James Webb Space Telescope in Chamber A
The James Webb Space Telescope was placed in the NASA Johnson Space Center Chamber A on 20 June 2017 to prepare for its final three months of testing in a cryogenic vacuum that mimics temperatures in space.
Chamber A can simulate an environment where the telescope will experience extreme cold – around 37 K (minus 236 ºC).
In space, the telescope must be kept extremely cold, in order to be able to detect the infrared light from very faint, distant objects. To protect the telescope from external sources of light and heat (like the Sun, Earth, and Moon), as well as from heat emitted by the observatory, a five-layer, tennis court-sized sunshield acts like a parasol that provides shade. The sunshield separates the observatory into a warm, Sun-facing side (reaching temperatures close to 200 ºC) and a cold side (about minus 220 ºC). The sunshield blocks sunlight from interfering with the sensitive telescope instruments.
(Original caption and image source can be found here.)