ACTIVITY TITLE: CCD Anneal
APPLICABLE SMOV REQUIREMENTS: L.10.4.5.1.8, L.10.4.5.1.9
DESCRIPTION: This purpose of this activity is to repair hot pixel damage to the STIS CCD that results from cosmic ray induced radiation damage due to cosmic rays. Radiation damage creates hot pixels in the STIS CCD Detector. Many of these hot pixels can be repaired by warming the CCD from its normal operating temperature near -83°C to the ambient instrument temperature (~ +5°C) for several hours. The number of hot pixels repaired is a function of annealing temperature. So although the CCD during Safing has been warmer (~ −5°C) than its normal operating temperature, the electronics have been off and the CCD has remained cooler than its temperature (+5°C) during anneal procedure.
Pre-anneal CCD characteristics are defined by a series of bias, dark and flat-field exposures (duration: 2 orbits). After these exposures execute, the CCD thermoelectric cooler (TEC) is turned off to allow the CCD detector temperature to rise (from ~ -80°C to +5°C). The CCD is left in the uncooled state for approximately 12 hours. At the end of this period, the TEC is turned back on and the CCD is cooled to its normal operating temperature. Since the CCD on Side-2 does not have a thermistor, at a minimum, a 3 hour period is necessary to ensure that the CCD is cool and stable. After the CCD has stabilized at its operating temperature, bias, dark and flat-field images are repeated to assess the post-anneal CCD performance (duration: 2 orbits). Flat field exposures permit evaluation of any window contamination acquired during the annealing period. The CCD window is coolest during the annealing period because the TEC is powered off. Under normal operations the TEC cools the CCD and the heat generated by the TEC power warms the CCD housing and the CCD window, which is attached to the housing.
IMPLEMENTATION METHOD: Stored commanding
DEPENDENCIES: Execute after STIS-04 and after the TEC has been on and cooling the CCD detector for a minimum of 3 hours. This permits acquisition of pre-anneal CCD performance data. There is no thermostat controlling the CCD temperature on Side-2. This activity needs to execute prior to all STIS SMOV4 activities requiring use of the CCD (e.g. STIS-06).
DURATION: 4 full internal orbits (15000 s) in addition to a 12 hour anneal period and a 3 hour (minimum) cool-down period.
DATA REQUIREMENTS: 0.5 Gbits.
ANALYSES & EXPECTED RESULTS: This activity will permit evaluation of the CCD performance after an extended period in SAFE mode and the effectiveness of the standard CCD annealing procedure under these conditions. This activity is necessary to prepare the CCD for the measurement of its baseline CCD performance characteristics which will be established as the result of STIS-06, the CCD functional test.
COMMENTS: This activity comprises the first three visits of the STIS CCD Hot Pixel Annealing program for Cycle 17 and may be regarded as part of the Cycle 17 calibration program.
AUTHOR/telephone/email: Mary Elizabeth Kaiserfirstname.lastname@example.org
DATE: September 26, 2007