0609 GMT February 22, 2018
Quoting Randy Kimble, a scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, UPI wrote, "One of the challenges of testing an infrared telescope is that room-temperature objects [such as the walls of the vacuum chamber itself, or the warm electronics systems inside it] glow at the wavelengths of light that the telescope is trying to measure.
"If not carefully controlled, that warm glow can provide an unwanted background in the telescope's images, which would compromise the optical testing."
Due to the telescope's extreme sensitivity to infrared light, scientists are using a cold, gaseous helium shroud inside Chamber A, where the Webb is located, as the innermost of two shrouds used to cool the Webb telescope down to temperatures it will experience while operating in orbit.
The shroud sits inside an outer liquid nitrogen shroud. The two shrouds are thin, cylindrical, metal shells that work together to lower the temperature of the area where the telescope sits.
The two shrouds are nested together inside the chamber similar to Russian Matryoshka dolls with the chamber as the largest ‘doll’, followed by the liquid nitrogen shroud, the cold gaseous helium shroud, and then the smallest ‘doll’ being the telescope itself.
The liquid nitrogen and cold gaseous helium flow through plumbing that crisscrosses the surface of their respective shrouds.
Scientists must protect the shroud doors, which provide access to the shrouds' interiors, to ensure unwanted infrared light is not able to interfere with the telescope.
To do this, engineers used a layer of black Kapton, a thin, opaque, plastic film used to curtain the door into the cold gaseous helium shroud and curtail the amount of light that can get into the shroud through the seam around the door.
Kimble said, "Many people have worked for years on the test design and implementation to keep infrared light, from warm sources in the test chamber, from getting into the telescope beam.
“The final visual inspections and blanket closeouts...are just the icing on that well-baked cake."