This Robotic Arm Slips James Webb's Mirrors Exactly Where They Need to Be

Illustration for article titled This Robotic Arm Slips James Webbs Mirrors Exactly Where They Need to Be

We’re openly obsessed with the assembly of the segmented origami mirror for the James Webb Space Telescope. A gorgeous photo released today reveals the secret of an enormous robotic arm used to place the mirror segments to within a paper’s width of perfection.

Here’s the full photograph:

Illustration for article titled This Robotic Arm Slips James Webbs Mirrors Exactly Where They Need to Be

James Webb Space Telescope is the first space telescope where the primary mirror is made of individual segments, each individually controlled to ensure perfect alignment. The mirror will fold up during launch, then unfold in space like an origami flower.

But before that can happen, the mirrors need to be mounted onto a frame. Precision is key for placement—every segment can be no more than the thickness of a piece of paper off from its ideal theoretical location. The telescope’s Program Director Eric Smith explains, “A human operator cannot place the mirrors that accurately, so we developed a robotic system to do the assembly.”

The telescope team built the Primary Mirror Alignment and Integration Fixture to lift, position, and lower each mirror segment. One team of engineers maneuvers the robotic arm, while another team takes laser measurements to precisely determine location. All locations are determined with respect to retroreflectors mounted to the frame of the telescope. Once the segment is in the right place, they bolt and glue it in position before moving on to the next segment.

We’re in love with the James Webb Space Telescope, tracking each step of testing the mirrors, getting them polished, and now finally installed. Once complete and launched, the infrared telescope will be the most powerful space telescope yet. It will be used in part to characterize exoplanets in the ongoing search for life beyond Earth.


You can watch telescope assembly (including placing the mirrors!) on a webcam live.


Image credit: NASA/Chris Gunn

Contact the author at or follow her at @MikaMcKinnon.


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Anyone know what the frame is made of? I’m wondering how they handle the different CTE’s of the various materials involved here. Is that Invar? Just curious...?