After the exciting deployment process is complete, the James Webb Space Telescope team is now taking on another challenge: aligning the telescope’s mirror segments. This slow, months-long process is necessary to fine-tune individual optical elements into one large, accurate telescope.
The main mirror of the telescope consists of 18 golden hexagons made of beryllium that fit together to form a huge mirror 6.5 meters in diameter. It also has a secondary mirror which is smaller round in shape and is located at the end of the boom arms. All of this requires careful tuning to be in the correct position to make the telescope as accurate as possible.
To achieve this, engineers began by sending commands to 126 actuators that would move the main mirror segments as well as six secondary mirror positioning devices to make sure they were working. Once confirmed, they could begin to move the segments away from the mufflers they sat on during take-off to absorb the vibrations in a process that would take around 10 days.
Adjusting the mirrors will take around three months in total and will require a lot of small, careful tweaks. “Getting there will take a little patience: computer-controlled mirror actuators are designed for very small movements measured in nanometers,” wrote Marshall Perrin of the Space Telescope Science Institute at blog post. “Each of the mirrors can be moved with incredibly precise precision, with adjustments as small as 10 nanometers (or about 1 / 10,000 of the width of a human hair). Now, instead, we use the same actuators to move one centimeter. So these initial deployments are by far the biggest moves Webb’s mirror actuators will ever make in space. ”
In addition, for safety reasons, each actuator must act individually and can only operate for a short time to limit the amount of heat generated and spread to very cold mirrors. So it will be a long and slow process to fine-tune your mirrors.
“This may not be the most exciting time in launching Webb, but it’s okay,” wrote Perrin. Do not rush. During the days in which we slowly deploy mirrors, these mirrors also slowly cool down, radiating heat into the coolness of space. The instruments also cool down in a gradual and carefully controlled manner, and the Webb continues to gently slide towards L2. It does it slowly and steadily for all these gradual processes that each day bring us a little closer to our ultimate goal of mirror alignment. ”