4 ms·

I am so relieved that it made it without hitting some debris, and that the hydraulics didn't fail for the unfurling. The unfurling was one insane piece of orche

I am so relieved that it made it without hitting some debris, and that the hydraulics didn't fail for the unfurling. The unfurling was one insane piece of orchestration, which just means many more opportunities to see a piece of space dust or something messing it all up. This image is fantastic, even though we can easily see that more work needs to be done with the alignment. It hopefully proves that alignment is all that's left.

chasil 5y ago
If one mirror's actuators fail, it's over. I hope they have long life. "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." https://en.m.wikipedia.org/wiki/James_Webb_Space_Telescope https://en.m.wikipedia.org/wiki/James_Webb_Space_Telescope
- cma 5y ago
  If only one fails couldn't they do two-exposures with all the functioning ones making the smallest movement they can? Then the failed one's contribution can be decorrelated between the two exposures and removed since it stays the same throughout.
- kibwen 5y ago
  AIUI if any one mirror fails then they can continue on with degraded performance, it wouldn't mean the immediate end of the telescope's usefulness.
ISL 5y ago
I believe that they have achieved diffraction-limited alignment. What about the image suggests that there is more work to do? The starburst pattern is part of the intrinsic PSF, not a signal of alignment error.
- frumiousirc 5y ago
  > I believe that they have achieved diffraction-limited alignment. What about the image suggests that there is more work to do? Some of the remaining misalignment is rather obvious in the higher resolution image. For example, look left of the main star and notice an "echo" of the main diffraction pattern that is not centered on a star. Also, if you follow that pattern's downward arm to where it meets a diagonal arm of the main pattern you see a rectangular bar of increased brightness. Perhaps it indicates the need for calibrating that part of the sensor. https://www.nasa.gov/sites/default/files/thumbnails/image/telescope_alignment_evaluation_image_labeled.png https://www.nasa.gov/sites/default/files/thumbnails/image/te...
  - sbierwagen 5y ago
    There's five echos, actually. (Look north, northwest, W, SW and S) Internal reflections, probably. HD 84406 is fairly bright, magnitude 6, eye-visible. In one of the blog posts they say it's too bright to be imaged in normal operations: https://blogs.nasa.gov/webb/2022/01/27/the-webb-team-looks-back-on-successful-deployments/ https://blogs.nasa.gov/webb/2022/01/27/the-webb-team-looks-b... (You don't spend tens of billions to put a telescope into orbit just to look at HD catalog stars) All the other sensor cruft would go away with dark-frame subtraction: https://en.wikipedia.org/wiki/Dark-frame_subtraction https://en.wikipedia.org/wiki/Dark-frame_subtraction They're apparently not bothering with that for mirror alignment photos. Another safe bet is that a bunch of the sensor noise is because all the instruments are still warm. NIRCAM is still at 42K, and MIRI is hotter. https://www.jwst.nasa.gov/content/webbLaunch/whereIsWebb.html https://www.jwst.nasa.gov/content/webbLaunch/whereIsWebb.htm... It doesn't look like they've turned on the instrument coolers yet.
MerelyMortal 5y ago
Big Sky Theory, meet Space. https://en.wikipedia.org/wiki/Big_sky_theory https://en.wikipedia.org/wiki/Big_sky_theory

chasil 5y ago

If one mirror's actuators fail, it's over. I hope they have long life. "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." https://en.m.wikipedia.org/wiki/James_Webb_Space_Telescope https://en.m.wikipedia.org/wiki/James_Webb_Space_Telescope

cma 5y ago
If only one fails couldn't they do two-exposures with all the functioning ones making the smallest movement they can? Then the failed one's contribution can be decorrelated between the two exposures and removed since it stays the same throughout.
kibwen 5y ago
AIUI if any one mirror fails then they can continue on with degraded performance, it wouldn't mean the immediate end of the telescope's usefulness.

ISL 5y ago

I believe that they have achieved diffraction-limited alignment. What about the image suggests that there is more work to do? The starburst pattern is part of the intrinsic PSF, not a signal of alignment error.

frumiousirc 5y ago
> I believe that they have achieved diffraction-limited alignment. What about the image suggests that there is more work to do? Some of the remaining misalignment is rather obvious in the higher resolution image. For example, look left of the main star and notice an "echo" of the main diffraction pattern that is not centered on a star. Also, if you follow that pattern's downward arm to where it meets a diagonal arm of the main pattern you see a rectangular bar of increased brightness. Perhaps it indicates the need for calibrating that part of the sensor. https://www.nasa.gov/sites/default/files/thumbnails/image/telescope_alignment_evaluation_image_labeled.png https://www.nasa.gov/sites/default/files/thumbnails/image/te...
- sbierwagen 5y ago
  There's five echos, actually. (Look north, northwest, W, SW and S) Internal reflections, probably. HD 84406 is fairly bright, magnitude 6, eye-visible. In one of the blog posts they say it's too bright to be imaged in normal operations: https://blogs.nasa.gov/webb/2022/01/27/the-webb-team-looks-back-on-successful-deployments/ https://blogs.nasa.gov/webb/2022/01/27/the-webb-team-looks-b... (You don't spend tens of billions to put a telescope into orbit just to look at HD catalog stars) All the other sensor cruft would go away with dark-frame subtraction: https://en.wikipedia.org/wiki/Dark-frame_subtraction https://en.wikipedia.org/wiki/Dark-frame_subtraction They're apparently not bothering with that for mirror alignment photos. Another safe bet is that a bunch of the sensor noise is because all the instruments are still warm. NIRCAM is still at 42K, and MIRI is hotter. https://www.jwst.nasa.gov/content/webbLaunch/whereIsWebb.html https://www.jwst.nasa.gov/content/webbLaunch/whereIsWebb.htm... It doesn't look like they've turned on the instrument coolers yet.

MerelyMortal 5y ago

Big Sky Theory, meet Space. https://en.wikipedia.org/wiki/Big_sky_theory https://en.wikipedia.org/wiki/Big_sky_theory