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Space Elevator

neal.fun

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Re: Space Elevator

#271

Post by estimator7292 »

BobaFloutist wrote: post #266
raducu wrote: post #194

Earlier quoted context omitted.

> Angela Collier has a video saying it's kinda ridiculous. There are other concepts like space fountains, orbital rings and sky hooks that seem more doable -- especially the sky hook seems close to do-able, especially on the Moon.

What if we just made a huge mountain? Space ramp? Is that anything?

IIRC there is no material we're aware of that has anywhere near enough compressive strength to build that high, regardless of how wide the base is.

Space elevators only (theoretically) work because the entire structure is in tension. And the only material we currently know of that can handle the tensile forces is carbon fiber.

Re: Space Elevator

#272

Post by estimator7292 »

lurquer wrote: post #242
jvanderbot wrote: post #143

Very cool. One thing I wish was better shown: space is close, it's just hard to go up. Our liveable breathable atmosphere is razor thin compared to the size of earth. In most cases, 100km is less than the distance between sizeable metropolitan areas. It's a day long bike ride. Air runs out less than a bus ride across town. A 15k jog/hike would put you in the stratosphere. Those jet aircraft that seem so high are clos…

> it's just hard to go up. Eh. Going up is easy. A Frenchman, a sheep, duck, and rooster solved the whole ‘up’ thing over two centuries ago. But going DOWN? That’s far more difficult. What wonders may lie beneath our feet: vast caverns, ore, underground oceans… hard to get to though.

Just dig a big hole, duh

/s

Re: Space Elevator

#273

Post by tsimionescu »

gambiting wrote: post #268
tsimionescu wrote: post #163

Earlier quoted context omitted.

Yes, you need a geostationary orbit for the tether, otherwise it would either fall down or spiral away with time.

Could you make it over double the length needed, so if it ever broke it would be pulled away from Earth and float into space and not crash into the Earth?

No. You'd need an even more magical material that can witstand at least double the tensile strength (since the parts that go above and below the GEO anchor would be pulling with about the same force in opposite directions). And if you destroyed the GEO point anchor, the cable would just split in two - everything that's below GEO would fall, everything that's above would float away.

Re: Space Elevator

#274

Post by tsimionescu »

vdqtp3 wrote: post #177
tsimionescu wrote: post #164

Earlier quoted context omitted.

Why advanced? It's a stationary target that's 35,000 km long. I don't think it would be that hard to hit. Not to mention, securing the cargo would be an extremely difficult task in itself, especially when one of the main thinga you'd like to raise through the space elevators is rocket fuel.

> stationary target that's 35,000 km long and what, 12" wide? 24"? that's still very difficult to target

In general, the more tensile strength you want in a cable made of a given material, the thicker you need to make that cable. Now sure, we can imagine whatever magical properties we want of our space elevator cable material, since no known material that could do this exists anyway. But it's far more likely that you'd need a cable that's a kilometer or more in diameter to achieve the tensile strength needed to support its weight at 35000 km of length, than it is to be a few inches wide.

Re: Space Elevator

#275

Post by adwn »

seer wrote: post #231
adwn wrote: post #46

Earlier quoted context omitted.

Almost all discussions around space elevators focus on the cable itself, how to manufacture and deploy it, and completely forget about the issues that would arise afterwards: 1) How do you attach the climber to the cable without affecting its structural integrity? By squeezing it really hard? A material that's optimized for longitudinal tension strength is probably not very tolerant of lateral compression. 2) How do…

If you somehow manage to get magnetic fields involved, so you are not afraid of friction with the cable itself, at 1.3 max apparent acceleration/deceleration (after a turnover) and including earth’s gravity you get 116min to geostationary. If you account for various inefficiencies like taking it slow in the lower atmosphere Ant whatnot, it still should be in the matter of hours. So totally feasible and even comfortab…

> If you somehow manage to get magnetic fields involved, so you are not afraid of friction with the cable itself, at 1.3 max apparent acceleration […]

This means that half-way after 58 minutes, the climber is traveling at 0.3 * 9.81 m/s² * 60 * 58 ~= 10.2 km/s ~= 36,720 km/h (!!!) relative to the cable. A tiny imperfection or wobble is going to make the climber crash into the cable, destroying both.

