Science fiction spacecraft sometimes have a section that spins to provide "artificial gravity" through centrifugal forces. I'm thinking in particular of the Discovery spacecraft from the 1968 Stanley Kubrick film 2001: A Space Odyssey.

Discovery One from the 1968 Stanley Kubrick film "2001: A Space Odyssey"

Most of the spacecraft is inertially fixed ("despun"), the exception being a rotating ring in the spherical bow section.

I can see how one could get power and electrical signals from the spun to despun sections, and the design put RF communications on the despun section. But how do you cool that spinning ring? The ISS does it with circulating fluids like water and ammonia and dumps the heat through gimbaled radiators. If there is a way to get coolants and other liquids across a rotating joint, especially one moving around and around at good clip, I'm not aware of it.

I know there are other ways of providing g-forces for long duration spaceflight, like having two sections connected by a tether and having them spin around each other. My question is whether a design like Discovery (or Wehner von Braun's spinning space stations) would really work.

Thanks in advance.

  • $\begingroup$ It would work. The question is what you want it for. If you want to provide gravity to ensure medial safety and bone density: a small centrifuge to work, eat, and sleep in, within a slightly larger ISS-style module would work fine. If you want it to provide continuous and absolute gravity to all occupants, like in a cylinder station or generation ship (like the LDSS Nauvoo): it's a stretch of current technology, given that a large radius may be required. I haven't done this as an answer, pending addition of supporting info $\endgroup$ Commented Oct 27, 2023 at 5:18
  • $\begingroup$ My first reaction is simply NOT to carry anything non-electrical between the sections. Carrying main power over on slip-rings is probably a good idea, but I think it would probably be advantageous to have independant life-support etc in each module. $\endgroup$
    – MikeB
    Commented Oct 27, 2023 at 11:16
  • $\begingroup$ It can all be managed, but its a lot more complicated than it might at first appear. Off center spinning objects in 0g especially with moving masses inside (people and stuff) do odd things: youtu.be/1n-HMSCDYtM $\endgroup$
    – Slarty
    Commented Oct 27, 2023 at 15:53
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    $\begingroup$ The ISS radiators are mounted on swivel joints that can go more than one full turn, but eventually they have to unwrap the internal hoses. $\endgroup$ Commented Oct 29, 2023 at 0:29
  • $\begingroup$ I've thought about this design problem a few times in the last year since reading The Expanse books (twice). One problem with a rotating habitation section and a fixed section is moving cargo, equipment, supplies or people back and forth. Everything wants to be right at the axis of rotation. The (discussed below) rotating fluid coupling needs to be at rotation axis. The least problematic passageway for people or equipment is on axis. $\endgroup$
    – BradV
    Commented Oct 29, 2023 at 20:03

3 Answers 3


Your title question is very broad, but as-written it seems restricted to "how do I plumb between two places rotating with respect to one another?"

There's a rotating house in La Mesa, CA that solves this problem. Inventor/first owner Al Johnstone has at least a couple patents on it including US703235B2 "Swivel joint apparatus and method for utility supply to a rotatable building" and Tom Scott has done a video on it. The central shaft is immobile and connects the outside utilities to cutouts. Those cutouts are sealed against the moving side of the house into annular chambers, which the moving side also taps into.

The video has wonderful illustrative graphics and Al Johnstone does a fine job explaining the apparatus in the interview. I feel more secure only reproducing the patent images here.

The rotating outer jacket:

Patent cutaway drawing for the portion of the utility supply that rotates with the house, showing the taps into the annular chambers

The inner, nonrotating service to the annular chambers: Patent cutaway drawing showing the stationary portion where pipes feed into the inner annular chambers and where the seals go

There are other conceivable schemes to move heat across a rotating boundary; presumably you could use conduction between bits of metal with suitable grease. But there's more than one reason to want to plumb across a rotating boundary anyway, and I think some version of this will be what folks would have to use to do it.

Per Woody's answer the plumbing portion of this seems to be essentially just a larger, adapted version of the "hydraulic swivel manifold." I typically avoid Youtube comments but I see commenters on the Tom Scott video also mentioned that (but not by name) and also applications in automatic transmission gearboxes. Also seems to be known as a rotary union (that has a very good cutaway depiction). I'm curious how far back the invention goes but haven't found that yet.

Spaceflight Development

It might be better to have this asked as a separate question so people could find this information more easily, but I've searched NTRS for the list of terms equivalent to rotary union from the relevant Wikipedia article and included whatever I've found that seems relevant. "Rotary coupling" and "rotary joint" are the only terms of all of them that seemed to generate relevant results.

