update on a proposed bakeout cxc sot & fot, acis instrument team and msfc project...

Chandra X-Ray Observatory CXC

SOT, FOT, ACIS & MSFC PS January 26, 20051

Update on a Proposed BakeoutUpdate on a Proposed Bakeout

CXC SOT & FOT, ACIS CXC SOT & FOT, ACIS Instrument Team andInstrument Team and

MSFC Project ScienceMSFC Project Science



Contributors to the Bakeout EffortContributors to the Bakeout EffortThe``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.



New Items since Last CUC Briefing (June 2004)New Items since Last CUC Briefing (June 2004)

•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



Chandra X-Ray ObservatoryChandra X-Ray Observatory

Optical Bench Assembly (OBA)

Integrated Science Instrument Module (ISIM)

OBA Vent Locations

ACISLocation

Contaminate Migration Path



OBA stove pipeOBA stove pipe

SnootSnoot

ACIS collimatorACIS collimator

SIM translation tableSIM translation table

SIM focus structureSIM focus structure

Optical bench (OBA)Optical bench (OBA)

OBA ventOBA vent

ACIS camera topACIS camera topACIS OBFACIS OBF

TRASYS model by NGST/ H. Tran et al.

Geometric model



10.DOP de-rated TOBF: Mass column

1: ACIS OBF1: ACIS OBF2: Camera top2: Camera top3: ACIS snoot3: ACIS snoot4: ACIS collimator4: ACIS collimator5: SIM trans table5: SIM trans table6: SIM focus struc6: SIM focus struc7: OBA stove pipe7: OBA stove pipe8: Optical bench8: Optical bench9: OBA vent9: OBA vent

1 dy 1 wk 1 mo 5 yr1 yr

DE-RATED

NOMINAL

O’Dell & Swartz (MSFC)



1.0DOP de-rated TOBF: Mass column

1: ACIS OBF1: ACIS OBF2: Camera top2: Camera top3: ACIS snoot3: ACIS snoot4: ACIS collimator4: ACIS collimator5: SIM trans table5: SIM trans table6: SIM focus struc6: SIM focus struc7: OBA stove pipe7: OBA stove pipe8: Optical bench8: Optical bench9: OBA vent9: OBA vent

1 dy 1 wk 1 mo 5 yr1 yr

DE-RATED

NOMINAL




Mass vaporization (evaporation or sublimation) rates of some organic compounds

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

-60 -50 -40 -30 -20 -10 0 10 20

Temperature T [K]

Vaporization rate D

tμv [μ g cm

-2 s

-1]

tetradecane pentadecane hexadecane heptadecane octadecane nonadecaneeicosane henicosane docosane tricosane tetracosane DOP

Limits on vaporization rates

Min to vent 0.2 g in 1 orb:

510-3 μg cm-2 s-1 @ Tcoldest

Min to vent 0.2 g in 1 orb:

510-3 μg cm-2 s-1 @ Tcoldest

Upper limit at OBF center:

110-7 μg cm-2 s-1 @ TOBF-

ops

Upper limit at OBF center:

110-7 μg cm-2 s-1 @ TOBF-

ops

Min to clean OBF in 1 orb:

210-3 μg cm-2 s-1 @ TOBF-

bake

Min to clean OBF in 1 orb:

210-3 μg cm-2 s-1 @ TOBF-

bake




Conclusions From New SimulationsConclusions From New Simulations

• 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.



Work Still to be Done (January 2004)Work Still to be Done (January 2004)

• 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

update on a proposed bakeout cxc sot & fot, acis instrument team and msfc project...

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