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I have seen a variety of outer space megastructures across sci-fi and the minds of most astrologists, such as Bishop Rings, O'Neill Cylinders, Bernal Spheres, and much more. What most of these interplanetary / interstellar giant space habitats have in common, other than their big size or massive need of resources to build, is that they need to continuously rotate to produce centrifugal or centripetal force, in order to give artificial gravity to the habitat inside.

However, even after looking into each page and also looking at artificial gravity, it is not clearly stated just what motor or method is used to produce this centrifugal / centripetal force. Assuming that we have all the resources we need, just what can help generate this artificial gravity needed for the space habitats?

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  • $\begingroup$ Are you asking how to start a habitat spinning (since rotational inertial will keep it spinning once it starts)? Or are you asking how the resultant forces simulate gravity for occupants inside the habitat? $\endgroup$ Commented Apr 8, 2020 at 4:34
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    $\begingroup$ Ever seen a pinwheel firework? en.wikipedia.org/wiki/Catherine_wheel_(firework) That's one way. You could also use an internal gyroscope. Seems too obvious to be a question, no? $\endgroup$
    – jamesqf
    Commented Apr 8, 2020 at 4:46
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    $\begingroup$ @CYCLOPSCORE The word "astrologist" is a synonym for astrologer .horoscopicastrologyblog.com/2014/02/10/… And I think that most designers of space habitats would be insulted to be called astrologers. $\endgroup$ Commented Apr 8, 2020 at 16:00

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Artificial gravity is produced by the rotating body, which is spinning. The centrifugal force results in the apparent gravity. What does keep the ring world spinning?

Newton's first law of motion states that any body will maintain its state of motion until an external force will perturb it.

That is, once a body it's spinning, it will keep spinning until an external force will alter this motion.

For a ring world once you make it spin, which can be be while you are building it up, it will keep spinning, lacking any substantial drag in the vacuum of space.

You might need some means of applying a torque once in a while, like artificial satellites do, and this can be achieved either with an even number of rockets adequately placed, or with reaction wheels.

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  • $\begingroup$ You could also use reaction wheels to achieve the same effect instead of just using thrusters.This would let you keep the energy. Though according to Atomic Rockets, Heinlein suggests using it for this reason but NASA always suggests thrusters. I'm not sure why. $\endgroup$ Commented Apr 8, 2020 at 5:18
  • $\begingroup$ @AdamReynolds, added. $\endgroup$
    – L.Dutch
    Commented Apr 8, 2020 at 5:34
  • $\begingroup$ @AdamReynolds The reasons are that friction between the now counter rotating wheels will eventually slow the habitat to a stop, and that reaction wheels are either heavy or very, very fast spinning. Thrusters are a one time burn and then you’ve got angular momentum forever. Other solutions like spinning up the wheels then separating them exist, but they get much more complex, and space dislikes complex. $\endgroup$
    – Joe Bloggs
    Commented Apr 8, 2020 at 12:13
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    $\begingroup$ One of my favourite solutions is spinning up two habitats while they’re fastened to each other then disconnecting them. Leads to hilarious trans-station flight plans if you want to land ‘in’ the ring. $\endgroup$
    – Joe Bloggs
    Commented Apr 8, 2020 at 12:14
  • $\begingroup$ Just have everyone inside run around the ring in the same direction like a hamster wheel. $\endgroup$
    – Pelinore
    Commented Apr 8, 2020 at 13:31
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Even if spinning, there is a likelihood after a while it will slow down, so you need a way to add energy to increase its spin

It is relatively easy to spin an object in space. There is no friction, so most of the energy that is added only needs to be added upon construction. You can do this perhaps with a temporary rocket burn to spin an O'Neill Cylinder or similar (Bishops ring) or use spacecraft to push it. Once done it would keep spinning and supply artificial gravity.

However, over time (slowly over long amounts of time) there would be events that occur both within the cylinder itself (water movement, heat and other movement) that will tend to alter this spin. Outside of the cylinder, tidal forces from nearby mass (solar, moon or planet) may interact with the components of the cylinder and slowly reduce its spin.

So, you would need to 'station keep' the spin to ensure the same artificial gravity. Only small amounts though is needed to keep it spinning. Spacecraft or small rocket burns could be used for this purpose.

Rather than keep using chemical fuel to spin, another solution is to have 2 x Cylinders, Spheres or Rings attached to each other through a common axis. So any spin control needed can be done using motors or gears as required at the connection point. This would allow a more efficient spin control without chemical rockets.

You would still need stationkeeping regardless to keep the object where you want it though, or its orientation towards the sun or certain direction, so it may not be possible to eliminate rockets altogether (or some other form of propulsion).

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A Rather Simple Approach.

  1. Construct a Toroid (a pipe wrapped in a circle)
  2. Insert battery operated scooter, could be remote controlled
  3. Start riding.
  4. As you ride, the Toroid will turn in the opposite direction.
  5. Continue until the Toroid (and all that is attached to the torid ) are moving
  6. at required velocity. Stop (this will slow it slightly).
  7. Recharge Electric scooter from solar panels.

Repeat when necessary.

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  • $\begingroup$ Step 6 will undo all steps before it. $\endgroup$
    – Zeiss Ikon
    Commented Jun 17, 2021 at 19:10

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