STIS Status

TIPSJuly 16, 2009

STIS Status

• STIS MIE anomaly– What is known

• STIS CCD status before the anomaly• STIS MAMA SMOV status

STIS MIE Anomaly• STIS currently suspended• Original suspend (day 187) : Main STIS CS computer unable to get

timecode update from MIE (MAMA Interface Electronics) that was needed to populate the header of a CCD exposure.

– Originally suspected that single event upset had hung up the MIE 486.• 2nd suspend (day 190): Suspended while attempting to copy MIE

memory to CS. Done before full reset in attempt to preserve MIE memory– Theorized that problem with MIE dump was caused by lack of full reset, and

hoped a full reset would clear the problem.– About 1/2 of MIE memory was successfully copied.

• 3rd suspend (191): Did full reset and successfully recovered STIS to operate, but suspended while attempting to copy MIE memory to CS.

– MIE copy to CS seems to have succeeded, but still suspended– Recovery included successful queries of MIE for time code update (I.e., the

original problem from day 187 did not recur). – Observed events suggest transient failure on MIE FIFO Flags interface

between CS and MIE?

STIS MIE Anomaly - cont• What we know:

• The three anomalies occurred during three different circumstances and have three different and - in some aspects - inconsistent signatures

• Observed events suggest transient failure on MIE FIFO Flags interface between CS and MIE

• Investigation is continuing• Perhaps MIE dump problem is separate from original time code

update problem?• STIS still suspended

• Hope to allow resumption of CCD operations soon, while analysis continues.• See if original anomaly reoccurs.• CCD observations could, in principle work around MIE problems• Since anomalies are not yet understood, implications for MAMA

observations are not yet known

• STIS CCD read noise slightly increased from ~ 5.4 e- in 2004 to ~ 5.7 e- now• Side 2 read-noise includes ~ 1 DN of semi-coherent 17 kHz pattern noise

– This pattern noise appears to be unchanged after SM4

STIS CCD Read Noise

STIS CCD Dark Current

• CCD housing temperature (OCCDHT) surrogate for CCD chip T• For comparison these plots scale darks to housing temperature of 18 C• Dark rate increases by 7%/degree of housing temperature• 2009 aft-shroud hotter than 2004

– When MAMAs on, OCCDHT 22-25 C– With MAMAs off, OCCDHT 16-18 C

• RN between 0.009 and 0.013 e-/s, fluctuating with temperature

TDS & CTE effects

• Standard monitor target AGK+81o266 (*’s) shows large scatter at low flux levels (right panel), even in 2004 - correlates with T

• Need to separate T dependence of CTE before deriving final throughput estimates

• CTE extrapolated to zero background as a function of flux level

• 2009 points are at colder T than older data– Expect reduced CTE losses at lower T

MAMA SMOV Status• FUV MAMA

– FUV MAMA HV ramped to full values– Fold test & flat look as expected– Dark current perhaps lower than expected

• NUV MAMA– Initial steps of NUV MAMA HV recovery completed– Have not yet ramped NUV HV to level where tube generates real

counts.• Still need to do initial internal lamp exposures and external

exposures with both MAMAs• Once MAMAs cleared for operations, most SMOV activities for

either or both could be completed in a week if time available.