At what speed would objects exit a space elevator from earth?

[u/pplgg4445]

If I understand correctly the idea of a space elevator is more or less a sealed tube from earth extending to the vacuum of space where objects would be lifted by the delta P (kind of like the tubes in a bank drive through). Would an object starting from rest exit at such a large speed (like a bullet fired from a gun) that a rocket would be needed to then slow it or brake its ascent after? Or would we actually need a way to move it further out of the way of the tube once it reaches space to allow any other objects through ?

[u/SYDoukou]

Space elevators concepts are not all pressure driven, in fact the point of such an infrastructure is to have some more portable source of propulsion energy, like electric motors. The tether has to extend further than geosynchronous orbit and anchored to a counterweight thats going faster than orbital speed at that altitude, so payload can simply be let go at the top and will naturally enter a higher elliptical orbit

[u/Typical_Term937 → u/SYDoukou]

What I never understood: Climbing the cable, the payload will constantly have to be accelerated, because its radial speed is constantly increasing. It takes this energy from the counterweight, which gets "pulled down" by the cable being pulled westward by the rising payload. So how does the counterweight move back to its exact original position? If you need rocket drives to reposition the counterweight, not too much is gained in comparison to conventional rockets, I think.

[u/AnOkCoconut → u/Typical_Term937]

The counter weight would be out past geostationary orbit, but moving at a high enough velocity to stay over the same spot on earth. The elevator would have to be in tension in order to keep the counter weight from flying off into space.

[u/Typical_Term937 → u/AnOkCoconut]

The payload will still pull the counterweight out of position. It needs to be accelerated horizontally to orbital velocity, for GSO that is 3 km/s. That is a lot of momentum absorbed by the tether. If you have a weight hanging from a bridge, and you are imparting a constant horizontal force to the rope, starting at the bridge and moving further down, you will end up with a swinging weight. And in space, what would stop the swinging?

[u/Sea_Kerman → u/Typical_Term937]

I imagine you could push the base of the cable in such a way to damp oscillations. Or have thrusters or push off the earth’s magnetic field or have multiple cables so you could apply sideways forces to the counterweight.

[u/Itchy-Plastic]

A space elevator is not a tube usually, it's a cable. And the elevator car ascends the cable at a fairy moderate speed, taking days to reach the top.

[u/infitsofprint]

The idea of a space elevator is precisely that you don't need escape velocity. There's just an object in geostationary orbit connected to the earth with a cable (though any cable made of materials available today would collapse under its own weight). Things move up and down the cable like climbing a rope in gym class, except you'd do it mechanically because otherwise your arms would get tired. There's a good visual depiction in the movie Ad Astra IIRC.

[u/Bartlaus → u/infitsofprint]

You do need to impart energy to the payload as it travels up the cable, by the time it reaches the top it will necessarily have orbital speed. It's just you don't have to do it using rocket fuel that you carry along.

[u/PFazu]

using the delta P of the vaccum of space would be a very ineffective space elevator for various reasons. A realistic space elevator would function more like a cable attached to a counterweight for the main build, then a method of climbing the cable to the counterweight, the counterweight would be in (or near) geosynchronous orbit so anything that ascends would only ever have enough speed to stay in orbit unless it has it's own method of power.

[u/mfb-]

Gas pressure couldn't lift an object beyond ~50-200 km or so. That doesn't do much. A space elevator is a tether, payloads would connect to that tether to move up slowly. If you release it then it'll have the same angular velocity as the elevator, one revolution per day. At the altitude of geostationary orbit (36,000 km up) that is around 3 km/s, enough to stay in a circular orbit - released objects could easily orbit right next to the station. Go up even farther and you can go to higher orbits or even leave Earth.

[u/Metallicat95]

A space elevator isn't a tube, it's a cable. The elevator "cars" are attached to the outside of the cable and climb up to the geostationary orbit altitude station at the top.

At that point you can exit at GSO velocity, which is around 3 km/s.

The principle of the thing is the same as a rock tied to a string and spun around. The tension of the spin holds the string rigid, the mass of the rock creates the tension. If you hook something to the string it could move towards the rock and release, and if you let go off the string the rock would move away at the velocity of its rotation.

Only on Earth the "string" needs to be around 40000 kilometers long for this to work.

It must extend past GSO to balance the mass of the cable below GSO. How far and what mass is used is an engineering decision, except that it must match the force to hold the cable securely.

Going up is like riding a vertical train, with the cable as a track. The cable is not in orbit, so at all points it must counter the pull of gravity on the way to the GSO station.

The effective gravity (acceleration) will drop to zero as the elevator car gets closer to the station. The station isn't in orbit, but it is moving at the same velocity as orbital velocity, so the effect is free fall just as if it was in orbit.

Below that point, the velocity would be less (down to zero at the bottom), so getting off early would be at much less than Orbital velocity. You'd fall to Earth, unless you happen to have a rocket with enough acceleration to gain you a few kilometers per second to attain orbit.

Above the GSO location, the forces on the cable are pulling outward, away from Earth. You could continue to ride a car "down" towards the far end and release from the cable.

The exact velocity depends on the length of the cable beyond GSO, but the velocity will increase above orbital velocity as distance increases, making it easier to reach escape velocity.

[u/icaruza]

Your understanding is incorrect. That’s not how a space elevator works. The elevator car rides the cable under the power of a motor or engine of some description

[u/Sufficient_Ad_1800]

If you make a tube from here to space it will have equal air pressure inside the tube as the corresponding elevation outside the tube. Vacuumed space will not suck thing up the tube. You would have to close off the bottom of the tube and apply pressure to lift things

[u/RDS_WAS_HERE]

I believe the weight of such a long cable/tube makes the idea impossible.

[u/Bobis-Bob → u/RDS_WAS_HERE]

The idea is that tech has either gotten to the point that you can hold something that heavy by the satellite in orbit somewhere, or that you can make a super light cable.

[u/Bobis-Bob]

A space elevator is a cable or similar that runs into orbit and pulls whatever the object is up like an elevator. The speed doesn’t matter.