Transcript stis status
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 ~ 39000 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.