The Webb telescope's Aft Optics System houses two of the mirrors that direct the light from the universe to the cameras in the observatory. In this episode of Behind the Webb, engineers show how they will test the alignment of the mirrors and the path of light through the telescope from end to end, ensuring proper images.
While engineers are using mostly test components, the actual Aft Optics System that will go into orbit is part of this test. As we get closer to launch, the full telescope will be tested.
NASA and Mary Estacion (STScI)
Publication: June 27, 2016