The James Webb Space Telescope (JWST) will observe primarily the infrared light from faint and very distant objects. But all objects, including telescopes, also emit infrared light in the form of heat energy. To avoid swamping the very faint astronomical signals with radiation from the telescope, the telescope and its instruments must be very cold, at an operating temperature of under 50 K (-370 ºF).
The observatory is dominated visually by the sunshield subsystem, which separates the observatory into a warm, Sun-facing side and a cold, anti-Sun side. The observatory will be pointed so that the Sun, Earth, and Moon are always on one side, and the sunshield will act like a parasol, keeping the Optical Telescope Element and the Integrated Science Instrument Module cool by keeping them in the shade and protecting them from the heat of the Sun and warm spacecraft bus electronics.
In addition to providing a cold environment, the sunshield provides a thermally stable environment. This is essential to maintaining proper alignment of the primary mirror segments as the telescope changes its orientation to the Sun. When fully deployed, the sunshield will be about the size of a regulation tennis court.
The sunshield has five layers of material, and each successive layer of the sunshield is cooler than the one below. The heat radiates out from between the layers, and the vacuum between the layers is a very good insulator.
ManTech’s engineering team measured the membrane shape to verify dimensional requirements are met. The test was done on all five layers of the sunshield to give engineers a very precise idea of how the entire sunshield will behave once in orbit.
After all five layers of the full-size sunshield completed the test and model analysis, they were sent to Northrop Grumman’s high bay in Redondo Beach, CA for testing on how the sunshield deploys from its folded state in the launch vehicle. The month-long testing uses flight-like material for the JWST sunshield, test frame, and hardware attachments. The test sunshield layer is made of Kapton®, a very thin, high-performance plastic with a reflective metallic coating.