The Space Elevator

[Thorgalaeg]

For all intents and purposes, it is zero, OK. But not effectively.

 

[hobbsyoyo]

That's what 'effectively' means dude.

 

[Thorgalaeg]

Nope, effectively means exactly, in fact, indeed... It is not zero in fact, dude.

 

[hobbsyoyo]

The way I've used the word here is standard in American English engineering parlance.

 

[onejayhawk]

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:

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.

Spider web is stronger than many things, cable steel for example, but not as strong a graphite. Carbon nanotubes are much stronger than graphite. Diamond is stronger still.

We can create an elevator now, in a lower gravity, such as the moon. It would invaluable to a lunar base. many things could be mined on the moon, not to mentioned refined. There is a library worth of techniques that are too dirty to use in a biosphere or too expensive to clean. Many processes use vacuum, which is expensive in an atmosphere. In space, zero and microgravity can be very useful.

That said, there is also military applications, which are scary. One of the primary reasons to not settle space is political, specifically the danger of terrorism. Gravity can turn a ton of rock into a near nuclear weapon. On a smaller scale, a prybar becomes an anti-tank round.

J

 

[hobbsyoyo]

On the space show a few weeks back they briefly talked about research into spider web manufacturing. It's not going well and the one company that tried to produce it out of goat's milk essentially failed. Doesn't mean it will always be thus, however.

 

[El_Machinae]

That's because spider spinnerets are astoundingly cool.

 

[eduhum]

The thing is, nano-tubes are very expensive and the line would be as thin as possible. With a considerable quantity of bio-fuel, biomass, or whatever you want to call it, a substance based on spiderweb but maybe on many other things that science can esteem cool to make the substance stronger, the resultant cable would be much wider and unbreakable, as well as automatically and consistently auto healing.

 

[El_Machinae]

Yeah, that's a really neat idea. If they could design a microorganism that produced CNTs, that would be boss. You couldn't put the organisms up on the tether, though, the infrastructure would get crazy heavy.

edit: unless the organisms (or a box of them) travelled up and down the tether, and they 'proofread' the CNTs as they go.

 

[uppi]

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.

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

That would solve the problem if you can create a net force in the right direction. I don't see an easy way to do that, because as much current has to go up as goes down and the earth's magnetic field is homogeneous over practical distances, the net force will sum up to effectively zero. If you make a loop you can create torque with respect to the axis of your loop, but no net torque with respect to the earth. What am I missing here?

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.

Nuclear power from Helium-3 might be a good source of energy in theory. In practice, we are very far away from being able to use it. Fusion of Helium-3 is an order of magnitude harder than doing Deuterium-Tritium fusion, and so far we haven't even been able to control that.

 

[Thorgalaeg]

That would solve the problem if you can create a net force in the right direction. I don't see an easy way to do that, because as much current has to go up as goes down and the earth's magnetic field is homogeneous over practical distances, the net force will sum up to effectively zero. If you make a loop you can create torque with respect to the axis of your loop, but no net torque with respect to the earth. What am I missing here?

Lets see, it is not that complicated indeed.

According to Faraday law when you move a conductor across a magnetic field you obtain a current along the conductor, right? Also this very current will generate a Lorentz force perpendicular to the conductor. Correct? (i suppose you already know all this, but this way everybody will understand it)

Well, In the case of a satellite attached to a long vertically oriented conductor orbiting Earth at the equator, where magnetic lines go north-south, if you use the right hand rule, you will see that electrons go up to down across the conductor naturally. There is not necessity for currents being the same up and down in a closed loop (and here is the quid i think), as electrons would be collected from the ionosphere at the upper extreme of the conductor and expelled at the lower one. Now if you use the left hand rule to see Lorentz force you will see that it goes retrograde so it tends to stop and deorbit the satellite.

Of course if you connect an electric generator which is powerful enough to defeat the naturally induced emf and to make electrons go down to up (for instance feed by solar panels) the Lorentz force vector will also invert and go prograde and it will boost the satellite to higher orbits.

 

[uppi]

Ok, so the canceling out of the forces is not a problem, because the reverse current goes via the plasma in the ionosphere and you don't care about the forces on particles there. Interesting.

That got me thinking: Why go for solar panels at all: After all you can make the CNTs to be solar panels themselves. A self powered cable would be cool.

