The Space Elevator

[SouthernKing]

The space elevator certainly holds great promise, if some nation(s) makes a conscious effort to build one, something that is looking less likely as time passes.

Dont know if it has been commented yet, but what about the skyhook?

It is not as cool as the real space elevator and you need a plane to board it, but it seems much more feasible.

This seems much more promising as a first step. I'm certainly not an engineer, but perhaps this could be a preliminary project on Earth, before a full-scale space elevator gets built. It seems like even building a "ring" of four or six of these around the equator wouldn't be that unfeasible.

 

[onejayhawk]

The elevator is an idea whose time has not yet come. It is simply not possible yet. Once someone demonstrates it is possible, they will go up all over.

Sky hook is a promising intermediary step. A lot of the materials tech can be tested this way. The problem with skyhooks is political. They are inherently a potential military asset. The same applies to non rocket launch vehicles. The elevator has the great advantage of being stationary.

J

 

[El_Machinae]

I'm not 100% that carbon nanotubes are even possible, or that if they can even be of sufficient strength. Granted, it's not something I'd know. I'm not a physicist or a chemist.

What I like about the whole deal is that CNTs have utility in a broad sense, so there will always be incentive to learn to create longer and purer CNTs. We'll bootstrap ourselves to an elevator, eventually, if it's possible. Pending ecological or economic catastrophes, of course.


Link to video.

There are remarkably few seminars on this topic. I can find a gazillion more seminars (aka, university lectures) on global warming than on this.

 

[hobbsyoyo]

The radiation will only be half that experienced in deeper space, because the Earth will block half of it.

A trip on the elevator takes you through the Van Allen belts which have generally worse than normal deep space radiation flux. If the trip through the belts is not fast, you will need shielding.

 

[onejayhawk]

There are remarkably few seminars on this topic. I can find a gazillion more seminars (aka, university lectures) on global warming than on this.

Global warming is where the money lives.

J

 

[El_Machinae]

Sigh. Fine.
I can find more seminars regarding Peak Oil than on the Space Elevator. And remember, CNTs pay for their development every step of the way

 

[uppi]

Electromotive force is applied to the conductor. It need not be wrapped around a rotor. It can be used to excelerate a considerable length of ribbon. Or you can draw power off and decelerate.
J

No matter how much force you can generate: You cannot accelerate something, without accelerating something else. In space there is nothing else, so you need to eject something to be able to accelerate your object. There is no way around that, it is a fundamental principle of physics.

In a space elevator there is the cable, that can supply momentum up and downwards because it is tethered to the earth and the counterweight. However, it cannot infinitely supply angular momentum without the counterweight crashing down or being corrected with an engine that ejects mass.

There are remarkably few seminars on this topic. I can find a gazillion more seminars (aka, university lectures) on global warming than on this.

There are very few seriously working on a space elevator right now. The theory has been more or less been sorted out by now and the preconditions are not there yet to work on a practical implementation. Research in CNTs is ongoing of course, but a space-elevator length CNT is so far away that you would not be taken seriously if you proposed directly working towards it. Especially when there are so many more interesting near term goals that are within reach.

So few people working on it means few people being able to give a seminar and few people being there to sit in the audience, which means there won't be many of those.

 

[hobbsyoyo]

You can accelerate objects in Earth orbit using a tether system that interacts with the earth's magnetic field. You do not absolutely have to have a electric or chemical-based propulsion system.

 

[Thorgalaeg]

No matter how much force you can generate: You cannot accelerate something, without accelerating something else. In space there is nothing else, so you need to eject something to be able to accelerate your object. There is no way around that, it is a fundamental principle of physics.

Errr... you are accelerating Earth through its magnetic field

 

[hobbsyoyo]

Well the Earth doesn't effectively see acceleration, but your spacecraft would if you used a tether.

 

[onejayhawk]

No matter how much force you can generate: You cannot accelerate something, without accelerating something else. In space there is nothing else, so you need to eject something to be able to accelerate your object. There is no way around that, it is a fundamental principle of physics.

In a space elevator there is the cable, that can supply momentum up and downwards because it is tethered to the earth and the counterweight. However, it cannot infinitely supply angular momentum without the counterweight crashing down or being corrected with an engine that ejects mass.

There are very few seriously working on a space elevator right now. The theory has been more or less been sorted out by now and the preconditions are not there yet to work on a practical implementation. Research in CNTs is ongoing of course, but a space-elevator length CNT is so far away that you would not be taken seriously if you proposed directly working towards it. Especially when there are so many more interesting near term goals that are within reach.

