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Space Elevator

neal.fun

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Re: Space Elevator

#191

Post by avmich »

JPLeRouzic wrote: post #7
avmich wrote: post #5

I don't understand why so many seemingly educated people keep discussing Earth space elevator. For a long time there is a conclusion that the elevator is incompatible with Earth satellites, which mostly fly below GEO, and elevator will collide with satellites, with all negative consequences. The inherent elevator problem has nothing to do with the material of the cable. Am I missing something?

Maybe because it's an old idea, from a time when non-GEO satellites were rare? (when I was a kid in the 60s/70s, the cool thing was geostationary satellites)

GEO is harder to achieve than LEO. There was never time when non-GEO satellites didn't outnumber GEO ones.

Re: Space Elevator

#192

Post by avmich »

sebzim4500 wrote: post #11
avmich wrote: post #5

I don't understand why so many seemingly educated people keep discussing Earth space elevator. For a long time there is a conclusion that the elevator is incompatible with Earth satellites, which mostly fly below GEO, and elevator will collide with satellites, with all negative consequences. The inherent elevator problem has nothing to do with the material of the cable. Am I missing something?

As satellite density increases every satellite will need a collision avoidance system anyway. And getting from geo to leo is way less difficult than launching to leo from the ground.

It's not clear. Maybe satellites will be assigned flypaths, like in aviation? Or you can have either a short-lived satellite, a GEO sat, a well-maintained constellation for communications or observations, singular exceptions like Hubble - or go fly away from Earth? Or something else? Not sure it's good idea for space elevator engineers to trust as much that all satellites will always behave as they, space elevator engineers, absolutely require. The error cost is pretty high.

Re: Space Elevator

#193

Post by midoridensha »

davidhyde wrote: post #2

At 74km/h you would reach space (100km karman line) in an hour and a half but you would need to keep going for another 20 days at that speed reach geostationary orbit in order to not fall back to earth when you exit the space elevator.

The other problem people seem to forget is radiation. The Van Allen belts expose people to a lot of radiation; normally it's not a problem, because either people stay under the belts (as in stations like the ISS which are at LEO), or for the few times humans went beyond LEO, to the Moon, they blasted through the belts very quickly and thus had negligible cumulative radiation exposure. But if you're sitting on a space elevator taking days to go through the VA belts, you'll probably get a fatal dose.

Wikipedia has an article that touches on this here: https://en.wikipedia.org/wiki/Space_elevator_safety

Re: Space Elevator

#194

Post by midoridensha »

Balero wrote: post #48
hammyhavoc wrote: post #41

Earlier quoted context omitted.

And so what about the downsides? The ultimate target for terrorists. If that comes down and it wraps itself around the Earth, it'll be devastating.

The structure wouldn't be able to passively stay together. If it was to be destroyed then it would burn up in the atmosphere like anything else. It is not made of a magic non-existent material that is infinitely strong. Of course if you had a massive dense asteroid attached that would not, so it makes sense to be careful with what is around it. But the orbital ring itself would break up and be no more dangerous than…

>I doubt, for example, that the new-IRA would get a united Ireland by destroying orbital infrastructure.

The most effective way for the new-IRA to unite Ireland would be to help the UK keep shooting itself in the foot, so that the Northern Ireland citizens get sick of regular Ireland being better off economically, and vote to join it.

Re: Space Elevator

#196

Post by runlevel1 »

Time of useful consciousness would be another interesting number to add. Here's a table of average times published by the FAA for a gradual ascent:

- 18,000 ft; 5,500 m: 20-30 min

- 22,000 ft; 6,700 m: 10 min

- 25,000 ft; 7,600 m: 3-5 min

- 28,000 ft; 8,550 m: 2.5-3 min

- 30,000 ft; 9,150 m: 1-2 min

- 35,000 ft; 10,650 m: 30-60 sec

- 40,000 ft; 12,200 m: 15-20 sec

- 43,000 ft; 13,100 m: 9-12 sec

- 50,000 ft; 15,250 m: 8-10 sec

Here's a demonstration of the effects of hypoxia and time of useful consciousness done in a hyperbaric chamber by SmarterEveryDay: https://www.youtube.com/watch?v=kUfF2MTnqAw

[1]: https://en.wikipedia.org/wiki/Time_of_useful_consciousness

Re: Space Elevator

#197

Post by ilikehurdles »

ilikehurdles wrote: post #176

I don't usually complete these little "fun internet" experiments but I thoroughly enjoyed this journey from start to end, and learned a bit on the way. My mind was blown a few times checking on the scrollbar thinking it's always over only to see we've barely just begun. Excellent.

Correction: almost* not always.

Re: Space Elevator

#199

Post by midoridensha »

once_inc wrote: post #43
virtualritz wrote: post #35

This is great. I just wish there was one way to switch all units. The temp. can be switched between F/C by tapping on it. The height is metric and seems fixed and then stuff in text bubbles is again imperial (e.g. mph instead of kph).

That is mostly because the international space community works with metric, so the Karman line is at 100km above earth, and converting to imperial units would be forced. Remember, there are only three countries that use imperial units; two third-world counties, and a global superpower.

The US doesn't use imperial units: it uses "US customary" units. Some of them are the same, but others are not. For instance, a gallon in the UK is very different from a gallon in the US, which causes miles-per-gallon ratings to be quite different between the two countries. The UK's gallon is properly called an "imperial unit" since the British actually had an Empire; the US did not.

Re: Space Elevator

#200

Post by robocat »

ta1243 wrote: post #76
hammyhavoc wrote: post #50

Earlier quoted context omitted.

I'm more concerned about what's already within our atmosphere and isn't going to burn up. That's a lot of kinetic energy, and nobody says it's going to destroy the Earth, I said it would be devastating. You're forgetting religious extremists and countless suicide bombers.

It would be cheaper to drop an equivalent massed object out of a plane. Or just use the plane as the weapon. You break a space elevator at the ground, it floats upwards. You break it at 30,000 foot then everything above the break floats away upwards, everything below "crashes" down, at a relatively low terminal velocity and thus with pretty low amounts of energy. An elevator isn't a tower, it's a rope handing from a…

> "crashes" down, at a relatively low terminal velocity

I would like to see an analysis. 100’s of tons of string falling and accelerating the surrounding sheath of air (acts absolutely nothing like a meteorite). A good physics question!

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