Update on a Proposed Bakeout

1
Update on a Proposed Bakeout CXC SOT
FOT, ACIS Instrument Team and MSFC Project
Science
2
New Items since Last CUC Briefing (January 2005)

• MIT/ACIS team conducted irradiation tests of
  flight spare CCDs at GSFC in May 2005. MIT/ACIS
  concluded that the CTI increase from another 30
  C Bakeout would most likely be smaller than
  previously believed, 5.
• MSFC Project Science continued to explore the
  sensitivity of the simulation results to the
  parameters (ie temperatures of the relevant
  surfaces, volatility of the contaminant)
• The ACIS contamination working group reviewed
  the new results in the summer and decided on July
  15, 2005 against recommending a Bakeout. The
  team felt that the uncertainties were too large
  to be able to predict the outcome of the Bakeout
  with any confidence.
• The Bakeout is therefore postponed indefinitely.

3
Docosane, nominal TOBF Mass column
ODell Swartz (MSFC)
e 0.30
1 ACIS OBF 2 Camera top 3 ACIS snoot 4 ACIS
collimator 5 SIM trans table 6 SIM focus
struc 7 OBA stove pipe 8 Optical bench 9 OBA
vent
4
Docosane, de-rated TOBF Mass column
ODell Swartz (MSFC)
e 0.30
1 ACIS OBF 2 Camera top 3 ACIS snoot 4 ACIS
collimator 5 SIM trans table 6 SIM focus
struc 7 OBA stove pipe 8 Optical bench 9 OBA
vent
5
Limits on Vaporization Rates
ODell Swartz (MSFC)
Min to vent 0.2 g in 1 orb5?10-3 mg cm-2 s-1 _at_
Tcoldest
Min to clean OBF in 1 orb2?10-3 mg cm-2 s-1 _at_
TOBF-bake
Upper limit at OBF center1?10-7 mg cm-2 s-1 _at_
TOBF-ops
6
Monitoring the ContaminantTransmission _at_ 700eV
Grant (MIT)
7
Monitoring the Contaminant C-K Optical Depth
Marshall (MIT)
8
Summary of Bakeout Effort

• There will not be a Bakeout anytime soon
• We will continue to monitor the contaminant
  buildup and improve the characterization of the
  absorption of the contaminant
• MIT/ACIS will analyze CTI measurements at
  temperatures between -90 C and -120 C to
  understand the temperature dependence of the CTI
  better
• Calibration files for the time-dependent and
  spatial-dependent absorption of the contaminant
  are available in the CALDB CIAO, we will
  continue to assess the accuracy of these
  corrections and update as necessary

9
Bonus Material ACIS FP Temperature Anomaly

• ACIS DEA-A autonomously shutdown on 15 Sep 2005
• Two unintended consequences of the recovery from
  this anomaly

1. FP temperature setpoint for -120 C was not
   loaded into the DEA-A
2. The A/D converter which reports the DEA
   Housekeeping data initialized into a low
   resolution mode

• The consequences of this were

1. 16 Sep 2005 - 05 Oct 2005 - the FP temperature
   was not regulating and was 1.3 degrees colder
   than reported in TLM
2. 06 Oct 2005 - 15 Oct 2005 - the FP temperature
   WAS regulating but the reported temperature was
   1.3 degrees warmer than the actual temperature
   (-118.4 C instead of -119.7 C)

• The FP temperature regulation is back to nominal
  as of 15 Oct 2005

10
FP Temperature Anomaly
DePasquale (SAO)