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Space Elevator

neal.fun

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Re: Space Elevator

#261

Post by CobrastanJorji »

Retric wrote: post #246
block_dagger wrote: post #243

Earlier quoted context omitted.

It's NOT rocket science?

You can reach space using air breathing jets. You can’t stay in space using air breathing jets.

I don't think there are any physics reasons why it'd be impossible, but certainly we can't do it with existing technology. You'd need an air breathing jet that could get a vehicle to go about five or six times faster than any current such engine has ever achieved (i.e. around mach 20-30), which is perhaps ridiculous, but I don't think it's necessarily impossible, just something we don't know how to do. There have been some (failed) efforts to get there, like the X-30.

Re: Space Elevator

#263

Post by actionfromafar »

pfdietz wrote: post #186
actionfromafar wrote: post #119

Earlier quoted context omitted.

Why is the water bad?

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?

Re: Space Elevator

#264

Post by rich_sasha »

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…

Likewise, it is crazy to me when I realised how thin our oceans are. I used to think of them as super deep (I mean, they are) but even the Mariana trench is a mere 0.2% of the Earth's radius. Average ocean depth is more like 0.05%.

Re: Space Elevator

#265

Post by BobaFloutist »

literalAardvark wrote: post #239
aDyslecticCrow wrote: post #166

Earlier quoted context omitted.

> Going fast enough sideways so you stay up there is the tricky bit. nah, thats the simple part. getting up there efficiently is the difficulty. once we're up, its just a matter of force over time to create a nice orbit. The faster you go, the more friction you face, and the more heat and vibration your equipment must endure. Going slower reduce friction and stress but use more energy just negating gravity. Slow rock…

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?

Re: Space Elevator

#266

Post by BobaFloutist »

raducu wrote: post #194
Pxtl wrote: post #176

Earlier quoted context omitted.

Which is another part of why a space elevator is nifty - by definition it extends out to a distance where you are going fast-enough-sideways. Now, I have no idea how practical it is to build one (Angela Collier has a video saying it's kinda ridiculous), but it's a cool idea. https://www.youtube.com/watch?v=Z5aHMB4Tje4 Also since rockets have moved away from hydrolox, it would be nice to have a greener launching syste…

> 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?

Re: Space Elevator

#267

Post by rsynnott »

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 isn't even necessarily _that_ hard to go up. It's just hard to go up _and reach orbital velocity_.

Re: Space Elevator

#268

Post by gambiting »

tsimionescu wrote: post #163
kqr wrote: post #138

Earlier quoted context omitted.

At first I was confused by this because the Kármán line is less than a percent of Earth's circumference up, but then I realised we're probably talking a geostationary anchor or something, which is very nearly a circumference up.

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?

Re: Space Elevator

#269

Post by estimator7292 »

CobrastanJorji wrote: post #261
Retric wrote: post #246

Earlier quoted context omitted.

You can reach space using air breathing jets. You can’t stay in space using air breathing jets.

I don't think there are any physics reasons why it'd be impossible, but certainly we can't do it with existing technology. You'd need an air breathing jet that could get a vehicle to go about five or six times faster than any current such engine has ever achieved (i.e. around mach 20-30), which is perhaps ridiculous, but I don't think it's necessarily impossible, just something we don't know how to do. There have bee…

Can an air breathing jet actually attain those velocities? I thought most supersonic aircraft use rockets after a certain point

Re: Space Elevator

#270

Post by tsimionescu »

icetank wrote: post #77
tsimionescu wrote: post #58

Earlier quoted context omitted.

While a space elevator doesn't contradict any fundamental limits of physics, that doesn't mean it's actually possible to build one. There is no reason to be certain that it's actually possible to create a material that has the required characteristics in terms of tensile strength to support it's own weight, plus the weight of the elevator, plus the weight of all the additional cabling. It also has to endure the huge…

The issue of the line falling back to earth is solved by putting the base of the elevator on water. If the top part of the elevator was cut of you could even detonate charges along the line to make sure all pieces fall into water.

I don't understand why you think that where you put the base of a 35000km cable makes a difference for where the rest of it would fall. I also don't understand why you think that a 35000 km long cable falling in the ocean from space would cause any less damage to the planet than it falling down on solid ground, or at least why the difference would be significant.
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