"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."
The actuator breaking wasn't as concerning after seeing the design.
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/
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.
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-...
"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
I think the actuator is an equivalent of a very clever Perl one liner.
It reminded me of a collaboration I had with a small Swiss company that did wonders with electro-discharge machining such as this flexure-based mechanism machined from a single block of aluminium: https://i.imgur.com/PDAVDmJ.jpg
Unrelated: reaction wheel assemblies (used for attitude control) typically would have one extra wheel as a "spare." Redundancy is important enough on spacecraft you expect it wherever it is practicable. I used to work in aerospace - spent enough time coding spacecraft simulation tools that I had to develop at least a working familiarity with how some of the common satellite bus systems are supposed to work :)
Doing each mirror separately would observe the photons before their wave functions are combined and so it would be the same as many small low resolution cameras instead of one big high resolution one. It defeats the purpose of a large mirror.
Before I saw the experiments in that video, I assumed photons were about as wide as their wavelength.
[1] "It's a golden oldie..."
[2] "... just to give the setup a nice high tech look and feel."
[3] "The physics behind this is pretty hefty, and not, like, youtube video material."
The laser used by the presenter has a coherence length longer than (or in the same ballpark as) the difference in optical paths in their experiement, so they get a clear interference pattern.
The Wikipedia article may explain. https://en.wikipedia.org/wiki/Coherence_length
Since you can measure coherence length (and higher-order temporal and spatial coherence statistics), it is part of the information carried by light from a luminous object that is available for imaging by a suitably designed camera.
Without phase information, you can combine different captures to improve SNR, but it won't improve the resolution. To improve resolution you need light interference, which requires phase information to be preserved.
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
But accurate reconstruction in the wild is just sooo far away. And for good reason - it would need to have insane amounts of experience and exposure to every bit of unusual data that existed in the world to get it right...
A engineering friend of mine was working on hardware related to mil satellite imagery, and was sent to a course that covered all the kinds of post-processing techniques they had to improve resolution and what could help those techniques upstream. He said that at the end of the course, the instructor said the bottom line was that while they could do all kinds of 'magic' to improve & enhance the photos, the best input to all their techniques that would yield the best end result, was to take a better photo in the first place.
So, yes, there really is no substitute to a good original image.
Think of the csi ‘enhance’ meme and why that is physically impossible without introducing potentially fake information.
In radio astronomy the phase information is actually collected and sometimes recorded, which is why you can have arrays of radio telescopes far apart that combine. The most extreme version of this is Very Long Baseline Interferometry (https://en.wikipedia.org/wiki/Very-long-baseline_interferome...) which was used to image the black hole at the centre of our galaxy (https://en.wikipedia.org/wiki/Event_Horizon_Telescope).
At infra-red and visible wavelengths, it is technically possible to collect some phase information, subject to noise though. So in principle it is possible to collect images including some phase at each mirror location instead of using a mirror, and then stitch them in a similar way to how it's done with radio. However, collecting the phase would be difficult and complex, especially with current technology, and likely to degrade the image so much that it's not worth doing anyway. Using mirrors is better.
In future, it is plausible that this will be done to combine images from optical telescopes far apart in space, for a very wide aparture. But it seems just as likely that they will use mirrors far apart in space, directing the incoming light to a small number of focal locations to combine the light in the optical domain first, before converting it to image data.
The full paper describing it is an excellent read:
https://www.esmats.eu/amspapers/pastpapers/pdfs/2006/warden....
I think the latter was posted to HN a few months ago.
It is their crewed program that is completely screwed by politics.