Tuesday, 27 July 2021

Why is the James Webb Space Telescope Delayed Again?


Astrum on Youtube explains: Has the JWST been delayed again?

The James Webb Space Telescope (JWST or "Webb") is a joint NASA-ESA-CSA space telescope that is planned to succeed the Hubble Space Telescope as NASA's flagship astrophysics mission. The exciting JWST will provide improved infrared resolution and sensitivity over Hubble, and will enable a broad range of interesting investigations across the fields of astronomy and cosmology, including observing some of the most distant events and objects in the universe, such as the formation of the so-called first galaxies.

The primary mirror of the JWST, the Optical Telescope Element, is composed of 18 hexagonal mirror segments made of gold-plated beryllium which combine to create a 6.5 m (21 ft) diameter mirror - certainly considerably larger than Hubble's 2.4 m (7 ft 10 in) mirror. Unlike the Hubble telescope, which observes in the near ultraviolet, visible, and near infrared (0.1 to 1 μm) spectra, the JWST will observe in a certain lower frequency range, from long-wavelength visible light through mid-infrared (0.6 to 28.3 μm), which will allow it to observe high redshift objects that are too old and too distant for Hubble to observe. The telescope must be kept very cold in order to observe in the infrared without interference, so it will be deployed in space near the so-called Sun-Earth L2 Lagrange point, and a large sunshield made of silicon-coated and aluminium-coated Kapton will keep its mirror and instruments below 50 K (−223.2 °C; −369.7 °F).

"Kapton" is a polyimide film developed by DuPont in the late 1960s that remains stable (in isolation) across a wide range of temperatures, from −269 to +400 °C (−452 to 752 °F; 4 to 673 K). Kapton is used in, among other things, flexible printed circuits (flexible electronics) and space blankets, which are used on spacecraft, satellites, and various space instruments.

The chemical name for Kapton K and HN is poly (4,4'-oxydiphenylene-pyromellitimide). It is produced from the condensation of pyromellitic dianhydride and 4,4'-oxydiphenylamine. Kapton synthesis is an example of the use of a dianhydride in step polymerization. The intermediate polymer, known as a "poly(amic acid)", is soluble because of so-called strong hydrogen bonds to the polar solvents usually employed in the reaction. The so-called ring closure is carried out at high temperatures of 200 - 300 °C (392 - 572 °F; 473 - 573 K).

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