1. LAT-PR-01278 Section 11-1 GLAST LAT ProjectMechanical Design Integration Peer Review, March 2003 Mechanical Design Integration Peer Review, March 2003 7. Appendix Mechanical Design Integration Peer Review, March 2003 7. Appendix 23 March 2003

2. LAT-PR-01278 Section 11-2 GLAST LAT ProjectMechanical Design Integration Peer Review, March 2003 1. Supplementary Information Abbreviated list of PDR Action Items and Responses Abbreviated list of Delta-PDR Action Items and Responses

3. LAT-PR-01278 Section 11-3 GLAST LAT ProjectMechanical Design Integration Peer Review, March 2003 PDR Action Items PDR 27: Pursue a system solution to the thermal design needed for the radiator repackaging effort. –Response: See LAT-PR-00707-0(3-1—ThermalAnalysis). The radiator design presented at the dPDR complied with all thermal design requirements with a 30 percent positive heater control margin. PDR 28: Factor in the long thermal time constant into planning for LAT TV and TB. –Response: See LAT-PR-00707-0(3-1—ThermalAnalysis), for a predicted estimate of the transient cool down response of the LAT in thermal vacuum test configuration. PDR 29: Pursue with the GLAST Project whether funding can be found to fabricate the radiators on the original schedule –Response: The schedule risks associated with late fabrication of the Radiators has been discussed with the GLAST Project Office. The six-month extension of the LAT schedule has provided adequate schedule float. Funding has been authorized to begin radiator fabrication in FY03. PDR 30: Consider second sourcing thermal control components, such as VCHPs and CCHPs, due to LM facility relocation to Mississippi. –Response: The LM heat pipe facility has been returned to the Sunnyvale plant and was certified in December 2003. PDR 31: Provide a matrix that shows TCS qualification and acceptance testing from component to subsystem to all-up LAT testing. Include mechanical and thermal environments. –Response: This is included into the LAT performance Verification Plan (LAT-MD-00408) which is available on the LAT website. Thermal test table and matrix are complete. Structural/vibration strategy is finalized, but values are provisional (pending final CLA done by SC contractor).

4. LAT-PR-01278 Section 11-4 GLAST LAT ProjectMechanical Design Integration Peer Review, March 2003 PDR Action Items (cont 1) PDR 32: Review individual box temperature requirements to ensure these limits are based on box capability not on the TCS capability. –Response: Box operating and test temperatures (acceptance and qualification) have been established, and are detailed in the LAT environmental specification (LAT-SS- 00788). This document is being reviewed by the Project. PDR 33: Conduct a delta mechanical/thermal PDR to evaluate technical, cost and schedule impacts of the thermal changes necessary to meet requirements with margin. –Response: Agreed. A Delta PDR for the mechanical/thermal subsystem was held in July 2002. As a result of a successful review, the mechanical/thermal subsystem preliminary design was baselined. PDR 34: Investigate using thermal coatings with higher emmissity (while maintaining a low absorptivity) for the radiator, such as AgTef or white paint. –Response: Three coating options have been investigated: a specific white paint, 0.25 mm thick FOSR, and OSR. Our choice is the thicker FOSR, which has an EOL emissivity of 0.85 (compared to 0.8 for the PDR coating). For CDR, a 0.25 mm FOSR is the baseline coating for the radiators. PDR 35: Perform a thermal vacuum cycle test on the flight grid assembly with heat pipes installed to verify workmanship. –Response: This has been added to the Mechanical Systems Test Plan. PDR 36: Define who will control the LAT survival heaters, the spacecraft or the instrument. –Response: There are two sets of survival heaters for the LAT. One set deactivates the VCHPs, and is run off a watch-dog switch in the SIU. The second set of survival heaters will be controlled by thermostats. These heaters are mounted on the Grid and Radiators Plate.

