Technicians successfully performed a critical test on Webb's 5-layer sunshield by fully deploying each of its uniquely sized layers to the same position that they will have while orbiting the Sun a million miles away from Earth.

As an infrared optimized telescope, it is imperative that Webb’s optics and sensors remain impressively cold, and its sunshield is key for temperature regulation. The sunshield separates the observatory into a warm side that always faces the Sun (thermal models show the maximum temperature of the outermost layer is 383 Kelvin or approximately 230 degrees Fahrenheit), and a cold side that always faces deep space (with the coldest layer having a modeled minimum temp of 36K or around minus -394 degrees F). The oxygen present in Earth’s atmosphere would freeze solid at the temperatures experienced on the cold side of the sunshield, and an egg could easily be boiled with the heat encountered on the warm end.

Image credit: NASA/Chris Gunn