5 ms·

The fact that one of the mirror segments was already severely damaged by a micrometeorite makes me hope that they hurry up... the lifetime may not be as great a

The fact that one of the mirror segments was already severely damaged by a micrometeorite makes me hope that they hurry up... the lifetime may not be as great as hoped.

bowsamic 4y ago
I heard that it's within their expected budget of damage and has literally zero impact on any parameter of the telescope due to the deformable optics
- baggy_trough 4y ago
  I think that understates the case. Have you seen the calibration image after the impact?
  - deelowe 4y ago
    My understanding is the strike happened while en route and the risk of strikes of similar severity is lower in final orbit.
    - baggy_trough 4y ago
      That is not correct because the damage is not present in the first calibration images that were released.
      - deelowe 4y ago
        You're right. Thanks for the correction.
  - sillysaurusx 4y ago
    I haven’t. Mind linking? I suspected the damage was a little more important than people were saying, but it sounds like you might know of some evidence.
    - bckr 4y ago
      Probably talking about this[] from[]. I think it's overstated, though. The telescope seems to have a lot of redundancy and flexibility. [] https://cdn.mos.cms.futurecdn.net/jNgqXUj6dDVWbSvkw5ngMk-970-80.jpg.webp https://cdn.mos.cms.futurecdn.net/jNgqXUj6dDVWbSvkw5ngMk-970... [] https://www.space.com/james-webb-space-telescope-micrometeoroid-damage https://www.space.com/james-webb-space-telescope-micrometeor...
      - ThisIsMyAltFace 4y ago
        > When Webb's mission began, the affected C3 segment had a wavefront error of 56 nanometers rms (root mean square), which was in line with the 17 other mirror portions. > Post-impact, however, the error increased to 258 nm rms, but realignments to the mirror segments as a whole reduced the overall impact to just 59 nm rms. For the time being, the team wrote Webb's alignment is well within performance limits, as the realigned mirror segments are "about 5-10 nm rms above the previous best wavefront error rms values."
        koheripbal 4y ago
        It sustained this strike - but more strikes like the one that happened are going to significantly reduce the lifetime of the telescope. There is no debating that that big strike was outside the model.
        topspin 4y ago
        > There is no debating that that big strike was outside the model. Yes it is. That means the model is wrong. Hopefully JWST doesn't devolve into a micrometeorite detector. That instrument could have been built and operated at far lower cost and one wonders if that shouldn't have been done beforehand.
        AprilArcus 4y ago
        It could be that the model is wrong, or it could be that the model is correct and the big strike was an outlier. Only time will prove.
_joel 4y ago
I wouldn't worry too much, they were expecting them (albeit this was a biggie). The L2 point it's at means there shouldn't be too much that collects around there, gravity wise, but it will happen again.
- koheripbal 4y ago
  Both the number and size of micrometeorites is larger than what was modeled. Hopefully it was just a fluke, but if not, this telescope will not survive it's intended lifespan. As such, NASA has already started a project to optimize the orientation of the craft to minimize strikes.
  - AprilArcus 4y ago
    "wavefront sensing recorded six localized surface deformations on the primary mirror that are attributed to impact by micrometeoroids. These occurred at a rate (roughly one per month) consistent with pre-launch expectations […] Of the six micrometeoroid strikes detected thus far through wavefront sensing, five had negligible effects". So the overall number of impacts is consistent with the modeled rate, but the size of the C3 event was outside the modeled rate.
nuclearsugar 4y ago
"Characterization of JWST science performance from commissioning" - 2022 July 12 https://arxiv.org/ftp/arxiv/papers/2207/2207.05632.pdf https://arxiv.org/ftp/arxiv/papers/2207/2207.05632.pdf Check out the chapter: 4.7 Micrometeoroids

The fact that one of the mirror segments was already severely damaged by a micrometeorite makes me hope that they hurry up... the lifetime may not be as great as hoped.

bowsamic 4y ago

I heard that it's within their expected budget of damage and has literally zero impact on any parameter of the telescope due to the deformable optics

baggy_trough 4y ago
I think that understates the case. Have you seen the calibration image after the impact?
- deelowe 4y ago
  My understanding is the strike happened while en route and the risk of strikes of similar severity is lower in final orbit.
  - baggy_trough 4y ago
    That is not correct because the damage is not present in the first calibration images that were released.
    - deelowe 4y ago
      You're right. Thanks for the correction.
- sillysaurusx 4y ago
  I haven’t. Mind linking? I suspected the damage was a little more important than people were saying, but it sounds like you might know of some evidence.
  - bckr 4y ago
    Probably talking about this[] from[]. I think it's overstated, though. The telescope seems to have a lot of redundancy and flexibility. [] https://cdn.mos.cms.futurecdn.net/jNgqXUj6dDVWbSvkw5ngMk-970-80.jpg.webp https://cdn.mos.cms.futurecdn.net/jNgqXUj6dDVWbSvkw5ngMk-970... [] https://www.space.com/james-webb-space-telescope-micrometeoroid-damage https://www.space.com/james-webb-space-telescope-micrometeor...
    - ThisIsMyAltFace 4y ago
      > When Webb's mission began, the affected C3 segment had a wavefront error of 56 nanometers rms (root mean square), which was in line with the 17 other mirror portions. > Post-impact, however, the error increased to 258 nm rms, but realignments to the mirror segments as a whole reduced the overall impact to just 59 nm rms. For the time being, the team wrote Webb's alignment is well within performance limits, as the realigned mirror segments are "about 5-10 nm rms above the previous best wavefront error rms values."
      - koheripbal 4y ago
        It sustained this strike - but more strikes like the one that happened are going to significantly reduce the lifetime of the telescope. There is no debating that that big strike was outside the model.
        topspin 4y ago
        > There is no debating that that big strike was outside the model. Yes it is. That means the model is wrong. Hopefully JWST doesn't devolve into a micrometeorite detector. That instrument could have been built and operated at far lower cost and one wonders if that shouldn't have been done beforehand.
        AprilArcus 4y ago
        It could be that the model is wrong, or it could be that the model is correct and the big strike was an outlier. Only time will prove.

_joel 4y ago

I wouldn't worry too much, they were expecting them (albeit this was a biggie). The L2 point it's at means there shouldn't be too much that collects around there, gravity wise, but it will happen again.

koheripbal 4y ago
Both the number and size of micrometeorites is larger than what was modeled. Hopefully it was just a fluke, but if not, this telescope will not survive it's intended lifespan. As such, NASA has already started a project to optimize the orientation of the craft to minimize strikes.
- AprilArcus 4y ago
  "wavefront sensing recorded six localized surface deformations on the primary mirror that are attributed to impact by micrometeoroids. These occurred at a rate (roughly one per month) consistent with pre-launch expectations […] Of the six micrometeoroid strikes detected thus far through wavefront sensing, five had negligible effects". So the overall number of impacts is consistent with the modeled rate, but the size of the C3 event was outside the modeled rate.

nuclearsugar 4y ago

"Characterization of JWST science performance from commissioning" - 2022 July 12 https://arxiv.org/ftp/arxiv/papers/2207/2207.05632.pdf https://arxiv.org/ftp/arxiv/papers/2207/2207.05632.pdf Check out the chapter: 4.7 Micrometeoroids