machinery permits the leaking of air from one pressure cell 638 to another pressure cell 638 using a control valve network or arrangement including fluid dampers. This machinery may be controlled and powered by pneumatic or electrical means as is convenient and can provide a means to communicate with elevator components. The elevator core structure 12 will be arranged along a linear axis such that the sums of centripetal, gravitational and external forces are minimized in the horizontal axes.

Active control machinery may be implemented to stabilize the structure against buckling or falling and to couple disturbance torques into other axes. FIG. 4A illustrates a typical harmonic control strategy. The primary control is exerted on the first bending harmonic of the core structure. A space elevator tower 10 with center of mass 780 at an altitude J under deformation by an external torque 782 must utilize a control law and actuator system (not shown) in order to adjust the center of mass 780 such that the attitude of the space elevator tower 10 is at an angle K to the normal in order to counteract the disturbance. Other structure bending moments, such as the examples shown in FIG. 4B and FIG. 4C do not displace the center of mass of the core structure. Consequently, these moments can be controlled independently by the variation of segment pressures along the core at a wavelength and period characteristic of the bending moment.

The tolerance that the controller must meet is determined from the elevator core structure stiffness and bracing, gyroscopic stability and base footprint. The presence of a gyroscopic stabilization system will cause an oscillation L, which is beneficial to control as it provides efficient energy storage of time-varying torques 782; oscillations may be damped by pneumatic damping so as to vary the pressure cell pressures at the elevator core structure harmonic frequencies so as to dampen oscillations actively. The energy that may be extracted by damping is given as the product of rate of change of pressure and sum of the compartment volumes. The control system typically acts on the first six harmonic bending moments of the elevator core structure 12 or until the structural bending modes have a wavelength in the vertical axis of length that is shorter than that of the length of the pressure compartments or a small multiple of that length. The first three moments for control are illustrated in FIG. 4A, FIG. 4B and FIG. 4C respectively. The damping effect may be achieved actively using a high pressure line-and-vent network system and passively by allowing support gas to vent from pressure cell to pressure cell along a connecting line network.

For reliability and repair, a segmented elevator core structure 12 with multiple pressure cells 638 is desirable in order to ensure that elevator integrity can be maintained during maintenance of pressure cells 638 and for leak repair. Failure tolerance can be enhanced by the duplication of subsystems used in other high technology systems, with critical systems such as compressors and gyro-stabilization wheels operated in hot-redundancy mode. A segmented elevator core structure 12 also enables the disassembly of the system during decommissioning and enables the elevator core structure 12 to be dismantled in a top-down process while power and pressure are maintained to the remaining elevator core structure 12 and systems.

FIGS. 5A-5C show alternative embodiments of the core segment 614 in accordance with the present invention. It is to be appreciated that the core segments of the present invention are not limited to the following examples, and that features of the following configurations may be combined to produce further variations of the core segments without departing from the scope of the present invention. Further variations include, but are not limited to, core segments 14 constructed in a variety of shapes with a variety of numbers of pressure cells 38, and core segments 14 constructed with more than one pressure cell 38 along the length of the core segment 14.

The core segment 614 of FIG. 5A comprises a cylindrical outer wall 630a of diameter C, and a coaxial cylindrical inner wall of diameter D. The cylindrical shell between the outer wall 670 and inner wall 631 is divided into a series of pressure compartments 672 by baffles 673 that span the radial distance between the inner wall 631 and the outer wall 670 and extend from the upper end 650a of the core segment 614 to the lower end 654a of the core segment 614. The pressure compartments 672 are pressurized with air or another suitable gas.

The core segment 614b of FIG. 5B is similar to the core segment 614 shown in FIGS. 3A and 3B. The core segment 614 of FIG. 5B is not hollow, but instead has an additional pressure cell 637b inside the ring of parallel pressure cells 638b. FIG. 5B also shows an example of an elevator shaft on the interior of one pressure cell 671 of a core segment 614b.

