[tzahola]

Dumb question: couldn’t a vacuum chamber and magnetic bearings overcome those issues?

[wahern]

Active Power's UPS systems do use magnetic bearings:

  Immediately after the output is transferred from bypass to
  the power stage, the flywheel field is excited which also
  provides magnetic lift to unload the flywheel bearings.

Source: http://www.activepower.com/en-US/documents/3801/wp108-operat...