Comments by "dkosmari" (@dkosmari) on "Primal Space" channel.

  1. It's called Control Moment Gyroscope, and suffers from the same limitations as reaction wheels: saturation. Over time the "center" position will drift, and gravity will bleed off torque from the CMG. Eventually, the train either needs to stop, to re-center the CMG so it matches the vertical orientation of the train, or it needs manual over-corrections from the operator to use gravity to bleed torque the opposite way. Having everyone standing on one side of the train for a photo op is cool, but it doesn't tell us how long the CMG can keep compensating for that. It can't change the center of mass, it can only apply a limited amount of torque to undo gravity-induced torque.
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  2. So he used (invented?) Control Moment Gyroscopes. It sounds cool at first, but it has the same problem as reaction wheels, which is saturation. There's no way to guarantee, during a long trip, the gyros won't be saturated. You'd have to stop, supporting both sides of the train with legs, just to reset the gyros back to neutral.
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  3.  @surfcello  There's absolutely nothing in that primitive mechanical system that suggests it could de-saturate the gyros by overcompensating the tilt.
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