After launch, engineers on Earth will need to make corrections to
the positions of Webb’s primary mirror segments to bring them
into alignment.
This will ensure they will produce sharp, focused images.
Webb’s primary mirror segments can be adjusted in extremely
minute movements.
In steps of about 1/10,000th the diameter of a human hair!
Engineers determine how much each segment must be moved
through a process called wavefront sensing and control.
During this process, engineers point Webb at a bright star and
take 18 out-of-focus images of that star, one from each
primary mirror segment.
They then use computer algorithms to determine
how much they must move the mirror segments to align them.
Alignment begins about 40 days after launch, taking
several months to complete.
Once Webb makes observations, its mirrors will be checked
every few days to ensure they are aligned.