The core segment 614c of FIG. 5C corresponds to the elevator core structure shown in FIG. 2A. The core segment 614c is comprised of four pressure cells 638c, supported in a four-square configuration by an open lattice brace structure 620c. FIG. 5C also shows an example of an elevator car 673 ascending the exterior surface of a pressure cell 638c.

At typical conditions on the Earth's surface, atmospheric air has a density of 1.29 kg m.sup.-3. For a pressurized vessel, the pressure variation with altitude may be derived by consideration of the gravitational force on a unit area air parcel as g.rho..differential.z=-.differential.p Eqn. 1

where g is the force due to gravity (9.8 ms.sup.-2 on Earth), .rho. is the mass density of the gas, p is the pressure and z is altitude.

At atmospheric pressures the behaviour of the gas may be characterized by the ideal gas law as p=.rho.RT Eqn. 2

where R is the gas constant in units normalized for Earth's atmosphere and T is the temperature in Kelvin. Assuming a constant pressure cell temperature and approximating gravity as constant over altitude the pressure at the top of a pressure cell of altitude z is calculated by integrating p(z)=p.sub.0exp(-z/H) Eqn. 3

where H=RT/g and is the scale height of the atmosphere (for Earth, H.about.7.6 km). The load capacity L in kilograms of a vertical cylinder of length l and diameter d that has no structural strength under compression is therefore

.pi..times..times..times..times..function..times..times. ##EQU00001##

where p.sub.0 is the pressure above the ambient pressure at the base of the cell.

Assuming the case of a simple single pressure cell 638 structure, the mass of such a segment is given as m.sub.element=.rho..sub.A.pi.dl Eqn 5

where .rho..sub.A is the density of the cell wall material. If the pressure cell is in firm contact with the ground, the apparatus must support only this structural mass as the mass of the pressurization gas may be supported from the base. If the pressure cell 638 is further up the structure, the supporting structure must support the pressure cell mass and the mass of the pressurization gas of density .rho. which is given as:

.rho..times..times..times..times..pi..times..times..times..function..func- tion..times. ##EQU00002##

where b is the absolute gas pressure at the base of a cell. Setting .rho. to the density of the ambient environment, this expression can also be used to compute the buoyant mass which is equivalent to the mass of atmospheric air displaced by the core structure. This mass may be subtracted from the mass of the pressurized core structure as it provides support for the core. The center of gravity of the support gas is given by:

.function..times..function..function..times. ##EQU00003##

In some alternative embodiments, other gases may be utilized with lower molecular masses than that of air. The mass advantages of other pressurization gases may be approximated by the ratio of their molecular mass with that of nitrogen gas (the dominant constituent of atmospheric air). Thus a structure pressurized with hydrogen will require 28/2=14 times less gas by mass and with helium 28/4=7 times less.

The force required to buckle a column under load is given as:

.pi..times.'.times. ##EQU00004##

where l' is the effective column length, E is the effective Youngs modulus of the wall material when the core is pressurized and I is the area moment of inertia. If the elevator core structure is braced from the base and gyroscopically pinned at the top l'=l. For a cylinder, I=.intg.y.sup.2dA=2.pi.tr.sup.3 where t is the thickness and r is the radius.

These results can be applied to an embodiment of a core design for an Earth-based elevator to access near space at 20 km altitude. In a specific embodiment, the elevator is constructed at 5 km altitude in one of four regions on the equator to reduce the required height of the elevator to 15 km to access 20 km altitude and to utilize advantageously the spin of the Earth.

Assuming an elevator core structure comprising core segments of the embodiment shown in FIG. 5A braced at the base and consisting of Boron pressure cells of constant wall thickness 1.2 cm, the core segment having a hollow cylindrical shape with an inner diameter D=229 m and outer diameter C=230 m, a 15 km elevator core can be supported by 150 bar hydrogen gas. Approximating the structure as two concentric cylinders, the mass of the structure is 7.5.times.10.sup.7 kg, and the mass of the pressurization gas needed is 3.3.times.10.sup.9 kg.

