Scientists and engineers on the NASA/ESA/CSA James Webb Space Telescope team have successfully worked through the second and third out of seven total phases of mirror alignment.
During this phase of Webb’s 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. Image credit: NASA / STScI.
“We still have work to do, but we are increasingly pleased with the results we’re seeing,” said Webb’s optical element manager Lee Feinberg, a researcher 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.”
After moving what were 18 scattered dots of starlight into Webb’s signature hexagonal formation, Feinberg and colleagues 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.
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 the sensor of Webb’s Near Infrared Camera (NIRCam).
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.
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 Webb 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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This article is based on text provided by the National Aeronautics and Space Administration.
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