It's coming together! The mirror alignment process for the James Webb Space Telescope has now been completed in two more phases. The team made more changes to the mirror segments this week. For the first time, all 18 mirror segments could work together to create one unified image.
This view of the star HD 84406 shows one image instead of the 18 that we saw earlier this week. Engineers at NASA say that the image will be even sharper after future alignment steps.
Lee Feinberg, an optical telescope element manager for Webb, said in a post that they are increasingly pleased with the results they are seeing.
The star that engineers and scientists are using to focus the telescope is a G-type main-sequence star that is a lot like our own Sun. The images of this star were taken by the NearInfrared Camera ( ) instrument at the JWST.
The two steps that were taken this week are segment alignment and image stacking. Most of the positioning errors for the segments are corrected by segment alignment. A process called Phase Retrieval uses mathematical analysis to determine the position of segments. The segments don't work together as a single mirror at this stage.
The team corrected large positioning errors of its primary mirror segments and updated the alignment of the secondary mirror.
The images from each segment are put on top of each other. The individual segment images are moved so that they fall at the center of the field of view to create a unified image. The light is put in one spot on the detector.
The resolution will be 5 times better if the light arrives at the detector in perfect unison.
Next, the team will make even smaller adjustments to the mirrors.
The mirror segments are still acting as small telescopes despite the fact that all the light from a star is in one place. The segments need to be lined up with an accuracy smaller than the wavelength of the light.
The fourth phase of mirror alignment is called Coarse Phasing, and the team is working on that. The team can identify and correct vertical displacement between the mirror segments. The single dot of starlight will be sharper in the coming weeks.
The process will be iterative, where once a certain level of alignment and focus is achieved, the engineers may have to go back and re-do certain steps to achieve perfect alignment.
Feinberg told me last month that you need to align the mirrors, check them, and then go back through the entire process again.
Team members are sharing their experiences and giving more information on the alignment process at the JWST blog.
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