5. LAT-PR-01278 Section 11-5 GLAST LAT ProjectMechanical Design Integration Peer Review, March 2003 PDR Action Items (cont 2) PDR 37: Provide a summary matrix showing candidate interface materials to be used in the thermal design. This should show location and advantage/disadvantage of each. –Response: Material and interface properties were presented at the Delta PDR. In addition, the document LAT Thermal Design Parameters Summary (LAT-TD-00224) summarizes the requirements, assumptions, and design parameters to be used in the design and analysis of the LAT thermal system. PDR 38: Define the blanket equivalent sink temperatures for the XLAT panel (facing the S/C) and the backside of the radiators. –Response: A more complete description of these interfaces was included in the May 2002 IRD. These were used for the LAT Delta PDR thermal analysis, and will be updated for CDR analysis as appropriate. PDR 39: Develop the thermal control system risks and risk mitigation list. Implement management of this list. –Response: A Mechanical Systems risk list has been developed, and includes TCS technical and development risks. This is part of the LAT Program Risk assessment document (LAT-TD-00857). PDR 40: Perform a high beta angle analysis to ensure the selected PDR analysis worst case hot/cold cases properly envelope all orbital scenarios. Also analyze "rocking" sky survey modes. –Response: High-beta angle analyses were performed for I-PDR and have been re-run using the final hot-case model. Conclusion: beta = 0 is the LAT hot-case orbit.

6. LAT-PR-01278 Section 11-6 GLAST LAT ProjectMechanical Design Integration Peer Review, March 2003 PDR Action Items (cont 3) PDR 41: How will the risks of freezing and thawing the VCHP/CCHP ammonia be mitigated. Identify freezing and thawing scenarios. Identify operational limitations. –Response: To assure that freezing is not possible the Radiator baseline design includes anti-freeze heaters mounted to the VCHPs, activated by thermal switches. Heater power for these heaters is included in the survival power budget. PDR 42: Evaluate the sensitivity of the tracker tray temperature with respect to the thermal interface gasket. –Response: Thermal analysis shows that TKR tray temperatures are relatively insensitive to changes in the thermal gasket conductivity. Thermal-vacuum testing of candidate gasket materials is underway. PDR 43: Provide an initial, top-level estimate of the cost/schedule impact of replacing a Tracker tower after complete instrument assembly. –Response: We would do this work using one project physicist, and two technicians per shift running 24/7 shifts. The schedule delay is 40 days, and the increase in cost is $153K. This effort will require 20 shifts per person over 40 days. PDR 44: All LAT Instrument designs incorporating composite joints should have these designs tested for joint allowables. In some cases, testing was already planned. –Response: Strength qualification testing has been included in the LAT Verification Test Plan. PDR 45: LAT Instrument and subsystems should be procuring fasteners in accordance with GSFC Fastener Integrity Requirements, 541-PG-8072.1.2. –Response: Fastener design, procurement, and test requirements are identified in the LAT-SS-00107 “LAT Mechanical Parts Plan.” These requirements are compliant with the LAT MAR.

7. LAT-PR-01278 Section 11-7 GLAST LAT ProjectMechanical Design Integration Peer Review, March 2003 PDR Action Items (cont 4) PDR 46: Reexamine all primary structure and alignment sensitive interfaces for LAT Instrument and provide positive shear restraint at these critical interfaces. –Response: Positive shear restraint is being used where possible. The CAL-Grid interfaces will use pre-loaded bolts and friction connections. The joint is being prototyped to qualify the joint design, and all pre-loaded bolts will include locking features. PDR 47: Provide the sine test philosophy for the LAT instrument/subsystems. –Response: Sine test philosophy has been added to the LAT Verification Test Plan. PDR 48: Generate a comprehensive strength qualification plan for the LAT instrument. –Response: Strength qualification plans have been added to the LAT Verification Test Plan.

