7 ms·

I really and truly hope for longevity. "The Webb telescope will use 132 small motors (called actuators) to position and occasionally adjust the optics as there

by chasil 5y ago

I really and truly hope for longevity. "The Webb telescope will use 132 small motors (called actuators) to position and occasionally adjust the optics as there are few environmental disturbances of a telescope in space. Each of the 18 primary mirror segments is controlled by 6 positional actuators with a further ROC (radius of curvature) actuator at the center to adjust curvature (7 actuators per segment), for a total of 126 primary mirror actuators, and another 6 actuators for the secondary mirror, giving a total of 132. The actuators can position the mirror with 10 nanometer (10 millionths of a millimeter) accuracy. "The actuators are critical in maintaining the alignment of the telescope's mirrors, and are designed and manufactured by Ball Aerospace & Technologies. Each of the 132 actuators are driven by a single stepper motor, providing both fine and coarse adjustments. The actuators provide a coarse step size of 58 nanometers for larger adjustments, and a fine adjustment step size of 7 nanometers." https://en.m.wikipedia.org/wiki/James_Webb_Space_Telescope https://en.m.wikipedia.org/wiki/James_Webb_Space_Telescope

jcadam 5y ago
Any indication how many of those actuators they can lose and still maintain functionality (i.e., are any of those "spares")?
- chasil 5y ago
  Good question. No idea.
- skykooler 5y ago
  None of them are spares per se; if any of them fail they will have to use the other four on that segment to point it away from the sensor and disable that segment.
- oceanghost 5y ago
  3 points in a plane, so maybe half?
  - TomVDB 5y ago
    No, they require 7 axes of movement. See the video that somebody else linked to.
  - TaylorAlexander 5y ago
    The actuators control the XYZ position and the pitch, yaw, and roll, plus curvature. There is no redundancy.
- infogulch 5y ago
  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: https://youtu.be/5MxH1sfJLBQ https://youtu.be/5MxH1sfJLBQ The actuator breaking wasn't as concerning after seeing the design.
  - mywacaday 5y ago
    Thanks for that video and channel. See what you mean about simple and accurate, strongly agree with the presenter calling it genius. Can't help but feel there is a strong lesson in there for software people.
    - krisoft 5y ago
      > Can't help but feel there is a strong lesson in there for software people. Hmm, can you elaborate on that? What is the strong lesson for software people specifically? Don’t get me wrong it is a beautiful design, and I’m a big fan of flexure designes in general. There is this amazing open source project which uses similar flexure mechanisms for very accurate positioning of microscope samples: https://openflexure.org/ https://openflexure.org/ But I fail to see any obvious takeaways which would generalise to software development. Other than perhaps “Think and work on the same problem for a decade and more and you might find a compact and elegant solution.” Which is nice, when one has that luxury.
      - ChrisMarshallNY 5y ago
        We tend to make complex solutions to simple problems. The thing about any problem, is that "the devil is in the details." It may seem simple, from a high level, but, once we start to "drill down" into the issue, the "rough edges" appear. At that point, we start to break out the baling wire and bubblegum, to kludge our original "graceful" design to meet the facts on the ground. It doesn't just happen for software. Hardware suffers from the same issue, but software makes it easy to start coding before modeling the requirements and context completely. I actually leverage this, in my own work. I call it "Evolutionary Design"[0]. It's not for the faint of heart, because a big part of it is recognizing when I'm rabbitholing, and tossing out what may be weeks of code, wholesale. I'm actually going through that process right now, with the app I'm developing. I'm working on the final feature set. [0] https://littlegreenviper.com/miscellany/evolutionary-design-specification/ https://littlegreenviper.com/miscellany/evolutionary-design-... "There's always an easy solution to every human problem; Neat, plausible and wrong." "The fact that I have no remedy for all the sorrows of the world is no reason for my accepting yours. It simply supports the strong probability that yours is a fake." -- H. L. Mencken “When the map and the terrain disagree; believe the terrain.” -- Swiss Army Maxim
- dtgriscom 5y ago
  My guess: any single one of the actuators could fail, and the other actuators could compensate by moving the plane of the mirror(s). The exception would be the curvature actuators. (IANAL, or the appropriate equivalent...)
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asah 5y ago
Can someone explain why alignment can't be done in software? i.e. collect data from each mirror separately, then switch together in software ?
- geocrasher 5y ago
  Yes. It's the same reason you can't take 10 out of focus pictures of yourself and get one in focus picture. You need actual good data to combine.
  - jfengel 5y ago
    You can, with enough processing (and knowledge of how out of focus it is). It worked for Hubble. But you get more good pictures if you get it in focus in the first place.
    - Keyframe 5y ago
      Deconvolution. Haven't followed that in awhile, but getting to original function was next to impossible. Recording calibration image and/or recent AI developments might've taken that into something awesome. I'll go and catch up on material!
      - toss1 5y ago
        We really need to watch it with trusting AI. While my example here isn't photo recognition, the same principle applies. I recently sat for a deposition where the stenographer used an "AI"transcription system. The result was literally pages of errata (vs the standard errata sheet that has space for about a dozen lines). The consistent error I noticed was that the erroneous words were (probably) the word most expected in that position, and NOT the word that I said. So, at a glance, it seemed like a really good transcription. In fact, many errors were barely noticeable to me and I had to go back to the audio recording to confirm. And these were errors that substantially changed the meaning, or even inverted it. This is not merely information loss — the least surprising/lowest information item was inserted instead of the real item — this is actual information CORRUPTION. I'd fully expect parallel phenomena from image - "AI - filling in the item most expected from the training set, and actively corrupting the data by stripping out the highest-value info bits and replacing them with the most expected. Beware
LeifCarrotson 5y ago
Here's a simple video of the Lego prototype of the actuator that the inventor, Robert Warden, had on his desk: https://youtu.be/3WBrqUa_1yk https://youtu.be/3WBrqUa_1yk The full paper describing it is an excellent read: https://www.esmats.eu/amspapers/pastpapers/pdfs/2006/warden.pdf https://www.esmats.eu/amspapers/pastpapers/pdfs/2006/warden.... I think the latter was posted to HN a few months ago.

