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How to achieve nanometer precision in space?

Breaking Taps4 HN recommenders · recommended in 3 months, 2022–2026
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explainer · intermediate · evergreen · 2022–2026 on HN

Breaking Taps explains how the cryogenic mirror actuators on the James Webb Space Telescope achieve nanometer precision using flexures. It shows a 3D-printed replica and how one motor handles both coarse and fine motion.

Commenters repeatedly recommend it in JWST threads as a great explanation of clever mechanical design that is accurate and long lasting.

Mechanical & precision engineeringSpace exploration & spaceflight#jwst#flexures#actuators#mechanicalengineering

6 comments from Hacker News

@infogulch2022-03 · in “First images from James Webb telescope exceed expectations”

The actuator is a genius flexure design that is both mechanically simple and accurate. Breaking Taps 3d-prints a working replica and describes the design. I highly recommend: ▶ this video The actuator breaking wasn't as concerning after seeing the design.

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@bigiain2026-01 · in “The (likely?) cheapest home-made Michelson interferometer”

I have a related question, how far are you turning the thumbscrews when making adjustments? I think M3 standard thread pitch is 0.5mm, so to a first approximation that almost 1000 wavelengths (if I have the SI units right in my head, and I'm not 3 orders of magnitude out?). I suspect the left/right and up/down adjustments have as fairly high lever ratio, but I can't imagine you could successfully adjust the in/out distance with any precision (not in the 690nm sense anyway)? Is the in/out distance not important so long as the beams are aligned? Dunno if you've seen it, but there's a great youtube video explaining how the actuators to align the James Webb mirrors work: ▶ this video including a 3D printable version of them: link "This is a replica of JWST's mirror actuators. Six of these actuators are paired into a hexapod / stewart platform arrangement and used to control 6 degrees of freedom of each mirror segment (tip, tilt, roll, x, y, z translation)."

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@mywacaday2022-04 · in “James Webb telescope's coldest instrument reaches operating temperature”

This video ▶ this video was posted here link about how the actuators work on the James Webb telescope. It's a great watch.

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@blenderdt2022-03 · in “First images from James Webb telescope exceed expectations”

Here a nice video that explains the mechanism that aligns each mirror: ▶ this video It is amazing that this is done with only a single motor. It works something like this: one direction of the motor sets which axis to align, the other direction sets the alignment of the chosen axis.

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@mywacaday2022-03 · in “Mars helicopter Ingenuity completes 22nd flight”

This video ▶ this video was posted here link about how the actuators work on the James Webb telescope. It's a great watch and shows how well thought out design can produce accurate and long lasting parts.

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