May 23, 2022

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The Webb Space Telescope team brings 18 points of starlight into a hexagonal formation

Credit: NASA’s Goddard Space Flight Center

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

Snap web alignment

This early Webb alignment image, with points of starlight arranged in a honeycomb-like pattern in the primary mirror, is called the “image matrix.” Credit: NASA/STScI/J. Dipascual

With the image array completed, the team has now begun the second phase of the alignment: “Fragment Alignment”. During this phase, the team will correct the large positioning errors of the mirror segments and update the secondary mirror’s alignment, making each individual point of starlight more focused. When the “general alignment” is complete, the team will begin the third stage, called “image stacking,” which will bring 18 light spots on top of each other.

web part selection mosaic

Early web alignment image explained

This mosaic image (above), showing 18 random copies of the same star, served as the starting point for the alignment process. To complete the first stage of the alignment, the team moved core mirror segments to arrange the starlight points in a hexagonal image array (bottom). Each point of starlight is marked by the corresponding piece of mirror that captured it. credit: NASA (top); NASA/STScI/J. DePasquale (bottom)

“We orient the clip points into this array so that they have the same relative positions as the physical mirrors,” said Matthew Lallo, systems scientist and director of the Telescopes Branch at the Space Telescope Science Institute. “During general alignment and image stacking, this familiar arrangement gives the wavefront team an intuitive and natural way to visualize changes in clip points in the context of the entire primary mirror. We can now actually watch the primary mirror slowly form into its exact, intended shape!”

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James Webb Space Telescope uses a process called wavefront sensing and control to perfect its vision in orbit. This animation illustrates that process. Credit: NASA’s Goddard Space Flight Center