5 ms·

This large impact was one outlier. So statistically, you can write it off as (hopefully) a fluke. Unfortunately, there were also over a dozen smaller impacts

This large impact was one outlier. So statistically, you can write it off as (hopefully) a fluke. Unfortunately, there were also over a dozen smaller impacts that, according to NASAs model, would have been very unlikely. Combining these data points clearly demonstrates that the micrometeor density model was wrong - which very sadly means that the projected lifetime of JWST is going to be reduced, maybe very significantly. NASA is currently exploring permanently altering the orientation of JWST to minimize impacts, but this also comes at the cost of reducing viewable space - thus limiting which science studies get telescope time. While NASA's PR department does a great job of telling everyone that everything is fine, and social media does its job of being an echo chamber for such glossy reporting, I hope that HN can take a more realistic view at this, very clearly, bad news. ...maybe even think outside the box about solutions or lessons to learn.

MichaelZuo 4y ago
What made them so confident in their assessment of a low micrometer density in the first place? Even as a freshman engineering student I remember that the exposed mirror design seemed oddly overconfident.
- tekla 4y ago
  What does this even mean? Are you saying as a freshman student you had insight into the statistical modeling of micrometeor impact probability and impact? The design of the optics was more or less finalized around the early 2000s. The exposed optics were kind of the entire point of the entire design. A very low quality post.
  - MichaelZuo 4y ago
    I usually don't reply to obvious trolling but I rather not see any eager freshmen mechanical engineering students be discouraged by a random troll. The basic principles of mechanical engineering have remained mostly unchanged for the last half century. NASA, including the mirror designers, have not discovered any new principles in the process of making JWST. Since even the most advanced technologies derive from these well established principles, at least in mechanical engineering, a sufficiently motivated and inquisitive student can learn enough within a year to formulate reasonable hunches.
- belter 4y ago
  JWST FAQ still says Q: "Will micrometeoroids damage the beryllium mirror?" A: "We tested beryllium discs for micrometeoroids using test facilities in the US and showed the micrometeoroids have negligible effects on the beryllium. Cryogenic beryllium mirrors have been flown in space exposed to micrometeoroids without problems. The Spitzer Space Telescope, launched in 2003, has a beryllium primary mirror. All of Webb's systems are designed to survive micrometeoroid impacts." https://www.jwst.nasa.gov/content/about/faqs/faq.html https://www.jwst.nasa.gov/content/about/faqs/faq.html
  - MichaelZuo 4y ago
    Public facing FAQs are not accurate descriptions of the actual engineering decision making. For example, 'All of Webb's systems are designed to survive micrometeoroid impacts.' is clearly only true below a certain bound, and untrue for a large enough impact event. There's no way JWST as designed, as launched, can survive 1 million micro meteorite impacts over a 1 minute duration. Maybe it could survive 100 or 1000, but the threshold is certainly there.
o_nate 4y ago
Curious if anyone has written about why estimates of the prevalence of small meteoroids at the L2 point were (possibly) too low? Were the estimates based on data about meteoroid prevalence entering the Earth atmosphere, and the prevalence is different at the L2 point?
- vanattab 4y ago
  I am not sure if the answer you seek is in here because I only have access to the abstract but here is a paper studying the effect of meteoroids on the jwst mirrors. https://adsabs.harvard.edu/pdf/2004ESASP.538..417S https://adsabs.harvard.edu/pdf/2004ESASP.538..417S https://www.spiedigitallibrary.org/conference-proceedings-of-spie/8442/84423A/Optical-transmission-for-the-James-Webb-Space-Telescope/10.1117/12.924841.short https://www.spiedigitallibrary.org/conference-proceedings-of... https://www.sciencedirect.com/science/article/abs/pii/S0734743X03001234 https://www.sciencedirect.com/science/article/abs/pii/S07347...
- belter 4y ago
  Sounds like the estimates about micro-meteoroids at L2 were too low. Back in 2014: "Aren't the mirrors of the James Webb Space Telescope too unprotected?" https://space.stackexchange.com/questions/4923/arent-the-mirrors-of-the-james-webb-space-telescope-too-unprotected https://space.stackexchange.com/questions/4923/arent-the-mir... and "Parking a telescope at a Lagrange point: is this a good idea from a debris point of view?" https://astronomy.stackexchange.com/questions/373/parking-a-telescope-at-a-lagrange-point-is-this-a-good-idea-from-a-debris-point https://astronomy.stackexchange.com/questions/373/parking-a-...
topynate 4y ago
The commissioning report, excerpted at https://news.ycombinator.com/item?id=32136991 https://news.ycombinator.com/item?id=32136991, says there were six micrometeoroid impacts during commissioning, and that this was a rate consistent with modelling. The outlier is certainly worrying but it may just be a bit of bad luck rather than a misprediction.
qikInNdOutReply 4y ago
Outside the box solutions? Get a high-temperature-supeconductor-magnet satelite out there, that flings ferro particles aside way ahead in the particle stream?