Constructed at 5 km altitude, the elevator core structure has a buoyant mass of 1.2.times.10.sup.7 kg giving a total mass of 3.31.times.10.sup.9 kg. The load capacity of the elevator core structure, in excess of that needed to support itself is 1.18.times.10.sup.7 kg of force equivalent. The buckling load at the top is 4.1.times.10.sup.8 kg, and at the center of gravity (located at 5.2 km up the core) the critical load is 3.36.times.10.sup.9, which exceeds the building mass by 5.times.10.sup.7 kg, including the mass of the pressurization gas, indicating that the core is structurally stable and able to support the raising of payloads of mass in excess of 100 tonnes.

Further margin may be obtained by tapering the thickness of the walls of the core segments, such that the walls are thinner at the upper end of the elevator core structure than at the base of the elevator core structure, lowering the center of gravity and reducing the structural mass. Alternatively, the core diameters may be tapered to increase the structural stiffness in the base. Additionally, the core can be segmented and pressurized equivalently without inducing an imbalance of support forces between segment walls. Other core designs may be analyzed by comparison with the two-cylinder design and by appropriate adjustment for the amount of wall material utilized.

Access to Low Earth Orbit (LEO) may be provided by means of a launch station located conveniently at the upper end 11 of a space elevator tower 10, where spacecraft without internal propulsion systems may be mated to conventional space-propulsion systems such as an orbital transfer vehicle that can provide the additional kinetic energy required to enter LEO. The energy and, consequently, the propellant needed for LEO is significantly reduced compared with surface launch due to the absence of a drag force experienced during atmospheric ascent and to the potential energy gained by being launched at high altitude.

FIGS. 6A and 6B show two launch-system configurations. It is to be appreciated that the launch systems of the present invention are not limited to the following examples, and that features of the following configurations may be combined to produce further variations of the launch systems without departing from the scope of the present invention.

The launch system shown in FIG. 6A provides a static main pod 816 for communications and tourism with an integral launch tube 884 inclined to inject a payload 886 through a port 888 in the side of the main pod 816. A gyro-stabilization system (not shown) is provided to translate launch shocks into oscillatory elevator core structure motion in order to enable damping. The back end 890 of the launch tube 884 may be pressurized before payload 886 release in order to have the payload 886 clear the space elevator tower 10 before chemical propulsion engines (not shown) are engaged.

The launch system shown in FIG. 6B makes use of an additional centripetal motion of angular rate N radians per second. Launch tubes 884 are mounted or deployed on a truss structure 892 such that the center of mass of the payload 886 is a distance P from the axis of rotation Q. In this configuration, an additional velocity, the product of N and P, is given to the payload 886 before release. The payloads 886 are released by damping the rotational motion such as to eject the payloads 886. The rotating mechanism may be mass balanced about the axis of rotation.

FIGS. 7A and 7B illustrate methods of constructing the space elevator tower 10. It is to be appreciated that the construction methods of the present invention are not limited to the following examples, and that features of the following configurations may be combined to produce further variations of the construction methods without departing from the scope of the present invention.

In the method shown in FIG. 7A, the elevator core structure 12 is erected vertically using a mechanism that extrudes core segments 14. Pods 24 containing control and stabilization machinery are embedded in the elevator core structure 12 as it is extruded by a roller system 995 from a stack of similar pods 24. Gas and power conduits 964 are lifted with each pod 24. The core segment walls and pressure compartments are formed as an extrusion molding of a liquid core material 996. Optionally, a winding mechanism 998 embeds fibers into the elevator core structure 12 in order to increase the elastic resistance of the structure. Pneumatic pressure and a roller mechanism may be used to raise and lower core sections.

FIG. 7B shows an alternative construction approach where core segments 14 are raised by means of a climbing construction elevator 899 that grips the external surface of the existing elevator core structure 12 as it raises and installs segments section by section. Advantageously, core segments 14 equipped with stabilization systems (not shown) may be energized by means of an umbilical connector 897 such that the new core segment 14 may be raised completely above the construction elevator 899 and installed on the existing elevator core structure 12 by means of a horizontal track (not shown) installed on the top of the construction elevator 999. The center of mass of the combined system may be adjusted actively during the core segment installation in order to maintain it over the elevator core structure's 12 surface footprint and to provide support for the elevator core structure 12 in the presence of external disturbance torques.

