GLAST Large Area Telescope: Mechanical Systems Peer Review March 27, 2003

1. 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

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

3. 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

4. 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

5. 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

6. 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

7. Impact of Changes on Subsystem Designs • LAT • No impact • TKR • No impact • CAL • Baseplate design has been modified for #8 fasteners • ACD • No impact • 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

8. 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.

9. 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

10. 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.

11. End of Section 3.2