1. Chandra X-Ray Observatory CXC SOT, FOT, ACIS & MSFC PS January 26, 2005 1 Update on a Proposed Bakeout CXC SOT & FOT, ACIS Instrument Team and CXC SOT & FOT, ACIS Instrument Team and MSFC Project Science MSFC Project Science

2. Chandra X-Ray Observatory CXC SOT, FOT, ACIS & MSFC PS January 26, 2005 2 Contributors to the Bakeout Effort 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.

3. Chandra X-Ray Observatory CXC SOT, FOT, ACIS & MSFC PS January 26, 2005 3 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

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

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

6. Chandra X-Ray Observatory CXC SOT, FOT, ACIS & MSFC PS January 26, 2005 6 OBA stove pipe Snoot ACIS collimator SIM translation table SIM focus structure Optical bench (OBA) OBA vent ACIS camera top ACIS OBF TRASYS model by NGST/ H. Tran et al. Geometric model

7. Chandra X-Ray Observatory CXC SOT, FOT, ACIS & MSFC PS January 26, 2005 7 10.  DOP de-rated T OBF : Mass column 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 1 dy1 wk1 mo5 yr1 yr DE-RATED NOMINAL O’Dell & Swartz (MSFC)

8. Chandra X-Ray Observatory CXC SOT, FOT, ACIS & MSFC PS January 26, 2005 8 1.0  DOP de-rated T OBF : Mass column 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 1 dy1 wk1 mo5 yr1 yr DE-RATED NOMINAL O’Dell & Swartz (MSFC)

9. Chandra X-Ray Observatory CXC SOT, FOT, ACIS & MSFC PS January 26, 2005 9 Limits on vaporization rates Min to vent 0.2 g in 1 orb: 5  10 -3  g cm -2 s -1 @ T coldest Upper limit at OBF center: 1  10 -7  g cm -2 s -1 @ T OBF-ops Min to clean OBF in 1 orb: 2  10 -3  g cm -2 s -1 @ T OBF- bake O’Dell & Swartz (MSFC)

10. Chandra X-Ray Observatory CXC SOT, FOT, ACIS & MSFC PS January 26, 2005 10 Conclusions 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.

11. Chandra X-Ray Observatory CXC SOT, FOT, ACIS & MSFC PS January 26, 2005 11 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