Le post des nouvelles des étoiles...

[Robert64]

ça fera toujours des merdes en moins en orbite basse !
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[Robert64]

Sur JWST, l'alignement des optiques se poursuit.
Etape du jour:

Segment Image Identification
Step 1

Nominal Event Time: Starts - Launch + ~6 weeks
Status: Ongoing | Replay Media Telecon | First Photons

Webb team members saw the first photons of starlight that traveled through the entire telescope and were detected by the Near Infrared Camera (NIRCam) instrument. This milestone marks the first of many steps to capture images that are at first unfocused and use them to slowly fine-tune the telescope. This is the very beginning of the process as Segment Image Identification begins.

We are pointing the telescope at a bright, isolated star (HD 84406) to capture a series of images that are then stitched together to form a picture of that part of the sky. We don’t have just one mirror looking at this star; we have 18 mirrors, each of which is initially tilted towards a different part of the sky. As a result, we’ll actually capture 18 slightly shifted copies of the star – each one out of focus and uniquely distorted. We refer to these initial star-copies as 'segment images.'

One by one, we will move the 18 mirror segments to determine which segment creates which segment image. After matching the mirror segments to their respective images, we can tilt the mirrors to bring all the images near a common point for further analysis. We call this arrangement an 'image array.'

(document Nasa)
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[krisscore]

Un site super intéressant qui compile dans une timeline les photos de notre astre, heure par heure ==> https://helioviewer.org/

Je trouve ça fascinant, surtout les éruptions solaires comparées à l'échelle de la Terre qui est toujours rappelée en fonction du niveau de grossissement choisi.

[Robert64]

Du côté du JWST...ça continue!
Webb Team Brings 18 Dots of Starlight Into Hexagonal Formation
(Blog Nasa)

This early Webb alignment image, with dots of starlight arranged in a pattern similar to the honeycomb shape of the primary mirror, is called an “image array.”
Credit: NASA/STScI/J. DePasquale

The Webb team continues to make progress in aligning the observatory’s mirrors. Engineers have completed the first stage in this process, called “Segment Image Identification.” The resulting image shows that the team has moved each of Webb’s 18 primary mirror segments to bring 18 unfocused copies of a single star into a planned hexagonal formation.

Webb_alignment_image-array_annotated-768x768.jpeg (48.81 Kio) Vu 475 fois

This image mosaic (top), which shows 18 randomly positioned copies of the same star, served as the starting point for the alignment process. To complete the first stage of alignment, the team moved the primary mirror segments to arrange the dots of starlight into a hexagonal image array (bottom). Each dot of starlight is labeled with the corresponding mirror segment that captured it.
Credits: NASA (top); NASA/STScI/J. DePasquale (bottom)

With the image array complete, the team has now begun the second phase of alignment: “Segment Alignment.” During this stage, the team will correct large positioning errors of the mirror segments and update the alignment of the secondary mirror, making each individual dot of starlight more focused. When this “global alignment” is complete, the team will begin the third phase, called “Image Stacking,” which will bring the 18 spots of light on top of each other.
“We steer the segment dots into this array so that they have the same relative locations as the physical mirrors,” said Matthew Lallo, systems scientist and Telescopes Branch manager at the Space Telescope Science Institute. “During global alignment and Image Stacking, this familiar arrangement gives the wavefront team an intuitive and natural way of visualizing changes in the segment spots in the context of the entire primary mirror. We can now actually watch the primary mirror slowly form into its precise, intended shape!”

AuthorAlise FisherPosted onFebruary 18, 2022
CategoriesJames Webb Space Telescope
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[Robert64]

La première vraie image (encore floue, pour l'instant)
D'après blog Nasa

Webb Mirror Alignment Continues Successfully

Alise Fisher
Posted on February 25, 2022
CategoriesJames Webb Space Telescope

Webb continues on its path to becoming a focused observatory. The team has successfully worked through the second and third out of seven total phases of mirror alignment. With the completion of these phases, called Segment Alignment and Image Stacking, the team will now begin making smaller adjustments to the positions of Webb’s mirrors.

PostGlobalAlignment-1200x1200.jpeg (44.3 Kio) Vu 441 fois

This hexagonal image array captured by the NIRCam instrument shows the progress made during the Segment Alignment phase, further aligning Webb’s 18 primary mirror segments and secondary mirror using precise movements commanded from the ground. Credit: NASA/STScI
After moving what were 18 scattered dots of starlight into Webb’s signature hexagonal formation, the team refined each mirror segment’s image by making minor adjustments, while also changing the alignment of Webb’s secondary mirror. The completion of this process, known as Segment Alignment, was a key step prior to overlapping the light from all the mirrors so that they can work in unison.

SegmentAlignment.gif (119.61 Kio) Vu 441 fois

This gif shows the “before” and “after” images from Segment Alignment, when the team corrected large positioning errors of its primary mirror segments and updated the alignment of the secondary mirror. Credit: NASA/STScI
Once Segment Alignment was achieved, the focused dots reflected by each mirror were then stacked on top of each other, delivering photons of light from each segment to the same location on NIRCam’s sensor. During this process, called Image Stacking, the team activated sets of six mirrors at a time and commanded them to repoint their light to overlap, until all dots of starlight overlapped with each other.

PostImageStacking-1200x1200.jpeg (38.13 Kio) Vu 441 fois

During this phase of alignment known as Image Stacking, individual segment images are moved so they fall precisely at the center of the field to produce one unified image instead of 18. In this image, all 18 segments are on top of each other. After future alignment steps, the image will be even sharper. Credit: NASA/STScI
“We still have work to do, but we are increasingly pleased with the results we’re seeing,” said Lee Feinberg, optical telescope element manager for Webb at NASA’s Goddard Space Flight Center. “Years of planning and testing are paying dividends, and the team could not be more excited to see what the next few weeks and months bring.”

Although Image Stacking put all the light from a star in one place on NIRCam’s detector, the mirror segments are still acting as 18 small telescopes rather than one big one. The segments now need to be lined up to each other with an accuracy smaller than the wavelength of the light.

The team is now starting the fourth phase of mirror alignment, known as Coarse Phasing, where NIRCam is used to capture light spectra from 20 separate pairings of mirror segments. This helps the team identify and correct vertical displacement between the mirror segments, or small differences in their heights. This will make the single dot of starlight progressively sharper and more focused in the coming weeks.
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[Robert64]

Mise au point télescope JWST.
Une étape supplémentaire franchie!
(source Nasa)

Step 4 : Coarse Phasing
Nominal Event Time: Starts - Launch + ~3 Months
Status: Ongoing

Although Image Stacking puts all the light in one place on the detector, the segments are still acting as 18 small telescopes rather than one big one. The segments need to be lined up with each other with an accuracy smaller than the wavelength of the light.

Conducted three times during the commissioning process, Coarse Phasing measures and corrects the vertical displacement (piston difference) of the mirror segments. Using a technology known as Dispersed Fringe Sensing, we use NIRCam to capture light spectra from 20 separate pairings of mirror segments. The spectrum will resemble a barber pole pattern with a slope (or angle) determined by the piston difference of the two segments in the pairing.
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[Robert64]

Petit point sur JWST:
(documents Nasa)

Un peu d'avance sur le planning:

Pour ce qui est du refroidissement des instruments, on s'approche doucement des températures nominales:

JWST6.jpg (30.36 Kio) Vu 359 fois

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[thierry38d]

Passionné tu es sur ce "projet".

Je suis l'évolution un peu aussi.

[rmsk]

Absolument fascinant.
Je n'y connais rien et en comprends peu, mais ça m'émerveille.

Tant de talents, tant de travail, tant de coopération entre équipes scientifiques, pour de la connaissance pure !

Remy (plus à l'aise en mer de Java ou au Conseil d'État)

[Sietch31]

T'inquiètes, personne ne serait vraiment à l'aise au fameux point L2

[Robert64]

:) Passionné tu es sur ce "projet".

Je suis l'évolution un peu aussi.

