The science instrumentation for the James Webb Space Telescope (JWST) has concluded its Phase A definition stage. We have developed a concept for the JWST Fine Guidance Sensor (FGS), which will form the Canadian contribution to the mission. As part of the JWST re-plan in early 2003, the FGS design was recast to incorporate a narrow-band (R~100) science-imaging mode. This capability was previously resident in the NIRCam instrument. This FGS science mode makes use of tunable filters and filter wheels containing blocking filters, calibration sources and aperture masks. The science function of the FGS Tunable Filters (FGS-TF) remains complementary to the NIRCam science goals. Narrow-band FGS-TF imaging will be employed during many of the JWST deep imaging surveys to take advantage of the sensitivity to emission line objects. The FGS-TF will also provide a coronagraphic capability for the characterization of host galaxies of active galactic nuclei and for the characterization of extra solar planets. The primary function of the FGS remains to provide the sensor data for the JWST Observatory line-of-sight stabilization system. We report here on the overall configuration of the FGS and we indicate how the concept meets the performance and interface requirements.
The MOPITT instrument operates on the principle of correlation spectroscopy where the incoming signal is modulated by gas filter and chopper mechanisms and synchronously demodulated within the signal processing system. The performance and flexibility required by the MOPITT instrument resulted in the development of a novel timing control and signal processing design. This design synchronizes modulation and demodulation from a central programmable timing control unit. The data collection system performs a highly linear sigma-delta analog-to-digital conversion prior to signal demodulation. The demodulation operation includes data averaging which reduces the sampled signal bandwidth and extends the signal to noise ratio of the data to in excess of the analog-to-digital converter's rated 16-bit dynamic range.