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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]

#71

Post by FiatLuxDave »

pennomi wrote: post #69
FiatLuxDave wrote: post #68

Earlier quoted context omitted.

Existing light gas guns can already hit 8 km/s: https://en.wikipedia.org/wiki/Light-gas_gun The biggest advantage of very high altitude reducing the friction problem isn't just that it stops your projectile from turning into plasma, it is that the size of the minimum viable projectile is reduced. People keep focusing on getting people or vehicles into orbit, but the main advantage of a gun-to-orbit system is that the…

You want to fire thousands of bullet size pieces of metal into low earth orbit? Holy Kessler Cascade, Batman!

While that's not my intention, if you actually wanted to damage satellites and cause a Kessler Syndrome scenario, it's hard to find a system that would have a bigger bang-for-your-buck.

I was rather envisioning a target satellite that is designed to absorb the pellet as an inelastic collision. It would probably resemble something like this: https://en.wikipedia.org/wiki/Black_body#/media/File:Black_b... . Of course, if it didn't work as designed, then it could be a problem.

The point was that a high altitude low-mass-per-shot gun system could get mass into orbit with a similar energy cost as a space elevator with significantly less upfront capital cost and no need for miracle materials.

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

#72

Post by ben_w »

metadat wrote: post #57
monkeyfun wrote: post #38

Earlier quoted context omitted.

Relatedly, have you ever heard of skyhook? Not the CIA one but the orbital infrastructure concept -- lets you literally just take a supersonic capable plane with no rocket engines whatsoever into space. Always love that concept with how it's actually engineer-able with current materials and sounds like it shouldn't work until you look closely.

This? https://en.wikipedia.org/wiki/Skyhook_(structure) Interesting idea, but if I'm understanding correctly, how do you stop the thing you hooked from swinging around and back down? Would you need to reel in 50 miles or whatever of cable?

You can just let go of it when it's high enough, it picks up (ground) speed on the way up.

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

#74

Post by ben_w »

dekhn wrote: post #49
darby_nine wrote: post #46

Earlier quoted context omitted.

> 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.

Even aluminium gets you to a trillion dollars in 6 years.

https://en.wikipedia.org/wiki/List_of_countries_by_aluminium... *

Calculation: http://www.wolframalpha.com/input/?i=1%20trillion%20USD%20%2...

* Old data, China has rapid growth in this sector and is now about 42 megatons/y, but that just changes the result from rounding down to 6 years to rounding up to 6 years: https://www.reuters.com/markets/commodities/china-2023-alumi...

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

#75

Post by ben_w »

JumpCrisscross wrote: post #32
spacebacon wrote: post #29

Several prompts later … The gap between current material science and the required advancements for constructing a magnetically levitated space elevator is significant. Let's break down the key areas where advancements are needed and assess the current state compared to the required state: 1. Superconducting Materials Current State: NbTi Superconductors: NbTi (Niobium-Titanium) superconductors are among the most commo…

> major hurdle is the ability to produce continuous lengths of high-quality CNTs What is an intermediate market for medium-length high-quality CNTs?

Presumably anything that wants a "medium"* length very strong cable; civil infrastructure comes to mind, might be useful for suspension bridges?

* quotes because all things are relative, by "medium" in the context of a space elevator you may have meant "continent sized"?

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

#76

Post by vinnyvichy »

JumpCrisscross wrote: post #15

NbTi has a critical temperature below 10K and generate fields of around 10 T [1]. The paper contemplates a 2T field. Could CeOFeAs permit cooling with hydrogen [2][3]? [1] https://en.m.wikipedia.org/wiki/Niobium%E2%80%93titanium [2] https://www.sciencedirect.com/science/article/abs/pii/S09214... [3] https://en.m.wikipedia.org/wiki/High-temperature_superconduc...

You might be better off with scaling FeSe or waiting for improvements in that class. you can use LN2

(H2 leaks are not just inevitable,large scale deployments of LN2 cooling already exist)

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

#77

Post by vinnyvichy »

https://youtu.be/gQjbzuOA2mU

(2024) Why physics favor Mass Drivers over heavy lift rockets

guy's voice similar to Bret Victor, (R&Deployment) economics slightly better than space elevator-- you can also use SC magnets but in easier config, repurpose Hyperloop research etc

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

#78

Post by db48x »

tadfisher wrote: post #52
anytime5704 wrote: post #47

Earlier quoted context omitted.

This seems like a great way to accidentally cause another global extinction event. I’m probably overestimating the size of the anchor.

The anchor would need to be beyond geostationary orbit to keep the center of mass geostationary, so a broken tether would result in the anchor departing "outward". The reason to use an anchor is to avoid creating a tether that's twice as long as it needs to be.

If you use an asteroid as an anchor, then you are doing it wrong. You made your space elevator half as long as it could be!

A longer elevator can fling you into the outer solar system. Just climb to the correct height, wait until the right phase angle, and let go.

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

#79

Post by db48x »

EasyMark wrote: post #67
more_corn wrote: post #59

Earlier quoted context omitted.

But if you break the tether halfway down the bottom half falls at 16,000 mph right? And then it’s burning and then it cracks like a whip. I don’t know about extinction, but not a fun time for anyone.

Aren’t they talking about a mess up on the asteroid trajectory? There is no way a space elevator cable snapping wipes out all life on earth, although I’m sure any populated areas it hits would be quite devastated.

A falling elevator would not wipe anyone out. They would place a protective balloon containing approximately 5 quadrillion tons of gas beneath it. The elevator would be paper thin and a couple of meters wide in the middle where it needs to be strongest. The parts that don’t burn will flutter and slowly fall to the ground.

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

#80

Post by adrian_b »

JumpCrisscross wrote: post #45
schiffern wrote: post #37

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), 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…

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.

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