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Magnetically levitated space elevator to low-earth orbit (2001) [pdf]

publications.anl.gov

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Re: Magnetically levitated space elevator to low-earth orbit (2001) [pdf]

#41

Post by pdonis »

mikewarot wrote: post #35

If we're pushing "out of the box" ideas, why not just use hydrogen balloons to hold up a railgun for the first 20,000 meters of altitude? The ambient pressure at the end would be about 1/10th of that at sea level. You could have outriggers with a very thin high voltage power line to enable station keeping via thrusters (repurposed quadrotor parts?) I wouldn't be surprised it the ambient electrostatic field from the a…

The main cost of getting to low Earth orbit isn't gaining altitude, it's gaining speed. Even if you could levitate a spacecraft to, say, 200 km altitude at zero cost in energy, you would still need about 97% of the energy to get it to orbital speed, that you would have needed to launch it from the Earth's surface.

Re: Magnetically levitated space elevator to low-earth orbit (2001) [pdf]

#42

Post by zardo »

mikewarot wrote: post #35

If we're pushing "out of the box" ideas, why not just use hydrogen balloons to hold up a railgun for the first 20,000 meters of altitude? The ambient pressure at the end would be about 1/10th of that at sea level. You could have outriggers with a very thin high voltage power line to enable station keeping via thrusters (repurposed quadrotor parts?) I wouldn't be surprised it the ambient electrostatic field from the a…

I think there might with the balloons blocking the entire sky.

Re: Magnetically levitated space elevator to low-earth orbit (2001) [pdf]

#43

Post by dekhn »

There's a simple point about space elevators that most people ignore.

We would only build a space elevator if it made economic sense. Given the reality of construction costs, even if we had the materials, it would like cost many trillions of dollars (at least) so whatever we used it for would have to produce much more value than that.

Even more importantly, if we had access to the materials necessary to build space elevators, there are other, much more pressing terrestrial needs that would use up all those materials long before somebody tried to build an elevator.

No matter how much fun it is to contemplate their existence, nobody has come up with a justification for the necessary investment required to build and operate one.

Re: Magnetically levitated space elevator to low-earth orbit (2001) [pdf]

#44

Post by s1artibartfast »

pdonis wrote: post #41
mikewarot wrote: post #35

If we're pushing "out of the box" ideas, why not just use hydrogen balloons to hold up a railgun for the first 20,000 meters of altitude? The ambient pressure at the end would be about 1/10th of that at sea level. You could have outriggers with a very thin high voltage power line to enable station keeping via thrusters (repurposed quadrotor parts?) I wouldn't be surprised it the ambient electrostatic field from the a…

The main cost of getting to low Earth orbit isn't gaining altitude, it's gaining speed. Even if you could levitate a spacecraft to, say, 200 km altitude at zero cost in energy, you would still need about 97% of the energy to get it to orbital speed, that you would have needed to launch it from the Earth's surface.

thats what the railgun is for. Altitude is to reduce friction and energy needed.

Re: Magnetically levitated space elevator to low-earth orbit (2001) [pdf]

#45

Post by JumpCrisscross »

schiffern wrote: post #37
JumpCrisscross wrote: post #31

Earlier quoted context omitted.

> 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.

Re: Magnetically levitated space elevator to low-earth orbit (2001) [pdf]

#46

Post by darby_nine »

dekhn wrote: post #43

There's a simple point about space elevators that most people ignore. We would only build a space elevator if it made economic sense. Given the reality of construction costs, even if we had the materials, it would like cost many trillions of dollars (at least) so whatever we used it for would have to produce much more value than that. Even more importantly, if we had access to the materials necessary to build space e…

> Given the reality of construction costs, even if we had the materials, it would like cost many trillions of dollars (at least) so whatever we used it for would have to produce much more value than that.

This doesn't seem that difficult given the potential value of mining. I suspect terrestrial politics would dominate this conversation—access to said elevator is far more interesting than any collective concern, and humans as they stand are not capable of resolving collective concerns on any level.

Re: Magnetically levitated space elevator to low-earth orbit (2001) [pdf]

#47

Post by anytime5704 »

al_borland wrote: post #16

I seem to remember reading about this in Popular Science around that time. Of all the things I saw in that magazine, the space elevator made of carbon nanotubes was always the one that stuck with me. Though I seem to remember PopSci taking about harnessing an asteroid, or something, and putting it geosynchronous orbit, as a means to create the top anchor point. 25 years later, it seems just as far fetched.

This seems like a great way to accidentally cause another global extinction event.

I’m probably overestimating the size of the anchor.

Re: Magnetically levitated space elevator to low-earth orbit (2001) [pdf]

#48

Post by tpchnmy »

stretchwithme wrote: post #21

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…

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

Re: Magnetically levitated space elevator to low-earth orbit (2001) [pdf]

#49

Post by dekhn »

darby_nine wrote: post #46
dekhn wrote: post #43

There's a simple point about space elevators that most people ignore. We would only build a space elevator if it made economic sense. Given the reality of construction costs, even if we had the materials, it would like cost many trillions of dollars (at least) so whatever we used it for would have to produce much more value than that. Even more importantly, if we had access to the materials necessary to build space e…

> Given the reality of construction costs, even if we had the materials, it would like cost many trillions of dollars (at least) so whatever we used it for would have to produce much more value than that. This doesn't seem that difficult given the potential value of mining. I suspect terrestrial politics would dominate this conversation—access to said elevator is far more interesting than any collective concern, and…

Trillions+ in mining value? What exactly are you proposing mining (platinum seems the most likely, IIRC my D&D)? remember that new sources affect the supply, which changes prices significantly, so it would have to be basically unobtanium to be worth it. And remember, since you developed all that tech just to make the space elevator... most of the mining you did is probably obsolete.

Re: Magnetically levitated space elevator to low-earth orbit (2001) [pdf]

#50

Post by pdonis »

s1artibartfast wrote: post #44
pdonis wrote: post #41

Earlier quoted context omitted.

The main cost of getting to low Earth orbit isn't gaining altitude, it's gaining speed. Even if you could levitate a spacecraft to, say, 200 km altitude at zero cost in energy, you would still need about 97% of the energy to get it to orbital speed, that you would have needed to launch it from the Earth's surface.

thats what the railgun is for. Altitude is to reduce friction and energy needed.

> thats what the railgun is for

A railgun that can provide a delta-v of 8 kilometers per second?

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