Science & Technology

James Webb Space Telescope: Mirror, Mirror … on the way!

Credits: NASA Goddard Space Flight Center

Once the major deployments are complete, Webb will continue its journey to the final halo orbit around L2. In the meantime, there are some small developments in the next few weeks that will constitute the beginning of the months phase of adjusting the telescope’s optical system. This week we started the process of moving the mirror segments (all primary and secondary) from their stowed launch positions. For more information, see Marshall Perrin of the Space Telescope Science Institute, home of the Webb Mission Operations Center.

“To support the movable mirrors while traveling into space, there are three rigid metal pegs on the back of each that can snuggle up to the corresponding holder sockets in the telescope structure. Before launch, the mirrors are all. , The pegs were placed so that they fit snugly into the socket, providing additional support. (Webb pushes the mirror closer to the structure of the telescope, making the mirror more secure during firing vibrations and acceleration. Imagine keeping it.) To clear the pegs, each mirror needs to be unfolded 12.5mm (about 0.5 inches). Socket. This gives the mirrors “room for roaming”. The mirror is ready at the start of the adjustment.

“It takes some patience to get there. Computer-controlled mirror actuators are designed for very small movements measured in nanometers. Each mirror is 10 nanometers (or human). With a small adjustment of about 1 / 10,000) of the width of the hair, you can move with incredibly fine precision. Currently, instead of moving beyond centimeters, we are using the same actuator. Therefore, these early days. Deployment is the largest movement of Webb’s mirror actuators in space.

“And we don’t do all of them at once. Mirror control systems are designed to operate only one actuator at a time. This method is (in terms of the complexity of control electronics). Simple and secure (because computers and sensors can closely monitor individual actuators during operation). In addition, each actuator to limit the amount of heat that enters the web’s very cold mirror from the actuator motor. Can only be operated for a short time at a time. Therefore, the large movement of 12.5 mm in each segment is divided into many short movements that occur in one actuator at a time. The script sent from the Mission Operations Center is human. Directing this process under supervision, alternating between segments, slowly and steadily moving one actuator at a time. At full speed, it takes about a day to move all segments by just one millimeter. It’s about the same speed as the grass grows!

“This may not be the most exciting period of Webb test runs, but it’s okay. It takes time. While we slowly deploy the mirrors, those mirrors also do them. As it radiates heat into the cold of the universe, it keeps cooling slowly. The instrument is also slowly and carefully controlled and cooled, and Webb also keeps slowly outwardly coasting towards L2. Do it slowly and steadily. All these step-by-step processes bring you a little closer to the ultimate goal of mirror alignment every day. “

— Marshall Perrin, Deputy Telescope Scientist, Space Telescope Science Institute

Animation James Webb Space Telescope Mirror alignment and phase adjustment process. credit: NASAGoddard Space Flight Center

James Webb Space Telescope: Mirror, Mirror … on the way! James Webb Space Telescope: Mirror, Mirror … on the way!

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