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It's long been proposed to build rotating colonies (ring worlds) in outer space.

That concept can also be applied to surface colonies in low-g environments. (Luna is at 1/6th of Earth gravity; Mars is at 1/3.)

Conceivably, spacecraft built for long trips could rotate to provide artificial "gravity" as well. Creating a large cross-section might not be so great in light of the idea of collision with space debris, but at present I choose not to make a thorough evaluation of the practical concerns of that. Acceleration could also be produced by attaching a tether and counterweight to the habitable module. This would reduce cross-sectional area.

But, what is possible is not necessarily what is the best solution. Are rotating habitats considered the standard solution for long-term human habitations in low-g environments? If not... why not?

rotating moon habitat

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  • $\begingroup$ Related: "Why are there no spacecraft rotating for artificial gravity?" space.stackexchange.com/questions/1308/… $\endgroup$
    – DJG
    Jul 21, 2019 at 1:41
  • $\begingroup$ The ultimate solution (outside of sci-fi gravity generators) is genetically engineering people to handle low gravity better. For example, increased bone and muscle density or more hand-like feet for navigation in low-g enviorments $\endgroup$
    – Dragongeek
    Jul 21, 2019 at 10:50
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    $\begingroup$ The IDEAL solution is continuous linear 1g acceleration. But that's sci-fi, and will be for the foreseeable future. $\endgroup$
    – Chris B. Behrens
    Jul 1, 2021 at 0:50
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    $\begingroup$ They don't have to be rings; paired modules (which can be spacecraft) with tensile connectors will do and synced drives could accelerate it without having to stop the rotation. If the tensile connector is a tube it can provide access between or paired tubes allow air circulation between. $\endgroup$
    – Ken Fabian
    Jul 1, 2021 at 3:35

3 Answers 3

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The current consensus is that living in zero G long term will have side effects, possibly lethal ones.

The current known ways to not have people exposed to zero G are:

  1. Have sufficient mass there is useful amounts of gravitation attraction
  2. Thrust continuously during travel
  3. Spin things up

Option one means that large amounts of energy are required arriving and departing, and is not very portable

Option two involves drive performance well outside anything feasible in physics as currently known, and may also have civilization ending side effects if built.

Option three is therefore the only one left hence showing up in designs. Even if the health effects can be managed there are tasks and processes easier to do with a defined 'down' (like eating, washing and using a toilet) that may justify the engineering complexity listed in DJG's answer.

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"Centripetal" section of Wiki article on Artificial Gravity says:

This form of artificial gravity has additional engineering issues:

  • Kinetic energy and angular momentum: Spinning up (or down) parts or all of the habitat requires energy, while angular momentum must be conserved. This would require a propulsion system and expendable propellant, or could be achieved without expending mass, by an electric motor and a counterweight, such as a reaction wheel or possibly another living area spinning in the opposite direction.

  • Extra strength is needed in the structure to keep it from flying apart because of the rotation. However, the amount of structure needed over and above that to hold a breathable atmosphere (10 tons force per square meter at 1 atmosphere) is relatively modest for most structures.

  • If parts of the structure are intentionally not spinning, friction and similar torques will cause the rates of spin to converge (as well as causing the otherwise stationary parts to spin), requiring motors and power to be used to compensate for the losses due to friction.

  • A traversable interface between parts of the station spinning relative to each other requires large vacuum-tight axial seals.

Possible solutions first bullet: Keep it spinning. Use photon momentum to spin it up and/or down. Get energy from solar panels.

... second bullet: Build it strong

... third bullet: maintain physical separation via magnets to reduce friction to near-zero, OR completely separate the spinning part from the non-spinning part, then spin down the spinning part if/when docking is required.

... fourth bullet: See third bullet, part 2, and/or exit to other parts of the system through a tunnel which goes parallel to, and is concentric with, the axis of rotation... kind of like the hole in a toilet bowl. Use a magnetic bearing for the seam. OR, go between via spacewalk.

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    $\begingroup$ re fourth point, magnetic bearings may help for low friction physical loads but will not form an air tight seal. If you have a non rotating section with a pressurized connection there will be some form of physical contact there both generating friction and needing maintenance. Not insolvable but adding complexity. $\endgroup$
    – GremlinWranger
    Jul 21, 2019 at 0:01
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    $\begingroup$ Good answer but i feel you missed the top reason why we dont use this form of artificial gravity... gyroscopic effects on a spinning ship would make changing course (moving in a direction other than a straight line) difficult in terms of extreme stresses and addictional fuel needed. $\endgroup$
    – Jeffrey Phillips Freeman
    Jun 30, 2021 at 18:55
  • $\begingroup$ @JeffreyPhillipsFreeman That's a fair point. So it sounds like a rotating station would need to have self-defense capabilities rather than relying on maneuvering to avoid space junk. $\endgroup$
    – DJG
    Jul 4, 2021 at 21:34
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    $\begingroup$ @DJG A rotating space station would have trouble turning. If it were in orbit this is an issue since it would have to maintain an orientation with the planet, for a hip it means it cant course correct. For a station ont he planet it means added friction (as the planet turns the station will exhibit torque). $\endgroup$
    – Jeffrey Phillips Freeman
    Jul 5, 2021 at 13:50
  • $\begingroup$ Well... would it really need to maintain an orientation with the planet? $\endgroup$
    – DJG
    Jul 5, 2021 at 16:12
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Space habitats do rotate, but not for artificial gravity.

  • The ISS rotates to face the Earth. The Shuttle also did this. This means one rotation per orbit, which does not create significant artificial gravity.

  • Rotation also prevents one side from staying in the sunlight and getting too hot. Apollo rotated specifically for this reason (the "barbecue roll").

  • Solar panels need to face sunlight (although usually just the panels are rotated, not the whole spacecraft).

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