NASA announced today that two more steps in aligning the James Webb telescope’s (JWST) mirrors have been accomplished. Webb’s performance indicates that it will meet or even exceed its design intent. “So far, we’re finding that the performance is as good [as] or better than our most optimistic projections,” explains Lee Feinberg, system manager for the Webb telescope.
As part of the announcement, a stunning image was released showing a sharp focus on the target star and many galaxies in focus behind it.
The primary mirror of the Webb telescope is composed of 18 separate segments that, when aligned correctly, act as one large mirror. As part of the mirror alignment process, each segment’s images are identified and gathered into a single point. The project was completed earlier this month. Essentially, the light had gathered in one place, but it was taking different paths from each segment, thus they didn’t act as a single mirror.
The Webb optical telescope element manager Marshall Perrin said that there were microns between the segments’ alignments. According to Perrin, the final alignment would take the segments to a nanometer-scale precision-“a few hundred atomic diameters is what we need here.”
That seems to be the case. “We have now achieved what’s called the diffraction-limited alignment of the telescope,” Perrin said. “The images are focused together as finely as the laws of physics allow. This is as sharp an image as you can get from a telescope this large.”
This is only the beginning for Webb
This is the point where the telescope’s primary instrument, the Near-Infrared Camera, is aligned with the mirror. In the next few steps, however, the telescope will be aligned with all three additional instruments so that all the mirrors can operate effectively. Along with NASA’s ability to adjust the positioning, shape, and curvature of each segment, the secondary mirror and instruments themselves can be shifted to ensure alignment.
Final tweaks may still be necessary after this process, but after that, all that remains is constant calibration to keep everything aligned. At the latest, NASA expects to complete the alignment process by early May.
The science can then begin–Webb operations’ Jane Rigby said that a full year’s worth of observations is already planned. Nobody has yet revealed what the high-priority science targets are for Webb yet, although everyone will admit to the selection of a few high-quality science targets that will yield beautiful images.
For the time being, all focus is on the galaxies appearing behind the star used for alignment. The process has proceeded smoothly, which has relieved researchers greatly. During this project, Rigby said, “If things didn’t work, we would have gone home.” Instead, the whole process has gone smoothly.
The administrator of NASA’s Science Mission Directorate, Tom Zurbuchen, said, “All the worries I had, they’re all behind us now.”