GLAST Large Area Telescope: Mechanical Systems WBS: 4.1.8 Section 13 Marc Campell SLAC

1. Gamma-ray Large Area Space Telescope GLAST Large Area Telescope: Mechanical Systems WBS: 4.1.8 Section 13 Marc Campell SLAC Mechanical Systems Manager marcc@slac.stanford.edu

2. Gamma-ray Large Area Space Telescope Overview Section 13.1

3. Mechanical Systems Organization

4. +Z +Z Mechanical Subsystems Overview Grid Box Assembly Grid Assembly Mid-Plate X-LAT Plate Assy SC “wings” Radiator Mount Bracket EMI Shields

5. +Z +Z Radiator Placement

6. Major Subassemblies • Grid Box Assembly • Mechanical Systems Top Assembly test configuration • Static Load and Thermal Cycle tests • Grid Box Base Assembly • Configuration delivered to I & T for LAT integration • Defines base configuration for LAT assembly drawings • Grid Assembly • Mechanical backbone • Radiators • Fabricated and tested by LM • X-LAT and Mid-plates • Fabricated and tested by LM

7. Design & Fabrication Responsibilities Mechanical Systems

8. Design Problem Areas • CAL-GRID Interface • Electronics-Box to X-LAT Interface

9. CAL-GRID Interface Design Problem Status • At PDR & dPDR the baseline design was a bolted interface that relied on friction between the CAL plates and the Grid to react shear forces. • By Peer Review, we had not demonstrated (EM test) that we could develop the coefficient of friction required at the most highly loaded (<10% of) locations with ample margin. • A pinned approach was implemented and analyzed.

10. CAL-GRID Interface Design Problem Resolution • The pins cannot carry the loads at the highly loaded locations. • Request to GSFC to re-evaluate loads that were specified to LAT which we believe may overstate the shear loads by a factor of 2 or 3 (but correctly state the SC – LAT interface loads) • Acceptable options that impact only Mech have been exhausted or rejected on principal • Other options under evaluation which impact at least the CAL subsystem as well

11. X-LAT to Electronics-Box Thermal Joint Design Problem Status • At PDR & dPDR the baseline design was a bolted and thermally bonded joint between bottom of each E-Box and the X-LAT plate. There were flexures between the top of the E-box stack and the CAL plates. • Concern raised that E-boxes were not serviceable • Large bonded area to de-mate. • Re-verification issues after re-integrating. • For Peer Review, trade study presented for design that • Carried the thermal load of E-Boxes into X-LAT heat pipes • Accommodate tolerance buildup from E-Box and Grid Box components • Repeatable interface (make & break) • Minimize schedule & verification impacts resulting from X-LAT plate removal for Electronics box access

12. X-LAT to Electronics-Box Thermal Joint Design Problem Resolution • Design changed to rigidly mount E-Box stack to CAL plate and create a thermally compliant thermal joint between the E-box & X-LAT plate • Trade study results indicate that Vel-therm gasket material optimally meets requirements and has the following characteristics: • Highly conductive graphite fibers • Mechanically compliant • Meets out-gassing requirements • Allows TEM/TPS to be mated to CAL through out its Acceptance testing • However, this approach has little Flight heritage and must be qualified for our application

13. Peer Review Significant Findings • Spacecraft to LAT mechanical interface finalization • Structural analysis and design margins not finalized • X-LAT to electronics box mechanical & thermal design not finalized • Unconventional design approach dependent on analysis results and engineering model development • Immature drawing/document status for grid and X-LAT plate • Calorimeter to grid interface concerns must be resolved

14. Peer Review Significant Findings • Is the design maturity, qualification and verification planning near CDR level? • With the exception of the electronics to X-LAT interface, Yes, but still missing an appropriate level of verification with the engineering models and final dynamics analysis. • Has the Subsystem identified open design issues and established appropriate resolution plans to ensure closure? • Yes, the issues have been identified but issues may still develop during engineering model testing and final analysis. • Is the Subsystem near readiness for manufacturing? • Many element of the subsystem are ready for manufacture (e.g. radiator), however other items need to wait until analysis and successful engineering model completion. • Has the Subsystem identified open manufacturing issues and established appropriate resolution plans? • Yes. Specific concerns are captured in the RFAs. • Are there other issues that should be addressed? • Mechanical assembly of the LAT will be a complex process that will require development of detailed processes and procedures. • The mechanical team has just recently staffed up. Re-plan of work that has been delayed needs to be completed and may delay design finalization