8. LAT-PR-01278 Section 11-8 GLAST LAT ProjectMechanical Design Integration Peer Review, March 2003 Delta PDR Action Items D-PDR 1: Check energy balance of key arithmetic nodes to ensure local areas are predicting temperatures that are adequately converged. –Response: Based upon steady state results from the hot design case, the following energy balances were obtained. –Tracker-->Grid(Cond): 126.4 W Input Tracker Dissipation=16X8.7=139.2 –CAL-->Grid(Cond): 86.1WInput CAL Dissipation =72.96W –Electronics-->XLAT(Cond): 364.9WInput Elec Dissipation =378.4 W D-PDR 2: Verification chart reporting Qual levels (required) should be based on Acceptance levels (planned) plus or minus 5 degrees C. –Response: Agreed. Where possible based upon the concept that at Qualification temperatures the unit can meet performance requirements at End of Life. Exceptions will be noted in the LAT Environmental Specification (LAT-SS-00788, "LAT Environmental Specification"). D-PDR 3: Flight analysis needs to be performed to assess heat pipe failure impact on TCS (as well as other elements of TCS i.e., heater, T/S). –Response: Agreed. The LAT accepts this required activity and plans to present heat pipe failure impact results at the LAT instrument CDR. D-PDR 4: Consider the use of TOTS for transfer orbit to reduce need for heater power. –Response: Agreed. The LAT accepts this required activity and plans to present the results of a transfer orbit analysis using the best information available at the time at the LAT instrument CDR.

9. LAT-PR-01278 Section 11-9 GLAST LAT ProjectMechanical Design Integration Peer Review, March 2003 Delta PDR Action Items (cont 1) D-PDR 5: Ensure electronics box worst case thermal analysis is done using Qual level (+60 degrees C) as the box boundary condition. –Response: Box operating and test (acceptance and qualification) temperature levels are detailed in LAT-SS-00788-01, "LAT Environmental Specification." QT is 55 degC for all boxes. The electronics subsystem is reviewing this, to ensure that all components in each box type can be qualified at this temperature. Any limiting components and rationale will be identified. D-PDR 6: Include an IR camera test as part of the NDT methods used on radiator panel to assess panel workmanship. –Response: The LAT will develop an IR test plan and cost estimate to complete IR testing on each radiator panel. IR testing is not currently part of the Radiator testing program, so the costs and benefits will be evaluated by a CCB at the time of review. D-PDR 7: Add thermal engineer (1 head) coverage for each TV/TB test shift for both LAT instrument tests as well as S/C level testing. –Response: Currently, the LAT project has 1 thermal engineer budgeted for one shift for the duration of both the LAT and Observatory thermal-vacuum testing (on-call 24/7). Chamber operators are also budgeted 24/7 for these tests. Given the slow time response of the LAT, the LAT thermal group does not feel that additional thermal engineering personnel on the second and third shifts is cost effective. D-PDR 8: Ensure that HP stress analysis accounts for mechanical loading due to both external as well as internal forces. Ensure that HP stress concentrations due to machining and bending is addressed in stress analysis. –Response: Accepted. The LAT Radiator design team accepts this required activity and plans to present the results of a heat pipe stress analysis at the LAT instrument CDR.

10. LAT-PR-01278 Section 11-10 GLAST LAT ProjectMechanical Design Integration Peer Review, March 2003 Delta PDR Action Items (cont 2) D-PDR 9: Assess ground cooling requirement associated with each phase of LAT I&T though Launch site. –Response: Complete. The LAT design engineering team has developed the test thermal requirements. These are shown in LAT-TD-00997-01, "LAT Test Thermal Requirements," March, 2003. Further detail of the test thermal requirements will be added to the detailed Test Planst. D-PDR 10: Account for interface delta Ts associated with shimmed locations @ grid/X plate –Response: Agreed. The LAT design engineering team accepts this required activity and plans to present the results of a thermal analysis that accounts for temperature changes across the X-LAT Heat Pipe shimmed interface at the LAT instrument CDR. D-PDR 11: Recommend cycling (8 times) the radiator VCHP/grid joint during TB test. –Response: Complete. LAT-MD-00408-01, "LAT Program Instrument Performance Verification Plan," (Released 18 Oct 2002), Section 7.5.2 states that the LAT (with Radiators) will be cycled 4 times during LAT thermal-vacuum, and 4 times during Observatory thermal-vacuum. During these tests, the joint will be in its flight configuration. D-PDR 12: Perform a panel venting analysis. Ensure adequate venting such that panel mechanical configuration will not be compromised. –Response: Agreed. The LAT accepts this required activity and plans to present the results of radiator panel venting analysis at the LAT instrument CDR.

