GLAST Large Area Telescope: Gamma-ray Large Area Space Telescope GLAST Large Area Telescope: Mechanical Systems Peer Review March 27, 2003 Section 3.2- Changes since Delta PDR Marc Campell SLAC Mechanical Systems Mgr. marcc@slac.stanford.edu

Topics Agenda Mechanical design changes since ∆PDR Impacts on Subsystem design Studies since Delta PDR

Design Changes Since Delta PDR X-LAT to E-Box thermal joint WAS: Rigid bonded joint with flexures at CAL-TEM interface IS: Rigid interface at CAL-TEM with compliant joint at X-LAT plate and a thermal velvet material (Vel-therm) used to fill gap between bottom box & X-LAT X-LAT plate WAS: honeycomb panel; IS: .125” plate CAL-Grid bolts: Use #8’s everywhere except at TRK cables pass-thru’s to increase clamping force on CAL plate

Design Changes Since Delta PDR Refined S/C interface stiffener (wing) to reduce grid distortions S/C attach method WAS: onto –Z surface of Grid IS: tang that protrudes down from wing S/C stayclear & center EMI shield design modified to accommodate above

Design Changes Since Delta PDR E-box harnesses WAS: bulkhead connectors in EMI skirt IS: 8 Connector patch panels into EMI skirts that E-box harness mount directly to Added 2 TCS external box & 2 brackets – mounting accommodated on Radiator Mount Brackets Added vents to EMI Electronics enclosure

Design Changes Since Delta PDR Radiator Heat Pipes WAS: U shaped bend to Grid IS: S shaped bend to Grid Radiator panel has top stepped for integration access Radiator – SC interfaces have been finalized SA Boom cutout size & location, strut locations Radiator reservoir size WAS 300 cc; IS: 75 cc Radiator VCHP extrusion WAS 1.75” wide; IS: 2.0” wide LM will design, fabricate and test X-LAT plates

Impact of Changes on Subsystem Designs LAT No impact TKR CAL Baseplate design has been modified for #8 fasteners ACD Electronics Improved reliability by reducing bulkhead connection External TCS boxes have been accommodated Conclusion: Changes consistent with PDR to CDR design maturity. Design changes have been incorporated within the Mechanical Subsystem

Studies since Delta PDR X-LAT to Electronics Thermal Joint Design Optimize joint design to accommodate Maximum thermal conductance Repeatable and verifiable thermal joint Ease of integration & removal to service E-boxes Compliance in X-Y plane required either at E-box to CAL or E-box to X-LAT Tolerance stack up of E-boxes, EMI skirts & CAL plates RTV, thermal gaskets, spring fingers, thermal straps and Vel-Therm traded Compliant joint at E-box to X-LAT interface with Vel-Therm material in between selected.

Studies since Delta PDR CAL-Grid interface shear load capability No bulk movement of CAL with 70 Fasteners & μ=.01 Isolated concern as small local motions of Grid wall underneath grid tabs Optimize wing design to reduce loads (FEM) Examined friction of various surface treatments Examined Tungsten Carbide flame spray as a way to guarantee high coefficient of friction at interface Maximized clamping force available from fasteners Examined backing bars on top of CAL tabs to create “double shear” joint Examined perimeter clamping bars that increase preload on all CAL tabs around the perimeter of the Grid Developed maps from FEM showing required coefficient of friction at each bolt location for a given clamping force

Studies since Delta PDR CAL-Grid interface shear load capability (cont) Summary: A friction joint will prevent bulk slippage of the CAL and maintain the LAT natural frequency. 89% of fasteners require μ < 0.2. Plan to run an analysis to show that load redistribution for the remaining 11% does not adversely affect the LAT natural frequency. GSFC has recommended that a bolted-pinned joint be adopted. Design implementation study and impact study would be the next step.

End of Section 3.2