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James Webb Space Telescope reaches another milestone as mirror alignment continues: Digital Photography Review

The James Webb Space Telescope has reached another milestone on its path to becoming a fully-operational observatory. NASA has announced that the Webb team has ‘successfully worked through the second and third out of seven total phases of mirror alignment.’ The team will now commence making smaller adjustments to the positions of Webb’s 18 primary mirror segments.

The news comes only a few weeks after NASA announced that the James Webb Space Telescope saw its first star using all of its primary mirror segments. That announcement came shortly after the telescope detected its first photons. The progress has been consistent and steady.

‘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

NASA writes, ‘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.’ The gif below shows the progress that the team has made by correcting large positioning errors.

‘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

Following the ‘Segment Alignment’ phase, the team then stacked the focused dots on top of each other so that the focused light from all the mirror segments delivered photons to the same location on the NIRCam’s image sensor. During the ‘Image Stacking’ process, the team activated six mirrors at a time and directed them to overlap one another. The completed image is below.

‘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

Even though the ‘Image Stacking’ phase features light from a star focused in a single location on NIRCam’s detector, the mirrors are still acting as 18 small telescopes, rather than a single large telescope. The next step is to refine the alignment further. NASA writes, ‘The segments now need to be lined up to each other with an accuracy smaller than the wavelength of the light.’

‘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.’

The next phase, the fourth, is called ‘Coarse Phasing.’ NIRCam will capture light spectra from 20 different pairings of mirror segments. This will allow the team to identify and correct vertical displacement – small differences in height – between the different mirror segments. This will result in a sharper dot of starlight.

NASA anticipates that full scientific operations will commence this summer. For more information on the James Webb Space Telescope and to learn about its mission, click here.

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