FIG. 8 shows an alternative application of the elevator core structure 12. With two or more ends in fixed contact with the ground the elevator core structure 12 may be utilized as a mass transit system 1000 to move passengers and cargo from one location to another. This structure may be deployed to connect densely populated suburban areas or to provide a permanent link to replace aviation routes. FIG. 8 illustrates a typical transit configuration with two ends 1002 that provide surface arrival and destination points and a gyro-stabilised core segment 14 arrangement of constant exterior diameter with gyros 1004 arranged such that their spin axes are substantially orthogonal to the segment's long axis 1006 in the regions near the apex 1008 of the core structure and are oriented with their spin axes parallel to the segment's long axis near the bases 1002.

Elevators with devices that grip the outside of a cylindrical core in a spiral arrangement may allow cars to pass each other and enable bi-directional travel along the core. This configuration is illustrated in FIG. 9, where a spiral mounting arrangement that encompasses at least half the core circumference 991 grips a circular central core structure 992 and supports pressurised elevator cars 993 with airlocks 994 and observation windows 995. Locomotion is achieved, for example, using drive wheels 996 in frictional contact with the exterior of the core segment. In normal operation, the elevator rises or descends the tower (A). When two cars meet, they are able to pass each other by adjusting their motion as (B). In the absence of other car switching mechanisms, only unidirectional travel may be possible, and cars must shuttle payload between stations.

While the present invention has been described in the specific embodiments as an essentially free standing tower (in this context the braced supports of FIG. 2C are considered to be part of the tower), it is to be understood that, where applicable, additional support mechanisms can be provided. Thus, in unobstructed locations, at least lower portions of the tower can be provided with guyed or cable supports. Generally, these do require the cables or guy wires to be attached to the ground at some distance from the tower, thereby requiring unobstructed access to locations some distance from the tower. Further, such cable or guywire supports are likely only to provide an advantage up to certain heights. While cable or guywires can provide useful lateral support to a tower, they do apply a downward force on the tower thereby increasing the requirement for the tower to withstand a vertical compressive load. Additionally, as the length of such cable guide wire increases, the weight of the cables is, effectively, carried by the tower as an increasing downward load on the tower.

Further, while the present invention has been described in terms of a structure that is largely or wholly supported by internal pneumatic pressure, with the structure otherwise being formed from generally flexible, sheet-formed material, it will be understood that, as desired, the structure can comprise, at least in part, rigid elements. In particular, for individual pods located along the main part of the top of the tower, it will likely prove beneficial to have at least some elements of these pods formed from elements and components that are more or less rigid and do not depend upon gas pressure to define the shape or component and to provide structural integrity. Thus, for example, the floor of each pod can be formed, in known manner, with some supporting grid of generally rigid beams, so as to provide a floor that, to users, will appear and feel substantially rigid and inflexible. Attachment of launch and launch systems themselves will also, likely and preferably, be formed from components that are largely rigid and self-supporting, i.e. do not depend upon pneumatic support.

Further, reference in this specification and the claims to `elevator` are intended to encompass suitable powered mechanisms or devices suitable for moving goods and/or people up and down the tower. In general, the tower is expected to have dimensions so large that unassisted movement of people or goods will be impractical. It is expected that the `elevator` will comprised individual elevator cars and that these would not be supported on cables, but rather would obtain power from a suitable source and would drive themselves. Nonetheless, for at least portions of the tower, other `elevator` concepts can be employed, e.g. cable supported elevators and/or other powered lifting devices, such as escalators, and all such powered lifting devices are included within the term `elevator` as used herein.

The tower of the present invention is intended for installation on any planetary body and would be dimensioned accordingly.
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sevenperforce
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Re: Use of 20km tall "space elevator"?

Postby sevenperforce » Thu Aug 27, 2015 9:16 pm UTC

It is a very poorly-written patent.

Moreover, the grandiose "The tower of the present invention is intended for installation on any planetary body and would be dimensioned accordingly" business is a headache.

