Pyrian on 12/4/2016 at 04:32
When I envision a space elevator, I think of something like a tram. A full loop kept in motion, bringing things down and up. This could be powered from the ground, and does a lot of great things. But there are major problems with that idea, not least that you need like 4+ times as much cord, and the main wheel would probably have to be built into a mountain.
Most designs are more static, which lets you make it thinner in the middle, but presents an interesting problem: How do you get up and down it? Sticking a rocket on the cable car is (A) potentially dangerous to the cable and (B) makes you wonder why you even bother having a cable. There's talk of using laser propulsion, which is a great idea that may be practical someday but isn't right now, and once again makes you wonder what the cable is for. (Coming down, I suppose.) You basically cannot have a self-powered crawler - there's no way to make the math on that work. The cable's length makes running a current down it impractical, unless you can somehow get a superconductor in there, which I doubt.
demagogue on 12/4/2016 at 05:01
I think they'd have some very redundant, very fail-safe slow mechanical process that may take a week or more to raise the thing, but it addresses the practical problems... Like why bother with cords? Have regular combustion-engine wheels that slowly roll up a corkscrew track. There could be some more rapid smaller elevators in stages around the sides for personnel or emergencies or the like too. And things can be geared for going up, as I imagine to get things down it'd be easier to just get them into the upper atmosphere and parachute them off from there.
nicked on 12/4/2016 at 05:53
The other problem with space elevators is the radiation the car is exposed to during the ascent/descent. It would take about five days to get to orbit height, during which time the radiation has cooked everything to a crisp - unless you add significant levels of radiation shielding, which then increases the mass of the car, giving you further problems. You've also got the fact that to be stable, the cable needs to be much thicker and the top than at the bottom, which makes the method of moving cars up and down more limited.
I hope I see space elevators during my lifetime, but I think the apocalypse is more likely. :D
Dia on 12/4/2016 at 10:40
I thought this guy explained pretty well why space elevators aren't exactly feasible; at least, not for the foreseeable future.
(
https://youtu.be/_2M73aXuORI)
Pyrian on 12/4/2016 at 14:51
Quote Posted by demagogue
I think they'd have some very redundant, very fail-safe slow mechanical process that may take a week or more to raise the thing, but it addresses the practical problems...
Yeah, but there's no real candidate for that position, even if we could build the elevator itself.
Quote Posted by demagogue
Like why bother with cords?
We're literally talking about a giant cord, and yes, one of the major counter-arguments is why bother with it? What does it accomplish that a rocket doesn't?
Quote Posted by demagogue
Have regular combustion-engine wheels that slowly roll up a corkscrew track.
That requires fuel - literally more fuel than you can carry. You can't pump the fuel up - you'd need regular pumping stations which would in concert use up more fuel than they could provide. There's basically no way around that problem except sending rocket loads of fuel up top, which in turn would be less efficient than just using rockets to carry your payload in the first place.
Quote Posted by nicked
The other problem with space elevators is the radiation the car is exposed to during the ascent/descent.
Eh, the car can be "shielded" - in most cases all you really need to do is put your passengers inside your payload. I'm more concerned about the
cable itself.
demagogue on 12/4/2016 at 16:12
By no cord I meant not cords lifting anything, but that wasn't the sticking point about needing some massive physical structure one way or another anyway.
The fuel would be laser power.
I'm not about to presume I've thought of anything that very smart people haven't already thought a lot about and know the ins and outs of though.
Pyrian on 12/4/2016 at 17:22
Quote Posted by demagogue
By no cord I meant not cords lifting anything...
I understood perfectly well what you meant, but the counter-point remains. IMO, lift is the one useful thing the cord might theoretically do. (That's what it does in a normal tram or elevator, after all.) Take that off the table, and the cord is even more pointless. Why does a lift system need a static cord there?
Quote Posted by demagogue
The fuel would be laser power.
You cannot internally combust - your idea - a laser. You can theoretically use a ground laser to generate thrust, but once again, that technology isn't particularly dependent on the presence of the cord. Basically that version of the space elevator can be seen as dependent on a technology whose existence would most likely make it obsolete. Finally you could use a laser to generate power, but again the photovoltaics themselves generate more weight than lift. I suppose that last is at least theoretically solveable?
Quote Posted by demagogue
I'm not about to presume I've thought of anything that very smart people haven't already thought a lot about and know the ins and outs of though.
I really think that super structures just fire the imagination. People
like them, practical or not.
demagogue on 12/4/2016 at 20:55
That sounds promising and cool. We may be able to see planets outside our system in my lifetime after all.
Quote Posted by Pyrian
You cannot internally combust - your idea - a laser.
Sheesh, "fuel" metaphorically/rhetorically, in quote marks, to mirror your phrasing. Of course it's not literally the fuel, but the power supply.
Pyrian on 12/4/2016 at 21:32
When I address both what you said and the more reasonable thing you may have meant, it's too late to come back with just "that's not what I meant". It's not like I didn't foresee and address that possibility.