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Solar sails are not fast and acceleration is not going to provide meaningful simulated gravity. For a long journey, spinning a ship to provided simulated gravity can provide health benefits.

Essentially the ship and sail configuration is a large weight (ship), hanging under a parachute. Except that in this case the parachute (solar sail) is providing lift away from the sun.

Keeping the system stable will be important; to conserve expendable fuel/energy, maximize thrust from the sail, and maintain the general welfare (homeostasis) of the mission.

What configuration of ship and sail provides the most stability, where the ship is providing 1G of centrifugal force at it's outer most deck?

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  • $\begingroup$ Not exactly a parachute; if the sail is light enough, it will flex and bend, which will make the wheel lose the momentum. Frankly speaking, for the foreseeable future I can see no way of having artificial gravity on sailcraft. $\endgroup$
    – Deer Hunter
    Commented Jan 10, 2014 at 15:09
  • $\begingroup$ Is the concern changing the rotation rate or angular momentum direction of the habitat? It seems like it must be, but the wording here doesn't exactly reflect that, so maybe the OP has something else in mind? $\endgroup$
    – AlanSE
    Commented Jan 10, 2014 at 19:26
  • $\begingroup$ @AlanSE not sure I understand what you are asking. My presumption is that the sail is not spinning, that the habitat is spinning, and that some corrections to keep the sail optimally aligned for thrust must be made. Seeking the most stable configuration of habitat placement and design. Where stable is defined by little or no (unintended) motion being transmitted from the habitat to the sail. $\endgroup$
    – James Jenkins
    Commented Jan 10, 2014 at 20:17

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You have to consider instabilities caused by moving masses in your rotating structure: basically, you're better off with a torus than a cylinder, or at most a cylinder with length no more than its diameter: What stability issues plague long artificial gravity cylinders?

Also, rather than try to rotate only the vehicle, you should get the rotation up to speed before deploying the sail. Not only are the engineering requirements simpler than rotating vehicle/non-rotating sail, but also the centrifugal force working on the sail will help unfold it and maintain its shape after deployment.

Most designs for solar sails involve enormous sails, often several kilometers in diameter, so sheer forces on the fabric of any rotating sail are not trivial as one approaches the circumference. This could be mitigated by allowing the sail to rotate at a slower rate than the vehicle, and/or by employing cutouts in the sail:

star sail

Suggested reading:

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  • $\begingroup$ I did not even consider spinning the sail. But if the ship is spinning to give 1G and the sail is spinning at the same speed. Would that limit the potential size of your sail? Just imagining the forces and trying to do any kind of maintenance at the edges seems to be problematic. $\endgroup$
    – James Jenkins
    Commented Feb 16, 2014 at 0:26
  • $\begingroup$ @JamesJenkins Sails could always be designed to be retractable if maintenance at radius stretching past the centrifuge / habitat ring would be required. I'd imagine size would be limited by centrifugal force the sail and support structure could tolerate, so largely dependent on its own weight per surface area and tensile strength. $\endgroup$
    – TildalWave
    Commented Feb 16, 2014 at 1:42
  • $\begingroup$ @TildalWave concur, but you would need to add significant mass just to have the rotation speed of the sail match the rotational speed of the ship. While this is good answer (I upvoted) I don't think it is the best possible answer. $\endgroup$
    – James Jenkins
    Commented Feb 16, 2014 at 11:14
  • $\begingroup$ @JamesJenkins: I can think of two possible engineering approaches to mitigate the problem. I'll add a third paragraph to my answer. $\endgroup$
    – Jerard Puckett
    Commented Feb 16, 2014 at 15:06

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