Space Elevator. . .

[tmaromine]

Some time ago, I was reading a thread about space elevators which was influenced from a game. (Halo 2, if one wants to know) There was some very interesting, and somewhat rather scientific, discussion the one in the game, and how it would have fallen to Earth when it was destroyed due to Earth's rotation and that stuff.

 

The elevator's location in game was near the equator, so if it lost its 'balance' ; its geosync counterweight failed to keep it in sync, and it fell, it some would wrap around Earth's equator, and some fly off into space. Last night I had the idea: would – theoretically – building a space elevator at one of Earth's poles / at "end" of the axis be best ? It wouldn't have the drag as it would at the equator, and would be like a drill spinning at the northernmost or southernmost end of Earth.

 

Of course, the poles are lands of ice, so building something like a space elevator might not be ideal due to that, unless it was anchored or something, but I just thought it most plausible at a pole than at the equator.

 

The thread. . .

[Sacri Sankt]

earths geostationary orbit is (apparently) about 35,786 km, wheras its equatorial circumfrence is 40,075.02 km, so it wouldnt quite wrap around the earth if it fell. afaik, it has to be over the equator to be geostationary, since if it were over the pole, it wouldnt be orbiting the earth and would drift off target and possibly fall.

[tmaromine]

...afaik, it has to be over the equator to be geostationary, since if it were over the pole, it wouldnt be orbiting the earth and would drift off target and possibly fall.

 

 

 

Well, that I didn't think of. So if at a pole, without a counterweight, would tethers from every side (well, around the elevator) keep it from leaning one way without being anchored from doing so in the immediate opposite direction be plausible ?(Like how thin cell towers are, tethered to the ground for four corners)

 

For all I know that could take stronger materials than the elevator itself'd be made of, and some very strong ground anchors on land, or anchored to a 'buried platform'.

[Janus]

Some time ago, I was reading a thread about space elevators which was influenced from a game. (Halo 2, if one wants to know) There was some very interesting, and somewhat rather scientific, discussion the one in the game, and how it would have fallen to Earth when it was destroyed due to Earth's rotation and that stuff.

 

The elevator's location in game was near the equator, so if it lost its 'balance' ; its geosync counterweight failed to keep it in sync, and it fell, it some would wrap around Earth's equator, and some fly off into space. Last night I had the idea: would – theoretically – building a space elevator at one of Earth's poles / at "end" of the axis be best ? It wouldn't have the drag as it would at the equator, and would be like a drill spinning at the northernmost or southernmost end of Earth.

 

.

 

The reason that you build a space elevator at the equator is that it is the Earth whipping it around in a circle that keeps it taut and helps support its weight. Building one at the pole wouldn't be possible, as then all the weight would have to be supported by the Earth's crust, and it wouldn't be strong enough.

 

Also, the counterweight is not placed at geosync, but further out. This way, it is made to orbit faster than is natural for its height. It will try to climb to a higher orbit which will produce the upward force that supports the weight of the elevator. In reality, the counterweight would be designed such that it more than compenstates for the weight of the elevator and has some left over upward pull.

[InfiniteNow]

A thread:

 

http://hypography.com/forums/space/5641-another-space-elevator-concept.html

 

...and a link:

 

Institute for Scientific Research, Inc.

 

 

Cheers. ;)

[tmaromine]

The reason that you build a space elevator at the equator is that it is the Earth whipping it around in a circle that keeps it taut and helps support its weight. Building one at the pole wouldn't be possible, as then all the weight would have to be supported by the Earth's crust, and it wouldn't be strong enough.

 

Also, the counterweight is not placed at geosync, but further out. This way, it is made to orbit faster than is natural for its height. It will try to climb to a higher orbit which will produce the upward force that supports the weight of the elevator. In reality, the counterweight would be designed such that it more than compenstates for the weight of the elevator and has some left over upward pull.

 

 

Ah, I see now...

 

A different part of the story; how would a space elevator be built ? Straight up doesn't seem realistic, since it needs the the pull to keep it from tumbling over. And since the counterweight wouldn't be geosync, the elevator couldn't be built down to Earth from it, since it wouldn't stay in orbit. (?, that's my logic of it, anyway.)

