Space Elevator Discussion

[Leszek]

Another issue with space elevators is that they are long, long enough to go around the world. If something happens to the CN tower in Toronto, generally the people in Moscow don't need to worry. Not so if it was a space elevator. This makes all sorts of political issues. Try to build one in Equador and get protests from Finland.

Any space elevator needs much more engineering than the simple "can it be done." For example does a space elevator in Equador (or anywhere else) need to comply with Polish safety standards? If something goes wrong it might kill Polish citizens. And Iranian, and Japanese... You get the point.

Any space elevator would have to deal with global political issues regardless of who builds it and where.

[SargeRho]

Severing the tether at the base, if it was also severed higher up, I think would cause it to fly upwards, instead of winding around the planet.

On Mars though, a mass driver assisted rocket might make more sense for mass transport to orbit.

[Rakaydos]

I like the idea of the Lunar Lagrange Elevator. Bulk materials in orbit are bulk materials in orbit- where you get them from hardly matters.

The DV budget to reach the earth-moon L2 point is less than geosynchronus orbit, IIRC. Putting a lagrange elevator down to the moon, you can set up a lunar mining and manufaturing base for cheaper than if you had to land the base on rockets. Then you can start shipping bulk mass into space, and from Lagrange, drop it into the Interplanetary Transport Network to anywhere in the solar system for literally meters of delta V.

[magnemoe]

Using electricity to move things into orbit is going to be cheaper than using methane and oxygen I think.

It is, however on moon you can also use an coil gun to launch bulk goods.

it would be much cheaper to build and maintain. The most interesting place on moon is the poles where it will not work.

[Legendary Emu]

In my opinion, I don't like space elevators. Mostly for the reasons presented here.

In my opinion, gathered from spending too much time on the Atomic Rockets website, either we could use laser launch things or orbital airships. The neat thing about the laser launch things is that you can have a large, expensive power plant that can have its power diverted to powering a city or something when it's not beaming stuff up (hah get it?).

Maybe I should have made the title "Alternative Launch Systems" or something.

[Mazon Del]

It is, however on moon you can also use an coil gun to launch bulk goods.

it would be much cheaper to build and maintain. The most interesting place on moon is the poles where it will not work.

One of the interesting things Liftport has pointed out is that you don't actually have to have the cables be at the equator on the moon. You can go fairly far north/south and you just have to make the cable longer. What ends up happening is that the counterweight will still be outwards from the equator, but the cable itself ends up curving towards the anchor point the closer to ground level you get. I think their plan is to have the anchor end up being rather close (within 10 degrees? I forget) of one of the poles (I think North is the desired one) and then you'd just set up a tram of some sort to take you the rest of the way.

The main cost saver for a lunar space elevator is not launching things back up the gravity well, but in bringing them back down. This is because of the fact that if your ship doesn't have to land, it doesn't need any descent systems. You could just have a cruising stage that docks at something like the ISS, flies off to the moon, docks with the elevator, refuels, and then heads back home. Never actually landing anywhere. Since you didn't have to carry any descent equipment anywhere, you get more cargo (people) and such that you can ferry about.

[magnemoe]

One of the interesting things Liftport has pointed out is that you don't actually have to have the cables be at the equator on the moon. You can go fairly far north/south and you just have to make the cable longer. What ends up happening is that the counterweight will still be outwards from the equator, but the cable itself ends up curving towards the anchor point the closer to ground level you get. I think their plan is to have the anchor end up being rather close (within 10 degrees? I forget) of one of the poles (I think North is the desired one) and then you'd just set up a tram of some sort to take you the rest of the way.

The main cost saver for a lunar space elevator is not launching things back up the gravity well, but in bringing them back down. This is because of the fact that if your ship doesn't have to land, it doesn't need any descent systems. You could just have a cruising stage that docks at something like the ISS, flies off to the moon, docks with the elevator, refuels, and then heads back home. Never actually landing anywhere. Since you didn't have to carry any descent equipment anywhere, you get more cargo (people) and such that you can ferry about.

Yes, however it would require an magnitude more traffic from moon than an coilgun launcher, that is an decent sized mining operation as in decent sized on earth.

One interesting thing is that you can use it to launch stuff interplanetary, not so much moon, probably more relevant on outer bodies.

[Tex_NL]

Sure. A ship without the need for a land/launch system can be lighter and carry more. Of course it will be more efficient than a ship that does need it. But that's not the point. Actually BUILDING the tether is insane. With the resources required you can fly hundreds of missions to the moon and back. Possibly thousands.

And as it has been said before: By the time we do have the tech to build a tether and make it more economical than regular launches it will already obsolete.

