Chandra X-Ray Observatory
CXC
Update on a Proposed Bakeout
CXC SOT & FOT, ACIS Instrument
Team and
MSFC Project Science
SOT, FOT, ACIS & MSFC PS
1
October 19, 2005
Chandra X-Ray Observatory
CXC
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.
SOT, FOT, ACIS & MSFC PS
2
October 19, 2005
Chandra X-Ray Observatory
Docosane, nominal TOBF: Mass column
1 dy
1 wk
1 mo
1 yr
CXC
5 yr
O’Dell &
Swartz
(MSFC)
e = 0.30
1:
2:
3:
4:
5:
6:
7:
8:
9:
SOT, FOT, ACIS & MSFC PS
3
ACIS OBF
Camera top
ACIS snoot
ACIS collimator
SIM trans table
SIM focus struc
OBA stove pipe
Optical bench
OBA vent
October 19, 2005
Chandra X-Ray Observatory
Docosane, de-rated TOBF: Mass column
1 dy
1 wk
1 mo
1 yr
5 yr
CXC
O’Dell &
Swartz
(MSFC)
e = 0.30
1:
2:
3:
4:
5:
6:
7:
8:
9:
SOT, FOT, ACIS & MSFC PS
4
ACIS OBF
Camera top
ACIS snoot
ACIS collimator
SIM trans table
SIM focus struc
OBA stove pipe
Optical bench
OBA vent
October 19, 2005
Chandra X-Ray Observatory
Limits on Vaporization Rates
CXC
O’Dell & Swartz (MSFC)
Mass vaporization (evaporation or sublimation) rates of some organic compounds
tetradecane
eicosane
pentadecane
henicosane
hexadecane
docosane
heptadecane
tricosane
octadecane
tetracosane
nonadecane
DOP
1.E+00
1.E-02
-2
-1
Vaporization rate Dtmv [mg cm s ]
1.E-01
1.E-03
1.E-04
1.E-05
1.E-06
1.E-07
Min to vent 0.2 g in 1 orb:
510-3 mg cm-2 s-1 @ Tcoldest
1.E-08
1.E-09
1.E-10
Min to clean OBF in 1 orb:
210-3 mg cm-2 s-1 @ TOBF-
Upper limit at OBF center:
110-7 mg cm-2 s-1 @ TOBF-ops
1.E-11
bake
1.E-12
-60
-50
-40
-30
-20
-10
0
10
20
Temperature T [K]
SOT, FOT, ACIS & MSFC PS
5
October 19, 2005
Chandra X-Ray Observatory
CXC
Monitoring the Contaminant:Transmission @ 700eV
Grant
(MIT)
SOT, FOT, ACIS & MSFC PS
6
October 19, 2005
Chandra X-Ray Observatory
CXC
Monitoring the Contaminant: C-K Optical Depth
Marshall
(MIT)
SOT, FOT, ACIS & MSFC PS
7
October 19, 2005
Chandra X-Ray Observatory
CXC
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
SOT, FOT, ACIS & MSFC PS
8
October 19, 2005
Chandra X-Ray Observatory
CXC
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
SOT, FOT, ACIS & MSFC PS
9
October 19, 2005
Chandra X-Ray Observatory
CXC
FP Temperature
Anomaly
DePasquale
(SAO)
SOT, FOT, ACIS & MSFC PS
10
October 19, 2005