Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Space Elevator

neal.fun

Post reply on HN
Print view View original

231–240 of 414 posts

Re: Space Elevator

#231

Post by seer »

adwn wrote: post #46
tempestn wrote: post #8

TIL it's estimated that over 48 tons of meteors hit the atmosphere every day. Regarding actual space elevators though, while they're not sci-fi to the extent of something like FTL travel - ie. they're technically not physically impossible - they're still pretty firmly in the realm of sci-fi. We don't have anything close to a cable that could sustain its own weight, let alone that of whatever is being elevated. Plus,…

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 comfortable.

Re: Space Elevator

#232

Post by GMoromisato »

I love this page and I donated, but I was (naively) expecting it to get to geosynchronous altitude, which is the actual top of a space elevator.

Of course, that would require a page 420 times longer, and I don't know if a browser would even support it.

Re: Space Elevator

#233

Post by ben_w »

seanc wrote: post #150
isgb wrote: post #133

> Space elevators are actually a possible idea being considered by scientists. > The hard part is making a strong enough cable. And finding enough elevator music... Most engineers would bring up a lot more issues than just finding a strong cable. Also, most attempts with e.g. carbon nanotubes have been abandoned ages ago https://www.newscientist.com/article/2093356-carbon-nanotube... . - We don't have a good ascent m…

Kim Stanley Robinson's description of a Martian space elevator falling and wrapping twice around the entire planet convinced me that they aren't a good idea. https://www.kimstanleyrobinson.info/content/clarke

In adition to being fictional, what would happen on Mars does not reflect what would happen on Earth as the Martian atmosphere is so much thinner than ours.

Re: Space Elevator

#234

Post by Sohcahtoa82 »

cl0ckt0wer wrote: post #169

I watch AC's video on this, it was quite entertaining: https://www.youtube.com/watch?v=Z5aHMB4Tje4 If you like factory games and space elevators, then try Satisfactory!

I really wanted to enjoy Satisfactory, but I really struggled with building a factory in first person perspective.

Factorio, Dyson Sphere Program, Captain of Industry...loved them all. Satisfactory? Just wasn't for me.

Re: Space Elevator

#236

Post by notahacker »

bisby wrote: post #209
gizmo686 wrote: post #180

Earlier quoted context omitted.

Isn't the entire point of the space elevator to be the ascent/descent mechanism? Once you have the cable up, you can grab onto it and pull yourself up.

A space elevator doesnt just take you to the karman line (like in the OP website), to get to orbit, you'd need to get up to geostationary height. That's 22,000 miles. What's the best way to pull yourself directly vertical along a cable for 22,000 miles? What's the best way to descend 22,000 miles quickly, but also with a braking mechanism that isn't going to require a heat shield? Some sort of slow cable car going at…

Unless we're using it for humans the transit time isn't that big a deal; "last mile" orbital transfer times are often measured in days anyway.

That "last mile" bit is going to entail independent propulsion anyway. Getting to the altitude if the ISS is a mere 10 hour trip at a sedately 40kph which isn't unpleasant even for humans, but the ISS orbits at nearly 29000kph (as will you if you let go of the space elevator at that altitude) and the velocities are only half as scary at the far end, so your rendezvous anywhere other than one specific point in geo is going to be complicated. But you've saved the fuel costs of escaping the earth's atmosphere that's rather significantly more than the fuel costs of other bits of your satellite mission, including reentry. (At least until the costs of building and maintaining and protecting the elevator are factored in, but who knows what unobtanium costs?)

Re: Space Elevator

#237

Post by mikkupikku »

> On June 21, 1972, Jean Boulet of France piloted an Aérospatiale SA 315B Lama helicopter to an absolute altitude record of 12.440 kilometres (40,814 ft).[68] At that extreme altitude, the engine flamed out and Boulet had to land the helicopter by breaking another record: the longest successful autorotation in history.[69]

I just had to look that up. Absolutely incredible.

Re: Space Elevator

#238

Post by ben_w »

SSLy wrote: post #156
kubanczyk wrote: post #151

Earlier quoted context omitted.

This presents a considerable risk of splitting English into several languages, none of them intelligible with the others.

have you ever been to Newcastle?

Aye man, wey aye, went doon there worra bairn, didn’t ah? Cannae remember much like, was only a wee nipper at the time, knaa what ah mean? Me mam an’ da took us doon the Toon when ah was nowt but a little’un, like. Divvent really remember owt aboot it proper, but aye, been the once when ah was just a littl’ bairn, me. Proper yonks ago that was, pet!

(Translation: yes, once as a kid).

Re: Space Elevator

#239

Post by literalAardvark »

aDyslecticCrow wrote: post #166
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.

> 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.

Re: Space Elevator

#240

Post by advisedwang »

aDyslecticCrow wrote: post #166
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.

> 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…

Energy for 1kg to reach LEO (800km * 1kg * 9.8m/s2) ~ 8MJ

Energy to reach LEO velocity ~ (1/2 * 1kg * (8km/s)^2) ~ 32MJ

Post reply on HN