Chandra X-Ray Observatory
CXC
1
SOT, FOT, ACIS & MSFC PS
January 26, 2005

Chandra X-Ray Observatory
CXC
The``ACIS Contamination Working Group’’ has been studying the ACIS contamination issue for the last two years. This presentation is a summary of that work. Those contributing directly to this presentation:
CXC: P. Plucinsky, A. Vikhilin, H. Marshall, N. Schulz, R. Edgar, D. Schwartz, S.
Wolk, H. Tananbaum, J. DePasquale, S. Virani, D. Dewey, L. David
MIT: M. Bautz, C. Grant, W. Mayer, R. Goeke, P. Ford, B. LaMarr, G Prigozhin,
S. Kissel, E. Boughan
PSU: G. Garmire, L. Townsley, G. Chartas, D. Sanwal, M. Teter, G. Pavlov
MSFC:
S. O’Dell, D. Swartz, M. Weisskopf, A. Tennant, R. Elsner
NGST: M. Mach, P. Knollenberg, D. Shropshire, L. McKendrick, R. Logan, R.
Giordano, T. Trinh, K. Chen, K. Henderson, F. Cottrell, J. Lamb, D. McGregor, H.
Tran, D. Lindemann, L. Harper, L. Ryan, A. Tao
LMA: N. Tice McMaster University: A. Hitchcock
Many others have contributed directly or indirectly.
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SOT, FOT, ACIS & MSFC PS
January 26, 2005

Chandra X-Ray Observatory
CXC
•
Tests on spare OBFs at NGST are complete and the project is convinced that OBFs will not be damaged during the bakeout
•
Chandra FOT determined that it is not safe to use the additional heaters on the SIM to heat the ACIS collimator/SIM interface
•
Project decided to postpone bakeout decision until the impact of not using the heaters was understood
•
MSFC Project Science generated new simulations with these colder surfaces and not surprisingly, the contaminant does not vent as effectively. The recommendation is to keep the OBF warmer than any of the surrounding surfaces during the bakeout.
•
Calibration team continues to work on the characterization of the contaminant (see Herman Marshall’s talk)
•
ACIS team is planning new irradiation tests to better understand the mechanism for the CTI increase from the room temperature bakeout in Sep 1999
3
SOT, FOT, ACIS & MSFC PS
January 26, 2005

Chandra X-Ray Observatory
CXC
ACIS
Location
OBA Vent Locations
Contaminate Migration Path
Optical Bench Assembly (OBA)
Integrated Science Instrument Module (ISIM)
4
SOT, FOT, ACIS & MSFC PS
January 26, 2005

Chandra X-Ray Observatory
CXC
SOT, FOT, ACIS & MSFC PS
5
January 26, 2005

Chandra X-Ray Observatory
CXC
OBA vent
SIM focus structure
SIM translation table
Optical bench (OBA)
ACIS collimator
Snoot
OBA stove pipe
SOT, FOT, ACIS & MSFC PS
ACIS OBF ACIS camera top
TRASYS model by NGST/ H. Tran et al.
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January 26, 2005

Chandra X-Ray Observatory
OBF
1 dy 1 wk 1 mo 1 yr 5 yr
O’Dell &
Swartz
(MSFC)
CXC
NOMINAL
DE-RATED
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
7
SOT, FOT, ACIS & MSFC PS
January 26, 2005

NOMINAL
Chandra X-Ray Observatory
OBF
1 dy 1 wk 1 mo 1 yr 5 yr O’Dell &
Swartz
(MSFC)
CXC
DE-RATED
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
8
SOT, FOT, ACIS & MSFC PS
January 26, 2005

Chandra X-Ray Observatory
CXC
O’Dell & Swartz (MSFC)
Mass vaporization (evaporation or sublimation) rates of some organic compounds tetradecane eicosane pentadecane henicosane
1.E+00
1.E-01
1.E-02
1.E-03
1.E-04
1.E-05
1.E-06
1.E-07
1.E-08
1.E-09
1.E-10
1.E-11
1.E-12
-60
Upper limit at OBF center:
1  10 -7 m g cm -2 s -1 @ T
OBF-ops
-50 -40 -30 hexadecane docosane
SOT, FOT, ACIS & MSFC PS heptadecane tricosane
-20
Temperature T [K]
9 octadecane tetracosane
Min to vent 0.2 g in 1 orb:
5  10 -3 m g cm -2 s -1 @ T coldest
-10 nonadecane
DOP
Min to clean OBF in 1 orb:
2  10 -3 m g cm -2 s -1 @ T
OBFbake
0 10 20
January 26, 2005

Chandra X-Ray Observatory
• If the contaminant has a volatility of less than 0.1 X DOP’s volatility, a one orbit +30 C bakeout will not move a significant amount of the contaminant
•
If the contaminant volatility is within an order of magnitude of
DOP’s volatility, a significant amount of the contaminant will vaporize and migrate to the cold surfaces at the top of the ACIS collimator and the SIM. The contaminant will then migrate very slowly back to the OBF and it may be years before a significant amount re-accumulates on the OBF
•
If the contaminant volatility is an order of magnitude higher than that of DOP, a significant amount of the contaminant will vaporize and migrate to the cold ACIS collimator and SIM surfaces. The contaminant will then migrate back to the OBF such that after 1 year, the thickness will be 1/3 of the original thickness.
CXC
10
SOT, FOT, ACIS & MSFC PS
January 26, 2005

Chandra X-Ray Observatory
•
ACIS team will conduct irradiation tests, analyze the results, and refine the prediction for the effect of another room temperature bakeout on the CTI
•
The working group will prepare another briefing for the Chandra project and seek approval for the bakeout
CXC
SOT, FOT, ACIS & MSFC PS
11
January 26, 2005