11. LAT-PR-01278 Section 11-11 GLAST LAT ProjectMechanical Design Integration Peer Review, March 2003 Delta PDR Action Items (cont 3) D-PDR 13: Evaluate alternate heat transfer paths between Tracker Grid in lieu of complete dependance on the gasket at the interface. Consider use of heat straps @ flex mount location to provide a path in lieu of gasket. –Response: Agreed. The LAT has baselined a copper thermal strap at the Tracker-to-Grid interface. This is a compliant metal connection that can elastically deflect more than what is needed to accommodate Tracker module motion during launch. The TKR has baselined high-emissivity paint on the Tracker sidewalls, to provide improved radiative coupling between modules. D-PDR 14: Include an i.r. scan of the front side of the radiators with a heat load on each evaporator prior to and after mechanical and thermal cycling tests at Lockheed/Martin. –Response: This RFA is redundant to RFA #6: The LAT will develop an IR test plan and cost estimate to complete IR testing on each radiator panel. IR testing is not currently part of the Radiator testing program, so the costs and benefits will be evaluated by a CCB at the time of review. D-PDR 15: Perform a venting analysis of the thermal radiators. –Response: This RFA is redundant to RFA #12: Agreed. The LAT accepts this required activity and plans to present the results of radiator panel venting analysis at the LAT instrument CDR. D-PDR 16: Be certain that a shimming at interfaces is included in thermal model. It does not appear that the X-LAT heat pipes shims have been included. –Response: This RFA is redundant to RFA #10: Agreed. The LAT design engineering team accepts this required activity and plans to present the results of a thermal analysis that accounts for temperature changes across the X-LAT Heat Pipe shimmed interface at the LAT instrument CDR.

12. LAT-PR-01278 Section 11-12 GLAST LAT ProjectMechanical Design Integration Peer Review, March 2003 Delta PDR Action Items (cont 4) D-PDR 17: Work contamination issues with the LAT project. Many cleaning steps were identified in the mechanical flow. How 'clean' must the structure and subsystems be? Define level of clearing required and if any bake outs are required. –Response: The GLAST LAT Contamination Control Plan, LAT-MD-00404, has been established to define the overall contamination control requirements necessary to establish hardware cleanliness for the GLAST LAT Project. The contamination critical hardware of the LAT shall meet the surface particulate and molecular cleanliness requirements of Level 750B per MIL-STD-1246. The LAT will perform thermal vacuum bakeouts of all hardware as necessary to ensure outgassing requirements are met. D-PDR 18: Do not install the X-LAT plate at SLAC until after thermal cycling test of LAT (prior to mass properties and before shipment to NRL). –Response: Accepted. The LAT is re-evaluating the test plans for tests leading up to thermal-vacuum tests, with an eye towards risk-mitigation and access for re-work. We are also investigating changes to the X-LAT Plate to make it easier to remove and re- integrate. The results of this work will indicate if leaving the X-LAT Plate off for early thermal testing is prudent. This will be detailed in the LAT Integration Plan and at the CDR. D-PDR 19: Implement a continuous risk management approach for use throughout the life of the project. Consider providing guidance and training to the subsystem managers to gain their support to promote a higher level of ownership for the system. –Response: In an effort to strengthen our CRM approach we have updated our plan to incorporate the process and analysis method used by NASA/GSFC/GLAST Project. This will be managed by LAT System Engineering.