James Webb begins careful, slow process of aligning mirrors

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With the exciting process of deployment complete, the James Webb Space Telescope team is now starting on its next challenge: aligning the telescope’s mirror segments. This slow, months-long process is needed to fine-tune the individual optics into a large, precise telescope.

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The telescope’s primary mirror consists of 18 gold-colored hexagons made of beryllium, which fit together to form a giant mirror 6.5 meters across. It also has a secondary mirror, which is a small round shape and is located at the end of the boom arms. All of these need to be carefully positioned to allow the telescope to be as accurate as possible.

To achieve this, engineers began by sending commands to 126 actuators, which would move the primary mirror segments as well as six instruments that positioned the secondary mirrors to make sure they were working. With that confirmed, they can begin removing the segments from the snubbers they sat on during launch to absorb the vibrations in a process that would take about 10 days.

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Adjusting the mirrors will take about three months in total, and will require many small, careful changes. “It will take a little patience to get there: computer-controlled mirror actuators are designed for extremely small speeds measured in nanometers,” wrote Marshall Perrin of the Space Telescope Science Institute. blog post, “Each mirror can be moved with incredibly fine precision, with adjustments as small as 10 nanometers (or about 1/10,000th of the width of a human hair). Now instead of going above a centimeter we are using the same actuators. So these initial deployments are by far the biggest moves Webb’s mirror actuators will ever make in space.”

In addition, each actuator needs to work one at a time for safety reasons, and may only operate for short periods of time so limiting how much heat it generates and dissipates in very cold mirrors . So it will be a long, slow process to tune the mirrors.

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“This may not be the most exciting period of Web’s commissioning, but that’s okay,” Perrin wrote. We can take the time. During the days when we are slowly deploying the mirrors, those mirrors are also slowly cooling as they radiate away the heat in the cold of space. The devices are also cooling slowly and in a carefully controlled manner, and the web is also slowly moving outwards towards L2. Slow and steady it does for all these gradual processes that move us closer to our ultimate goal of mirror alignment every day. ,




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