15. Major RFA’s and Overall Status • 19 of 46 RFA’s owned by Mechanical Systems • 0 closed • X submitted • Y open, ECD June 1st • Z open, ECD July 1st

16. RFA Response

17. RFA Response

18. RFA Response

19. RFA Response

20. Mechanical Systems’ Status Summary • Final Design Established With Known Closure Plans For Design Trades • X- LAT Plate To Electronics ICD - ECD: 7/15/03 • Xx/yy Drawings Complete, zz/yy Drawings Draft – ECD 8/15/03 • EM Model Tests Complete - ECD: 7/28/03 • Internal & External Interfaces Established • Yy TBX’s with closure planned – ECD: 7/12/03 • Performance Analyses Show Compliance Including Sufficient Design Margin • Any Exceptions noted with recovery plans • Qualification & Verification Plans In Place • Subsystem Risk Areas Identified And Mitigation Plans Established • Cost & Schedule Manageable • $$ Variance with recovery plans established • XX Week Schedule Float to Flight Delivery Need Dates

21. Summary • Mechanical Systems detailed design and analysis indicates that all requirements will be met. • Mechanical Systems has accommodated changes since dPDR. • Overall design is in good shape • Grid Box Assembly design is nearly complete. • Radiator and Heat Pipe designs are nearly complete. • Cal-Grid interface is still in development. • Risk list items are understood & mitigation plans are in place. • Radiator design has matured and fabrication will begin after I-CDR. • Aluminum billets for Grid are on order. • LM’s X-LAT team has come up to speed quickly and made several design improvements. • LM has team in place to execute to their plan.

22. Summary (con’t) Plans for Further Work • Engineering Modeling • Complete the remaining testing • Analysis • Complete detailed part stress analysis • Define Grid Box Assembly SLT cases • Design • Release Radiator and X-LAT specifications & Interface Def. Dwg. • Finalize CAL-Grid interface & incorporate into design • Finalize wing, EMI skirt & Radiator mount Bracket designs • Finalize X-LAT to Electronics design • Lockheed Martin • Complete detailed design and analysis • Finalize test plans • Program Management • Negotiate & award LM Phase II (fabrication) contract • Award Grid Assembly contract

23. Gamma-ray Large Area Space Telescope Requirements Section 13.2

24. Topics Agenda • Mechanical Systems Mass Budget • Mechanical Systems Power Budget • Requirements Flow down And Document Status • Key Mechanical Systems Requirements (Level 3) • Heat Pipe Performance Requirements • Radiator Design Requirements • Main X-LAT Design Requirements • Driving X-LAT Thermal Requirements

25. Mechanical Subsystem Mass Budget

26. Mechanical Systems Power Budget Nominal Operation 35 20.4 Survival 220 152.0 Operational Mode Power Allocation,W Estimate,W

27. Requirements Flow-Down and Documentation Status X-LAT Design Spec LAT-SS-001240-2 LAT Stay-Clear Drawing LAT-DS-00040-5 LAT Envir. Spec LAT-SS-00778-1 10 Feb 2003 LAT Perf Spec LAT-SP-00010-1 31 Aug 2000 X-LAT Plate SCD LAT-DS-01247-1 Radiator Design Spec LAT-SS-00394-1 Mech Systems Subsystem Spec LAT-SS-00115-2 Mid-Plate SCD LAT-DS-01257-1 Subsystem ICD’s Subsystem IDD’s Grid Box Design Spec LAT-SS-00775-1 LAT Thermal Design Param’s LAT-TD-00224-3 Top Flange Heat Pipe SCD LAT-DS-01393-1 Thermal Control Sys. Perf. Spec LAT-SS-00715-1 LAT Dissipated Power Summary LAT-TD-00225-3 LH/RH Down Spout Heat Pipe SCD LAT-DS-01392-1 LAT-DS-01393-1 LAT Instrument Layout Dwg LAT-DS-00038-3 Radiator IDD LAT-DS-01221-1

28. Key Mechanical Systems Requirements (1of 2) Sect Requirement Design Margin Comply Method Req.Source 8 Configuration 8.1. Mass The total mass of Mechanical Systems <345 kg 329.3 15.7 Y I LAT-TD-00125-1 8.3. Stay-Clear Volume and Dimensions Radiator positioned according to IRD Appendix A >1.89m 1.895 Y I IRD 3.2.2.3 When on, Radiator VCHP heater power < 35 W 20.4 14.6 Y D TD-00125-1(Derived) When off, orbit-average survival heater power 152.0 68(45%) Y D IRD 3.2.4.1.7.6 (Derived) <220 W @ 27 V min 387 W@ 35V (incl 30% Control margin) When off, peak survival heater power < 560 W Ok Y T, A IRD 3.2.4.1.7.6 (Derived) 8.5. Stiffness Fixed-base first-mode > 50 Hz 55.5 Hz 11% Y T IRD 3.2.2.8.1.2 8.6. Provisions for Integration and Test During Obs T-Vac, TCS capable of full functionality Ok Y T, A IRD 3.2.2.8.1.2 “lying on its side”

