# Would a rotating habitat work on the surface of a moon?

While we hear a lot about rotating habitats as a space structure, I happen to know there are a large number of small worlds and moons out there cursed with low gravity, which has a similar effect to microgravity on the human form. So, I was wondering this: could a centrifuge work to create Earth-like “gravity” on a small low-gravity body, or would the planet’s own gravity lead to negative effects?

• You can actually try one of these on Earth, they're pretty fun: en.wikipedia.org/wiki/Gravitron en.wikipedia.org/wiki/Round_Up_(ride) en.wikipedia.org/wiki/Rotor_(ride) Dec 30, 2022 at 20:58
• Dec 30, 2022 at 21:20
• Dec 30, 2022 at 21:29
• @user3067860 is right: the Gravitron is a great local carnival ride. Worth going out of your way for. (Warning: not fun for drunk people or those who get motion-sick.)
– Tom
Dec 31, 2022 at 0:42

It depends on what you want to achieve

A centrifuge in a not-zero gravity environment would be a bit hard to use.

Since you are supposed to stay on the cilindrical wall of the centrifuge, the walls should be sloped (imagine the centrifuge having a section of an inverted trapezoid), in order to take into account the existing gravity of the planet.
The higher the gravity of the planet, the more sloped the wall (in zero gravity the walls would be vertical, which is waht you'd see in a rotating space station).

The problem is that in this setup, the exact acceleration of 1g would be possible only on a specific height of the wall: going lower (where the radius is shorter) you would feel lower centrigufal forces, so a lower gravity, while you would have the opposite effect going higher (larger radius).
Moving along this slope (perpendicular to the rotation) you would experience a strong Coriolis (lateral) force, and a rapidly varying gravity force.

If you need just a place where to have physical activity in a static spot (e.g spinning) and in a 1g environment in order to avoid the loss of muscular and bone mass, then I think it would be ok. But if you need a comfortable living place, probably you'd be out of luck

• If the average radius is large relative to the difference between upper and lower rims, the difference in centripetal acceleration would be negligible. Larger radius also reduces Coriolis effect. Dec 30, 2022 at 13:04
• To put some numbers to this, it's expected that the rotation rate would need to be once every 30 seconds at most, so 220-some meters radius for full gravity. In lunar gravity, you'd still need ~99% of full rotational gravity, and a "gravitationally level" floor would be sloped about 10 degrees with respect to the axis. A 100 m tall truncated cone that's 225 m in radius for a full gravity at the widest end would be 208 m across at the narrow end and still have about 95% effective gravity. This isn't an issue for comfort. Dec 30, 2022 at 14:29
• That's enough, however, that party balloons (helium filled, that is) will tend to cluster as the "bottom" side. They'll do this in a car going around a corner, due to the minuscule difference in air density from inside to outside. Dec 30, 2022 at 14:57
• So medically would using centrifuges as 'seeping stations' only along with regular exercise at standard lunar gravity be enough to reduce/stop losses in muscle and bone density during a prolonged stay on the moon. Staff working in shifts could spend 8 hours a 'day' in a sleeping cubicle.
– Mon
Dec 31, 2022 at 0:26

Ever seen a photo of a high-banked race track? The kind where you don't need to steer at all to make a corner, just very slightly manipulate the throttle? Or one of those "barrel of death" carnival stunts where a performer rides a motorcyle on the inside of a (fairly small) cylindrical cage?

Okay, now picture that, but with rails (several of them, for smoothness and reliability), and the habitat built on the rail carriage. You'd still need at least one radius arm going to the hub to allow loading and offloading people, equipment, and supplies at low/no velocity relative to the parent body, but this would be far easier engineering than building a whole wheel, and because the "track" is anchored to the local bedrock there's no need to balance loads across what might be a very large diameter circle (a couple kilometers, at least, to keep Coriolis-based dizziness tolerable).

Besides dizziness, larger radius also decreases the fractional change or felt "gravity" and the Coriolis effect from changing radius as you move "across" the habitat from upper to lower edges. This could be further addressed by designing the floor plans such that few if any active spaces span the whole width, and/or by limiting the width (building like a mobile home or, well, a train).

yes, if built like a centrifugal governor, 1g can be simulated on the surface of any body that has a gravity between 0 and 1g.

There could be a mast that is the main structure of the ground station, on top of it hinged beams supporting habitats. When spinning the arms will rise at an angle that keeps the "down direction" down, whatever the desired value of simulated gravity

(source)

• This answer would be improved by providing more detail about why the linked Wikipedia article supports an answer to the question. Otherwise, it risks being deleted as "link-only" because links can rot, rendering these answers useless afterward. Dec 30, 2022 at 14:44
• What's nice about this answer is it shows how an angle can be used to balance the force of planetary gravity with the centrifugal force to produce simulated gravity normal to the seat. Would be nice to see a vector diagram. Dec 31, 2022 at 21:19

Astronauts (during launch) and fighter pilots (during manoeuvres) experience forces of several times earth gravity. They train for this in centrifuges on earth. https://en.wikipedia.org/wiki/High-g_training

So yes, a centrifuge on the moon is possible, though you'd want something more space - efficent than the example in the article above. In order to have plenty of space inside, you'd probably want a train running on a circular banked track.