STIS STATUS
Charles Proffitt
TIPs May 21, 2009
STIS Status •
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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.