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My spaceship includes a technology that creates artificial gravity (AG). For all intents and purposes the inner workings of the device are unknown. It's essentially a black box. What is understood is that the device exponentially increases the gravitational pull of matter inside it when it is fed power. Gravity can be increased to earth gravity or near neutron star levels, which allows for warp travel. The problem is that doing that would kill everyone in the process and crush the ship into a pebble. It needs a way to be cancelled or else it won't be much use.

I checked this question and it gave me an idea. Gravity is additive and can't be negative. However if two sources pull in opposite directions it should cancel itself out. So after a bit of brainstorming a ring would be the best option. Gravity is multidirectional, so the gravity emanating from a ring would pull things outside but gravity inside the ring should be neutral.

Theoretically, would this gravity donut design work? What else (aside from how the AG works) would need to be taken into account?

Be constructive please.

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  • $\begingroup$ I'm assuming no part of the gravity-generating system is itself affected by gravity (or at least artificial gravity) - otherwise it would tear itself apart. $\endgroup$
    – DWKraus
    Commented Sep 21, 2021 at 21:36

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Gravity is additive and can't be negative. However if two sources pull in opposite directions it should cancel itself out. So after a bit of brainstorming a ring would be the best option. Gravity is multidirectional, so the gravity emanating from a ring would pull things outside but gravity inside the ring should be neutral.

In the Planiverse, you would be correct... but if your ship exists in 3 dimensions, a ring is definitely not the best option. Gravity would only cancel out exactly in the center.

If you want the gravity of the ship's material to cancel out in its interior, you need a spherical shell.

And if you want a constant gravitational field in the interior spaces which is nevertheless lower than the exterior field, you need a spherical exterior with an interior spherical habitable volume that is offset from the center of the entire ship (in which case, the interior gravity will be everywhere parallel to the offset between centers inside the habitable volume, in the direction of the thicker wall).

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  • $\begingroup$ Would an additional gravity "plate" generating 1G through the center of your sphere leave everyone in the ship at one G? (possibly with a few holes near the edge for ship systems/passage from one side to the other) $\endgroup$
    – DWKraus
    Commented Sep 21, 2021 at 21:34
  • $\begingroup$ @Logan R. Kearsley Good thing that you pointed that out. So there could be two AG rings or an AG tube around the spacecraft for other shapes than a sphere. $\endgroup$
    – LiveInAmbeR
    Commented Sep 21, 2021 at 22:40
  • $\begingroup$ @DWKraus Nope. You would need an extremely large plate (technically infinite, but very large will get you close) below the habitable volume to get a uniform field. Offset spheres are much more practical. $\endgroup$
    – Logan R. Kearsley
    Commented Sep 22, 2021 at 1:24
  • $\begingroup$ @LiveInAmbeR A tube has the same problems as a ring. People would end up pulled to the inner surface. A pair of rings produces a more complex field, depending on their relative orientation. $\endgroup$
    – Logan R. Kearsley
    Commented Sep 22, 2021 at 1:28
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I see where you are getting from, but the effect that is going to kill this solution, along with everything inside it, is "Tidal Forces".

Say a person is in the very center of the ring with gravity pulling in all directions. The head is going to be closer to one side of the ring while the feet are closer to the other side. The part of the ring close to the head pulls stronger on the head than the part of the ring opposite to the head. Same with the feet.

The net effect is that the head, arms, and legs will all be pulled in different directions, ripping you apart.

If you make the ring bigger and make sure everyone stays close to the ring's surface, then you still have the ring near you crush you to the floor with almost full force, and the other side pulling at you much more weakly.

We can have the Earth being positioned between the Sun and Jupiter, because the distance to both bodies is very large, and in comparison to that distance, the Earth is very small. And it also produces its own gravity to hold it together. On the scale of a space ship, and with the gravity of a neutron star, any atomic bonds would instantly be ripped apart.

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    $\begingroup$ @NuclearHoagie It absolutely does not work for for a uniform 2D ring. The shell theorem of inverse-square forces is only valid for 3D shells. The near field tidal effects of a 2D ring approach those of a infinite rod. $\endgroup$
    – Logan R. Kearsley
    Commented Sep 21, 2021 at 20:34
  • $\begingroup$ @LoganR.Kearsley Hm, it seems you are correct. I was misled by some other comment on this site, so I'll delete my erroneous statement to avoid propagating the error. $\endgroup$
    – Nuclear Hoagie
    Commented Sep 21, 2021 at 20:55
  • $\begingroup$ This is both right and wrong. You are experiencing tidal forces right now. However, they are very, very small. What matters is the difference in force across your body, which is inversely proportional to the size of the sphere. For a small sphere — say, 100m — you will probably have a very bad day. For a very large sphere — Earth diameter, for example — you should be fine. In either case, the volume of "reasonable gravity" is not very large, proportionately. What I don't know offhand is how much shear is "too much". $\endgroup$
    – Matthew
    Commented Sep 21, 2021 at 21:39

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