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JWST’s Primary Mirror has gotten the lion’s share of attention, and rightly so. But recently I’ve been trying to find out how the FSM is moved. I’ve found what appears to be photos of the FSM lab testing setup but cannot see anything of mounting or actuation. I’ve found lots of vendors and information on piezoelectric systems and voice coil systems but no direct discussion of JWST’s FSM. It would make sense to me for two of the Primary Mirror actuators to be adapted to the FSM since it seems like relatively simple 2 axis tilting is required.

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Yes, the FSM tilts on two axes, atop a rotary X-Flexure. This is moved by four custom-designed voice coil actuators, which have a force constant of about 2.2 newtons per amp. (Heat dissipation from the coils and their power cables was tricky to solve.) The actuators are part of a 30 Hz closed loop controller. This was designed by Ball Aerospace and Technologies Corp., and is described in a paywalled paper by Ostaszewski and Vermeer in Proc. SPIE 6665 (2007), Fine steering mirror for the James Webb Space Telescope.

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  • $\begingroup$ I don't have the link anywhere I can find, but I saw a couple youtube videos a while back explaining the flexure mechanism and one where someone even designed and operated a 3D printed model of it based on the best information they could find. If anyone finds those they'd be nice additions to this answer or as a separate answer. $\endgroup$ Apr 17, 2022 at 13:48
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    $\begingroup$ is it this video? youtu.be/5MxH1sfJLBQ $\endgroup$ Apr 17, 2022 at 14:08

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