So few people working on it means few people being able to give a seminar and few people being there to sit in the audience, which means there won't be many of those.

There is an opposite reaction. You are engaging the Earth's magnetic field. You decelerate the rotation of the Earth. The force is normal to the current and the magnetic field. That would work for your primary adjustment. Fine tune from that.

I can believe there is little work, which is a pity. We could build this on the moon right now. Earth is a much more difficult proposition. Material technology is not good enough to start the serious work of ironing details. In a generation that may change. For the moment we are like Julia, conceiving fractals but being unable to do the computations.

J

 

[CavLancer]

Centrifugal force? The Earth is spinning and anything attached to it will be flung outwards were it not counteracted by gravity, yes? In space there is no gravity so the counterweight would tend to pull on its opposite number, the Earth. In an immeasurable amount the counterweight would cause the Earth to wobble, and wobble with it, right?

 

[Thorgalaeg]

Well the Earth doesn't effectively see acceleration, but your spacecraft would if you used a tether.

Earth effectively sees acceleration, may it be mm or amstrons/s^2. It also sees acceleration every time you launch a rocket to space. Newton third law applies always not matters how different in mass are the objects.

 

[eduhum]

People, sort to cut short this discussion, but I'd like to know if these ideas of how should one (or multiple) space elevators be created are realistic enough:

Some weeks ago, we all saw in the news another major advancement in DNA science. I have a position I don't think I share with nearly anyone else in the world (trying not to be presumptuous about it).
The discovery and mastering of DNA structures will not only grant humanity great advancements in medicine but will also permit to create new life, with a written unique DNA code. Who could have predicted 40 years this world full of smartphones and computers? The next advancement of humanity will be the profit of natural resources in a organic and efficient way, and these new inventions will counteract the disappearing of the natural resources.

Did you know that spiderweb is the world's most strong material compared to it's size?
What if scientists and engineers created a DNA structure that, when turned on, and attached to a source of energy and "food", would develop treelike to form a cable to space, much stronger than nano carbon and self healing?

On top of that (in both senses), as this new type of construction would allow for a much more cheaper way to construct the space elevator, a factory should be put on space, so that spaceships would be built above the atmosphere, making possible the construction of dozens of them, movie-like, and thus the establishment of sustainable lunar bases where Helium-3 would be mined, a resource much energy-filled than oil and uranium if I'm correct, and much more cleaner, to make the whole operation financially sustainable.

 

[Thorgalaeg]

Spider web is the strongest material in nature they have already obtained carbon nanotubes fibers much stronger than it and, theoretically, a pure enough carbon nanotube fiber would reach a strenght several orders of magnitude that of spider web fiber.

Maybe genetic engineering could be used to create some kind of bacteria capable of producing carbon nanotubes though. That would be great.

 

[El_Machinae]

I can believe there is little work, which is a pity.

Well, this is a time when you can be the change you wish the world to see.

The ISEC has a journal that needs subscribers. Liftport has a kickstarter out there. I personally try to spend $50/year (the per capita average in my country) on space development, just to put my money where my mouth is and effectively double my contribution. That's less than 3 pitchers of beer. It's casually affordable, but it take specific effort. Watch $50 (or $80, or whatever) leave my wallet ain't easy, but it's less than a dollar a week. That's candybar scales worth of spending.

 

[hobbsyoyo]

Earth effectively sees acceleration, may it be mm or amstrons/s^2. It also sees acceleration every time you launch a rocket to space. Newton third law applies always not matters how different in mass are the objects.

Which is effectively 0.

 

[El_Machinae]

Yes, putting stuff up the SE will rob the Earth of some of its momentum, but we deem it to be negligible. In the year 40,000 CE, we'll see if our descendants resent us.

 

[Thorgalaeg]

Which is effectively 0.

Nope, it is near to zero, but not zero. It cant be zero.

 

[hobbsyoyo]

Yeah, something the size of a space elevator may have a noticeable impact at some point in the distant future. But ordinary tether systems used on satellites currently and rocket launches have effectively no impact on the Earth. Similarly, powered and un-powered flybys of planets by space probes have effectively 0 effect on the flown-by planet/moon but mathematically, there is a finite (but extraordinarily small) loss of momentum from the planet/moon.

Nope, it is near to zero, but not zero. It cant be zero.

Hence the continued use of the word 'effectively' in my posts. For all intents and purposes, it is zero. Further, any effect from a tether would get swamped out by all the other perturbations the Earth experiences from all other sources except in the case of a large Space Elevator tether over very long time scales.
* I am reminded of a joke someone posted about the difference between engineers and mathematicians!