Design for the NIRSpec Optical Assembly Cover

NIRSpec is a near-infra-red spectrometer and one of the four instruments onboard the James Webb Space Telescope (JWST). The JWST observatory will be placed at the second Lagrange point (L2). The instrument will be operated at about 30 Kelvin.

Temperature stability and controlled heat rejection to dedicated JWST radiators are important issues of the NIRSpec thermal design. Besides thermal insulation, the NIRSpec Optical Assembly Cover also has to provide light tightness and stray light suppression to prevent unwanted light entering the instrument. Air tightness is needed to allow a controlled purge gas flow for contamination prevention while allowing proper air venting during launch. Because of mass constraints a cover employing two-foil Kapton blankets supported by aluminum posts and a wire tent was chosen. Failure tolerance and cleanliness are other important design drivers.

This paper describes the design solutions established to fulfil the contrary requirements