Rotating Space Stations

[J'Dona]

I'm investigating the mechanics behind rotating space stations for a science fiction piece that I'm writing, and I'm curious as to how some parts of it work and hope that maye someone here has links or an explanation of certain parts, or even just advice (like: stop writing fiction and get a real life, you nerd). I'm going to continue looking up on it after I've posted this anyway. I know a lot of people won't be interested by this or consider it irrelevant, but if people here learn something then surely that's a positive use for the forum? Nobody has to respond anyway; I'm getting ideas just from writing this. But the actual problems I have are vague and I'm really just feeling some uincertainty over the whole thing, so links would probably be the quickest and best way to sort this out.

 

I understand how the rotation of space stations can simulate gravity on a person, and I've been reading up on Coriolis forces (and this java applet has certainly helped there http://vislab.cs.wright.edu/~rbryll/CORIOLIS/Coriolis_Rob.html). But some other sources mention the need for a flywheel to conserve angular momentum, and I'm confused as to why that might be needed. I imagine this station having rotating and non rotating parts (rotating for habitation, non-rotating parts for easy cargo transfer and docking), and I don't know how a flywheel might come into this. Of course it's not necessary to have non-rotating parys, and probably easier to have the entire station rotating, and I assume that in space it would continue to rotate for ever in that case. The centre (or center...) of the station would still have almost zero gravity, which would make moving cargo easier, and not too difficult to dock with if it's not turning very quickly, though there would still be delays in cargo.

 

If this station were built some time around 2050-2075, when space planes would probably be very common and transport into space cheap, then we can assume that the station is able to be built very large with strong alloys and materials, using the rather large wealth that some countries are likely to have in the future. I know some of you (if you're read this far) are probably rolling your eyes because I'm inserting dubious clauses like that in now, citing future technology as a solutoin to my problems, but this isn't a practcal argument after all, only theoretical. With materials of a greater tensile strength and significant resources able to be cheaply put into space, this space station's radius could be large, maybe on the order of several hundred metres (or meters!). A radius of 500m would need to turn once every 44.9 seconds or so to simulate a gravity of 9.8 ms^-2. At 1000m it's still only 63.5 seconds. Incidentally a 1000m radius would give a circumferece of 6.28km, or about 3.9 miles. If the rotating section is, say 50m across (which isn't much), there would be a floor area of about a third of a km² on the bottom floor at least, which is enough to house a large population.

 

In case it is relevant, this station is supposed to be the major point of traffic between the Earth and mining colonies or cities on the Moon, and (in reference to the post about the Earth-Moon barycenter I made yesterday) would be built at the Lagrane 1 point, using thrusters to stabilise itself. Power is not a problem because at this point the Moon is being strip-mined for the helium-3 for fusion power (apparently another name for the helium-3 isotope is tralphium), and this station itself serves as the main hub of transfer of helium-3 to Earth.

 

Again, I'm sorry to post this science-fiction related... thing, but as I've mentioned before in the scifi forum thread, if I posted this on a science fiction forum I'd get a load of technobabble, and I'm looking for real science here. I feel like a fool for asking questions about such things without precise points I need answering, to sorry about that.

 

 

 

EDIT: Just so everyone knows why I posted this when I really don't have to, as such, it's because my goal over my gap year is to produce one piece of writing every day for the whole time, which will last about 15 months. Since I need to make a complete mechanical and historical description of this station by the end of the day, I made this post as a backup in case I couldn't find anything on my own. :/

[YT2095]

an idea I had some time back was to have a middle stationary peice, like you said for docking etc...

and 2 other sections either side of this, rotating in opposite directions but both at the same rate, that way you wouldn`t need to use rocket fuel to "Top up" the spin every now and then, you could use electric motors, and the center stationary part could have the solar panels angled directly at the sun and not have to move at all.

since they rotate in opposite directions there`s no need for an "anchor"

[J'Dona]

Ah, I thought for some reason that if you had two rings on the station rotating in opposite direction, that they wouldn't cancel but rather double the effect, but that was judst me not thinking it through properly. That would probably work out well, but I was just hoping for a solution that didn't split the population in two, as that would cause problems in moving people in between. Unless of course you had some system set up where... nevermind. That would take up too much power. :/

 

Another idea I had was to have the whole station rotating, including the docking "pylons" or whatever you want to call them, except for one thing. The pylon has a number of rings which can move independantly on the outside. When a ship approaches, the rings rotate so as to stop rotating relative to the ship allowing it to dock easily, whereupon the ring resumes and spins again with the ship attached, simulating some light gravity on the ship itself if it's held in the right way, though the ship or space plane would need to load/uload from the "top" for the gravity to be real, and it would be different as you moved out along the wings, so that might be difficult. Another problem with this is that as the ring rotates it makes the station rotate very slightly in the opposite direction, and when the ship docks it effectively gains msas, which affects the rotation again, so the station would be expending fuel every time something docked.