C'est quand même la mise en service du télescope le plus performant de tous les temps.
La connaissance va progresser et on va s'apercevoir, comme d'hab' de l'énormité de tout ce qu'on ignore.
Et je salue aussi la performance d'engineerie que constitue la mise et station de ce...monstre.
Bon, faut dire qu'avec 10 Mds de $, on peut faire des choses...
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[Robert64]

T'inquiètes, personne ne serait vraiment à l'aise au fameux point L2

Bah! 56° au soleil, -230° à l'ombre, c'est presque tempéré...en moyenne!
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[Robert64]

Absolument fascinant.
Je n'y connais rien et en comprends peu, mais ça m'émerveille.

Tant de talents, tant de travail, tant de coopération entre équipes scientifiques, pour de la connaissance pure !

Remy (plus à l'aise en mer de Java ou au Conseil d'État)

Ouais, mais les premiers qui s'y sont risqués, au XVème et XVIème siècle, ils n'était pas tellement à l'aise non plus.
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[tfpsly]

Une vidéo intéressante sur les 5 voiles Sunshield du JWST, comment leurs formes (elles ne sont pas identiques) ont été vérifiées, et à partir de 29:30 pourquoi il y en a cinq, et elles doivent avoir une forme précise une fois déployées - elles ne sont pas de simples miroirs.

[Robert64]

Et du côté du WEBB, ça roupille ?
Ben non! :
(blog Nasa)

Checking Out the Mechanisms in Webb’s NIRSpec Instrument

"This week, the Webb team has been working on the fourth stage of mirror alignment, called Coarse Phasing, which measures and corrects smaller height differences between the mirror segments.

In the meantime this past week, Webb’s Near-Infrared Spectrograph (NIRSpec) team successfully finished the check-out and initial characterization of three crucial onboard mechanisms. Today, members of the team join us to share more about the inner workings of this instrument, which was contributed by ESA (European Space Agency):

“To work properly as a spectrograph, NIRSpec has three mechanisms: a Filter Wheel Assembly (FWA), a Grating Wheel Assembly (GWA), and a Refocus Mechanism Assembly (RMA). The gratings in the GWA spread the incoming light over its colors or wavelengths to make a spectrum. The filters in the FWA block the wavelengths that are outside the range of interest to prevent contamination between different optical paths, or ‘orders.’ The RMA adjusts the instrument focus.

This NIRSpec diagram shows the placement of the Filter Wheel Assembly (FWA), a Grating Wheel Assembly (GWA), and a Refocus Mechanism Assembly (RMA). Credit: STScI

“We operated the Filter Wheel Assembly first, cycling it through all eight of its positions in both forward and reverse directions. Those eight filter wheel positions include five long-pass order-separation filters, two finite-band target acquisition filters, and an ‘opaque’ position that serves as the instrument shutter. At each position, we recorded a set of reference data. This data showed us how well the wheel was moving and how accurately it settled into each position. Between each FWA position, we downloaded ‘high-capacity buffer’ data from the positioning sensors, and the NIRSpec team analyzed the data. The data showed that the wheel moved very well even in the first attempt.

We then used a very similar procedure for the Grating Wheel Assembly, which also performed excellently the first time. The GWA is shaped like a miniature Ferris wheel and holds eight optical elements, consisting of six diffraction gratings, one prism, and a mirror. These dispersers separate the incoming light by wavelength, generating spectra that are detected by NIRSpec’s sensor chips.

“The Refocus Mechanism Assembly includes a linear translation stage that holds two flat mirrors. It will be used to fine-tune the instrument focus, compensating for any change in the overall focus position of the Webb telescope that may occur throughout the observatory’s lifetime. After various initial retrievals of the RMA telemetry acquisition chain, the mechanism was moved forward a few hundred steps from launch position. Just like with the FWA and GWA, we used high-capacity buffer readouts to collect reference datasets. After the initial move, we commanded the RMA mirrors to their previous best focus position; successful completions of this test showed us that the RMA is a well-behaved and healthy mechanism.
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