The Lemon Fool

After 3 months Webb is now on commissioning Step 6 (of 7), Telescope Alignment Over All Instrument Fields Of View

https://www.webb.nasa.gov/content/webbLaunch/whereIsWebb.html

As explained on the site, as time goes on some previous steps may need to be reiterated.

Final Cooling - MIRI

https://webb.nasa.gov/content/webbLaunch/whereIsWebb.html

Precedes Mirror Alignment Step 7

"The Mid-Infrared Instrument (MIRI) carries detectors that need to be at a temperature of less than 7 kelvin to operate properly. This temperature is not possible on Webb by passive means alone, so Webb carries an innovative cryocooler that is dedicated to cooling MIRI's detectors."

James Webb telescope's MIRI instrument goes super-cold

BBC News

It is perhaps the very definition of cool. The Mid-Infrared Instrument on the James Webb Space telescope is now at its super-low operating temperature.

"The UK-assembled instrument has reached a decidedly chilly -267C, or just six degrees above "absolute zero".

This unimaginably low temperature is not far short of the point where all atoms are supposed to stop jiggling.

MIRI's frigid status will allow the Webb observatory to see the distant Universe in unprecedented detail."

James Webb Space Telescope in final stretch

BBC News

James Webb, astronomy's new super space telescope, has taken another major step to full operational capability.

"The $10bn successor to the Hubble Space Telescope is now fully focused and aligned. Light bounces perfectly off its mirrors to form pin-sharp imagery in all four of its instruments."


(Personally don't like the meaningless "super" in "super space telescope" - it's an infra-red telescope. Nor "bounces"!)

James Webb telescope damaged when mirror hit by larger than expected micrometeoroid

https://www.independent.co.uk/tech/nasa-telescope-james-webb-rock-micrometeroid-b2097332.html

Nasa’s James Webb Space Telescope has been hit by a piece of space rock.

One of the large mirrors that powered the segment was hit by a micrometeoroid that was larger than expected and bigger than engineers were able to test on the ground, the space agency said.

Though assessments are still continuing, the telescope still appears to be operating well enough, but the collision had a “marginally detectable effect in the data”, Nasa said in its announcement.

The object hit one of the pieces of mirror that allow the telescope to work sometime between 23 and 25 May, the space agency said in its announcement.

...I was recently wondering about something like this, with its large exposed mirror.

XFool wrote:...I was recently wondering about something like this, with its large exposed mirror.

Is the telescope manufactured in a way that would facilitate a repair mission to repair damage, the sort of thing that was done with Hubble to correct errors in the optics.

Regards,

odysseus2000 wrote:

XFool wrote:...I was recently wondering about something like this, with its large exposed mirror.

Is the telescope manufactured in a way that would facilitate a repair mission to repair damage, the sort of thing that was done with Hubble to correct errors in the optics.

No. It is impossible, as it is not in a low Earth orbit. In fact it is almost 1 million miles from Earth.

The damage is small and not unexpected, it has been struck five times already. The latest hit was just on the larger than normal size and has left a "dimple" in one of its 18 main mirror segments.

Official press release on the micrometeorite strike :
https://blogs.nasa.gov/webb/2022/06/08/ ... d-impacts/

First "official" images are due on 12 July :
https://www.nasa.gov/feature/goddard/20 ... oming-soon

but they've already released a picture as part of the initial calibration - at this stage they were just lining up each mirror on a single star, the previously unknown galaxies in the background are incidental :
https://www.nasa.gov/press-release/nasa ... ccessfully



(full size at https://www.nasa.gov/sites/default/file ... abeled.png)

Ummm ... well I do hope the remaining alignment steps will get rid of the lines coming out of the star and some of the other brighter objects ... one doesn't expect such artefacts from such an expensive bit of kit!

mc2fool wrote:Ummm ... well I do hope the remaining alignment steps will get rid of the lines coming out of the star and some of the other brighter objects ... one doesn't expect such artefacts from such an expensive bit of kit!

Isn't it inevitable using a segmented main mirror? Presumably only significant on very bright/overexposed images.

