The James Webb Space Telescope, currently moving in space, is now ready to deploys its mirrors

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NASA controllers on Tuesday completed the deployment of the space ’s five-membrane sun shield, 70-foot. The fifth and final membrane, which like the other four had the thickness of a human hair, was locked into place at 16:58 GMT. The unfolding and tensioning of the sunshield involved 139 of Webb’s 178 release mechanisms, 70 hinge assemblies, eight deployment motors, roughly 400 pulleys and 90 individual cables totaling roughly one quarter of a mile in length. “Unfolding Webb’s sun shield in space is an incredible milestone, crucial to the success of the mission,” said Greg Robinson, Webb’s program director at Nasa Headquarters. This was the first time the shield had been unfurled in the unique “Zero-G” environment of space. The five-layered sunshield will protect the telescope from the light and heat of the Sun, Earth, and Moon. Together, the five layers reduce exposure from the Sun from over 200 kilowatts of solar energy to a fraction of a watt.Webb must be cooled with the sun shield to fantastically cold temperatures (operating temperature will be -230 Celsius) or its own infrared glow will swamp the signals it’s trying to detect.

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Like the sun shield, the telescope’s two principal reflectors must be now deployed by the controllers, who are based at the Space Telescope Science Institute (STScI) in Baltimore, Maryland. The end of this week should see the 74cm-wide secondary mirror extended on 8m-long booms in front of the primary mirror. The telescope is currently moving out to a position 1.5 million km from Earth. “This is the first time anyone has ever attempted to put a telescope this large into space,” said Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate.