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I have a spherical spaceship that is about 2 kilometers in diameter with an outer clear, yet strong shell. This spaceship is largely made up of empty space occupied by air. Aside from this the spaceship has concentric rings that spin to produce artificial gravity on the surface of the rings. Ignoring other problems, what sort of air currents would be found inside the ship?

Edit: Also assume that most of the heat found in the ship would come from nuclear powered engines at the core of the sphere. Also the ship is largely used for scientific expeditions, with the ring surfaces being home to a living biosphere

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    $\begingroup$ Hi Thalassan! (cool username, btw) I'm having a bit of trouble understanding what exactly your question is. Are you asking about air currents within a 2km hamster ball? I think we'll need some more information about the interior of your ship (where are the engines, is it compartmentalized, is it full of air, etc.) before we can give you good answers. Can I recommend you move this question to the Sandbox, where users will help you make it on-topic and answerable? It's the perfect place for questions you're still developing. $\endgroup$
    – Dubukay
    Dec 13, 2018 at 6:54
  • $\begingroup$ Thanks Dubukay, Yes it is basically a 2Km hamster ball. The spaceship isn't really compartmentalized, its an "open-air" spaceship of sorts. Also in my edit I added the location of the ships power source to try and show where the ship's heat is coming from! $\endgroup$
    – Thalassan
    Dec 13, 2018 at 6:59
  • $\begingroup$ as always, be aware that spaceships need to shed heat, not retain it. for that, a huge sphere is the worst case. your crew will cook. $\endgroup$
    – ths
    Dec 13, 2018 at 9:46
  • $\begingroup$ thats just not true and even if it were from an engineering perspective(once you can survive having people live that close to the plant in the first place,) thermal energy is relatively easy to conduct out of an engineered system into subsystems which can in turn make use of that thermal energy to produce electrical energy. Besides which, diffusion across a large surface area/volume is exactly the simplest mechanical method of heat dispersal, having a heating/cooling/electrical/plumbing system that radiates from a central location is by far the simplest proposition. Shed heat is wasted energy. $\endgroup$
    – Giu Piete
    Dec 14, 2018 at 1:31
  • $\begingroup$ Do you mean the sphere is banded, as opposed to concentric rings, btw? $\endgroup$
    – Giu Piete
    Dec 14, 2018 at 1:49

2 Answers 2

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If we disregard the rings, it's a globe full of air at a constant pressure, with a central heat-source.

So the nearest analog is probably the convection current systems of our own planet core.

You must have seen the diagrams of them in high school. Just scale it right down in size and temperature, air moves more easily, but the temperatures are smaller, so all in all there'd be some air movement but I doubt it'd be particularly noticeable as more than a breeze as warm air reaches the skin of the globe, cools off conductively and is forced aside by more warm air moving outwards.

The real kicker will be the existence of a massive fast-spinning (Spincalc says 140mph) ring with terrain, acting like a turbine and producing a distinct air current of its own.
The Wind-shear is going to be a doozy. I wouldn't want to be flying an aircraft anywhere near the ring.

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  • $\begingroup$ Convection doesn't work in the absence of gravity. (Explanation: the force which powers the convection currents is Archimedean buoyancy. There is no buoyancy in the absence of gravity.) $\endgroup$
    – AlexP
    Dec 13, 2018 at 13:14
  • $\begingroup$ You make a fair point. in which case on balance I'd expect the temperature to be roughly speaking a gradient from hot to cold, but mostly stiflingly hot because radiative cooling from the skin of the sphere sucks. The spinning ring however would definitely set up a pretty impressive spinning current around the inside of the sphere. People on the ring might not notice once it stabilised. $\endgroup$
    – Ruadhan
    Dec 13, 2018 at 14:00
  • $\begingroup$ Surely displacement is still a thing without gravity, as all it requires is energy in a system, on earth that energy is mostly directly or indirectly provided by gravity... that doesn't mean gravity is required for either displacement or convection. That feels like a question, but I'm baffled as to how one could consider that convection is not a thing in the absence of gravity. $\endgroup$
    – Giu Piete
    Dec 14, 2018 at 1:22
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    $\begingroup$ @GiuPiete The entire EMU suit is water-cooled and heavily insulated against extremes of temperature. If I'm understanding right, it uses a water-tank in the backpack as a heat-sink. It takes a lot of work to survive in space :) Here's the wiki page $\endgroup$
    – Ruadhan
    Dec 14, 2018 at 9:55
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    $\begingroup$ Here's some more info on the life support systems in the backpack $\endgroup$
    – Ruadhan
    Dec 14, 2018 at 9:59
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For a radius of 1km you will have a tangential velocity (at the outer edge of the ship) of about 350 km/h. For comparison the Earth's tangential velocity at the equator is 1,674.4 km/h. On Earth the principal effect of this rotation is the coriolis effect, which causes polar wind currents to effectively curve in the opposite direction of the rotation of the Earth. If it weren't for this rotation, wind currents would mostly be North-South due to differences in temperature/pressure.

For your spaceship, if it is made of disconnected rings, there would be little effect - an air current would only be felt if the rotational velocity is changed. The air in the ring would reach a similar velocity as the ring itself due to friction.

If the rings are "open" to the rest of the ship then you will introduce significant wind shear - as you get closer to the surface of a rotating ring the wind current will increase up to more or less the same velocity as the ring itself (it depends on the width of the ring).

If the ship is not perfectly symmetric, there would also probably be convection currents with air being kicked up by the ring reaching the reactor at the center, heating up and being accelerated back towards the surface of the ship.

I made a shitty ms paint of what the current might look like, looking at a ring from the side. It depends a lot on the actual topology and temperature gradients, and I could be completely wrong since this is not my area of study. Depending on geometry you could also end up with a convection current that is perpendicular to the rotating ring.

enter image description here

Since the ship is relatively small, though, I would not expect air currents (as felt on the rings) to be comparable to strong winds on Earth. With only 1km in diameter your air would all be moving at similar velocities due to friction with itself. Multiple rings at different radii (concentric rings, not sure if that's what you really meant), could complicate the issue. However, if you designed the ship so that all the rings are on the same plane, your air would actually move more in unison. Of course if you stepped off the ring onto the static surface of the ship, you would feel a very strong air current in the direction of the rotation, kind of like standing right next to a bullet train as it passes at full speed.

edit: reading other comments, perhaps "convection" is a misnomer for the flow caused by differences in pressure - although there is an effective gravity in this scenario due to centripetal force, so I am not sure.

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