Spinnin' Space stations

Yes, I do know how to use Google and paper. I'm just too lazy to do it myself when I can ask a question and get someone else to do it .

The international space station cost 10 Billion for just the design, according to http://www.spaceprojects.com/iss/. The hardware cost an additional 25 Billion.

If you build a space station with artificial gravity, you don't have to have all the astronauts excercising all the time. You may want some to stay for prolonged periods in 0 g, for research purposes, but you won't have to put up treadmills.

Part of that design cost went to make the Bigelow modules you wish to use.

The reason to put people into orbit IS the Zero G. A more practical design would be a central station with 68 modules clustered, and 5 modules on the end of tethers circling the central platform. You spend your work day in Zero G, with the equipment and your free time in 1G at the end of the tethers.

The reason to put people into orbit is not to be in zero g. It is not to conduct science. It is because space is Cool, with a capital C. That's why the space program lost support after the US beat the Russians to the moon. It no longer had a meaning. No space program can support itself solely based on science. It just costs to much. Science (different science, but still science) can be done more efficiently on Earth. The only reason for Nasa's continued existance is that people think that there is something cool about space. In other words, they have an underlying reason that is mainly based on entertainment.

Most science and industry done in zero G will likely be done in un-manned, or seldom-manned stations. Having people on board adds all sorts of vibrtions that just mess up what ever you science is up to.

Okay, how about a slightly different solution. Massive weight, longish tether, habitat. The spin would be off centre due to the huge mass, meaning the arc traced by the habitat side could be much larger, and therefore better for generating the "gravity" feel.

Yeah, I know, huge mass is gonna be the issue, but think about the very soon to be retired shuttle fleet! Perhaps one of them doesn't return from it's last mission, instead becoming the basis of the counterweight.

Any thoughts?

Why use a shuttle when they keep dumping progress supply craft from the ISS in the ocean? Get a group of them bolted together for your counterweight, you could even send up a framework that used the docking mechanisms on the progresses to cluster them together and provide an anchor point for your tether.

Unfortunately for you, your system is not going to help you understand the problem and/or the solutions any better. If anything, it's going to lead you to believe you know something about the problem, when in fact you don't. That's probably worse than the position you were in before you asked the question.

For instance, if you do the math yourself, the relationship between the mass of the space station and the forces exerted on the support structures reveal themselves to be connected in a surprisingly elegant way. The exact details of that relationship depend on the configuration of the station, but you don't need to know the details.

johno

I forgot about the Progress ships. What a waste of materials to just dump them in the ocean. I've always thought it would be better to 'chute them to a ground landing, and reclaim the what material we could. What with the improved guidance we have (auto piloted parafoil sort of thing), we could perhaps aim it for a nice safe area for recovery.

Anyway, yes, those cargo pods would indeed be useful as counterweights. Shame they can't be used for anything more useful.

Hi shuki

lets do some math and see (please math gurus correct me if im wrong because this has been a long while)

f=m*g (g=9,8)
f=m*v*v/r
C=2*pi*r

so the speed (v) at witch a wheel has to travel is
m*g = m*v*v/r
g = v*v/r
v = \/(g*r)

r (m)....v (m/s)......C (m).......t (s) (round trip)
25........15,6..........157..........10,0
50........22,1..........314..........14,2
100......31,3..........628..........20,1
250......49,4..........1570.......31,7
500......70.............3141........44,9

now remember this construction has to be balanced, just like the wheel on a car otherwise it will break up in no time... this will be incredibly difficult to build

cheers,

c

cheeers

Unlike the wheel on a car, this structure would not have an axle. It will naturally rotate around it's center of gravity/ center of mass. It will, in effect be self balancing as long as there are sufficient supports connecting the mass on one side to the mass on another side.
If we are discussing a ring structure, pretty much the same criteria applies, but with an additional variable. If the spin of the ring causes it to deform slightly into an elliptical shape, the mass furthest from the center will become "heavier" causing it to deform more. This deformation is acceptable as long as it does approach the yield strength of the materials used for construction. A few steel cables strung across the center of the ring would be sufficient to prevent any deformation.

johno

If we can't have a whole station spinning away, perhaps just a small section could provide a small but comfortable area that could offer a small respite from the zero G.

I'm reminded of one of those centrifuge pods that train pilots and astronauts how to deal with high G. The balance weight is large and close to the centre, whilst the crew capsule is hanging way out there, experiencing higher G. A ladder to the centre to access the rest of the station.

Ala the condition of Discovery in the movie/book "2010"?
There's no reason it couldn't be. In fact manned Mars missions pretty much will require a spinning partial G configuration.

Do I need to drag up that if the STS had been designed with a little more forethought, all those EFTs that got tossed into the oceans could have made a nicely sized wheel space station by now....

You right about that johno. I do remember that building a rotating structure is introduces massive constructional problems. I skip the math if you don't mind .

It would be nice to calculate some basic forces that are introduced into a rotating structure and see what is needed to keep it together. This would give a much more solid foundation for a good discussion. So my proposition is we have to come up with a basic (very simple) structure and see what forces are introduced?

Anyone?

cheers,

c.

I'll bite. The simplest structure I can think of, at least in terms of calculations, is 2 equal mass pods connected by a tether, the pods rotate around each other to cause 10m/s^2 acceleration. (10m/s^2 for simplicity)
To do the calculations you'll probably need values for the mass and dimensions. Lets pick a mass of 10,000kg for each pod and 100m for the length of the tether.

<math>
At 1G, each pod will exert the same amount of force on the tether as it would if it were suspended from a tether on the surface of Earth. Now, picture 2 pulley wheels on a crane-like structure, with the the tether cable running through the pulleys and a pod suspended from each end of the cable. This is a simplified model of the stress that would be experienced by the structure if it was rotating in space. The cable only experiences 10,000kg or 100,000N of tensile stress. The tether itself will become 'lighter' as it gets closer to the center of rotation, so I'm going to leave the additional effect it has on the forces out of this simplified model. Kevlar seems to be one of the best materials for a tether because of it's high tensile strength, approx 3.6GPa. The cross-section area of the tether would have to be 100,000N/3,600,000,000Nm^2 = 0.00002778m^2 = 27.78mm^2 or about 6mm in diameter. That doesn't seem so bad.
</math>

This shows that the length of the tether doesn't matter until it starts to become long enough and massive enough to cause a significant change to the total mass of the station. So that was an unnecessary piece of information. Elegant, huh?

I know there are lots of factors that have been omitted, but can anyone spot a mistake in the above exercise.

johno