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August 8th, 2019

NASA's James Webb Space Telescope's Secondary Mirror Deploys for the First Time at Northrop Grumman Clean Room

NASA’s James Webb Space Telescope’s Secondary Mirror Support Structure (SMSS) was deployed for the first time using the telescope’s flight electronics at Northrop Grumman’s clean room in Redondo Beach, California.

This milestone marks another major interaction of the Observatory (Optical Telescope and Integrated Science Instrument [OTIS] module and the Spacecraft Element [SCE]), working together as they will in orbit.

Upper image is courtesy of NASA and C. Godfrey, STScI.

Lower image shows Engineers Perry Knollenberg (left) and Paul Reynolds (right) inspecting Webb’s secondary mirror’s outboard hinge at Northrop Grumman’s clean room in Redondo Beach, California. Photo is courtesy of Northrop Grumman.

The SMSS is the tripod connecting Webb’s round 0.74 meter diameter secondary mirror to the Optical Telescope Element (OTE). The OTE’s large mirror, known as the primary mirror, is comprised of 18 hexagonal segments making up the 6.5 meter diameter mirror. The OTIS acts as the eye of the observatory with the OTE acting as the lens, gathering light coming from space and providing it to the science instruments, which act as the retina.

Webb’s secondary mirror is the second surface that light from the cosmos hits on its path into the telescope. The secondary mirror is supported by three struts that extend out from the large primary mirror. The struts are hollow tubes made of carbon fiber composite that is about 40-thousandths of an inch (about 1 millimeter) thick, built to withstand the extreme temperatures of space.

Every interaction with Webb is complex, especially building and testing it in a 1-G environment where gravity affects everything. Webb is designed to work in a zero-G environment, therefore testing deployments on the ground requires offsetting and negating the effect of gravity to simulate on orbit conditions.

A view of NASA’s James Webb Space Telescope’s Primary Mirror and deployed Secondary Mirror Secondary Mirror Support Structure at Northrop Grumman’s clean room.

Photo is courtesy of the company.

The deployment was the first time Webb’s secondary mirror’s deployment and latching motors were driven by the electronics in the spacecraft bus, which used the flight software reading the flight telemetry in the exact same way that it will be done in flight. In this joint effort, electrical and mechanical engineering teams across NASA and Northrop Grumman worked together to successfully execute this milestone.  This was also the last time the SMSS will be deployed on the ground — the next time will be after launch in space.

Scott Willoughby,VP and Program Manager, James Webb Space Telescope, Northrop Grumman, said that moving into a phase where the company can begin using Webb’s actual flight electronics in the spacecraft to operate all elements in the remainder of the observatory is remarkable. The deployment of the SMSS marks a successful milestone for Webb, as the firm moves toward full integration of OTIS to the SCE later this year.