Jan 13

Day 19: Moving Mirrors

Engineers Matt Macias and Eve Woolridge take a close look at the James Webb Space Telescope’s primary mirror at NASA Goddard. Credit: NASA/Chris Gunn

What’s Up with Webb – home

Webb’s 18 hexagonal gold mirror segments have been safely locked into a “stowed” position since launch. This is for their protection, since even with a perfect launch such as was provided by the Ariance 5 rocket, the telescope and mirrors experience considerable vibrations as it escapes Earth’s gravity. 

Now that the telescope is fully deployed, engineers started to unlock and move the mirror segments this week in preparation for focusing. This is a slow and deliberate process, and the full release of the mirrors will continue over the next 10 days.

Focusing Webb’s 18 mirror segments so they act as a single mirror is no easy task. Each segment is controlled separately by six tiny mechanical motors, or actuators, located on the segment’s back. Engineers move the actuators in extremely small increments.

Lee Feinberg, Webb Optical Telescope Element Manager at NASA Goddard explained on the NASA Webb website, “Aligning the primary mirror segments as though they are a single large mirror means each mirror is aligned to 1/10,000th the thickness of a human hair. What’s even more amazing is that the engineers and scientists working on the Webb telescope literally had to invent how to do this.”

Focusing the mirror for each of Webb’s instruments will start after it reaches its destination at L2 and continue for the next 3 months. Once operational, the mirror will be checked every few days to make sure it stays in focus.

See the video here for more information: