5 ms·

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.

by 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.
baggy_trough 4y ago
Yes, that's what I'm referring to. You don't consider that severe damage to a mirror segment? It looks like somebody shot it with a gun. It's unable to get properly back into alignment over the full segment.
- zaarn 4y ago
  If you check the reporting on the incident, they are able to calibrate almost all of this away and use the telescope as normal. It's bad but not that bad. That the telescope would be hit was expected so it can account for this amount of damage.
- bckr 4y ago
  I think it looks devastating. The people who run the thing think it's fine. I'll defer to the people who run the thing. See ThisIsMyAltFace's comment.
- welterde 4y ago
  It's not really an issue since it's only a minute reduction in light gathering power and the active optics was able to correct the mirror deformation after re-calibration. Speaking of telescope being shot with a gun.. There is a telescope in Texas (Harlan J. Smith Telescope at McDonald observatory) that was shot a few times by someone in the 1970s in the hopes of shattering the main mirror. The overall effect however was only a 1% reduction in the light gathering power and the telescope is still in regular use today. You can find a picture of the primary mirror here [1]. [1] https://astroanecdotes.com/2015/03/26/the-mcdonald-gun-shooting-incident/ https://astroanecdotes.com/2015/03/26/the-mcdonald-gun-shoot...
- lapetitejort 4y ago
  This [0] is what a telescope looks like when shot with a 9mm gun, seven times. The telescope lost 1% efficiency. 0: https://astroanecdotes.com/2015/03/26/the-mcdonald-gun-shooting-incident/ https://astroanecdotes.com/2015/03/26/the-mcdonald-gun-shoot...
  - bckr 4y ago
joering2 4y ago
Hopefully next iteration will have multiple mirrors built in as a backup. At least one round behind each visible mirror, and then release broken one, let it fly away, and push the new one out, call it "shark teeth lensing replacement system / STLRS".
- XorNot 4y ago
  Next iterations will be very different since SLS and hopefully Starship will exist and be able to be used to launch: JWST was built the way it was partly because it had to fit in the launch vehicle they knew was available. There's a future where we never do anything like it again because reusable rockets mean multiple launch orbital assembly is just plain cheaper.
- jacquesm 4y ago
  Chances are that a broken segment flying away will do massive damage to the telescope.
  - airstrike 4y ago
    Not if we zap it with an antimatter ray as it flies away
    - jacquesm 4y ago
      When I got up this morning I felt like I had overslept but not by that much.
  - dev_tty01 4y ago
    It just needs a tiny bit of acceleration in the right direction as it is released. It would then just drift away. That is just clever mechanical design and similar things have been done in other craft.
    - jacquesm 4y ago
      Have a look at the structure of the JWST, I don't see many 'safe paths' that would work regardless of orientation. Those segments are pretty much bound to hit each other if you eject them at an angle (they are quite thick) and that would make them aimed straight for the focal point. At a guess: all such theories have been debated and rejected by the people that built then thing in the first place.
dotnet00 4y ago
I agree that it's fairly overstated as the telescope was supposed to be able to work even if the 'wings' with 3 mirrors segments each had failed to unfold. Performance will certainly drop with collisions, but I seriously doubt it would get bad enough for telescope performance to be worse than having 6 less mirror segments. The bigger concern would probably be how much sunshade damage the telescope can handle, although fortunately there's a good bit of redundancy on that too.

by bckr 4y ago

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.

baggy_trough 4y ago

Yes, that's what I'm referring to. You don't consider that severe damage to a mirror segment? It looks like somebody shot it with a gun. It's unable to get properly back into alignment over the full segment.

zaarn 4y ago
If you check the reporting on the incident, they are able to calibrate almost all of this away and use the telescope as normal. It's bad but not that bad. That the telescope would be hit was expected so it can account for this amount of damage.
bckr 4y ago
I think it looks devastating. The people who run the thing think it's fine. I'll defer to the people who run the thing. See ThisIsMyAltFace's comment.
welterde 4y ago
It's not really an issue since it's only a minute reduction in light gathering power and the active optics was able to correct the mirror deformation after re-calibration. Speaking of telescope being shot with a gun.. There is a telescope in Texas (Harlan J. Smith Telescope at McDonald observatory) that was shot a few times by someone in the 1970s in the hopes of shattering the main mirror. The overall effect however was only a 1% reduction in the light gathering power and the telescope is still in regular use today. You can find a picture of the primary mirror here [1]. [1] https://astroanecdotes.com/2015/03/26/the-mcdonald-gun-shooting-incident/ https://astroanecdotes.com/2015/03/26/the-mcdonald-gun-shoot...
lapetitejort 4y ago
This [0] is what a telescope looks like when shot with a 9mm gun, seven times. The telescope lost 1% efficiency. 0: https://astroanecdotes.com/2015/03/26/the-mcdonald-gun-shooting-incident/ https://astroanecdotes.com/2015/03/26/the-mcdonald-gun-shoot...
- bckr 4y ago

joering2 4y ago

Hopefully next iteration will have multiple mirrors built in as a backup. At least one round behind each visible mirror, and then release broken one, let it fly away, and push the new one out, call it "shark teeth lensing replacement system / STLRS".

XorNot 4y ago
Next iterations will be very different since SLS and hopefully Starship will exist and be able to be used to launch: JWST was built the way it was partly because it had to fit in the launch vehicle they knew was available. There's a future where we never do anything like it again because reusable rockets mean multiple launch orbital assembly is just plain cheaper.
jacquesm 4y ago
Chances are that a broken segment flying away will do massive damage to the telescope.
- airstrike 4y ago
  Not if we zap it with an antimatter ray as it flies away
  - jacquesm 4y ago
    When I got up this morning I felt like I had overslept but not by that much.
- dev_tty01 4y ago
  It just needs a tiny bit of acceleration in the right direction as it is released. It would then just drift away. That is just clever mechanical design and similar things have been done in other craft.
  - jacquesm 4y ago
    Have a look at the structure of the JWST, I don't see many 'safe paths' that would work regardless of orientation. Those segments are pretty much bound to hit each other if you eject them at an angle (they are quite thick) and that would make them aimed straight for the focal point. At a guess: all such theories have been debated and rejected by the people that built then thing in the first place.

dotnet00 4y ago

I agree that it's fairly overstated as the telescope was supposed to be able to work even if the 'wings' with 3 mirrors segments each had failed to unfold. Performance will certainly drop with collisions, but I seriously doubt it would get bad enough for telescope performance to be worse than having 6 less mirror segments. The bigger concern would probably be how much sunshade damage the telescope can handle, although fortunately there's a good bit of redundancy on that too.