by chasil 5y ago

jcadam 5y ago

Any indication how many of those actuators they can lose and still maintain functionality (i.e., are any of those "spares")?

chasil 5y ago
Good question. No idea.
skykooler 5y ago
None of them are spares per se; if any of them fail they will have to use the other four on that segment to point it away from the sensor and disable that segment.
oceanghost 5y ago
3 points in a plane, so maybe half?
- TomVDB 5y ago
  No, they require 7 axes of movement. See the video that somebody else linked to.
- TaylorAlexander 5y ago
  The actuators control the XYZ position and the pitch, yaw, and roll, plus curvature. There is no redundancy.
infogulch 5y ago
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: https://youtu.be/5MxH1sfJLBQ https://youtu.be/5MxH1sfJLBQ The actuator breaking wasn't as concerning after seeing the design.
- mywacaday 5y ago
  Thanks for that video and channel. See what you mean about simple and accurate, strongly agree with the presenter calling it genius. Can't help but feel there is a strong lesson in there for software people.
  - krisoft 5y ago
    > Can't help but feel there is a strong lesson in there for software people. Hmm, can you elaborate on that? What is the strong lesson for software people specifically? Don’t get me wrong it is a beautiful design, and I’m a big fan of flexure designes in general. There is this amazing open source project which uses similar flexure mechanisms for very accurate positioning of microscope samples: https://openflexure.org/ https://openflexure.org/ But I fail to see any obvious takeaways which would generalise to software development. Other than perhaps “Think and work on the same problem for a decade and more and you might find a compact and elegant solution.” Which is nice, when one has that luxury.
    - ChrisMarshallNY 5y ago
      We tend to make complex solutions to simple problems. The thing about any problem, is that "the devil is in the details." It may seem simple, from a high level, but, once we start to "drill down" into the issue, the "rough edges" appear. At that point, we start to break out the baling wire and bubblegum, to kludge our original "graceful" design to meet the facts on the ground. It doesn't just happen for software. Hardware suffers from the same issue, but software makes it easy to start coding before modeling the requirements and context completely. I actually leverage this, in my own work. I call it "Evolutionary Design"[0]. It's not for the faint of heart, because a big part of it is recognizing when I'm rabbitholing, and tossing out what may be weeks of code, wholesale. I'm actually going through that process right now, with the app I'm developing. I'm working on the final feature set. [0] https://littlegreenviper.com/miscellany/evolutionary-design-specification/ https://littlegreenviper.com/miscellany/evolutionary-design-... "There's always an easy solution to every human problem; Neat, plausible and wrong." "The fact that I have no remedy for all the sorrows of the world is no reason for my accepting yours. It simply supports the strong probability that yours is a fake." -- H. L. Mencken “When the map and the terrain disagree; believe the terrain.” -- Swiss Army Maxim
dtgriscom 5y ago
My guess: any single one of the actuators could fail, and the other actuators could compensate by moving the plane of the mirror(s). The exception would be the curvature actuators. (IANAL, or the appropriate equivalent...)

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deleted 5y ago

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asah 5y ago

Can someone explain why alignment can't be done in software? i.e. collect data from each mirror separately, then switch together in software ?

geocrasher 5y ago
Yes. It's the same reason you can't take 10 out of focus pictures of yourself and get one in focus picture. You need actual good data to combine.
- jfengel 5y ago
  You can, with enough processing (and knowledge of how out of focus it is). It worked for Hubble. But you get more good pictures if you get it in focus in the first place.
  - Keyframe 5y ago
    Deconvolution. Haven't followed that in awhile, but getting to original function was next to impossible. Recording calibration image and/or recent AI developments might've taken that into something awesome. I'll go and catch up on material!
    - toss1 5y ago
      We really need to watch it with trusting AI. While my example here isn't photo recognition, the same principle applies. I recently sat for a deposition where the stenographer used an "AI"transcription system. The result was literally pages of errata (vs the standard errata sheet that has space for about a dozen lines). The consistent error I noticed was that the erroneous words were (probably) the word most expected in that position, and NOT the word that I said. So, at a glance, it seemed like a really good transcription. In fact, many errors were barely noticeable to me and I had to go back to the audio recording to confirm. And these were errors that substantially changed the meaning, or even inverted it. This is not merely information loss — the least surprising/lowest information item was inserted instead of the real item — this is actual information CORRUPTION. I'd fully expect parallel phenomena from image - "AI - filling in the item most expected from the training set, and actively corrupting the data by stripping out the highest-value info bits and replacing them with the most expected. Beware

LeifCarrotson 5y ago

Here's a simple video of the Lego prototype of the actuator that the inventor, Robert Warden, had on his desk: https://youtu.be/3WBrqUa_1yk https://youtu.be/3WBrqUa_1yk The full paper describing it is an excellent read: https://www.esmats.eu/amspapers/pastpapers/pdfs/2006/warden.pdf https://www.esmats.eu/amspapers/pastpapers/pdfs/2006/warden.... I think the latter was posted to HN a few months ago.