> 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].
> 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.
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.
> 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.
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+%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."
The top of a space elevator, by definition, is not an orbiting object.
Depending on the height of the space elevator, the speed of its top will be smaller, equal or greater than the speed required at that height for a stable circular orbit.
The top of a space elevator will have the same angular velocity as the Earth. The angular velocity of an orbiting object is equal to that of the Earth only when it is on a geosynchronous orbit (i.e. an extremely high orbit in comparison with those of most satellites or in comparison with the height of the space elevator from this proposal).
In order to launch a satellite from a space elevator without additional acceleration, it is not necessary for its height to be that of a geosynchronous orbit.
For smaller heights, any object released from the top will fall towards the Earth on an elliptical orbit. If the height is big enough, the elliptical orbit will not intersect the solid Earth or the atmosphere of the Earth. Nevertheless, the minimum height for this is still on the order of a few tens of thousands of km, i.e. at least 100 times the height of the space elevator from this proposal.
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.
>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.
Jack Welch is (in)famous for his management style and the impact that his style has had on American business.
I won't opine too much on it, but the most concise way to put it is an extreme concentration on producing shareholder value as quickly as possible at the expense of basically everything else.
And calling food rolled in khobz a sandwich is a stretch. At what point is any bread-like plus non-bread-like a sandwich? E.g. a pizza or a beef pie or peshwari naan is a sandwich (yes I’ve seen the cube rule!)
Well yeah. I think it can be argued that a significant portion of what we consider food is a homomorphism of tasty-thing-in-or-on-bread. There are other families, this is one of the bigger ones.
Yeah I recently moved out to a rural village in the balkans and it's amazing how they eat greasy food with bread, so it makes sense to use the bread to pick up the greasy food with. It's a no brainer really.
Bread is and has always been a non-sticky, non-greasy, and dry way of picking up food.
Buying lunch - 1 Selling your home - 10