The Optical Components of the NIRSPEC Wheel Mechanisms

The Near-Infrared Spectrograph (NIRSPEC) on board the James Webb Space Telescope can be reconfigured in space for astronomical observation in a range of NIR sub-bands as well as spectral resolutions. Reconfiguration of the NIRSpec instrument will be achieved using a Filter Wheel Mechanism (FWA) which carries 7 transmission filters and one reflective mirror and a Grating Wheel Mechanism (GWA) which carries six gratings and one prism. The dispersive components on the grating wheel (GWA) cooperate with the edge transmission filters mounted on the filter wheel (FWA) which block the higher dispersion orders of the gratings. The paper gives an overview on the design of all optical elements, their key requirements and the employed manufacturing approach. Test results from breadboard and component level qualification phase are also given.