The filter wheel assembly (FWA) is an integral and important sub-system of the Near Infrared Camera (NIRCam)
instrument on the James Webb Space Telescope (JWST). The optic elements in each of the four FWA mechanisms on
NIRCam are used to conduct science operations as well as calibration of the NIRCam instrument and the JWST
observatory. The FWA mechanism can position one of 12 different filters in the optical path of the camera and position
one of 12 different pupil optics in the same path. The filters and pupil optics are mounted in two separate wheel
assemblies in the FWA that can be positioned independently to provide the desired optical configuration for imaging.
Along with the rest of the instrument, the FWA operates at cryogenic temperatures and is used for both short and long
wavelength imaging. This paper reviews significant elements of the FWA mechanism design.
We will discuss a fret wear solution developed for the James Webb Space Telescope NIRCam filter wheel
assembly by implementation of a hard coating. With mechanisms and structures designed for space flight
application, titanium is often selected as the choice material of construction. Titanium offers a low-density
high strength material that is good for use with many optical instruments due to its' favorable thermal
properties. An important factor to consider with titanium mechanisms and structures are component fits
and the vibration environment that must be survived during launch. In many instances, small (slip) fits
between titanium components can cause fret wear during launch induced vibration. Titanium is
particularly susceptible to fret wear, although other materials also demonstrate the fret wear. Fretting is
adhesive failure of a material that experiences impact and micro-slip with an adjacent part. The
mechanism of fret wear involves small particles that are pulled from the surface of parts that turn into hard
oxides that further accelerate the wear between the parts. To mitigate fret wear, the mechanism or
structure can be designed to eliminate all slip fits altogether, lubricants may be added to the wear surfaces
or hard coatings can be applied to the wear surfaces when the other approaches are not feasible. For the
NIRCam filter wheel assembly, which must operate at 35K and remain optically clean, only hard coatings
are feasible. A discussion of several coating alternatives and associated wear testing will be presented
along with the selection of an optimal solution.
The mechanical design of any optic mount requires an understanding of the sensitivities of the optical design. The design of the filter optic mounts used on the James Webb Space Telescope - NIRCam filter
wheel assemblies have been designed to support the optics in a manner that does not compromise optical performance, while coping with several environmental conditions. We will review the design of the NIRCam filter optic assemblies and confirm the merits of the approach chosen to mount the optics, considering thermal, vibration and stress effects.
Lockheed Martin is developing an innovative and adaptable optical telescope comprised of an array of nine identical afocal sub-telescopes. Inherent in the array design is the ability to perform high-resolution broadband imaging, Fizeau Fourier transform spectroscopy (FTS) imaging, and single exposure multi-spectral and polarimetric imaging. Additionally, the sensor suite's modular design integrates multiple science packages for active and passive sensing from 0.4 to 14 microns. We describe the opto-mechanical design of our concept, the Multiple Instrument Distributed Aperture Sensor (MIDAS), and a selection of passive and active remote sensing missions it fulfills.