STIS STATUS Charles Proffitt TIPs May 21, 2009

STIS Status - Status of Repair Results of FT Amp B Bias Anomaly Changes to SMOV Plan

Status of STIS Repair LVPS 2R Card Successfully inserted Aliveness test passed –All commanded mechanisms moved –Heaters work –+30 V lamp power supply available Functional test passed with some issues

Functional Test Readout electronics for both MAMAs tested Images for all three detectors read out CCD primary amp (D) may have a modest increase in read noise (5.3 e - -> 5.8e - ) Issues –Due to error in commanding, CCD shutter did not open to record lamp light –CCD Amp B showed a bias anomaly

STIS CCD AMP B Bias Anomaly Image taken using CCD B amp –Had bias level elevated by ~ DN 2 most significant bits always = 1 –Looks as if it a used different gain than that commanded –Tiger team formed to see if this might represent an electrical problem that might endanger STIS CCD or STIS Instrument

STIS CCD AMP B Bias Anomaly - cont All measurable telemetry, including voltages and current completely nominal for commanded gain settings. Preliminary conclusion that nature of fault is very unlikely to result in a dangerous short (digital rather than analog error) An Interpoint Converter should protect the rest of STIS even if a short to a power line were to occur. 2 examples of a similar anomaly found in pre-launch amp B data Detector was unusually cold due to long power-off during repair Can’t turn off affected amp and still use CCD (missing drain voltage would flood detector) As long as the B amp is powered no safety reason not to use it. –Amp D normally preferred because of lower read noise, but amp B useful for some charge transfer calibrations. –If anomaly is persistent, can use Amp A & C combo for these tests.

Preliminary Plan Since any risk appears extremely small and STIS CCD supports the majority of STIS Science, will proceed with using STIS CCD. Will slip STIS SMOV schedule approximately one week, so engineers and management can confirm preliminary recommendations before recovering STIS from safe.