29. Key Mechanical Systems Requirements (2 of 2) Sect Requirement Design Margin Comply Method Req.Source 9 LAT Alignment 9.1. Alignment Stability Maintain TKR alignments to < 7 arc-seconds,1 s radial, Y T, A MSS 3.3.1.11.1.2 4.1 arc-sec Peak to-Peak 2.9 arc-sec + 5 s during normal LAT operation 10 Structural Load Environment 10.1. Structural Loads Capable of exposure to static launch loads Ok Y T, A IRD 3.2.2.8.2 Capable of withstanding static loads in thrust and lateral Ok Y A IRD 3.2.2.8.2 simultaneously 11 Thermal Environment and Heat Loads 11.1. Process and Interface Heat Loads 612W LAT+ 38W Rad @ 24 deg C Maximum process power indefinite dissipation Y T, A IRD 3.2.4.1.1 5 degC calc+ 1 deg C operating Capable of normal operation when loaded by 75 W/Rad Y T, A IRD 3.2.3.4.5 0W/Rad 73.4W/Rad From SC solar arrays 11.3. Environment Heat Loading and Orbital Parameters Provide thermal control with LAT pointed 2pi/24/7/365 Y T, A MSS 3.3.2.3 (Derived) during any normal LAT mode Capable of maintaining thermal control during exposure Y T, A IRD 3.2.3.5 to IR, Albedo, Solar fluxes (Derived)

30. Heat Pipe Performance Requirements Based on: Results of Overall LAT Thermal Math Model Verification Methods A: Analysis T: Test Margin is determined by: EP/Req Must be > 1.3

31. Driving Design Requirements(Radiator: Mechanical)

32. Driving Design Requirements(Radiator: Structural)

33. Driving Design Requirements(Radiator: Thermal)

34. Driving Design Requirements(X-LAT)

35. Gamma-ray Large Area Space Telescope Design Grid Box Assembly Section 13.3

36. Drawing Tree

37. +Z +Z Grid Box Assembly Design CAL-Grid Interface Mid-Plate X-LAT Plate Assy Radiator Mount Bracket Heat Pipe Patch Panel EMI Shields S/C Mount Interface

38. Grid Design Drivers • Provides structural backbone for all LAT Subsystems • Provides electrical ground for all LAT Subsystems • Provides thermal path to Radiators for all LAT Subsystems except Electronics boxes (carried by X-LAT plates) • Embedded Heat Pipes in top flange of Grid to move heat out • Downspout Heat pipes tie Grid to Radiators • Thermostatically controlled heaters on Grid corners are part of LAT thermal control system Construction • Machined from 10” thick 6061 AL plate • Heat treated to T6 after rough machining • Grid surface is alodine, class 3. Electrically conductive and good surface for adhesive bonding thermal components, harness supports, Tracker cables, MLI supports, EMI tape etc • Integral purge grooves allow for N2 purging of the CAL’s during ground operations

39. +Z +Z Grid Structure Helicoils for CAL bolts Top Flange Heat Pipes Purge grooves

40. Calorimeter to Grid Interface • This interface is part of the Grid stiffness design. • Interleaved CAL baseplate tabs are bolted to –Z surface of Grid • CAL baseplates close-out the Grid structure which increases natural frequency of LAT • Bolted interface applies clamping force over large area (~4223 mm2 per CAL) to develop shear load capability • 2 pins per Grid bay locate CAL and are used to locate hole pattern in Grid and other features such as Tracker cable cut-outs in Grid walls • Perimeter backing bars engage the outer tabs of the outer CAL’s to double the clamping force on these highly loaded tabs

41. X-LAT Plate to E-Box Thermal Joint • Thermal joint design drivers • Carry thermal load of stack of E-Boxes into X-LAT Heat Pipes • Accommodate tolerance stack up E-Box and Grid Box parts • Be repeatable & reliable • Minimize schedule & verification impacts due to removal of X-LAT plates for access to Electronics • Vel-therm gasket material selected • Highly conductive graphite fibers • Mechanically compliant • Meets out-gassing requirement

