JWST Countdown To Terror 😳

[cajen2]

Having trouble with your collimation? Just focus on star HD 84406 in Ursa Major. That's the one they're using to align the JWST mirrors! 😄

[gilesco]

1 hour ago, cajen2 said:

Having trouble with your collimation? Just focus on star HD 84406 in Ursa Major. That's the one they're using to align the JWST mirrors! 😄

Looks like a good candidate:

[kirkster501]

Has any more data been released yet about the mirror positioning guys?

[gilesco]

I imagine they're still cooling towards 45 deg K - I expect they won't turn on the imager until it is cold enough.

[Gfamily]

3 hours ago, kirkster501 said:

Has any more data been released yet about the mirror positioning guys?

The initial positioning of the mirror segments means that each one is going to be producing its own image and these are going to be fairly randomly distributed about the nominal centre of the field of view.

The initial activity will be to produce a mosaic covering an area of  24' by 25' (600 arc minutes). This will require about 100 separate images being captured by the one of the NIRCam imager sensors. If not all 18 segment images are captured in this initial mosaic, more frames will be added to widen the field. 

When the locations of the 18 image components are known, the next process will be to identify which mirror component relates to which image and this will be done by centering on the image and giving each mirror segment "a little pirouette" - when the image moves, they'll know which mirror produces it. 

When the images from all the mirrors have been identified, the mirrors are moved to bring all images together into a hexagonal pattern within the 3' by 3' field of view of one of the NIRCam sensors. 

A combination of focusing and de-focusing of the individual images allows waveform calculations to be made to allow the precise configuration of each of the primary mirror segments AND the secondary mirror to be determined 

There are 131 distinct adjustments available on the Primary Mirror segments, and 113 distinct adjustment modes available to the Secondary.

One issue is that there are multiple sensors that occupy different areas of the overall image field of the telescope  - so the focus has to be optimised not just for the 3' x 3' field of NIRCam, but across the wider area so that data can be captured for MIRI, NIRSpec, NIRISS and the Fine Guidance Systems (FGS)

 

A summary is here 

https://www.spacefoundation.org/wp-content/uploads/2019/07/Acton-Scott_WAVEFRONT-SENSING-AND-CONTROL-FOR-THE-JAMES-WEBB-SPACE-TELESCOPE.pdf

 

Thanks due to Mark McCaughrean at ESA (on twitter) for pointing me in the direction of this data

Edited January 28, 2022 by Gfamily
Spelling

[Laurieast]

Following Webb’s Arrival at L2, Telescope Commissioning Set to Begin.

https://blogs.nasa.gov/webb/2022/01/31/following-webbs-arrival-at-l2-telescope-commissioning-set-to-begin/

[Laurieast]

Photons Incoming: Webb Team Begins Aligning the Telescope.

https://blogs.nasa.gov/webb/2022/02/03/photons-incoming-webb-team-begins-aligning-the-telescope/

[CCD-Freak]

On 04/02/2022 at 03:20, Laurieast said:

Photons Incoming: Webb Team Begins Aligning the Telescope.

https://blogs.nasa.gov/webb/2022/02/03/photons-incoming-webb-team-begins-aligning-the-telescope/

Not a simple process......This isn't like collimating your Dob !!!  8^P

[Macavity]

Pleased to see there is some (small) degree of redundancy re. Cameras etc. But a
lot of stuff still has to "work 100% and/or first time"? Still quite "Nail Biting"?!? 😮

[powerlord]

Exactly Still time for that '23 what ? centiwhat ? I just assumed it was inches you meant' moment.

[Laurieast]

Webb Is Chilling Out:

https://blogs.nasa.gov/webb/2022/02/10/webb-is-chilling-out/

[Laurieast]

NASA to Discuss Webb Telescope Progress, Mirror Alignment:

https://www.nasa.gov/press-release/nasa-to-discuss-webb-telescope-progress-mirror-alignment

[IB20]

So it has taken a selfie… Incredibly, incredibly cool.

 

[Gfamily]

3 minutes ago, IB20 said:

So it has taken a selfie… Incredibly, incredibly cool.

 

Illuminated by starlight! Amazing.

And here's the initial configuration mosaic image showing the 18 individual element images

[DaveS]

They're going to have fun collimating *that* lot

[Roy Cropper]

Nah, Cheshire cap and they'll have that done before their cup of tea gets cold!

[tomato]

That's about as good as I got my 8" F4 SN collimated back in 1990...🙄

[gilesco]

1 hour ago, Gfamily said:

Illuminated by starlight! Amazing.

And here's the initial configuration mosaic image showing the 18 individual element images

Now thats pretty good, I reckon they can sort out about 15/18 pretty quickly. Some of the others will be a bit more tricky.

[Sunshine]

Here's the same image with corresponding mirror segment.

Photons Received: Webb Sees Its First Star – 18 Times – James Webb Space Telescope (nasa.gov)

Edited February 11, 2022 by Sunshine

[DaveS]

 

[kirkster501]

It is unbelievable how the electronics operate at these supremely low temperatures.  This is not just hardened electronics - i.e. military grade.  This is something else entirely.  At these temperatures conductivity changes too.

[kirkster501]

How did it take the selfie?  So there is a webcam on there after all?!

[UKDiver]

21 hours ago, IB20 said:

So it has taken a selfie… Incredibly, incredibly cool.

Possibly not cool enough yet.

[Laurieast]

25 minutes ago, kirkster501 said:

How did it take the selfie?  So there is a webcam on there after all?!

From Twitter:
Dr Heidi B. Hammel@hbhammel·20hThis diagram of NIRCam optics is complicated, but the take-away is that when the "Pupil Imaging Lens" is in the beam, we see the *mirror* in focus, rather than the *sky* in focus. This mode is used for only alignment and engineering, not for science.

[Sunshine]

Video from the horses mouth detailing the image of first star, if you think collimating your maksutov is a pain, this one is quite a head buster to collimate.

 

Edited February 12, 2022 by Sunshine