Spectrometer

The spectrometer, shown in Figure 2-4, consists of a stainless steel vacuum housing, an entrance aperture wheel assembly, a stainless steel diffraction grating, a photon counting microchannel plate detector, a reference calibration lamp, and two redundant vacuum ion pumps. The spectrometer housing is fabricated of stainless steel to produce a clean vacuum environment and a stable, passive thermal design. Because its thermal expansion coefficient ($\alpha = 1.7 \times 10^{-5}~{\hbox{$^\circ$}}~\rm C^{-1}$)is considerably higher than that of the INVAR metering structure, the location of the mounting ring on the spectrometer was chosen such that the different thermal expansion rates of the stainless steel housing and the INVAR metering structure produce no net change in the location of the spectrometer entrance aperture relative to the primary mirror over the operating temperature range of the telescope.

 

Figure 2-4: The spectrometer consists of a stainless steel vacuum housing, an entrance aperture wheel assembly, a stainless steel diffraction grating, a photon counting microchannel plate detector, a reference calibration lamp, and two redundant vacuum ion pumps.