Segmented Space Telescope Mirror Phasing

Space telescopes like JWST launch with a primary mirror folded into 18 independent hexagonal segments, each on its own set of actuators. Right after deployment those segments point in slightly different directions, so a distant star shows up as 18 separate smudges instead of one sharp image. This simulator scatters the segments with an adjustable amount of nanometre-scale piston and tip/tilt error, then runs a wavefront-sensing-and-phasing control loop that drives every segment toward a common focus — watch the 18 dots on the focal-plane panel converge into a single point while the RMS wavefront error and Maréchal-approximation Strehl ratio update live.