Sunshield (JWST)

Sunshield is a component of the James Webb Space Telescope, designed to shield the main optics from the Sun's heat and light. This is part of a space telescope, that after it is launched has booms that extend out unfolding a large metal-coated sheet of material. This material blocks the Sun's light and heat, so the telescope, which is like an eye, can see the faint light coming from stars and galaxies. Much like the way a hat with a rim shades its wearer's eyes, the Sunshield shades the telescope. The Sunshield segment includes the layers and its deployment mechanisms, which also includes the trim flap.

The layers of the sunshield provide an insulating layer like a vacuum flask or double layer coffee cup. The layers in between the 5 layers of sunshield, which is something like a candy wrapper the size of a tennis court. Each layer is as thin as a human hair, and is coated with aluminum, this makes it reflect light like a mirror. The purple color of some layers comes from the material silicon which helps the shield be tougher and reflect heat, and is the same material in most computer chips. The telescope is trying to use the Sunshield to stop itself from being warmed by infrared radiation from the sun and other nearby planetary objects, which would otherwise inhibit normal operations of onboard instruments.

The Sunshield acts as large parasol allowing the main mirror and optics and the instruments to passively cool down to at least 50 Kelvin (-370 °F, or -223 °C). It consists of layers of Kapton and is big enough to shade the main mirror and secondary mirror, with only one instrument, the one that observes mid-infrared, needing extra cooling. It has five layers to help stop the conduction of heat, and the layers also have a special coating to emit and reflect heat into space. The first layer is 0.002 inches thick and the rest of the layers are 0.001 inches thick. The kite-shaped sunshield about is 22 meters by 10 meters in size. In operation it will receive about 300 kilowatts of solar radiation, but only pass 23 milliwatts on the other side. It is a V-groove radiator and causes a temperature drop of 300 degrees kelvin/Celsius (570 degrees Fahrenheit) from front to back. The reason why the telescope needs to be cold, is that it needs to be colder than the object that it is attempting to observe. It needs to be that cold to observe heat at those wavelengths, and the Sunshield is a critical part of the telescope to achieve temperatures low-enough for the type of observations it is planning to make. The sunshield membrane is one of the enabling technologies that allowed the design of JWST to be built.

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Wikipedia