Scientific Requirements for Thermal Control and Scheduling of the STIS MAMA detectors after SM-3

The installation of the Aft Shroud Cooling System (ASCS) on the next HST servicing mission will increase the scientific productivity of STIS by reducing the dark current in the MAMA detectors. The “dark glow” now observed in the FUV-MAMA detector is expected to go away at the ~24 ο C nominal operating temperature after SM3. For the NUV-MAMA, typical dark currents will range from 800 to 1100 cts/s. However, for periods of roughly 10 days at a time, the dark current can be reduced to 200-450 cts/s. This is accomplished by warming the NUV-MAMA to ~38 ο C for about 15 days, then cooling rapidly to as low an operating temperature as possible (20 o C is assumed here). This ISR presents an analysis of the NUV-MAMA dark current behavior during the HDF-S campaign, where a similar “cooling campaign” was attempted. It then makes predictions for the NUV-MAMA performance after SM3 and presents recommendations for the number and duration of cooling campaigns. Finally, some preliminary technical requirements for such campaigns are set out.