42. Midplate to X-LAT Thermal Joint, 2 PLCS, Approx. 60 #6 Fastenerseach side Bolting X-LAT Plate to EMI Shields, Approx. 60 #8 Fasteners per Plate Vel-Therm X-LAT Plate Midplate X-LAT Plate EMI Shields EMI Shields GRID Electronics Stack Cross-Section • 4 cm wide Vel-Therm strip placed around perimeter of each box optimizes conduction vs contact pressure required Note: View along Y-axis

43. +Z EMI Shield Design Drivers • Encloses LAT Electronics boxes (EMI tight) • Consists of 4 Radiator Mount Brackets, 4 Heat Pipe Patch Panels, 4 X-side Shields and 4 center Shields • Mechanically supports 3 way heat pipe joint – Downspout, X-LAT and Radiator HP’s • Supports X-LAT plates • Provides mounting for Connecter Patch Plates from Electronics • Provides for venting of enclosure Construction • 6061-T6 AL machining, alodine • Pieces bolted to Grid & each other

44. Radiator Mount Bracket Design Drivers • Supports & locates Radiators & their Heat Pipes • Supports & locates X-Lat Plates & their Heat Pipes • Provides access to ACD mounting bolts • Supports & locates alignment optic • Provisions for mounting Heater Control Box or Heater Control Connector Bracket for Thermal Control System • Corner lugs for MGSE attachment (sized to carry entire Observatory mass with 2 lugs if required) Construction • 6061-T6 Al machining, alodine • Bolts to 3 orthogonal surfaces of Grid corner

45. Spacecraft Interface Stiffener (Wing) Design Drivers • Primary function is to spread the point load inputs from the Spacecraft & locally stiffen the Grid against the lateral loads. • Distortions in this area drive the CAL-Grid interface design • Defines Spacecraft interface to LAT (bolted – pinned joint) Construction • 6061-T6 machining, alodine • Bolted, pinned & keyed to Grid +Z

46. Work to Close Out Structural Design • CAL-Grid interface under review with GSFC • Finalize design of perimeter backing plate • Investigating making the Spacecraft Interface (Wing) an integral part of the Grid • Finalizing details of Spacecraft mounting w/ Spectrum • Mass & stress optimization of EMI shields and Radiator mount brackets • Radiator mount bracket X axis compliance requirement for differential contraction of Radiators & Grid • Awaiting results of LM thermal analysis • Finalize design implementation of Vel-therm joint

47. Stress Analysis Topics • Cal-Grid interface load recovery • Grid Stress analysis • Radiator Mount Bracket analysis • Summary and Closure Plan

48. CAL Interface Load Recovery • CAL-Grid bolted friction joint • 1152 screws (72 per CAL module) • Joint allows CAL bottom plate to stiffen LAT by closing out bottom side of Grid • Load recovery • Interface loads are backed out from the FEA model by resolving nodal forces at the interface into shear and normal loads at the bolt locations • Required friction coefficients are generated, given a set screw preload and a perimeter backing strip • EM bolted joint tests are underway to validate friction coefficient and joint behavior Histogram Showing Required Friction Coefficients Qual Friction Coefficients for CAL-Grid Joint

49. Grid Stress Analysis • Grid stress analysis indicates positive margins of safety for all regions • Highest stresses occur in transition regions around SC mount • Nominal maximum Von Mises stress is order of magnitude below yield for material • Large corner radii in the actual design, not included in the model, limit stress risers • Top flange in model has a weighted-average cross section which is no more than twice the minimum cross sectional area • Grid material properties • Material: 6061-T6 aluminum (6061-T651, stress-relieved, then heat-treated during fabrication) • Sy = 240 MPa (35 ksi) • Su = 290 MPa (42 ksi) • Factors of safety (per NASA-STD-5001) • Metallic structures • Yield: FSy = 1.25 • Ultimate: FSu = 1.4

50. Radiator Mount Bracket Analysis • Design Loads and critical load cases • Loads defined in Environmental Spec • FS=1.25 (PFQ) used for launch loads • FS=1.40 used for lift case • Assume Observatory lift load is carried in 2 of 4 fittings • Critical Load Cases Studies • Lift case induces the highest stresses • Margins of safety are good for all design cases • Calculated stiffness is high, which is conservative for loads determination • The radiator attachment bracket meets or exceeds all design requirements CASE X [N] Y [N] Z [N] +X/-Z 994 0 -1670 -X/-Z -994 0 -1670 +Y/-Z 0 333 -1670 -Y/-Z 0 -333 -1670 LIFT 0 0 32400