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Space Elevator

neal.fun

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Re: Space Elevator

#391

Post by philipwhiuk »

kulahan wrote: post #288
hwillis wrote: post #126

Earlier quoted context omitted.

Any discussion of aurora which do not mention space tornados: https://en.wikipedia.org/wiki/Space_tornado Is inherently incomplete. Not necessarily because they're needed to explain it, but they do need to be brought up at any time possible because they're cool.

These are cool. I wonder how much they screw with satellites etc.? How predictable are they? It seems like it's just a deadly, mostly-invisible wall of energy flying around at unbelievable speeds!

They basically only occur over the poles.

Re: Space Elevator

#392

Post by ben_w »

adwn wrote: post #275
seer wrote: post #231

Earlier quoted context omitted.

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…

A more relevant criticism of that peak velocity is that it significantly exceeds Earth escape velocity (and is 6/7ths of solar EV from here) and therefore wastes energy: https://en.wikipedia.org/wiki/Escape_velocity#List_of_escape...

Re: Space Elevator

#393

Post by Retric »

LorenPechtel wrote: post #358
Retric wrote: post #287

Earlier quoted context omitted.

Basically when you cut thrust you must pass through that altitude again or escape orbit. So either fire a rocket in space to circularize the orbit or reach more than Earth’s escape velocity 25,020 mph (11.186 km/s, 40,270 km/h) ~ Mach 32.6, due to some drag in air to thin for any kind of air breathing engine to work. X-30 was aiming far lower ~Mach 20. Nuclear could make it more realistic than any form of chemical co…

Or go high enough to let the moon alter your orbit into one that doesn't hit the atmosphere.

Yea thus ‘Basically’ you can also escape earth’s orbit slightly more easily using the sun. However, none of this really helps much you’re still looking at more than escape velocity in atmosphere with a purely air breathing engine due to drag.

Re: Space Elevator

#394

Post by LorenPechtel »

fijiaarone wrote: post #189
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,…

Have you ever tried to balance a string on its end? It gets harder, the longer the string is. There aren’t any other physics than that.

Tension, not compression. Doesn't matter how floppy it is.

Re: Space Elevator

#395

Post by LorenPechtel »

gtowey wrote: post #286
GMoromisato wrote: post #232

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.

actually geosync isn't the top. You need to extend beyond that & have a counterweight that balances the weight of everything below the point of geosynchronous orbit. Otherwise it would fall down.

Counterweight or just more cable. IIRC it's 170k (miles? kilometers?) if you use no counterweight. And note how fast that outer end is moving, it can throw things pretty hard.

Re: Space Elevator

#396

Post by LorenPechtel »

Cthulhu_ wrote: post #40
trinari wrote: post #24

Earlier quoted context omitted.

but every behaviour has a cost. In cast of flight altitude its energy and distance to food, water, mating zones.

Going up there's currents, going down... gravity. Sure it costs energy, but there's bound to be a tradeoff. Travel distance? Sight range?

It costs something metabolically to be able to survive that high up.

Re: Space Elevator

#398

Post by ajmurmann »

pavlov wrote: post #224
ajmurmann wrote: post #216

Earlier quoted context omitted.

I also found the pacing to be inconsistent at best.

The Lee Pacing is consistently great though.

Honestly the Cleons story line has been the only storyline I consistently enjoyed. All other ones suffered from both pacing and idiot plot issues at various times.

Re: Space Elevator

#399

Post by bentt »

kmacdough wrote: post #258
bentt wrote: post #172

Seems like even before we do an elevator, we should get _something_ tethered to the ground to be in space. Like... anything! That'd be a huge accomplishment.

No engineer actually thinks a space elevator is possible. It would be a silly waste of resources.

I have a feeling engineers said the same about going to the moon under Kennedy.

Re: Space Elevator

#400

Post by hinkley »

LorenPechtel wrote: post #357
hinkley wrote: post #339

Earlier quoted context omitted.

The best way I’ve seen it described is that the first 9.8 m/s² of thrust only makes you hover in place. So the more g forces you generate the higher the efficiency of the engine - as long as thrust per kg of fuel doesn’t dip too far. This all changes in outer space, where 0.01g is a valid propulsion mechanism for long duration missions.

Yup. Look at the launch trajectory of the Webb telescope. The upper stage engine was too weak for the orbital insertion and the booster had to waste energy putting it higher than need be so the upper stage engine had altitude to trade for time to keep the telescope from hitting the atmosphere. But it was the optimum solution because that engine had a long burn to take it to L2. Hauling less engine to L2 was worth mor…

God bless the Webb team but if a manager came to me to pitch a software project with as many sequential events that had to go perfect I would have told him to fuck right off. After I stopped laughing so hard I couldn’t breathe.

I made a pikachu face when they returned the first image.

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