How do you connect a spinning centrifuge to a non-rotating central collumn?

[Kerbface]

Most centrifuge ship designs I've seen have the centrifuge spinning distinctly from the core ship. Now it's easy enough to understand how to make this work in something like the Discovery where the entire centrifuge is contained within the pressurised section of the ship, but what about when it's spinning in the open vaccuum? How do you possibly seal it without causing loads of or even unsurmountable friction? A centrifuge would need to have minimal friction so that power could be used at a slower rate than it was regenerated or at least enough for a full mission.

[Canopus]

I think this would be possible by using something that is called "slip ring". Going to do some research on it now.

[Nibb31]

It is indeed a complex problem. You want it to be reliable, low friction, and airtight. Any lubricants and seals need to be vacuum-rated while maintaining friction properties. You also want a way to transfer fluids, comms, and power through that rotating connection. Because the vessel is pressurized, if your rotating joint leaks or any of those fluid connectors fail, then lives are actually at risk, and there is no taking it apart or replacing the joint in EVA like on the ISS solar panels.

It's not impossible, but it's very very difficult engineering challenge and probably not worth the extra cost. It would be much easier to rotate the entire ship.

[Thaniel]

Rotating joints are being used industrialy today. And they can be made relatively leak-free. But not completely. While something may be constructed that is usefull, I'd say that the most practical sollution would be to either spin the whole ship as Nibb31 sugests, or have the rotating part be mostly self-contained. In short, it may be harder to think small and minimalistic rather than go for a whole ring with all lifesupport and supplies contained within.

[Canopus]

I recommend to read this site:http://www.projectrho.com/public_html/rocket/artificialgrav.php It has great information on the different methods to create artificial gravity.

[Kerbface]

Yeah, I agree rotating the entire ship would probably be more practical. I've heard that a fully rotating ship would be difficult to turn but even if you've got the ship stationary while the habitat spins, I think the gyroscopic effect would make changing orientation difficult so you'd probably have to stop the centrifuge regardless.

Still, I can think of situations, like a station that requires use of both gravity and microgravity areas and needs stationary sections if it needs to dock several craft (if it's one or two at a time, spinning the ships at the centre like in 2001 would be okay) would really benefit from the partially rotating ship idea.

[K^2]

There are ionic liquid lubricants that can form an almost perfect air seal, hardly evaporate even in vacuum, and allow for very low friction. Of course, the joints have to be built to within a few microns for this to be effective. So while the solution is conceptually simple, it is extremely expensive.

[Nibb31]

I can't think of a situation where microgravity would be desireable while the vibrations and countereffects of a rotating section would be acceptable. One of the reasons the CAM module was cancelled on the ISS was because the vibrations that it would generate would have disturbed many of the microgravity experiments in other modules.

As for turning the ship, this wouldn't be a frequent occurence on interplanetary flights. You'd have to figure out if the fuel spent to stop and restart the gravity rotation would outweigh the extra fuel spent to counteract the gyroscopic effect of the spinning ship. It might not be worth it for small trajectory changes but only for larger turns.

[Kerbface]

As for turning the ship, this wouldn't be a frequent occurence on interplanetary flights. You'd have to figure out if the fuel spent to stop and restart the gravity rotation would outweigh the extra fuel spent to counteract the gyroscopic effect of the spinning ship. It might not be worth it for small trajectory changes but only for larger turns.

How would one turn a ship while it was rotating on a different axis? Surely that would make things a little difficult.

[Thaniel]

Maybe ferrofluids can be used in a liquid seal, held in place by magnetic fields? While that initialy could sound like it would be sensitive to power fluctuations, it could use permanent magnets.

[Flixxbeatz]

How about letting a part of the ship rotate, but the crew quarters would be inside in a chamber inside the ship but separated from the ship itself by some medium?

Like this:

                           [OUTER SPACE]
|-----------------------------------------------------------------|
|         [OUTER WALL (part of rot. assembly, rotating)]          |
|-----------------------------------------------------------------|
|                       [SEPARATION MEDIUM]                       |        
|      |---------------------------------------------------|      |
|      |   [INNER WALL (crew quarters, non-rotating)]      |      |
|      |---------------------------------------------------|      |
|      |                                                   |      |
|      |                                                   |      |
|      |                                                   |      |
|==TO==|                                                   |==TO==|
|======|                 [Crew Quarters]                   |======|
|=SHIP=|                                                   |=SHIP=|
|      |                                                   |      |
|      |                                                   |      |
|      |                                                   |      |
|      |---------------------------------------------------|      |
|      |   [INNER WALL (crew quarters, non-rotating)]      |      |
|      |---------------------------------------------------|      |
|                        [SEPARATION MEDIUM]                      |
|-----------------------------------------------------------------|
|        [OUTER WALL (part of rot. assembly, rotating)]           |
|-----------------------------------------------------------------|
                            [OUTER SPACE]

The only question here would be entry and exit points. If the medium is made of some fluid, exit and entry points should be at some point of the ship, far from the rotational assembly.

[Nibb31]

How would one turn a ship while it was rotating on a different axis? Surely that would make things a little difficult.

What's wrong with RCS? If the ship is spinning, you just have to vary the thrust of each RCS pod in order to maintain a constant thrust vector, but that's far from impossible if it's computer-controlled.

Also, this:

[Tommygun]

This discussion made me think of the seals used in Newt suits.

They maintain an airtight seal and allow full rotation on one or more axis.

Something along this line might do it. You could have just the airlock and a transitioning room that doesn't spin connected to the rest of the ship or have almost two separate ships connected together.

One part is all space flight and the other half living and science etc. I guess the problems with vibrations and micro gravity would depend if you are using the craft for transportation or as a station.

For a transportation vehicle, I don't think you would be doing sensitive experiments.

http://en.wikipedia.org/wiki/Newtsuit

[Kerbface]

What's wrong with RCS? If the ship is spinning, you just have to vary the thrust of each RCS pod in order to maintain a constant thrust vector, but that's far from impossible if it's computer-controlled.

Also, this:

I thought monopropellant would probably do fine if the vector was continually altered, but since I wasn't an engineer I thought I'd ask anyway.

[nyrath]

I've heard that a fully rotating ship would be difficult to turn but even if you've got the ship stationary while the habitat spins, I think the gyroscopic effect would make changing orientation difficult so you'd probably have to stop the centrifuge regardless.

Well, actually that turns out not to be the case.

http://www.projectrho.com/public_html/rocket/artificialgrav.php#id--Tumbling_Pigeons

Now, one would think that such a centrifuge would act as a titanic gyroscope, doing its best to prevent the ship from changing its orientation. Aerospace Engineer Bill Kuelbs Jr points out that if the centrifuge is a sufficiently large percentage of the ship's total mass, it will not prevent turning. What it will do is alter the axis of any turning force by ninety degrees. Rev up a toy gyroscope and try to turn it to see what I mean.

The solution is fairly simple. The turning thrusters will have to be effectively at ninety degrees to where you'd expect. In reality, this means that when the centrifuge is spinning, the "pitch the nose downward" control button will actually fire the "yaw to the left" thruster. An alternative solutions is to have two centrifuges that are spinning in opposite directions.

[Rune]

Forgetting for a second why you would want to do something like this, I'd say the easiest way would be to not need a seal at all. Use airlocks and "elevator cars" to move people around the joint, and maintain only mechanical connections to transfer loads. Even if both sides need independent life support as a result, that can be sen as a nice redundancy.

Rune. "Elevator cars": Basically, you get into a room, it unhooks, starts spinning, hooks, and you step out after getting your directions back.

[tomf]

The quote on the website about doing free-fall experiments on a cat has made my day.

[Kerbface]

Forgetting for a second why you would want to do something like this, I'd say the easiest way would be to not need a seal at all. Use airlocks and "elevator cars" to move people around the joint, and maintain only mechanical connections to transfer loads. Even if both sides need independent life support as a result, that can be sen as a nice redundancy.

Rune. "Elevator cars": Basically, you get into a room, it unhooks, starts spinning, hooks, and you step out after getting your directions back.

Interesting, but I'm a little unclear on exactly how this works, if it's not too much trouble could you sketch out a diagram on paint or something?

[Technical Ben]

Kerb, the rotating parts rotate normally on mechanical spindles. Each rotating section is self sealed. To get in or out you fly a little docking craft into it. So treat each rotating section as a separate ship entirely. Only they are connected, but as they are self sealed, you can stick the rotating joint on the outside.

[Kerbface]

Kerb, the rotating parts rotate normally on mechanical spindles. Each rotating section is self sealed. To get in or out you fly a little docking craft into it. So treat each rotating section as a separate ship entirely. Only they are connected, but as they are self sealed, you can stick the rotating joint on the outside.

Wait, I think I got it clearer now, so on the non-rotating section there is an unpressurised area which contains a pressurised container only attatched to it by some sort of docking system. Then on the other side of the unpressurized area there is the part that connects to the rotating habitat, unsealed also. When you want to move from the non-rotating part to the centrifuge, you enter the pressurised container through the docking port and the container will undock. It will then rotate to the same rate as the centrifuge while remaining within the constraints of the unpressurised area and then move slightly to dock with the centrifuge on the other side.

Do I have it right? Seems like it would work fine even if it would make moving between the two locations a little slow, but people doing so would probably need to take some time to adjust their heads to the rotation anyway.

[Rune]

Wait, I think I got it clearer now, so on the non-rotating section there is an unpressurised area which contains a pressurised container only attatched to it by some sort of docking system. Then on the other side of the unpressurized area there is the part that connects to the rotating habitat, unsealed also. When you want to move from the non-rotating part to the centrifuge, you enter the pressurised container through the docking port and the container will undock. It will then rotate to the same rate as the centrifuge while remaining within the constraints of the unpressurised area and then move slightly to dock with the centrifuge on the other side.

Do I have it right? Seems like it would work fine even if it would make moving between the two locations a little slow, but people doing so would probably need to take some time to adjust their heads to the rotation anyway.

Exactly. And if you do this at the center of rotation, the relative speed is minimal. The room itself is a nice place to get your bearings and can work double-duty as an airlock. It is bound to have maintenance benefits, at the very least.

Rune. Now we could get into "why would you want hab space in a non-rotating section" part.

[Technical Ben]

I loved the "tumbling pigeon" idea in the link on Atomic Rockets dot com. The ship design I made in sketchup uses just about ever possible artificial gravity going. It would end up having a use in almost ever orientation. Both acceleration created g, rotational g, auto-rotating pod, "tumbling pigeon", landing on a gravitational body, and some magnetic fields to apply needed forces just to keep the crew from floating away during a free fall orbit.

[Thaniel]

Exactly. And if you do this at the center of rotation, the relative speed is minimal. The room itself is a nice place to get your bearings and can work double-duty as an airlock. It is bound to have maintenance benefits, at the very least.

The "elevator" could be permanently connected to the rotating part of the vehicle at the center of rotation with a hydraulic arm. It would also include a motorized rotating joint wich would be used to spin/despin the room, and move it for docking with the ring. The motion won't need to be more than a few cm. enough to clear any docking mechanism. But since this will be in a controlled environment, the need for guiding mechanisms can be kept to a bare minimum. It could also be two separate rooms in paralel, for redundancy if there is a leak in one of them. It could also contain tanks for transfering supplies on an automatic level.

actualy, there is a lot of possibilities with this sollution, even safety, redundancy and automation can be catered for, along with serviceability. It depends on space alowances and needs.

[Lazurkri]

Exactly. And if you do this at the center of rotation, the relative speed is minimal. The room itself is a nice place to get your bearings and can work double-duty as an airlock. It is bound to have maintenance benefits, at the very least.

Rune. Now we could get into "why would you want hab space in a non-rotating section" part.

Your system lines up nearly perfectly with Mechwarrior "Gravity Decks" where they have spinning decks inside larger ships and stations to simulate gravity while the rest of the station/ship stays in Zero-G.

[Rune]

Well, the thing about good engineering is, any decent engineers will come up to similar solutions to the same set problem. There is such a thing as "the right way" to solve a problem (or at least a couple of decent ones). Must be this one is sensible if you guys agree on its possibilities. I doubt I can take credit for it, though, It is likely I have already read about/seen something similar before.

Rune. Of course, we need a thorough engineering analysis to examine it further... but it's funnier to conceptualize concepts than to analyze them.