  • "Rotary coupling" includes "NASA Tech Briefs" Rotary Coupling Extends Life Of Hose

    Conceived for use on Space Station to transfer vapors across rotary joints to directional radiators for condensation or to transfer liquids to gimballed payloads for evaporation

    Rotary Fluid Coupling. I stumbled across the actual tech brief (which is in a magazine?) somehow while looking for a different one.

    Rotary coupling for heat-transfer fluid contains four lines for vapor and four corresponding liquid-return lines

    and (I'm guessing presented during the Space Station Freedom design effort--ID is prefixed with 1986?) conference paper A steerable radiator for spacecraft application

    Future large space structures such as the Space Station will have high dissipation and long life requirements which dictate the requirements for steerable radiators. Several rotary coupling concepts were considered to accomplish heat transport across the steerable radiator system's rotating interface. Rotary fluid couplings were chosen over rotary contact couplings or flexible lines because of low temperature gradients and operational flexibility.

  • "Rotary joint" has the Tech Brief Rotary Joint for Heat Transfer

    Rotary joint exchanges heat between two heat pipes - one rotating and one stationary. ... wicks in central artery of heat pipe separate into multiple strands that lead to concentric channels on rotary interface side of stationary disk. Thin layer of liquid sodium/potassium alloy carries heat from one member of rotary joint to other. Liquid conducts heat efficiently while permitting relative motion between members. Polypropylene rings contain liquid without interfering with rotation.

So at least some actual engineering thought/work went into rotary unions for radiators on US space stations. I haven't yet tried to look into why the current ISS radiators aren't plumbed this way.

  • 2
    $\begingroup$ @Fred Do those have the revolving section plumbed, or do they revolve around the plumbed section? I don't claim to have perfect knowledge but I've found Tom Scott's research to be very high-quality, so when he's surprised that a revolving section is plumbed or that an elevator goes sideways I believe it's rare. $\endgroup$
    – Erin Anne
    Commented Oct 27, 2023 at 18:29
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    $\begingroup$ @Fred: I believe in most of them it is not the entire restaurant that is rotating but only an annular floor. Which means all the light fixtures in the ceiling and the kitchen and bathrooms in the center are fixed, so there are no connections going through the floor, electrical, fluid, or otherwise. $\endgroup$ Commented Oct 28, 2023 at 8:38
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    $\begingroup$ @uhoh I think slip-rings are either more intuitive or people are more aware of them? I certainly knew about them before I heard about the house I mention; so had Tom Scott. OP mentions "I can see how one could get power and electrical signals from the spun to despun sections" in the question. $\endgroup$
    – Erin Anne
    Commented Oct 29, 2023 at 0:54
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    $\begingroup$ The ISS uses roll-rings to transmit electrical and data connections across the rotary joints. See space.stackexchange.com/questions/55211/… $\endgroup$ Commented Oct 29, 2023 at 14:52
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    $\begingroup$ Erin Anne, thanks for the great answer. I guess there must be a way to do it if you're determined enough, although the solution was something I never encountered. BTW, I took slip rings for granted. I used to work at Hughes back in the days they were building only dual spin spacecraft. Every one of them had a Bearing and Power Transfer Assembly, or BAPTA, with plenty of slip rings to transfer power and signals across the joint (kInd of a lost art, I think). The spin rate was around 60 RPM. $\endgroup$ Commented Oct 30, 2023 at 1:10

The problem of how to transmit fluids through a swivel was solved for excavators. The hydraulic connection between the cab and the tracked base in excavators is called a hydraulic swivel manifold. These operate reliably at very high pressure.

enter image description here

enter image description here

Very good video link of operation:


Electrical power can be transmitted using a commutator, as in an electric motor


In addition to the other answers and considering some side view of the vessel like this one.

kubrick's discovery

(image source)

The rotating part is inside the spherical hull, presumably the hull is completely filled with air.

it might be possible to opt for air cooling.

There is a residual space available for that purpose, between centrifuge periphery and hull, that can be equipped with cooling fins,

These cooling fins benefit from not requiring dedicated fans, since the air is already circulating as a result of the centrifuge's rotation.

the air heated by cooling rotating equipment is the same as that occupying the rest of the sphere, and can in turn be cooled by an air conditioner placed in a separate non-rotating location.

cooling fluid could still be used in closed loop inside the spinning part, between fins and equipement to be cooled.

enter image description here

(same image edited for illustration purpose)


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