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Here's a good paper on the mirror actuators [1]. Skimming, they look like hexapod rotary stepper architecture that would not need power to hold a position, only to change position.

[1] https://www.esmats.eu/amspapers/pastpapers/pdfs/2006/warden....

Steppers make good sense for that application, what a beautiful design. 7 nm step size with a repeat accuracy of 1 nm is insane precision.

It is a beautiful design, isn't it?

I'll speculate that the engineers who designed this and other ground-breaking aspects of JWST feel the same euphoria that Beethoven might have felt on completing his 9th symphony.

I think beauty wears many masks, but she's in every human effort to bring something new into the world.

"Cryogenic Nano-Actuator for JWST" https://www.esmats.eu/amspapers/pastpapers/pdfs/2006/warden....

Electromagnet with a constant current running through it would do the job nicely I would think? Keep in mind that with the sun always shining where Webb is that power is not really their first constraint.