[Mazon Del]

Magnemoe: You can actually utilize space elevators as launchers as well for interplanetary space. You have your anchor set where it normally would be, but you let the tether extend outwards for a length behind the tether. As the cart rides its way up, once it passes the anchor its gaining speed from the centripetal motion of the elevator, the longer you have the cable past the tether the greater this effect ends up being. Or rather, the longer your cart follows the tether. It could choose to release at any point. It's aiming ends up being roughly as useful as a coil gun. The coil gun designs I've seen end up being either fixed emplacements or ones with just a little bit of traverse and elevation, but only by a few degrees. Useful to be sure, but not enough to instantly win the coilgun.

Tex_NL: We already have the tech to make the Lunar space elevator. The material that Liftport is using for their Earth based balloon tests IS the material they intend to use on the moon. By their calculations it has sufficient material strength with safety margin. Additionally, I think you may be overestimating the cost of the materials for the Lunar elevator. It's material cost is a fraction of what we'd need for an Earth based elevator. For the tether alone it might not take more than two-three launches to get it up there. The space based counterweight will require an asteroid tug of some sort (much like the one that NASA is building to bring one into lunar orbit already) to get things in position. Add a manned or unmanned launch or two to get the system built on the asteroid followed by at least one landing to set up the anchor. You are talking about maybe around 10 launches depending heavily on the design, but I'd heavily doubt you'd need more than 20. And a great many of those you can "discount" because they are fulfilling the exact same purpose for the coilgun.

[-Velocity-]

This popped up today-

http://www.gizmag.com/space-elevator-lunar-lift-liftport/35119/

Interesting, they think can apparently just use Kevlar for the lunar elevator ribbon. Now, this group is almost certain to fail, but what if some space-faring nation or someone like SpaceX decided to try to tackle it? You would completely eliminate the need for the actual lander spacecraft. Once the space elevator is in place, it's just a fully resusable, solar powered structure. A major problem with transporting people though would be that it takes a very long time to travel up and down the tether- it still takes like a whole month even if your cable car moves at the speed of a bullet train.

A crazy idea- what if instead of a single cable, you actually had like a conveyor belt? So the car does not actually move on the belt, the belt itself is moved- you wheel it up by turning one way, and wheel it down by turning the other. You could reduce the trip to like a week if you could get up to like 1500 km/h.

For high speed transport, I think that this conveyor approach would be superior, because you can remove the power source and climbing gear (which would have to be pretty beefy for high-speed operation!) from the car itself, and put it on the surface. Also, you could probably reduce cable wear.

You'd probably need a more complicated and heavy counterweight station design though.

Edited December 10, 2014 by |Velocity|

[Mazon Del]

That's odd. I don't remember them saying they were using Kevlar last I chatted with them. I cannot remember what it was, but it had some interesting sounding name that I would have recognized if it was Kevlar.

[Nibb31]

A crazy idea- what if instead of a single cable, you actually had like a conveyor belt? So the car does not actually move on the belt, the belt itself is moved- you wheel it up by turning one way, and wheel it down by turning the other. You could reduce the trip to like a week if you could get up to like 1500 km/h.

The energy involved in moving a 36000km conveyor belt at 1500km/h is huge, also starting and stopping it is going to cause tremendous stress on the system.

It's amazing how people tend to believe that a space elevator would be cheap. The cost of developing, building and operating one would be far from cheap. The cable cars are always going to need amounts of energy to cover the distance at any reasonable speed while fighting gravity, and energy isn't cheap.

[Bill Phil]

Even if the cost is 20 billion, that money could be used to buy ~45 Delta IV Heavy launches, which gets you about 1300 metric tons to orbit. So... I'd rather have the 45 DIVHs.

[Kibble]

You can avoid almost all of the major problems of a space elevator (tensile strength requiring massive exotic materials, that pesky atmosphere, the climber having to fight gravity, the extreme length, and unworkable taper ratios) by having it just not tethered to the surface. This is called a space tether, but I think the words are backwards, and a space elevator should be any big cable with a climber and junk, but a space tether is one that is attached to the surface - but anyway you can have re-useable single stage launchers that don't have to endure atmospheric reentry, rendezvous with the tether foot in space, and dock and release the payload. Plus the tether can use electrodynamic blah blah to reboost itself. And it doesn't have to use tapered carbon nanotubes, it can probably just be a coilABLE boom. The MXER tether improves this basic design with the amazing Canfield Joint, a special kind of gimbal which can be used to keep the solar panels on the tether pointed at the Sun (without tangling up high-power cables).