To detect faint infrared light from the extraordinarily ancient, distant objects that are the telescope's primary targets, its sensitive mirrors and instruments must be cooled below -370 degrees Fahrenheit. The observatory's sunshield, which is the size of a tennis court when fully deployed, helps keep these instruments in the shade, protecting them from the heat of the sun and the hotter parts of the telescope. This photo shows a one-third-size sunshield layer undergoing tension testing.