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Space Telescope Imaging Spectrograph
STIS-19

ACTIVITY TITLE: FUV Dark Measure

ID: STIS-19

APPLICABLE SMOV REQUIREMENTS: L.10.4.5.4.1

DESCRIPTION: The STIS MAMA HV power supplies are turned on only during each day’s block of SAA-free orbits. The FUV MAMA dark current glow has been observed to increase with the length of time the FUV HV power supply has been on. The rate of this daily increase has changed over the years and also appears to be sensitive to temperature. To measure the rate at which the dark current increases, a series of five 1380s FUV MAMA dark exposures spread over 5 or more orbits of a single SAA period shall be taken as soon as possible after the completion of STIS-17. All exposures will be internals and fit into occultation orbits. A second similar block of five exposures should be done near the end of the SMOV period when the temperature of the aft-shroud and STIS are in the range expected for normal Cycle 17 operations.

IMPLEMENTATION METHOD: Stored commanding

DEPENDENCIES: First iteration of five visits should start as soon as practical after the completion of STIS-17, FUV MAMA HV Recovery. The second iteration should be done later, after all significant heat sources in the aft-shroud (including the COS detectors) are operating, and the temperature of the STIS FUV MAMA tube is within the typical range expected for Cycle 17 operations.

DURATION: 300 minutes (ten 1800 s internal visits divided into two groups)

DATA REQUIREMENTS: 0.67 Gbits.

ANALYSES & EXPECTED RESULTS: The FUV dark current will be measured over the whole detector and in the standard regions used to monitor the FUV dark current. These results will be compared to previous trends (STIS ISR 2007-02) and used to estimate the dark current behavior expected during cycle 17.

COMMENTS:

AUTHOR/telephone/email: Charles Proffitt/410-338-4938/proffitt@stsci.edu

DATE: September 7, 2007