James Webb begins aligning three of its instruments

The James Webb Space Telescope recently hit a big milestone when engineers completed the alignment of its mirrors. But there is still a lot to do before the telescope is ready to begin science operations this summer. With the mirrors aligned with Webb’s instruments, NIRCam, now the team needs to work on aligning the other three instruments, and it recently began to do that with a process called multi-instrument multi-field (MIMF) alignment.

The six-week MIMF alignment process will align the three instruments plus Webb’s guidance system, called the Fine Guidance Sensor (FGS). This process is necessary to allow Webb to switch seamlessly between its different instruments. All the cameras observe at the same time, so if researchers want to look at a particular target like a star using different instruments, the telescope needs to be repointed to move the target into the field of view of the new instrument.

NASA scientists have shared more about how the MIMF alignment works in a blog post. “After MIMF, Webb’s telescope will provide a good focus and sharp images in all the instruments. In addition, we need to precisely know the relative positions of all the fields of view,” wrote Jonathan Gardner, Webb deputy senior project scientist, and Stefanie Milam, Webb deputy project scientist for planetary science, at NASA’s Goddard Space Flight Center.

“Over last weekend, we mapped the positions of the three near-infrared instruments relative to the guider and updated their positions in the software that we use to point the telescope. In another instrument milestone, FGS recently achieved ‘fine guide’ mode for the first time, locking onto a guide star using its highest precision level. We have also been taking ‘dark’ images, to measure the baseline detector response when no light reaches them – an important part of the instrument calibration.”

The next instruments to be aligned will be the Near-Infrared Spectrograph and the Near InfraRed Imager and Slitless Spectrograph, which along with NIRCam are the three near-infrared instruments. The final instrument, the Mid-Infrared Instrument or MIRI, will be the last to be aligned as it still needs to be cooled down to its operating temperature, which is an almost unfathomably chilly seven degrees above absolute zero.

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