If a space elevator is built, what type weight would it need to be able to support on Earth? How much of its load is displaced by it being partially in space. Would the huge pressure differentials cause any great
Also, would it be possible to generate energy from the orbital rotation of the moon around the Earth? Say around the time space elevators become as common as skyscrapers and maglev trains as common as planes. During this time we decide to build a track(probably high above ground) stretching all the way across the world. And on this track was a nano-tube cable that extended from the track to the moon, connected to this and probably buried deeply into the moon. On Earth the rotational force of the moon would propel that cable causing the track to turn like a giant rotor.
Considering the orbital speed of the moon is 2288Mi/h (1023.056m/s) and the structure that it would be moving would be several million tons, maybe billions (I assume our structures will be stronger, but weigh much less in the future), wouldn’t we be able to create enough energy to power all of humanity forever (or for as long as the moon sticks around)?
Say the structure weighs 1 billion tons or 907184740000km, 1023m/s that is 4.74697569 × 10^17 J/s.
The average nuclear power plant produces 1000000000 J/s.
You can certainly extract energy from orbiting bodies. Of course, the orbit of the moon will decay as you extract energy from it.
Space probes do this all the time with gravity assist maneuvers which “slingshot” past a large body. The probe has more energy and than when it started, which was taken at the expense of the larger body. But when you’re talking about a probe that weighs a few hundred kilos, the planet Jupiter isn’t going to miss that tiny bit of momentum.
I’m not sure what you’re trying to ask, here (even aside from the truncated sentence, which I assume can be ended with “problems”). The Earth end of the elevator cable only needs to support however large a payload as you want to be able to send up at once, plus some safety factor. So, for instance, if you want to be able to launch ten-ton satellites, then it needs to be able to support ten tons. The difficult part isn’t the Earth end of the cable, but the middle, which needs to be able to support the weight of a payload plus the weight of the rest of the cable. And pressure differences don’t matter at all, since it’s a cable, not a tube, and even if it were a tube, it’s just one atmosphere.
Would the elevator itself act as a generator as it passed through the magnetosphere in the course of its orbit? what about static electricity as the air currents flowed past it? Might those create unequal potentials to be tapped?
And on the energy from orbital motion or whatever, I seem to recall the space shuttle attempting to measure the power from such things and finding so much that it burned out the device they were using to measure it.
Actually, most gravity assist (“swingby”) maneuvers only contribute modestly, if at all, to the total kinetic energy of the vehicle. However, they are used to significantly change the momentum of the vehicle. To make the difference clear, remember that energy is a scalar value (U=1/2mv^2), i.e. without regard to direction, whereas momentum is a vector quantity (p=mv) for which direction is an innate component. Both the energy and the impulse transfer do, as indicated above, come at the “expense” of the kinetic energy and momentum of the planet. (Some swingby maneuvers also involve propulsive corrective maneuvers near the point of periapsis where the thrust will have the most influence on the vehicle’s course and more overall propulsive efficiency.
As for the proposal of the o.p., it sounds as if he’s suggesting some kind of energy capture via a pullcord type of arrangement extracting energy from the orbit of the Moon around the Earth. Aside from the massive practical difficulties of this, it would also have the Moon adding a rotational component to the Earth that has a non-zero cross product with the Earth’s normal rotation. The degree of influence this would have depends on how much energy you attempt to extract from the relative motion between the Moon and the Earth, but there is an inevitable change in the Earth’s angular momentum that will cause it to pitch over on its axis and add a nutational component. In other words, the Earth will bob and twist as you attempt to extract energy, which I think we will all agree is a bad thing to do to your delicately habitable world.
A space elevator “cable” isn’t like a normal building structure; instead of being in compression grounded to the foundation, it will be in tension via an “anchor” that is just slightly higher than geostationary orbit, and a second anchor that attaches to ground. The orbiting anchor pulls at the cable via tidal forces to keep it in tension, such that at the very bottom near the Earth’s surface it need only support the weight of whatever payload it will be carrying. On the way up the tension will increase, but the amount of load pulling down on it per unit length decreases as you approach GEO. Chronos is correct in stating that the point of maximum tensile loading is probably somewhere in the middle, but the details depend on the cable construction and how it tapers. Bigger concerns are how you anchor it at the ground, avoid destructive harmonics in the cable, protect it from orbital debris, and maintain and repair it in situ. It’s actually probably easier not to directly anchor it to the ground but instead have some kind of floating anchor that damps motion at the ground end but doesn’t require a rigid constraint.