MichaelZuo 4y ago

What made them so confident in their assessment of a low micrometer density in the first place? Even as a freshman engineering student I remember that the exposed mirror design seemed oddly overconfident.

tekla 4y ago
What does this even mean? Are you saying as a freshman student you had insight into the statistical modeling of micrometeor impact probability and impact? The design of the optics was more or less finalized around the early 2000s. The exposed optics were kind of the entire point of the entire design. A very low quality post.
- MichaelZuo 4y ago
  I usually don't reply to obvious trolling but I rather not see any eager freshmen mechanical engineering students be discouraged by a random troll. The basic principles of mechanical engineering have remained mostly unchanged for the last half century. NASA, including the mirror designers, have not discovered any new principles in the process of making JWST. Since even the most advanced technologies derive from these well established principles, at least in mechanical engineering, a sufficiently motivated and inquisitive student can learn enough within a year to formulate reasonable hunches.
belter 4y ago
JWST FAQ still says Q: "Will micrometeoroids damage the beryllium mirror?" A: "We tested beryllium discs for micrometeoroids using test facilities in the US and showed the micrometeoroids have negligible effects on the beryllium. Cryogenic beryllium mirrors have been flown in space exposed to micrometeoroids without problems. The Spitzer Space Telescope, launched in 2003, has a beryllium primary mirror. All of Webb's systems are designed to survive micrometeoroid impacts." https://www.jwst.nasa.gov/content/about/faqs/faq.html https://www.jwst.nasa.gov/content/about/faqs/faq.html
- MichaelZuo 4y ago
  Public facing FAQs are not accurate descriptions of the actual engineering decision making. For example, 'All of Webb's systems are designed to survive micrometeoroid impacts.' is clearly only true below a certain bound, and untrue for a large enough impact event. There's no way JWST as designed, as launched, can survive 1 million micro meteorite impacts over a 1 minute duration. Maybe it could survive 100 or 1000, but the threshold is certainly there.

o_nate 4y ago

Curious if anyone has written about why estimates of the prevalence of small meteoroids at the L2 point were (possibly) too low? Were the estimates based on data about meteoroid prevalence entering the Earth atmosphere, and the prevalence is different at the L2 point?

vanattab 4y ago
I am not sure if the answer you seek is in here because I only have access to the abstract but here is a paper studying the effect of meteoroids on the jwst mirrors. https://adsabs.harvard.edu/pdf/2004ESASP.538..417S https://adsabs.harvard.edu/pdf/2004ESASP.538..417S https://www.spiedigitallibrary.org/conference-proceedings-of-spie/8442/84423A/Optical-transmission-for-the-James-Webb-Space-Telescope/10.1117/12.924841.short https://www.spiedigitallibrary.org/conference-proceedings-of... https://www.sciencedirect.com/science/article/abs/pii/S0734743X03001234 https://www.sciencedirect.com/science/article/abs/pii/S07347...
belter 4y ago
Sounds like the estimates about micro-meteoroids at L2 were too low. Back in 2014: "Aren't the mirrors of the James Webb Space Telescope too unprotected?" https://space.stackexchange.com/questions/4923/arent-the-mirrors-of-the-james-webb-space-telescope-too-unprotected https://space.stackexchange.com/questions/4923/arent-the-mir... and "Parking a telescope at a Lagrange point: is this a good idea from a debris point of view?" https://astronomy.stackexchange.com/questions/373/parking-a-telescope-at-a-lagrange-point-is-this-a-good-idea-from-a-debris-point https://astronomy.stackexchange.com/questions/373/parking-a-...

topynate 4y ago

The commissioning report, excerpted at https://news.ycombinator.com/item?id=32136991 https://news.ycombinator.com/item?id=32136991, says there were six micrometeoroid impacts during commissioning, and that this was a rate consistent with modelling. The outlier is certainly worrying but it may just be a bit of bad luck rather than a misprediction.

qikInNdOutReply 4y ago

Outside the box solutions? Get a high-temperature-supeconductor-magnet satelite out there, that flings ferro particles aside way ahead in the particle stream?