Apparently he is proposing an active stabilization system in the form of gyrostabilizers. Very heavy gyrostabilizers. Distributed up and down the lighter-than-air tower. Does anyone else see a problem here?

Besides, a gyrostabilizer will not help in dealing with twisting of the tower. Nor will it really keep the tower from tipping over; the sections between gyrostabilizers can still bend wildly.

I'm really not sure how he imagines this can be "scaled up" to reach LEO. Perhaps he means it could be used as the base for a conventional space elevator?

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Re: Use of 20km tall "space elevator"?

Postby Tyndmyr » Thu Aug 27, 2015 9:52 pm UTC

sevenperforce wrote:I'm really not sure how he imagines this can be "scaled up" to reach LEO. Perhaps he means it could be used as the base for a conventional space elevator?


Look, if the seven meter model works, the rest can simply be left as an implementation exercise.

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Re: Use of 20km tall "space elevator"?

Postby krogoth » Fri Aug 28, 2015 1:56 am UTC

Tyndmyr wrote:
sevenperforce wrote:I'm really not sure how he imagines this can be "scaled up" to reach LEO. Perhaps he means it could be used as the base for a conventional space elevator?


Look, if the seven meter model works, the rest can simply be left as an implementation exercise.
Square-cube law be damned! We'll build it under water so we don't have such an issue!
R3sistance - I don't care at all for the ignorance spreading done by many and to the best of my abilities I try to correct this as much as I can, but I know and understand that even I can not be completely honest, truthful and factual all of the time.

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sevenperforce
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Re: Use of 20km tall "space elevator"?

Postby sevenperforce » Fri Aug 28, 2015 4:05 pm UTC

This idea won't work -- not even close -- but I do see some promise here if we mix this with a space fountain tower.

Start by building a tower out of cylindrical, lighter-than-air pressurized rings similar to those described in the patent. Extend it upward until it starts to get a little unsteady:

simple.png
simple.png (8.27 KiB) Viewed 5199 times

Next, mount large helical vanes (likely using a lightweight frame containing an envelope that can be pressurized with hydrogen) on the outside of the tower such that they serve as a vertical wind turbine:

vanes.png
vanes.png (14.94 KiB) Viewed 5199 times

The vanes would be attached to a generator that produces electrical power. The power is transmitted down cables to the base of the tower, where the current is plugged into large wind turbines which are used to blow air from the surface into the central column of the tower.

The air from the surface is pushed into the "tube" and moves upward, transferring upward momentum to the tower. This forces the tower to remain vertical:

with turbines.png

So the turbines mounted along the outside of the tower convert the high-altitude wind energy into electricity, which it then uses to power an open-cycle fountain tower. The near-neutral buoyancy of the tower cells enables them to be easily aligned by the upward flow of high-pressure air.

Conceivably, vent ports could be built into the sides of the tower at various points to enable the high-pressure air to escape in order to more immediately correct misalignment of the tower. However, the upward flow would likely be sufficient for most purposes. Unlike the design in the OP, this version IS extendable beyond 20 km, albeit with diminishing returns. Moreover, the turbines would likely generate considerably more power than the tower required to stay up.

If a large positive-buoyancy ring was mounted at the very top, it would serve to further align and stabilize the overall structure and add a measure of redundancy.

The powerful, high-pressure upward flow of air could also serve as a means of practically energy-free upward transport, as the tower would effectively be the largest indoor skydiving (vertical wind tunnel) construct in existence. A series of vertical tracks mounted to the inside of the tube could be "ridden" either upward or downward by using a horizontally-oriented sail. In another case, the inside of the tube could be cleared of vehicles in order to enable it to serve as a dynamic launch tube. While the maximum attainable speed would of course be far less than orbital speeds, it would be enough to place a spacecraft on a substantial vertical trajectory at high altitude, greatly reducing launch costs.

Alternatively, the rocket components and fuel could merely be towed to the top and launched from there.

The tower would need to be placed relatively close to a source of water, so that electrolysis from the tower's power generation to produce hydrogen to replenish slow leaks would be possible. The electrolysis would also serve as a source of oxygen, perhaps to supply spacecraft with oxidizer.

Thoughts?


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