Question space elevator space station

Jun 1, 2022
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I was playing with an ideal. using the left over materials from asteroid mining to build a solar array and relay system to transfer power to a space elevator slash spacestation part power receiver input antenna. I think I could charge 100 billion a month about 10 bucks a person. thinking of having a machine to build up the array as I mine to keep making it more powerful. what do you think?
 
May 14, 2021
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OK, so, first, a one km diameter asteroid has a mass of something like 5 trillion kilograms or so, first you have to stop its rotation so you can hook an engine to it, Karbal Space Program style, then point it in the right direction and thrust it to a transfer orbit to earth. That might take a fuel tank maybe the size of the asteroid itself, costing kazillions of dollars. I’m skeptical of the value of that. Then anything left after we remove the good stuff will likely not be suitable for constructing anything useful.

The other thing is, as we have discussed on another thread, to me, a space elevator may be impractical because we would have to remove every spacecraft and every bit of debris in low earth orbit. The space elevator must be erected on the equator, and every orbit, no matter it’s inclination, must intersect the equator. Anything in orbit must eventually collide with the elevator.

We could have a number of spacecraft in a zero inclination orbit far from the elevator, but, it would have to have fuel for stationkeeping so that it does not drift into the elevator, but only at geostationary orbital altitude.
 
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Has anybody actually looked at the stress distribution on a structure that is hundreds, if not thousands of miles tall? Do we even have materials that can handle those stresses?

Remember, that parts below the stationary orbit will be in compression. Parts above will be in tension. Putting more mass above stationary altitude does allow for some "lift" to be transmitted down the structure for the parts below, but whether it is supported from below or "hanging" from above, this would be a massive structure that would involve some enormous stresses in both compression and tension, even if the design is balanced to minimize both.

And, don't forget the side-to-side forces. What will it take to keep this thing from developing vibrational waves that run up and down its length, threatening to tear it apart laterally.

And, how do you actually construct it? If you start from the ground-up, everything is in compression, and would have to be built like a huge pyramid. If you start from orbit and try to hang things down, the "hanging" part needs to "be held" up by things going above the stationary orbit altitude. But, would things really just naturally "hang down"? I don't think so. I think orbital mechanics would tend to make the structure depart from the radial direction. Remember, it is in inertial free-fall, so the whole structure would need to maintain an angular momentum that makes it rotate once every sidereal day (86164.0905 seconds or 23 h 56 min 4.0905 s or 23.9344696 h), even as it is being built, so that it maintains its position along a radial line to the center of the Earth.

Do we really have any quantitative engineering evaluation that says we have, or even know of materials to make it theoretically possible, not to mention feasible to construct or even profitable?
 
May 14, 2021
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Many years ago, a magazine article stated that Kevlar could support its own weight so that an elevator could be constructed from that. Later, I read a novel where an elevator wa constructed in Ecuador from 3 strands braided from carbon fiber. Later in the novel, some group blew up the base and the elevator fell about one and a half times around Earth killing millions.

Edit: It may have been Pillar to the Sky by William R. Forstchen.
 
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Pogo, I have no doubt that magazine writers say things like that - but it doesn't mean that it is true. I remember reading a magazine article decades ago, which said that a ring placed around the base of a pole or cable extending from Earth's surface to beyond synchronous orbit altitude would experience "cosmic lift" and rise to the top without being pulled by any cable. Anybody who thinks that is true would never pass my old junior high school basic science class.

So, thinking about "Kevlar can support its own weight" in realistic terms, how much Kevlar, how much does it weigh, and how does that compare to the measured tensile strength of Kevlar? I am willing to bet that you can't make a 22,000 mile plus Kevlar cable that can support its weight when hanging by one end. But, it is a complex calculation, due to the change in "weight" of the segments as they are at higher altitudes with higher "centrifugal force" counteracting gravity. So I am going to leave it to the people who want to convince me to do the work to show that it does support its own weight.

While I am at the debunking business for this concept, I should also point out that the idea of having an extremely tall tower based on Earth's surface needs to consider the response of the Earth's surface to the extreme weight of the tower. The force on the base of a tower 22,000 miles tall would likely be enough to drastically deform the surface. If the base is broad enough for the base to not break through the crust, sink into the mantel and start melting at its lower end, then it would bow the crust downward in a very substantial manner, which would probably induce substantial earthquakes, which would produce lateral loads on the tower structure that probably would cause it to collapse.

Think about it this way, ice sheets on land are known to cause Earth's surface to sink towards the center by substantial amounts, and those are sheets of material with densities less than 1 gm/cc and not more than 2 miles thick. What do you think would be the effect of something that is more than 11,000 times thicker and more dense? Even Kevlar is 1.44 gm/cc, and steel is in the range of 7-to-8 gm/cc. The forces would be enormous, whether for a small base of extremely incompressible material (diamond maybe), or a wider, and thus more massive base.
 

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