XFool wrote:

mc2fool wrote:Ummm ... well I do hope the remaining alignment steps will get rid of the lines coming out of the star and some of the other brighter objects ... one doesn't expect such artefacts from such an expensive bit of kit!

Isn't it inevitable using a segmented main mirror? Presumably only significant on very bright/overexposed images.

I dunno but I'd hope not! I mean how useful is that? Take a look at the 12 pointed object at the very top right of the image -- looks like something you'd stick on top of a Christmas tree!

mc2fool wrote:Ummm ... well I do hope the remaining alignment steps will get rid of the lines coming out of the star and some of the other brighter objects ... one doesn't expect such artefacts from such an expensive bit of kit!

All stars have the points due to the struts holding the secondary mirror, you can see it in this Hubble image, you only notice it on the bright ones though. Some of the science is explained here :
https://www.abc.net.au/science/articles ... 253961.htm

mc2fool wrote:Ummm ... well I do hope the remaining alignment steps will get rid of the lines coming out of the star and some of the other brighter objects ... one doesn't expect such artefacts from such an expensive bit of kit!

BTW, the telescope optical alignment steps were completed several weeks ago - though future fine adjustments can be made if needed. They are setting up the instruments now.

viewtopic.php?p=497529#p497529

XFool wrote:

mc2fool wrote:Ummm ... well I do hope the remaining alignment steps will get rid of the lines coming out of the star and some of the other brighter objects ... one doesn't expect such artefacts from such an expensive bit of kit!

BTW, the telescope optical alignment steps were completed several weeks ago - though future fine adjustments can be made if needed. They are setting up the instruments now.

viewtopic.php?p=497529#p497529

I didn't spot that the "Alignment Milestone" article Hallucigenia linked to which talks of "remaining alignment steps" was from the 16th of March...

Hallucigenia wrote:All stars have the points due to the struts holding the secondary mirror, you can see it in this Hubble image, you only notice it on the bright ones though.

Yes, that makes sense as Webb has three struts holding the secondary mirror - hence three diffraction lines giving six star points. I was thinking of the six points corresponding to the hexagonal mirror segments.

odysseus2000 wrote:

XFool wrote:...I was recently wondering about something like this, with its large exposed mirror.

Is the telescope manufactured in a way that would facilitate a repair mission to repair damage, the sort of thing that was done with Hubble to correct errors in the optics.

Regards,

Why would we send a mission to repair it when we could just hold a big placard up at the Jubilee flypast saying "Dear UFO, please fix the hole in our telescope"?

GS

XFool wrote:

Hallucigenia wrote:All stars have the points due to the struts holding the secondary mirror, you can see it in this Hubble image, you only notice it on the bright ones though.

Yes, that makes sense as Webb has three struts holding the secondary mirror - hence three diffraction lines giving six star points. I was thinking of the six points corresponding to the hexagonal mirror segments.

Hallucigenia: thanks for the explanation.

Both: but the big star in the centre has 8 points, the two horizontal ones being weaker than the 6 others. And the one at the top right has 12 with the horizontal ones being amongst the brightest, as are with the umm, multi pointed one that's pretty much horizontal with the big star and about a quarter way into it from the left hand side...

GoSeigen wrote:

odysseus2000 wrote:

XFool wrote:...I was recently wondering about something like this, with its large exposed mirror.

Is the telescope manufactured in a way that would facilitate a repair mission to repair damage, the sort of thing that was done with Hubble to correct errors in the optics.

Regards,

Why would we send a mission to repair it when we could just hold a big placard up at the Jubilee flypast saying "Dear UFO, please fix the hole in our telescope"?

GS

Who is to say it wasn't a probing gone wrong?
Our alien cousins might not know that the telescope is a device rather than a denizen of this cul de sac of the Milky Way.

Our alien 'friends' would be extremely advanced by our standards, having presumably travelled at faster than light speed to get here from a galaxy far far away. I'm sure they would identify the JWT as man made but probably regard it as so primitive it would not be worth repairing.

Alternatively they are too busy planning the earth invasion, a la Independence Day. The principle of survival of the fittest probably means they would regard us as little more than an insect infestation!