James Webb obtained the first images of stars, and now it’s time to begin aligning the equipment that will power the $10 billion observatory operation.
NASA is calibrating the mirrors of the observatory. Engineers have completed the first step of this approach, known as “Segment Image Identification,” The scientists modified each of Webb’s 18 primary mirror segments to align 18 unfocused replicas of a single star in a hexagonal pattern. Then, each starlight dot is tagged with the mirror segment that captured it.
After completing the image array, the team moved on to the second alignment step, known as “Segment Alignment.” During this step, the team will repair substantial positioning faults in the mirror segments and update the secondary mirror alignment, making each dot of starlight more precise. When this “global alignment” is complete, the team will go on to the next phase, “Image Stacking,” which will stack the 18 light spots 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!”