 

And a different story altogether: Would a tubular ring around Earth to attach the elevator to, and that would be the "upper most floor" that the elevator would lead to, be plausible ?

 

 

Thanks for the thread link. Perhaps I will post in it, though it's ten months old; I'll at least read it.

 

And the ISR page, that I'll've to read too.

[Janus]

Ah, I see now...

 

A different part of the story; how would a space elevator be built ? Straight up doesn't seem realistic, since it needs the the pull to keep it from tumbling over. And since the counterweight wouldn't be geosync, the elevator couldn't be built down to Earth from it, since it wouldn't stay in orbit. (?, that's my logic of it, anyway.)

 

You start at geosync and you build out at the same time as you build down. The trick is to keep the center of mass of the entire structure at geosync (tidal forces will keep it pointed straight up and down). Once the lower end reaches the Earth, it can be anchored and you can attach the counterweight to the other end.

[tmaromine]

You start at geosync and you build out at the same time as you build down. The trick is to keep the center of mass of the entire structure at geosync (tidal forces will keep it pointed straight up and down). Once the lower end reaches the Earth, it can be anchored and you can attach the counterweight to the other end.

 

Ok, I understand. Thanks for explanation.

[silverslith]

the novel was Fountains of Paradise by arthur c clark.

They built one on mars first, had to play hopscotch with deimos. Well worth a read, very technically accurate.

The Fountains of Paradise - Wikipedia, the free encyclopedia

 

I think on the moon would be a hoot. You'd either need an equatorial railway cause the moon spins too slow, or a cable to each pole.

the base train would only need to travel at 200-400km perhr, so achievable to dock with etc. that'd be possible with our best modern materials. They'll not hang more than 100km in earth grav, somewhat short of 36000 needed.

[Theory5]

Hmmm. I dont have much to add just somthing to keep people thinking, and to answer some questions i had. I read a short story about a space elevator that was pretty interesting. In this story I belive they did build it on the equator and teathered it to the ground, I dont know it was technically accuarate, but it seemed to have some technical information. lemme see if i can find the book,nope i cant find it. it talked about something i cant really remember, some sort of material or sheet of metal that would keep the elevator cables from breaking. but it also talked about that the elevator confused migrating birds, and the birds just kept flying around and around the cable. I think a space elevator with our technology is not impossible but somewhat idiotic. we leave all this debris in space (we as in all humans) and the space elevator will encounter it. Also, might somthing that big throw the earth off ballance? not by much, im talking by very small amounts. miniscule. and what use would the space elevator server, and how would we get it up and down? propultion system? that would cost alot. or some sort of pully like we have in elevators now? that wouldnt work. and how would we repair it? in the book i talked about they had nanobots continuously checking it and such.

[freeztar]

You start at geosync and you build out at the same time as you build down.

 

I don't understand this. What about wind? How would you build down from the upper atmosphere?

 

Why can't we just tie a cable on a rocket and let it take it up for us? Anyone got 40,000 km of heat-proof cable? :naughty:

[CraigD]

I think a space elevator with our technology is not impossible but somewhat idiotic.

…

and what use would the space elevator server, and how would we get it up and down? propultion system? that would cost alot.

One of the main appeals of a space elevator is that, once you’ve built it, and ignoring the cost of maintaining it, it’s very inexpensive to get stuff from the bottom to the top of it. Doing the math (or cheating, and having a small, dumb computer program estimate things for you :naughty:), you’ll find that, using a traction motor to move your payload up a space elevator, it takes about 48 megajoules per kilogram lifted to geostationary orbit. Assuming you’ve got some sort of conductor to carry electricity to your motor, at current commercial rates for electricity, that would cost about US$1.40 per kg. By comparison, it costs about $50,000/kg now, using a commercial rocket (not including the cost of insuring your payload against the possibility of it blowing up).