 

 

EDIT: Just found an excellent article here: http://www.permanent.com/s-centri.htm I'm only halfway through now, but it explains artificial gravity quite well, so I think I can decide on some dimensions from this, which should help in determining the shape and structure based on the resulting angular velocity.

 

 

EDIT2: One question that should really be on my Earth-Moon barycenter thread, but I don't want to bring it up again just to ask it or make a new post for it as that would be spamming: how much might the position of L1 vary with the Moon's perigee and epogee, and would a station there need to expend a prohibitive amount of fuel to remain there, or no more than if the point did not fluctuate?

[[Tycho?]]

I dont see why an flywheel device would be needed. It should work fine without one I would think.

[J'Dona]

I think the flywheel would be necessary only if you had different parts of the station rotating at different speeds, like the rings rotating around a "stationary" central shaft or some such, because otherwise friction between the different parts would mess up the angular momentum and the rotational rates. That's only if you have individual moving parts though.

 

By the way, I finished the description of the station on time but I'm not saying where I've posted it online so as not to embarrass myself. I've settled for a station with two rings which rotate together with the whole station, including the central shaft, except for two parts at the end of the shaft away from the rings which rotate against the station so that they appear relative to incoming spacecraft, allowing them to dock. In the centre of the shaft is a flywheel to keep the station's rotation constant at the rings. Maybe I didn't need two rings, but I suppose the extra shaft spcae allows more room for the flywheel and cargo, and the docking ports.

[NavajoEverclear]

hey good luck on your writing. I'm a writer too but have been dormant for some time (i'm picking up momentum recently, hopefully i can achieve something radical). I've written a few books before, but only crap that i'm not satisfied with, though some of my friends liked them. I just consider all that preperatory work, and i'm starting to gain direction again. Actually talking about it is motivating, thanks for bringing this up.

 

What's a flywheel device. One question-- how do you travel from one wheel to another (one that's moving to one that is stationary, or at a different speed). Also have you read Orson Scott Card books? I've started and am really enjoying it (the Ender and the paralel Shadow series, i haven't looked into his other serieses yet)

 

Keep writing and improving. are you published? Sounds like with all the research you've done that you have the drive to be a cool author

[J'Dona]

Thanks... it seems like there are quite a few writers on these forums. I know what you mean about "being dormant" for a while. The first major thing I wrote (a novella, and still the largest) took about two years, which just goes to illustrate what I mean by that. When you say you've written a few books though, how large are you talking about? I'm just wondering what you mean by dormant, that's all, because if they're big then it shows that you've got the discipline whilst you're writing them, which is all the matters, it's just the space in between that's a problem.

 

I think a flywheel device is basically some way of keeping the rotation of a station in space constant while things are moving on it. If you had, say, a station with one ring connected to a stationary shaft in the middle, going through the middle of the ring, you could have spacecraft docking at the middle (which isn't turning) and still have the ring rotating, simulating gravity. But if in this case, eventually friction between the two will start to turn the shaft along with he ring, and the ring's rotation will slow down. I think you can counter the slowing effect on the ring by having a flywheel on the shaft turning opposite the shaft, so that overall the same force is slowing the ring as is speeding it up, and rotation and gravity are constant. You'll have to constantly put power into the shaft and flywheel though, to overcome the frictoin and not slow down themselves, or the shaft will start rotating and make docking a problem. In the design I chose, the two rings move together and are directly linked, so they travel across on enclosed bridges of some sort (or enclosed high-speed trams, as they're 400m apart). I tried thinking of how to travel between rings at different speeds, but any solutions I could come up wit were bizarre and dangerous, so it might be more problematic than it's worth, particularly as you'd have to go through diffreent gravities to get there.

 

Thanks for the compliments though... and no, there's no way I'm published yet. You're right that everything at this stage is just preparatory work; my current goal to write at least 1000 words a day is mainly to improve my writing so that when I come to do the stories that I've wanted to do for a while now, and put a lot of thinking into, I won't mess them up. If it's all research and preparatory work, then you're improving your skills for when you write something later, and you'll do it better. Just take confidence in these words by David Gerrold: "Your first million words are for practice. They don't count. Remember that. After you've written a million words, then you can take yourself seriously." A million words is about ten novels...

 

But if you write, say, 2750 words a day, then you'll have written a million words in just one year. If that's about seven hours a day, it's about the same as people spend watching TV in the USA, or the same that people spend playing RPG's in Korea. For ten novels.