One of the fascinating bits is how much engineering has gone into keeping the detectors cold. Because JWST is (primarily?) taking images in the mid-IR region, it is crucially important to keep the detectors cool otherwise you'd just be swamped in background noise. Keeping things cold in space is despite it being a cold place actually extremely difficult, because you can't use convective cooling. If something sits in the sun "all-day" it gets warm, so the whole reason for the sunshield is to keep the instruments cool. On top of that they are using active cooling for the (IIRC) first time on a satellite. I saw a presentation from one of the engineers two years ago and it's absolutely fascinating stuff.