James Webb Space Telescope sunshield

To make observations in the near and mid infrared spectrum, the JWST must be kept very cold (under , some parts under 40K), otherwise infrared radiation from the telescope itself would overwhelm its instruments. Therefore, it uses a large sunshield to block light and heat from the Sun, Earth, and Moon, and its position near the Sun-Earth Lagrange point keeps all three bodies on the same side of the spacecraft at all times. Its halo orbit around L2 avoids the shadow of the Earth and Moon, maintaining a constant environment for the sunshield and solar arrays. The sunshield acts as large parasol allowing the main mirror, optics, and instruments to passively cool to or cooler, and is one of the enabling technologies that will allow the JWST to operate. The kite-shaped sunshield is about in size, from front to back. The sunshield has five layers to mitigate the conduction of heat. and Kapton is known to degrade after long term exposure to Earth conditions. The sun-facing layer is thick, and the other layers are thick. All layers are coated on both sides with 100 nm of aluminum, and the Sun-facing sides of the outermost two layers are also coated with 50 nm of silicon "doped" with other elements. This helps the material survive in space, radiate excess heat, and to conduct electricity, so a static charge does not build up on the layers. The sunshield allows the optics to stay in shadow for pitch angles of +5° to −45° and roll angles of +5° to −5°. The layers are designed with Thermal Spot Bond (TSB), with a grid pattern bonded to each layer at intervals. This helps stop a rip or hole from increasing in size should one occur. ==Design and manufacture==

Northrop Grumman designed the sunshield for NASA. The sunshield is designed to be folded twelve times so it can fit within the Ariane 5 rocket's diameter by shroud. When it deployed at the L2 point, it unfolded to . The sunshield was hand-assembled at ManTech (NeXolve) in Huntsville, Alabama before it was delivered to Northrop Grumman in Redondo Beach, California for testing. During launch it was wrapped around the Optical Telescope Element and then later unfolded. During development the sunshield layer material was tested with heat, cold, radiation, and high-velocity micro impacts. Layers The layers are designed so the Sun, Earth, and Moon shine on layer one almost exclusively, sometimes a tiny portion of layer two, and on the other side that the telescope elements only see layer five and sometimes a tiny amount of layer four. The separation between layers, in the vacuum of space, prevents heat transfer by conduction and aids in radiating heat out of the way. Silicon doping of the material causes the purple hue. ==Deployment==

. The sunshield component attaches to the main spacecraft, and its booms expand outward spreading out the heat shield and separating the layers. During launch the shield is folded up; later, when it is in space, it is carefully unfurled. • telescoping booms • stem deployers • spreader bars • cable drives There are two stem deployers inside the telescoping booms. At the end of each MBA is a spreader bar. After a successful launch on 2021 December 25 from the Guiana Space Center, the post-launch deployment of the JWST sunshield proceeded as follows. On December 31, 2021, the ground team at the Space Telescope Science Institute in Baltimore, Maryland began the deployment of the two telescoping "mid-booms" from the left and right sides of the observatory, pulling the five sunshield membranes out of their folded stowage in the fore and aft pallets, which were lowered three days earlier. Deployment of the left side boom (in relation to pointing direction of the main mirror) was delayed when mission control did not initially receive confirmation that the sunshield cover had fully rolled up. After looking at extra data for confirmation, the team proceeded to extend the booms. The left side deployed in 3 hours and 19 minutes; the right side took 3 hours and 42 minutes. Tensioning of layer one, closest to the Sun and largest of the five in the sunshield, began on 2022 January 3 and was completed at 3:48p.m. EST. Tensioning of the second and third layers began at 4:09p.m. EST and took 2 hours and 25 minutes. On January 4, 2022, controllers successfully tensioned the last two layers, four and five, completing the task of deploying the JWST sunshield at 11:59a.m. EST. ==Timeline==

• 2007 or before, Technology Readiness Level (TRL) 6 achieved for the sunshield membrane. • 2018 March 27, NASA announced the presence of tears in the sunshield, contributing to launch delays. • 2021 December 25, successful launching of the James Webb Space Telescope from the Guiana Space Center. • 2021 December 31, initial deployment of the telescoping booms to support and unfurl the sunshield. • 2022 January 3, initial tensioning and separating of the first three layers of the sunshield. ==See also==