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How is the elevator car in a space elevator accelerated horizontally? That's what reaching orbit is, right? Horizontal acceleration? The car starts out on th

How is the elevator car in a space elevator accelerated horizontally? That's what reaching orbit is, right? Horizontal acceleration? The car starts out on the ground at 465m/s. It has to accelerate to 11,068 km/h. What makes it accelerate? The cable, without any force applied to it anywhere? Or is there a rocket on that car? To put mass into orbit, you have to accelerate that mass. And do it without decelerating the elevator. There are no free lunches.

JumpCrisscross 2y ago
> How is the elevator car in a space elevator accelerated horizontally? Momentum transfer from the cable, which is attached to an orbiting counterweight. In this design, some of that momentum would be borrowed from the Earth’s rotation via the cable’s coupling to its magnetic field. In general one boosts the counterweight directly or, more practically, by sending things down [1]. [1] https://space.stackexchange.com/questions/22447/how-will-the-angular-momentum-of-a-space-elevator-be-preserved https://space.stackexchange.com/questions/22447/how-will-the...
- schiffern 2y ago
  This paper's design has no orbiting counterweight, and only reaches an altitude of 200 km. A launch loop can harvest energy and momentum from the rotor to accelerate payloads, but I don't see any such mechanism here.
  - JumpCrisscross 2y ago
    > This paper's design has no orbiting counterweight Which is why I say I “in this design, some of that momentum would be borrowed from the Earth’s rotation via the cable’s coupling to its magnetic field.” The cable is an electrostatic counterweight because we’re using electromagnetism, not the comparably weak gravitation.
    - schiffern 2y ago
      Problem is "some of the momentum" isn't nearly enough to reach orbit (climbing the tower only gains you 3% of orbital speed, or 0.1% the kinetic energy), and there's no hint of a mechanism that's supposed to accelerate a payload the rest of the way to orbital speed.
      - JumpCrisscross 2y ago
        > Problem is "some of the momentum" isn't nearly enough to reach orbit (climbing the tower only gains you 3% of orbital speed, or 0.1% the kinetic energy) Where is your math? The top of the elevator is travelling at orbital velocity. This is trivial to show in designs with a counterweight. (Here, the magnetic coupling makes it less intuitive.) If you are on an orbiting object, i.e. the top of a space elevator, you’ve achieved orbital velocity.
        schiffern 2y ago
        Sorry, just returned to correct my error -- I drastically overestimated the velocity gain. In truth you only gain about 2.3 m/s (i.e. 0.03% orbital velocity) when climbing to the top of the elevator. Math is simply final velocity minus initial velocity: https://futureboy.us/fsp/frink.fsp?fromVal=%28earthradius+%2B+200+km%29+%2F+siderealday+-+earthradius+%2F+siderealday&toVal=#calc https://futureboy.us/fsp/frink.fsp?fromVal=%28earthradius+%2... >The top of the elevator is travelling at orbital velocity. This is trivial to show in designs with a counterweight. Per the paper this design only reaches 200 km in altitude, therefore it has no counterweight (a counterweight would need to be somewhere above 35,786 km altitude). Speed at the top is far below orbital velocity, so it requires a method of acceleration. The paper acknowledges this. From the abstract: "At the top of the loop, vehicles may be accelerated to orbital velocity or higher by rocket motors, electromagnetic propulsion, or hybrid methods."
        schiffern 2y ago
        Probably need that factor of tau. Don't math tired, folks! :) https://futureboy.us/fsp/frink.fsp?fromVal=2+pi+%28+%28earthradius+%2B+200+km%29%2Fsiderealday+-+earthradius%2Fsiderealday+%29&toVal=#calc https://futureboy.us/fsp/frink.fsp?fromVal=2+pi+%28+%28earth...
Benjammer 2y ago
One thing with a space elevator that makes it so much more efficient than rockets is precisely because you don't necessarily need the payload itself to supply this horizontal acceleration. The space elevator is attached to the ground at one end, and the other is way up in orbit. There must be forces in play _already_ for the entire thing to stay standing, before you get to any concept of a payload/car. Part of the idea of building the elevator in the first place is to solve for these orbital forces in a generalized way independent of the payloads themselves. It's like strapping various sized rockets to your various specific payloads, versus building a generalized model of a rocket ship, and then just putting the various payloads inside the generalized rocket ship. Space elevator is a further evolution of the concept. You don't even need to use the rocket ship abstraction anymore. You're generalizing/abstracting the orbital transition itself into the structure of the elevator, and then just send things up and down it. The payload now only needs to worry about moving along the elevator, the elevator itself has already "solved" for the orbital horizontal acceleration by nature of its structure existing in the first place. In terms specifically of mass/energy conservation, as the other reply said, energy is borrowed from either the earth's rotation and/or kinetic energy from a counterweight at the end of the elevator up in orbit.
- schiffern 2y ago
  >you don't necessarily need the payload itself to supply this horizontal acceleration. The space elevator is attached to the ground at one end, and the other is way up in orbit. On a conventional space elevator this is true. You just go up to 35,786 km altitude (AKA geostationary orbit) and let go. However the structure described in this paper only goes up to 200 km altitude, so it still needs a horizontal acceleration system.
tpchnmy 2y ago
If we are talking space elevators, we should consider using 'there ain't no such thing as a free lunch' with regards to Larry Niven
deleted 2y ago
[deleted]

JumpCrisscross 2y ago

> How is the elevator car in a space elevator accelerated horizontally? Momentum transfer from the cable, which is attached to an orbiting counterweight. In this design, some of that momentum would be borrowed from the Earth’s rotation via the cable’s coupling to its magnetic field. In general one boosts the counterweight directly or, more practically, by sending things down [1]. [1] https://space.stackexchange.com/questions/22447/how-will-the-angular-momentum-of-a-space-elevator-be-preserved https://space.stackexchange.com/questions/22447/how-will-the...

schiffern 2y ago
This paper's design has no orbiting counterweight, and only reaches an altitude of 200 km. A launch loop can harvest energy and momentum from the rotor to accelerate payloads, but I don't see any such mechanism here.
- JumpCrisscross 2y ago
  > This paper's design has no orbiting counterweight Which is why I say I “in this design, some of that momentum would be borrowed from the Earth’s rotation via the cable’s coupling to its magnetic field.” The cable is an electrostatic counterweight because we’re using electromagnetism, not the comparably weak gravitation.
  - schiffern 2y ago
    Problem is "some of the momentum" isn't nearly enough to reach orbit (climbing the tower only gains you 3% of orbital speed, or 0.1% the kinetic energy), and there's no hint of a mechanism that's supposed to accelerate a payload the rest of the way to orbital speed.
    - JumpCrisscross 2y ago
      > Problem is "some of the momentum" isn't nearly enough to reach orbit (climbing the tower only gains you 3% of orbital speed, or 0.1% the kinetic energy) Where is your math? The top of the elevator is travelling at orbital velocity. This is trivial to show in designs with a counterweight. (Here, the magnetic coupling makes it less intuitive.) If you are on an orbiting object, i.e. the top of a space elevator, you’ve achieved orbital velocity.
      - schiffern 2y ago
        Sorry, just returned to correct my error -- I drastically overestimated the velocity gain. In truth you only gain about 2.3 m/s (i.e. 0.03% orbital velocity) when climbing to the top of the elevator. Math is simply final velocity minus initial velocity: https://futureboy.us/fsp/frink.fsp?fromVal=%28earthradius+%2B+200+km%29+%2F+siderealday+-+earthradius+%2F+siderealday&toVal=#calc https://futureboy.us/fsp/frink.fsp?fromVal=%28earthradius+%2... >The top of the elevator is travelling at orbital velocity. This is trivial to show in designs with a counterweight. Per the paper this design only reaches 200 km in altitude, therefore it has no counterweight (a counterweight would need to be somewhere above 35,786 km altitude). Speed at the top is far below orbital velocity, so it requires a method of acceleration. The paper acknowledges this. From the abstract: "At the top of the loop, vehicles may be accelerated to orbital velocity or higher by rocket motors, electromagnetic propulsion, or hybrid methods."
        schiffern 2y ago
        Probably need that factor of tau. Don't math tired, folks! :) https://futureboy.us/fsp/frink.fsp?fromVal=2+pi+%28+%28earthradius+%2B+200+km%29%2Fsiderealday+-+earthradius%2Fsiderealday+%29&toVal=#calc https://futureboy.us/fsp/frink.fsp?fromVal=2+pi+%28+%28earth...

Benjammer 2y ago

One thing with a space elevator that makes it so much more efficient than rockets is precisely because you don't necessarily need the payload itself to supply this horizontal acceleration. The space elevator is attached to the ground at one end, and the other is way up in orbit. There must be forces in play _already_ for the entire thing to stay standing, before you get to any concept of a payload/car. Part of the idea of building the elevator in the first place is to solve for these orbital forces in a generalized way independent of the payloads themselves. It's like strapping various sized rockets to your various specific payloads, versus building a generalized model of a rocket ship, and then just putting the various payloads inside the generalized rocket ship. Space elevator is a further evolution of the concept. You don't even need to use the rocket ship abstraction anymore. You're generalizing/abstracting the orbital transition itself into the structure of the elevator, and then just send things up and down it. The payload now only needs to worry about moving along the elevator, the elevator itself has already "solved" for the orbital horizontal acceleration by nature of its structure existing in the first place. In terms specifically of mass/energy conservation, as the other reply said, energy is borrowed from either the earth's rotation and/or kinetic energy from a counterweight at the end of the elevator up in orbit.

schiffern 2y ago
>you don't necessarily need the payload itself to supply this horizontal acceleration. The space elevator is attached to the ground at one end, and the other is way up in orbit. On a conventional space elevator this is true. You just go up to 35,786 km altitude (AKA geostationary orbit) and let go. However the structure described in this paper only goes up to 200 km altitude, so it still needs a horizontal acceleration system.

tpchnmy 2y ago

If we are talking space elevators, we should consider using 'there ain't no such thing as a free lunch' with regards to Larry Niven

deleted 2y ago

[deleted]