The James Webb Space Telescope Observatory - Sunshield

    The James Webb Space Telescope 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 Webb 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 deg F).

    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 that will be about the size of a regulation tennis court.

    Why does the sunshield have five layers instead of just a single thick one? 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. One big thick sunshield would conduct the heat from the bottom to the top more than 5 layers separated by vacuum.

    Here is a photo of a full-scale engineering model, called the pathfinder. Credit: Northrop Grumman

    Want to know more?  Visit the James Webb Space Telescope project home page.