Questions on Spaceflight

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Re: Questions on Spaceflight

Postby CarrieVS » Wed May 13, 2015 1:52 pm

I'm asking this in terms of a sci-fi world I'm building, more than whether this question would even arise.

Supposing a Star-Trek-like level of space exploration/colonisation was ever to happen, obviously it would all start from space stations in orbit. But how does everything and everyone that we need get there? Are we going to need the Space Elevator, or is it feasible that we'd still be using rockets to get everything to orbit?

I ask because I'd been assuming space elevator in my invented world, but it just occurred to me that a space elevator isn't just a really tall building. No matter what you build it out of, I'm pretty sure that's not going to work. It surely needs to be hanging from something in geostationary orbit. Which unless I'm very much mistaken means it needs to be at the Equator. Which has very interesting implications for the balance of political power in this hypothetical future.
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Re: Questions on Spaceflight

Postby Matt the Czar » Wed May 13, 2015 7:50 pm

Try nuclear engines. Efficient. Strong. Scary. But most of all badass, and a staple of Heinlien. Go to the site atomic rockets for the science, and general spaceflight things in general.
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Re: Questions on Spaceflight

Postby Learned Nand » Wed May 13, 2015 8:02 pm

To be clear, Matt is talking about these engines, not nuclear powered engines that heat up hydrogen and fire it out as a reaction mass. Those are efficient, but not high thrust.

You're right that to get a lot of stuff into space would require an unconventional propulsion system, and that space elevators need to be at the equator. No existing material could make a space elevator, but carbon nanotubes may be able to, so if you have a carbon nanotube elevator that is acceptable.
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Re: Questions on Spaceflight

Postby Matt the Czar » Wed May 13, 2015 8:11 pm

Launching a small aerodynamic pod via underground nuke would work too, and life hundreds of tons. However, it would jelly any humans from the g forces.
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Re: Questions on Spaceflight

Postby CarrieVS » Wed May 13, 2015 10:12 pm

Thanks!

I think I am going to go with space elevators, just because I'm really warming to the idea of the political changes it would result in. And it just so happens that the regions with equatorial land work out very interestingly in relation to my existing ideas about the future world.

But it's good to know there's possibilities for efficient powerful rockets - I guess the elevators would be the preferred way to get to orbit, but it wouldn't have to be an emergency to justify a rocket launch.
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Re: Questions on Spaceflight

Postby Learned Nand » Thu May 14, 2015 12:25 am

Yeah, the only disadvantage of the nuclear pulse rockets is, because you're detonating tons of nuclear weapons, there will be massive radiation, and you'd need a fine control system to place the objects in a precise orbit. Currently we can't develop the rockets due to a nuclear test ban treaty.
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Re: Questions on Spaceflight

Postby CarrieVS » Thu May 14, 2015 10:33 am

Plate tectonics. F*cking plate tectonics.

How far do you think the landing/anchor point at the bottom of a space elevator can move before it's a problem?
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Re: Questions on Spaceflight

Postby Matt the Czar » Thu May 14, 2015 1:11 pm

Never. Otherwise the results would be catastrophic.
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Re: Questions on Spaceflight

Postby CarrieVS » Thu May 14, 2015 1:26 pm

Surely there has to be some tolerance? Even if the tolerance is millimetres, there has to be a certain amount of error, engineering doesn't work if there isn't.

Plates move 2-5cm a year, so we're talking decades to move one end of a 22,000 mile long cable one metre.

And I don't even know what the other end is doing - how precisely can you position an object the size of a large space station in geostationary orbit? And then there's the wind, all the way through the atmosphere...

Oh and earthquakes, there'd have to be some way of dealing with earthquakes.


Would the Earth endpoint need to be a platform on two-way rails, with some sort of dampeners for vertical movement, or would it just need to be shifted a little every few years?
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Re: Questions on Spaceflight

Postby Learned Nand » Thu May 14, 2015 8:29 pm

It's quite possible you'd have the root of the space elevator be a barge rather something fixed to the ground. In that case, plate tectonics wouldn't matter.

Carbon Nanotubes are famously stretchy, so that makes me want to say it could move a few miles, but I have absolutely no idea. The wikipedia article suggests that there could be moving anchors to avoid weather issues, among other things, so I don't think you have to worry too much about that.

You'll probably be interested in this article about space elevator safety. It talks about several challenges and some proposed solutions to those challenges.
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Terry Pratchett wrote:The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it.

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Re: Questions on Spaceflight

Postby Qinglong » Fri May 15, 2015 1:38 am

You might also be interested in The Fountains of Paradise by Arthur C. Clarke which was about the construction of a space elevator.
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