A climber with a mass of 10 tonnes requires 10^4 kg * 1.3 * 9.81 m/s² ~= 127.5 kN of force to accelerate at 1.3 g. At the ~56 minute mark, the climber reaches a speed of ~9,888 m/s. This means it requires a power output of 127.5 kN * 9888 m/s = 1.26 GW (!!!) to achieve this acceleration, plus overhead for the power electronics and transmission. Even at a voltage of 1 kV, that's around 1,500,000 A (!!!) of current that you have to transmit and invert.

If you have a way to reliably transfer that amount of power without touching the cable which is moving at 10 km/s relative speed, or with touching but without immediately melting the cable or the collector, let me know :-)

> So totally feasible

lol no

Re: Space Elevator

#276

Post by lazide »

BobaFloutist wrote: post #265
literalAardvark wrote: post #239

Earlier quoted context omitted.

It's not that simple though. The rocket equation still applies so it's almost as hard to do (you just get rid of atmospheric drag), and failed launches are also extra catastrophic. Even more, your delta v required is still huge. I can't be bothered to run the numbers right now but most of the delta v is in the orbital velocity, not in the altitude.

Delta v feels reductive, since your fighting negative acceleration to go up and a fraction of that to go laterally, no?

They’re the same thing. Either you go sideways really fast, or go straight up really far (geo-synchronous distance).

Either way, you need the same total velocity delta.

Re: Space Elevator

#277

Post by pfdietz »

actionfromafar wrote: post #263
pfdietz wrote: post #186

Earlier quoted context omitted.

In the stratosphere it both contributes to IR opacity, increasing global warming, and can provide ice surfaces on which ozone destruction is amplified. The stratosphere is normally extremely dry, so even small inputs can have an effect that would be invisible in the much moister troposphere.

Aha, so in the stratosphere we should use oxygen / solid carbon boosters?

Their Isp is very low, unfortunately, because the molecular weight of the combustion gas is too high. Ditto for oxygen/carbon monoxide.

Maybe the Isp could be increased by mixing in some helium, but helium is very expensive.

Re: Space Elevator

#278

Post by [deleted] »

jvanderbot wrote: post #143

Very cool. One thing I wish was better shown: space is close, it's just hard to go up. Our liveable breathable atmosphere is razor thin compared to the size of earth. In most cases, 100km is less than the distance between sizeable metropolitan areas. It's a day long bike ride. Air runs out less than a bus ride across town. A 15k jog/hike would put you in the stratosphere. Those jet aircraft that seem so high are clos…

[deleted]

Re: Space Elevator

#279

Post by JumpCrisscross »

BobaFloutist wrote: post #265
literalAardvark wrote: post #239

Earlier quoted context omitted.

It's not that simple though. The rocket equation still applies so it's almost as hard to do (you just get rid of atmospheric drag), and failed launches are also extra catastrophic. Even more, your delta v required is still huge. I can't be bothered to run the numbers right now but most of the delta v is in the orbital velocity, not in the altitude.

Delta v feels reductive, since your fighting negative acceleration to go up and a fraction of that to go laterally, no?

> since your fighting negative acceleration to go up and a fraction of that to go laterally

They’re both acceleration. At high thrust, virtually equivalent.

Re: Space Elevator

#280

Post by JumpCrisscross »

block_dagger wrote: post #243
messe wrote: post #158

Earlier quoted context omitted.

> it's just hard to go up Going up is the comparatively easy part, it's not exactly rocket science. Going fast enough sideways so you stay up there is the tricky bit.

It's NOT rocket science?

You can build a decent sounding rocket with just trial and error.
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