JWST's Near InfraRed Spectrograph (NIRSpec) - filter wheel view
This view of JWST's Near InfraRed Spectrograph (NIRSpec) shows the filter wheel - in the centre of the instrument. This carousel holds eight interchangeable filters.
Behind the filter wheel is a multi-layered optically opaque baffle (looking somewhat like a wrinkled sheet) to protect the instrument from stray light. During launch, very strong sound waves propagate within the instrument and some parts of NIRSpec, in particular the micro-shutter assembly, are very sensitive to the pressure differences across this baffle. A labyrinth of openings is incorporated into the baffle to allow the passage of air during launch. The openings have a secondary purpose of allowing air through during depressurization of the spacecraft. Two of these square openings can be seen here in one of the layers, with bars across them.
The refocus mechanism assembly (RMA) is in front of the filter assembly. The white back of one of the two RMA mirrors, showing the stiffening ribs can be seen. This mirror is attached to the grey strut with triangular cross members. Behind this mirror, and at an angle to it, is the reflective side of the second refocusing mechanism mirror. These mirrors are coated with a highly reflective protected silver coating.
The RMA compensates for any changes in the telescope's focal position that may occur during launch and throughout the mission lifetime - it ensures that the telescope focal surface is correctly reimaged on the micro-shutter assembly.
The shiny square in the foreground is a gold-coated contamination witness sample. It is a very light, standard device used to monitor the cleanliness during assembly and testing of spacecraft. Once in space, it will serve no further function.
NIRSpec is developed by ESA with EADS Astrium Germany GmbH as the prime contractor.