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

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

#91

Post by richk449 »

schiffern wrote: post #70
richk449 wrote: post #56

Earlier quoted context omitted.

Many technologies are developed long before they are viable because they have military value. Access to space is currently a major national security issue, so a space elevator could be a manhattan project. Some technologies are developed by the free market before they are economically viable too. LEO constellations for instance (both the original - iridium, and starlink).

>developed by the free market >iridium For some reason I was skeptical of this (suspiciously tidy) myth-making, and the more I look into it the more I'm convinced I was right to be skeptical. Turns out the relevant engineers -- Ken Peterson and Ray Leopold -- both worked on military and government communications systems immediately prior to being hired at Motorola and starting the Iridium project. Peterson's bio is r…

Pretty much everything that has to do with space was first developed by governments for military purposes. Rockets, satellites, communications, imaging, etc.

I think your point supports the general thesis that many technologies are developed before they are economically viable.

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

#92

Post by batch12 »

amy-petrik-214 wrote: post #89
s1artibartfast wrote: post #62

Earlier quoted context omitted.

Yes, that would be the proposal. Existing ship mounted railguns already shoot projectiles around 3km/s. It is generally thought that they could be scaled up to 8 km/s and larger size. The main problem is that if you fire human sized objects that fast at sea level you end up with a plasma ball due to air friction. This isn't an issue with chemical rockets because they start at 0 and accelerate to Vmax, whereas the rai…

[flagged]

Please use your llm elsewhere.

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

#93

Post by hinkley »

dredmorbius wrote: post #85
hinkley wrote: post #82

Earlier quoted context omitted.

What I was never clear on is whether that makes them more interesting or less realistic.

The one thing that's clear is that this makes tethers a more challenging engineering problem than a naive / uninformed view might have suggested. This is almost always the situation in engineering applications. The simple approach based on first principles turns out to be massively influenced by second- and higher-order effects. See Admiral Hyman Rickover's "Paper Reactors" for a classic take on this: https://whatisn…

Reminds me of a futurist I read years ago who was sure super critical water oxidation would solve all of our pollution problems. Ceramics are a “Pick two” material. You can handle heat, pressure or corrosion. SCWO requires all three. Some clever team invented composite ceramics trying to fix the problem, but that was a decade or two ago and still it’s a niche solution used for truly pernicious toxins and that’s about it, so I’m guessing it either didn’t work long term or was made out of unobtanium.

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

#94

Post by ray_v »

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.

Doesn't the fact that you don't need to deal with as much air at higher altitude make it much easier to increase the extra amount of delta v needed?

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

#95

Post by pdonis »

s1artibartfast wrote: post #62
pdonis wrote: post #50

Earlier quoted context omitted.

> thats what the railgun is for A railgun that can provide a delta-v of 8 kilometers per second?

Yes, that would be the proposal. Existing ship mounted railguns already shoot projectiles around 3km/s. It is generally thought that they could be scaled up to 8 km/s and larger size. The main problem is that if you fire human sized objects that fast at sea level you end up with a plasma ball due to air friction. This isn't an issue with chemical rockets because they start at 0 and accelerate to Vmax, whereas the rai…

> Existing ship mounted railguns already shoot projectiles around 3km/s.

Projectiles of what mass? And with what acceleration? As I understand it, with feasible railgun lengths the acceleration is well above the limit of human tolerance, and the projectile mass is significantly smaller than a typical payload put into LEO by conventional rockets.

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

#96

Post by seanhunter »

chmod775 wrote: post #87
askvictor wrote: post #54

Earlier quoted context omitted.

Depends where the tether breaks. If it's somewhere along the middle, then the Earth-side section would fall to Earth. KSR's Mars trilogy examines the impacts (pun intended) of this.

Even an optimal space elevator needs to support a sizable portion of its own tether weight with the tether itself. For a solid non-magnetic tether to be at all realistic, the tether material would likely be so light relative to it's length/volume, it'll never be at all dangerous regardless of how high you drop it from - its terminal velocity would be tiny. I can drop some yarn, fishing line, whatever, from whichever…

But I thought the whole point of an elevator is you elevate things. Which means the line falling wouldn't be the biggest problem- that would be the payload falling to earth surely?

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

#97

Post by buildbot »

anytime5704 wrote: post #47
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.

Light Foundation TV series spoilers below -

In the first episode, a space elevator is bombed. It’s pretty catastrophic! I think a lot of people underestimate the forces involved in something of this scale collapsing.

“ The tether wrapped around the planet like a garrote.

It cut 50 levels down.”

This is obviously fiction, but so is this research and the general concept of space elevators.

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

#98

Post by schiffern »

schiffern wrote: post #66
JumpCrisscross wrote: post #45

Earlier quoted context omitted.

> 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…

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…

Probably need that factor of tau. Don't math tired, folks! :)

https://futureboy.us/fsp/frink.fsp?fromVal=2+pi+%28+%28earth...

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

#99

Post by schiffern »

richk449 wrote: post #91
schiffern wrote: post #70

Earlier quoted context omitted.

>developed by the free market >iridium For some reason I was skeptical of this (suspiciously tidy) myth-making, and the more I look into it the more I'm convinced I was right to be skeptical. Turns out the relevant engineers -- Ken Peterson and Ray Leopold -- both worked on military and government communications systems immediately prior to being hired at Motorola and starting the Iridium project. Peterson's bio is r…

Pretty much everything that has to do with space was first developed by governments for military purposes. Rockets, satellites, communications, imaging, etc. I think your point supports the general thesis that many technologies are developed before they are economically viable.

Definitely agree! Just observing that when the credit line is "some technologies are developed by the free market," people seem inclined to forget that part. Cheers

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

#100

Post by buildbot »

seanhunter wrote: post #96
chmod775 wrote: post #87

Earlier quoted context omitted.

Even an optimal space elevator needs to support a sizable portion of its own tether weight with the tether itself. For a solid non-magnetic tether to be at all realistic, the tether material would likely be so light relative to it's length/volume, it'll never be at all dangerous regardless of how high you drop it from - its terminal velocity would be tiny. I can drop some yarn, fishing line, whatever, from whichever…

But I thought the whole point of an elevator is you elevate things. Which means the line falling wouldn't be the biggest problem- that would be the payload falling to earth surely?

The falling line would be a problem still - using fishing line as an example ignores scaling. The seed cable for example in some designs is 20 tons by itself: https://en.wikipedia.org/wiki/Space_elevator_construction

So possible 100s to thousands of tons falling for 5+ days…

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