Today, the final deployment of the primary mirror for the Webb telescope was successfully completed; earlier this week the secondary mirror had deployed successfully to its position in front of the primary mirror, and a couple of days ago, the first “wing” of the mirror was moved into place. The second “wing” deployment was executed this morning, taking about four minutes to do so, once the command to begin the sequence was given.
The next two-plus hours were spent carrying out the final latching and stabilization of all the mirrors; this was done very slowly and carefully. The latches had to be put into place and calibrated at the correct tension across the entire primary mirror, similar to how when one changes a tire, the bolts are tightened in a particular sequence to ensure that the tire is vertical when finally installed. If one bolt is tightened too much too soon, it can cause the tire to be off-kilter.
Now, the Mission Operations Center will wait about a week or so for everything to cool down even further, and then begin to maneuver each individual mirror, such that the entire primary mirror will be one smooth surface. Each mirror can move with 6° of freedom, can change its curvature, and each one has seven actuators (mounted on the rear of the mirror).
Each actuator can move the distance of a fraction of the width of a human hair; this minute movement is required as each of the 18 mirrors will be adjusted. First, they begin by focusing on a random bright star; with each of the mirrors reflecting 18 different images. Gradually, each mirror will be manipulated to bring the image into focus at the center of the primary mirror (the dark area, which is the “workhorse” section of the telescope); which is called “stacking the images.” It is expected to take up to three months.