At the same time I am wondering, if CNTs would actually be stable enough in the harsh conditions in space. All that radiations has to result in a lot of defects over time.

 

[peter grimes]

On page 20 of the Edwards PDF he discusses some tests regarding atomic oxygen:

If this is the case, we are testing this now, then we would expect to see the matrix to be preferentially etched on the fibers and the carbon nanotubes be exposed. Eventually the entire surface of the fiber will be exposed nantubes and the erosion of the matrix will cease.

A ctrl-F for "radiation" returned 0 results

 

[hobbsyoyo]

On page 20 of the Edwards PDF he discusses some tests regarding atomic oxygen:


A ctrl-F for "radiation" returned 0 results

The fact that they don't take radiation into consideration makes me suspect. It's definitely a challenge for all spacecraft and for something that traverses the Van Allen Belts regularly (as a space elevator would), it would be a pretty significant challenge.

Nuclear power from Helium-3 might be a good source of energy in theory. In practice, we are very far away from being able to use it. Fusion of Helium-3 is an order of magnitude harder than doing Deuterium-Tritium fusion, and so far we haven't even been able to control that.

I am fairly certain you have this backward. Helium-3 fusion is an order of magnitude easier than doing Deuterium-Tritium, but we don't have access to sufficient quantities of Helium-3 at the moment. We do have access to Deuterium and Tritium but it's a very hard process to crack, which is why it hasn't happened yet. But if the theoretical calculations pertaining to Helium-3 are correct (and we have access to it), it would be fairly easy to pull off at our current technological level.

That's the premise behind the excellent sci-fi movie Moon where they are mining Helium-3 on the moon (where it is deposited by the solar wind) to power commercial fusion reactors on Earth. In fact, Helium-3 is one of the few things that could be commercial mined in space for a profit with current rocket technology as it is that rare on Earth.

 

[eduhum]

Mining operations and also basically any infrastructure built on the moon would (or will) have an extreme challenge. Moving the soil has great consequences: the suspension for thousands form now of millions of small very razor sharp particles that the weak lunar gravity will only put down with great effort. The places were human objects, manned or not, are already altered.
If we care to maintain an 'ecosystem' for the lack of a better word, were this be only for our own security, this hard problem must be solved.

Also, about the extreme weight that a treelike organic structure made to act as a space elevator would have to support, I think that the borrowing of the plants DNA for the form of their roots to create very large roots for that space elevator, kilometer-like long, I think it would help a lot, as well as the counterweight in space.

 

[Thorgalaeg]

How is Hellium-3 fusion easier than D-T fusion? He-3 has two protons while any isotope of hydrogen has only one. So, electrostatic repulsion in any reaction involving He will be at least twice that in any reaction involving hydrogen isotopes only. Which means you will need much more energetic collisions to defeat it, so much higher temperatures than the ones currently needed and we can barely manage right now.

 

[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?

Can someone please tell me why I'm wrong? Thanks...

 

[CavLancer]

How is Hellium-3 fusion easier than D-T fusion? He-3 has two protons while any isotope of hydrogen has only one. So, electrostatic repulsion in any reaction involving He will be at least twice that in any reaction involving hydrogen isotopes only. Which means you will need much more energetic collisions to defeat it, so much higher temperatures than the ones currently needed and we can barely manage right now.

I read somewhere that fusion reactors using Hellium-3 don't disintegrate as quickly.

 

[Thorgalaeg]

I didnt know fusion reactors desintegrated quickly or at all. In any case i think that we wont know until we can keep them working longer than some seconds.

BTW about your question, you are right to some extent. The counterweight will displace the center of rotation of the Earth a bit towards itself.

But there is gravity in space. astronauts at the ISS are not in a real zero-gravity environment, but in an apparent one caused by centrifugal force and gravity cancelling each other. In fact if you stop the ISS which is orbiting at 30,000 km/h, it will fall to the ground like a stone. Since the counterweight is at a geostationary orbit over a point near the equator and rotating synchronized with Earth, which means at a given angular speed of 360º every 24 hours, it will need to be about 36,000 km high where tangential speed will cause a centrifugal force enough to cancel gravity, lower than that it would fall down and higher it would go up into space.

 

[hobbsyoyo]

Did some reading and I am wrong about helium 3 fusion. Apologies