James Webb Space Telescope inside Chamber A
The James Webb Space Telescope's combined optical and science instrument element (OTIS) undergoing cryogenic testing inside Chamber A at NASA's Johnson Space Center in September 2017. The temperature inside the chamber was approximately 40 kelvin (-233 degrees Celsius).
A photogrammetry camera was placed inside the chamber to measure the telescope's alignment and to monitor the effect of extremely cold temperature on the black Kapton® material that is fitted to block unwanted light from behind the telescope. Also visible are the hexagonal primary mirror segments. The bright "stars" shining in this long-exposure photograph are photogrammetry targets that were used to measure extremely precise movements of the telescope as it cooled.