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James Webb Space Telescope

sunshield deployment

The whole telescope will be shielded from Sun and Earth light by a large sunshield. It is sized about 22 x 10 meters, giving it a instantaneous Field-of-Regard that covers about 40% of the sky at any time. The sunshield will be folded around the Optical Telescope Element during launch, giving it protection, and will be unfolded during orbit insertion.

JWST showing Sunshield subsystem

The sunshield has a 5 layer, "V" groove radiator design of lightweight reflecting material. It reduces the 300 kilowatts it receives from the Sun to a mere 23 milliwatts at the back, sufficient to sustain a 300K temperature drop from front to back. With a back sunshield temperature of ~ 90K, the primary mirror, the optical truss, and the instrument payload can radiate their heat to space and reach cryogenic temperatures of 30-50K. These low temperatures and the total blocking of direct or reflected sunlight are crucial to the scientific success of JWST. Combined with the L2 orbit, the large sunshield provides a stable, cold environment with a minimum of background radiation.

The images below are representations of the cold and warm sides of the sunshield.

JWST warm side
JWST cold side