# How can I connect the rotating portion of my space craft to the non-rotating?

I have a large rotating (think wagonwheel) portion of a space-craft that, at the hub, connects to a non-rotating scientific research station. Imagine a football (soccer) field sized research and logistics station in microgravity, connected to a hub of a rotating space colony.

The floating scientists in the football field get to the hub, and then travel by ladder (or lift) to the spinning, near-Earth gravity colony.

My problem is connecting electricity (okay that's easy) as well as water, drainage, and sewerage from the non-rotating part to the rotating part. It needs to be one system. Has this been considered before? It's doing my head in.

• Do you remember 2001 Space Odyssey? Like that. See: Centripetal Motion - 2001 A Space Odyssey Jan 7, 2016 at 22:50
• Having water and sewage, or anything else needing "draining" is not really something I'd want in the micro-gravity portion of a station/ship. Drain pretty much implies gravity. Water and other liquids won't stay where you put them, unless sealed. Jan 7, 2016 at 22:51
• @Theraot - the scene does not address the poster's question. Jan 8, 2016 at 3:40
• Interesting. In that scene, the radius is about 2.5 humans, so roughly 5m. In order to spin such that you'd experience 1g at the bottom, which means you experience 0.8g at your waist and 0.6g at your head. If it's optimized for 1g at your waist, then it's 1.25g at your feet and 0.65g at your head. I wonder what that feels like. Jan 8, 2016 at 15:43
• Sorry @Seeds - "pumped" might be a better word? Jan 8, 2016 at 21:02

We're actually pretty good at rotary couplings like this. Consider that yee average semi truck has equipment to control the tire pressure while driving, which involves a rotating connection just like you need. It just involves a few carefully chosen bearings that can handle the continuous rotation.

• +1 for 'We already do this', but how would these bearings affect the maintenance schedule of the station? Surely they require regular refits? Jan 8, 2016 at 10:51
• Here's a crossectional view and detail on how they work. AFAICT they are pretty durable. There are also seven holes in the space station, which may also be of interest. Jan 8, 2016 at 15:46
• @Draco18s: Thanks for the info! I haven't particularly got much in the way of hydraulic engineering knowhow, I just always wonder about the longevity of rotating parts :D Jan 9, 2016 at 14:36

Have the wheel's spinning mechanism come down into the center of the station, not just rotate on the "skin". At the very middle have the pipes connecting to the station, but the end of said pipe is on "super advanced, sci fi" ball bearings. Basically, a car wheel.

The not so great part of this approach is that your station will be effectively cut in half by the wheel, and you will only be able to travel from one side to the other through whatever tunnel you build in the middle of the wheel.

It would be far easier for the systems to not be connected and simply have tanks on the wheel which are transferred to the station for processing.

why is the hub 'stationary' to the rest of the ship?being in the hub is going to be micro-gravity any way. A large enough wheel you won't notice in the center.

However, if that isn't really good enough then you can always add an 'extension' to the hub that is 'doesn't move' or more accurately moves in the opposite direction to counter acceleration, this extension could have the 'axle' like AndreiRom stated, where it is hollow for transportation and one rotates around the other.

Remember that movement is all relative in space. Anything that is accelerating is causing a 'gravity' effect. And acceleration is any change in speed AND/OR direction, which is why spinning at a constant rate is still constant acceleration.

So any time the ship changes course or speed there will be 'gravity' applied to the hub and everything inside it.

Rotary connections and slip rings are all common engineering practice on Earth. A tank uses slip rings to pass electrical energy from the generator in the hull (either powered by the main engine or an APU) to the turret, and the crew commander in the turret communicates to the driver in the hull via an intercom, who's signals are also sent through the slip ring.

Wheeled armoured fighting vehicles and many commercial heavy trucks use rotary connections from the body to the wheels in order to send air from a body mounted compressor to the tires in central regulation air pressure systems. Hydraulic systems use something similar, and I see no reason these cannot be scaled to allow electrical energy, signals, fluids or gasses to pass from rotating parts of the spacecraft to the zero gravity "hull".

Once thing to consider is dealing with fluids and gasses is actually more difficult in zero gravity than under real or simulated gravity, so any realistic spacecraft or space station with a rotating section might find it beneficial to keep the fluid and gaseous systems in the "wheel" and avoid sending them to and from the hub.