As the JWST must be kept very cold to make accurate observations of distant astronomical objects, it has been designed with a large sunshield that blocks light and heat from the Sun. In order for such a shield to work properly, the Sun's rays must be constantly coming from the same direction. To achieve this outcome, JWST will be put into a relatively large "halo orbit" around L2. From the L2 point, the Earth constantly shades one third of the Sun's light as it periodically wobbles about the Earth-Moon barycenter; occasionally lunar eclipses will partially obscure more of the solar disk. However, the radius of the telescope's orbit around L2 will be so large that neither the Earth nor Moon will eclipse the Sun, allowing the shield to deal with a relatively constant sunlight environment. This was considered to be more important than attempting to utilize the Earth's shadow to block some of the sunlight, in an orbit nearer the exact L2 point.[citation needed] JWST's sunshield, made of polyimide film, has membranes coated with aluminum on one side and silicon on the other.
The sunshield is designed to be folded twelve times so it will fit within the Ariane 5 rocket's 4.57 m × 16.19 m shroud. Once deployed at the L2 point, it will unfold to 12.2 m × 18 m. The sunshield was hand-assembled at Man Tech (NeXolve) in Huntsville, Alabama before it was delivered to Northrop Grumman in Redondo Beach, California for testing.
