SIS Detector

The imaging spectrograph includes two, redundant detectors. Either one can be used since the pop-up mirror, which enters the optical path when the second detector is to be used, is retractable. Only one detector is operated at a time. The detector characteristics are listed in the following table. The use of the secondary detector will lower the sensitivity of the imaging spectrograph due to the extra reflection of the pop-up mirror. The sensitivity with the secondary detector in place will be approximately 75% of the sensitivity with the primary detector since the pop-mirror has the ARC #1200 MgF₂ overcoat. The sensitivities listed in the table are for the original SAIC detector in the primary position.  The newer Photek detectors are less responsive in the UV but have a more stable, band-limited response that is desirable for these observations.

The detector consists of a microchannel plate intensifier with a wedge and strip anode. Since maintanence of performance specifications over the mission lifetime is a design driver, the HVPS is commandable so that the detector gain can be maintained at 4x10**6 even at a charge extraction rate as high as 10 Coulomb/yr.