How to achieve nanometer precision in space?

Robert Warden here. I wrote the paper back in 2006. I just wanted to say how impressed I am with your reverse engineering! Your graphics and description are very well done. Back then, we didn't have easy access to 3D printers, so I built the first model out of Legos, which is still on my desk! Wishing you all the best - Bob

Wow really interesting, thanks for making this video. I had wondered how they did this! I've been thinking "how do they handle the backlash on such an actuator?" Turns out..... they LEAN INTO IT. Well done!

I'm one of 20 flight systems engineers who will be responsible for the JWST spacecraft over the life of the mission. I basically understood how this mechanism worked but seeing it in action is hugely informative. Thank you for taking the time to learn, reverse engineer, and share this with the world. This video will become a standard part of our training program.

I led the extremely talented team that developed the Telescope Elements at Ball (Primary Mirror Assemblies, Secondary Mirror Assembly and Aft Optics Subsystem). I must say the reverse engineering of Bob's actuator shown in this video is impressive. What will really blow your mind is how we designed the hexapod and other support structure to not deform the mirror surface during hexapod motion at 50 kelvin, while having the structural integrity to survive launch. Also mind bending is how we polished the mirrors at ambient after taking them cold to create a deformation map at cryo and then polishing the inverse at ambient. crazy tech. BTW, these same actuators are used for the ROC (Radius of Curvature) actuator in the center of each primary mirror segment as well as the six secondary mirror hexapod actuators. Good video.

The sophistication of the JWST mirror actuators is especially interesting to me in contrast with ours. I work on the motion control hardware and software systems for the Hobby-Eberly telescope, a 1990s telescope design with 91 hexagonal segments. While our mirror segments have a similar job to do and roughly similar levels of precision, our system is much simpler, with only three degrees of freedom -- tip, tilt, and piston (no translation or rotation, and we can't warp our ~115kg ceramic glass mirror segments). Our system has three separate actuators per segment, with a similar level of gear and lever reduction, but a very different mechanical design. I'm really impressed with the level of thought that went into the JWST actuator design, and just as amazed as anyone else at the engineering effort that has gone into building such a system that must operate for years with no maintenance.

In case you use them on things beyond demos, it's worth noting that those small steppers don't have an exact 1:64 reduction. Instead they have a multistage gear train which results in a 25792/405 ~= 63.684 gear reduction EDIT: I received a follow up question and decided to crack open one of my steppers to confirm and found that it has a different gear train than some other manufacturers! You can find reports of the 25792/405 = (31*32*26*22)/(11*10*9*9) reduction on the arduino forums. Mine contains a (32/9)*(22/11)(27/9)*(24/8) = 64:1 drive train. So it seems it can vary and you need to test which one you have, or open up the case and start counting.

When I first saw your channel, I thought it was going to be "just" another machinist channel (which is no bad thing) but your take on "engineering meets science" really does hit the spot. Keep up The Great Work.

This is the first time I see compliant mechanisms being used for their absolute full potential where no other type of system could achieve such simplicity and effectiveness. Truely an amazing design!

This was amazing to watch, you really did it justice! Dad initially made the actuator out of legos, it’s great to see the final product in space! Thanks for an enjoyable presentation!

Very slick! Being able to drive fine and coarse with a single motor like that is absolutely fantastic. I could kinda see it coming part way through when I saw both the cam and the bevels, but I couldn't figure out how the bottom didn't move all the time... that double disk is hilariously great. Question though - how does it prevent back-driving? you mentioned at the beginning wanting something that didn't need an active motor to station-keep, so I'm assuming it's possible to turn the stepper off and have it stay put., but there's no worm and wheel or anything that I would "expect" to make it one-way. does it have to do with the flexure mechanism, or just a lot of friction in the preliminary planetary?

I worked with optical engineers and scientists at Eastman Kodak. So I totally enjoyed the challenge you took up; to create a model of the JWST hexagonal mirror actuators. You really filled in the details I was wondering about. BALL Aerospace or NASA should thank you or recognize you for your effort to science/tech educate others. Awesome! Thanks very much.

I've found the exact same paper recently too, thought about replicating this too! What a great coincidence! What a great design they came up with

🎙New shop space... new acoustic problems! I was so excited to film this video that I neglected to put up acoustic treatment first. Sadly the reverb ended up being awful (no surprise, it's literally a metal-walled barn). I knocked the reverb down in post but tried to be gentle to avoid artifacts; hopefully it doesn't sound too much like a tin-can or robo-voice. I'll get some acoustic panels on the walls ASAP! Thanks for your patience! 🙏

My significant other, who normally is not at all interested in space or tech stuff, had read about the JWST in some magazine, and was for some reason blown away by the nanometer scale adjustments possible in the mirrors. I thought it was adorable =) She couldn't wrap her mind around how such a thing was possible. And neither could I (the family space nerd). So huge thank you for this enlightening video explaining one of the most remarkable details about the JWST that "no one is talking about".

Had to read through Warden's paper and it really amazes me how simple the combination of components is and what this unit is capable of.

I'm really excited about the rest of the presentation, but the first mind blowing moment was learning that Ball does aerospace engineering. I feel like I need to go learn more about that company's history now.

From mason jars to beer cans to space telescopes...its a natural business progression. 🙂 This is really a fascinating mechanism.

I was thinking about you in relation to these actuators just the other day! I was reminded of that open source microscope platform that you showed off; similar in that they both move very small amounts, i guess

Using the backlash to do the fine adjustment is pure genius. True out-of-the-box thinking. Normally when trying to achieve high precision, designers try to minimize backlash, not maximize it.

That is an absolutely INCREDIBLE solution to having coarse and fine movement with a single driver. Absolutely beautiful. Wonderful work, and even better presentation!