 

Ecologically, a space elevator is also very attractive, since you no longer have to contend with rocket exhausts (which, though currently infrequent compared to other sources of surface pollution, even now do some nasty things to the upper atmosphere). As far as upsetting the Earth’s revolution, a space elevator is no more disruptive than a satellite of similar mass, both of which are negligible.

 

Concerns about clobbering birds and airplanes, getting clobbered by terrorists, and a lot of wear-and-tear concerns, go away if your space elevator doesn’t actually reach the ground, but has it’s “base station” 10 km or so above the ground. We’re currently quite good at getting large amounts of people up to such altitudes for not much money, and doing it this way also means your satellite doesn’t need to be in a perfectly equatorial or geostationary orbit. This allows your base station to cover some ground, including periodic passes over places where people and materials that would like to get into orbit and beyond are found (eg: The US, Europe, Australia, or just about anywhere other than the tropical but not-much-developed equator).

 

It also means your orbit can be lower, and your cable shorter, making it a lot cheaper. Since space elevator material is near the edge of possible to physical engineering science (actually, its currently a good bit to the “currently impossible” side of the edge), making it shorter could be the difference between it being possible, or not. Freeztar’s

What about wind?

issue get addressed by the don’t-reach-the-ground design, since there’s much less air, and hence, less wind, in all but the lowest few tens of kilometers of atmosphere.

 

The main problem, beyond the “can it be done at all?” engineering problems, is the economic reality that you can’t just ignore the cost of building and maintaining a space elevator. When you seriously try accounting for these costs, the payload to LEO cost/kg rises from the neighborhood of $1.40 to that of $3000. Some proposals for very efficient next-generation rocket ships propose to have costs not much greater than this.

 

The Wikipedia article “Space elevator economics” gives a decent summary of what its title suggests. Hypography is full of conversation on the subject, including some pretty detailed engineering estimates – try the search function for the key words “space elevator”, or my favorite discussion in 5641, especially around the post “Space elevator cable mass & size calculating program”.

[Jay-qu]

Thats an interesting way to approach the problem craig, but would it work?

 

You say it wouldnt have to be in a perfect equatorial or geostationary orbit. Wouldnt this put stresses on the cable, an extreme example would be dragging a peice of string through air. The bottom 'lags' behind the top - this would be accentuated by the fact that the top has no air resistance while the bottom does.

[CraigD]

Thats an interesting way to approach the problem craig, but would it work?

Would it work? - always the critical engineering problem.

 

You say it wouldnt have to be in a perfect equatorial or geostationary orbit. Wouldnt this put stresses on the cable, an extreme example would be dragging a peice of string through air. The bottom 'lags' behind the top - this would be accentuated by the fact that the top has no air resistance while the bottom does.

I haven’t messed much with detailed calculations, so my best current guess is a vague “you’d have to balance all the factors to come up with an optimal design.” A couple of encouraging observations and speculations:

• Any free-hanging orbital cable tends to align itself in a vertical position.
  
• At altitudes higher than 10 km or a few tens of km, the force on the cable due to air resistance is much lower than in the lowest few km. Heat and erosion can be an issues, but the cable system already must be designed to cope with this.
  
• Through streamlining, the lower base could be designed to move at a pretty high speed.
  
• If the aircraft used to rendezvous with it is of a super or hypersonic design, it’s “landing” can be more of a docking maneuver.
  
• The base could be given aerodynamic control surfaces, allowing it to contribute to the stability of the systems.
  
• The elevator car, and the cable itself can be given, a streamlined cross section, improving it’s low-altitude performance.
  
• The central station not only need not be in a perfectly equatorial orbit, it need not be in a perfectly circular one. If slightly elliptical, the cable can spend most of its time at a higher altitude, with less air resistance, dipping with only 2 low-altitude “dips” during which the aircraft can rendezvous with it.
  

These are all very brainstormy ideas, in need of some high-quality modeling. My main intention in throwing them out in such a sketchy form it to show that throwing out conventional assumptions about space elevators – “thinking outside the box” – brings out many possibilities, perhaps significantly enhancing the feasibility and lowering the cost of a space elevator.