Could someone explain to me how a space elevator works? In particular,

Things that hit the atmosphere at 30km/s get destroyed by it. Slow stuff only needs to worry about hitting the ground.

It just sits there, doesn't move at all, there is no friction to generate heat. A station on the space uses centripetal force to keep the cable tight. An elevator climes up and down that cable.

>>8825934
Reminder: it only takes 10% of the rocket fuel to reach the altitude of orbit. The other 90% of the rocket fuel is used to move really really fast laterally, parallel to the ground. Being in orbit is not just being high; it's also moving really really fast. Google Newton's explanation of orbit of a sufficiently fast cannon ball.

When things come back down from orbit, most of the damage from the atmosphere is because of that lateral motion. You could survive a fall from the altitude of satellites, if you also happened to not be in orbit, e.g. relatively stationary compared to the ground beneath you, plus an oxygen tank (approx).
https://www.quora.com/Could-a-person-survive-falling-from-space-to-earth

>>8825960
Oh, but of course hitting the ground would be very bad for you.

Correction: depends on how high up you started. High enough, and you gain enough speed before hitting the thick parts of the atmosphere that things go bad for you.

>>8825934
You tie a really strong cable to a mass above geocentric orbit. Above this point a mass rotating with the earth experiences centrifugal force greater than gravitational force from the earth. This centrifugal force holds our tether taut.

We then climb the tether. Now where things get interesting is where we decide to get off. As we climb the tether our horizontal speed increases, at about 66% of geostationary we have so much speed that if released from the cable, we are able to enter a highly elliptical orbit with it's lowest point above the atmosphere. If we release at geostationary we get a circular orbit. Releasing above geostationary, we end up with an elliptical orbit that has its highest point above the height we released. If we go high enough we can even escape the earth entirely

It's not moving with respect to the atmosphere. You put the anchor in a place that avoids the jet stream, high winds, and the occurence of hurricanes and lightning storms is relatively rare.

>>8825957
Basically this. As a whole, the tether-counterweight system is in geostationary orbit (or slightly above), but since the assembly also rotates with the orbit (and the Earth's rotation) the lower portion of the tether is just dangling benignly through the atmosphere while the outer portion and counterweight swing around over 22,000 miles away.
>>8825960
>>8825963
Not sure I really see the direct relevance of any of that to OP's question.

It does give rise to an interesting subject, though. You said that
>When things come back down from orbit, most of the damage from the atmosphere is because of that lateral motion.
Which is somewhat true, but for altitudes above a few hundred miles, that lateral motion is actually crucial to their survival. With such a near-orbital reentry, the object reenters at a shallow angle, with a fairly modest descent rate. Thanks to this, the object can skim through the upper atmosphere for thousands of miles, scrubbing off all that speed relatively gradually and harmlessly. Too steep a reentry, with too high a descent rate, and the distance and time available to scrub this speed shortens considerably on account of the atmosphere's rather short scale height and short reach - so accelerations stack up to catastrophic levels quickly. This holds true even when the lateral velocity component is nonexistent, despite net velocities being several times slower. In fact, falling off a space elevator from just a few hundred miles would most likely be fatal, no matter how much protection you had, due to the extreme forces and accelerations from plunging into the dense atmosphere, or impact with the surface. This same hazard holds true for MOST of the space elevator ascent; and it is only near the very top of the ascent that a shallow-angle, survivable reentry or stable orbit becomes possible.

I have another question:
Why is it more effective to use a space elevator than rockets? Shouldn't it take the same amount of energy to bring an object up there? What am I missing?

>>8826315
Generally having a space elevator means that you can just use some electricity to bring the object up and then launch them from space using all the fuel they can take.

If you launch from the ground your only option to actually give the object enough energy to break out of Earth's gravity is using tons of fuel, which means you have way less of it to use in actual space. And generally rocket fuel costs.

>>8826325
but total energy spent is the same, right?

So why wouldn't these things just break apart?

>>8826328
Generally yes and no. Rocket fuel means that a lot of energy gets wasted on heating up things rather than moving the rocket forward, but that's the problem of efficiency. Both ways need the same amount of energy to be spent on moving the rocket though.

The problem is that packing the rocket full of fuel is hard since it also needs to fly weighted down by that fuel. Using external ways of moving it into the orbit makes for more space onboard the rocket for just about anything.

>>8826330
iron stronk

>>8826334
I see. Thanks.

>>8826335
this strong, though?
It doesn't feel right.
And wouldn't something like this be really really heavy?

>>8826330
Diamond cable

What if a terrist drives a truck into the bottom of the wire?

>>8826352
It's supposed to have a center of mass in geocentric orbit, so I guess it would stay or slowly drift away.

>>8826342
it can be made to have 0 weight, but it will probably be just heavy enough.

>>8825934
>how a space elevator works
They don't because they are stupid.
>how it goes through the atmosphere without being destroyed
That is irrelevant because of speeds used.
You come from space, you (your spacecraft) is cold, you enter the atmosphere.
You do it at 100mph. The change of temperature is big but it's okay. You also experience, obviously, a sudden wind of .. 100mph. Atmosphere is still very VERY thin, but still.
That's our basic hypothetical space elevator (that doesn't exist) speed. Or faster or slower, doesn't matter, it's nothing.

Apollo command module re-entry speed was 6.83 miles .. per second.
24500 miles per hour.
That's the kind of thing that requires a heat shield, you see ?

But do not worry, space elevators not possible for now and probably never.

>>8826335
>>8826342
>>8826330
They would break apart. There is no material in existence with enough tensile strength to make a space elevator in Earth's gravity well. Even carbon nanotubes are inadequate, and that's assuming you could make a 36,000km length one when making one meter is a struggle.

By the way, this doesn't rule out the concept entirely - if there's ever a permanent human presence on the moon you could throw up a simple Kevlar space elevator almost immediately to easily leave the lunar surface without a rocket.

>>8826498
>you could throw up a simple Kevlar space elevator almost immediately to easily leave the lunar surface without a rocket.
Yeah, but leaving the moon seems trivial to begin with.

Would it ever be possible to see an orbital ring from the ground? How far off would you see those tethers?

>>8826598
Well you would see a very thin line, the GEO is 22236 miles away.

File: apollo-anniversary-10-130722.jpg (127KB, 670x440px) Image search: [Google]

127KB, 670x440px

>>8826581
It's significant. Over 20% of the mass of the lunar lander was propellant so it could leave the moon again.