GLAST LAT ProjectQuarterly Review of the GLAST/LAT Project, August 14, 2001 Martin Nordby1 GLAST Large Area Telescope: Mechanical Systems Martin Nordby Stanford Linear Accelerator Center Mechanical Systems Engineer Gamma-ray Large Area Space Telescope

GLAST LAT ProjectQuarterly Review of the GLAST/LAT Project, August 14, 2001 Martin Nordby2 Outline  Issues and Recommendations from previous reviews  Technical status  LAT analysis  Structural analysis  Thermal Systems Analysis  Interface design  Technical issues  Schedule  Cost issues

GLAST LAT ProjectQuarterly Review of the GLAST/LAT Project, August 14, 2001 Martin Nordby3 LAT Mechanical Layout Thermal/micro-meteorite shield (MLI and ceramic blankets) Radiator (aluminum) LAT Model with Radiators and Subsystem Stay-Clears Grid support structure (aluminum) Spacecraft mount points (4x) Radiator mounts to SC Heat pipes on top of Grid (aluminum) Anticoincidence Detector (ACD) surrounds TKR Tracker (TKR) mounts to top flange of Grid Calorimeter (CAL) inside Grid Electronics (Elec) mounts to CAL bottom plates Radiators mounts to Grid and Spacecraft (SC)

GLAST LAT ProjectQuarterly Review of the GLAST/LAT Project, August 14, 2001 Martin Nordby4 Issues from May 2001 Quarterly Review Transient thermal behavior of the LAT –Issue 1: transient behavior is driven by LAT, Radiator, and SC operating scenarios, none of which are well defined –Action: GLAST operating scenarios being set and reflected in updated IRD; Radiator and LAT operating scenarios becoming understood –Issue 2: transient response of LAT has never been modeled –Action 2: transient response of LAT and Radiators fully modeled, and design of thermal control system updated as a result; More analysis in progress LAT—Spacecraft interfaces –Issue: design, structural and thermal interfaces are still immature –Action: some progress during SC study; still an issue Grid prototyping –Issue: prototype testing must be done to validate FEA model details –Action: prototyping thus far shows design carries >75% margin in CAL joint. Further CAL and Grid heat pipe prototyping underway

GLAST LAT ProjectQuarterly Review of the GLAST/LAT Project, August 14, 2001 Martin Nordby5 Recommendations from the Feb 2001 Review Finish performance specifications by PDR –LAT-SP “LAT Performance Spec” revision in-progress to reflect better understanding of operations and thermal requirements –LAT-SS D4: Mechanical Systems Spec finished draft ready for approval by LAT projectLAT-SS D4: –Missing: Mechanical Systems Level IV spec’s for Grid, Radiators, Thermal Control System being drafted now (drafts complete by PDR) Finish interface control documents by PDR –LAT-DS D3: LAT Instrument LayoutLAT-DS D3: –LAT-SS D3: LAT-Cal Mech Interface Control DocumentLAT-SS D3: –LAT-DS : CAL-LAT Interface Definition DrawingLAT-DS : –LAT-SS D2: LAT-ACD Mech Interface Control DocumentLAT-SS D2: –LAT-TD D1: LAT Thermal Design Parameters Summary LAT-TD D1: –LAT-TD D1: LAT Dissipated Power for Thermal DesignLAT-TD D1: –LAT-TD D0: LAT Thermal Operations AssumptionsLAT-TD D0: –Missing: TKR and Electronics Mechanical ICD’s (drafts complete soon after PDR)

GLAST LAT ProjectQuarterly Review of the GLAST/LAT Project, August 14, 2001 Martin Nordby6 Structural Analysis LAT2 finite element model delivered Modal analysis results –Drum-head mode, F 4 = 64.8 Hz –IRD Requirement: > 50 Hz Structural analysis –Bowing of Grid closes 2.5 mm gap between TKR modules by 0.39 mm –LAT stiffness dependent on CAL bottom plate LAT Distorted-Shape Axial Deflection Contour Plot Drumhead mode F4 = 64.8 Hz -Back out bolt forces -Design joint, pick bolt -Torque test -Tensile test -Validate FEA model with shear pull test Detail of FEA Model at CAL Mount Tensile Test of CAL Joint

GLAST LAT ProjectQuarterly Review of the GLAST/LAT Project, August 14, 2001 Martin Nordby7 Thermal Systems Development TSS reduced thermal radiation model delivered LAT on-orbit transient thermal model complete –Used to characterize LAT performance due to varying environmental heat loads Radiator development –Detailed Radiator thermal model complete –Design decisions: Two thermally coupled 2.7 m 2 Radiators on opposing Y-sides Variable-Conductance Heat Pipes to regulate Radiator active area, compensating for variations in heat loading Active control system to operate VCHP’s and keep LAT temperature stable to +/- 3 o C –Detailed mechanical design and structural analysis just beginning This is starting late, the result of delays in Radiator work start-up, and needed changes to their thermal design Planning to catch up to schedule this fall

GLAST LAT ProjectQuarterly Review of the GLAST/LAT Project, August 14, 2001 Martin Nordby8 Thermal Systems Development (2) LAT steady-state thermal behavior –650 W of dissipated power –Grid bows 173  m due to temperature gradients –TKR tips 22 arc-sec –Requirement: 30 arc-min LAT performance due to +/- 3 o C swings in Radiator temperature –Transient temp gradients tip TKR’s –Tipping: 3.7 arc-sec –Req: max misalignment = 7 arc-sec Response to time-varying process power draw –TKR tip = 3.0 arc-sec for  P = 68 W –Req: tip < 7 arc-sec for  P = 350 W –Design mod: shunt electronics heat directly to Radiators Distorted-Shape Temperature Contour Plot (red = hotter) Tip = 3.7 arc-sec Temp Variation for 5.25 Orbits (red = Rad interface, blue = CAL plate) T min = -0.3 o C

GLAST LAT ProjectQuarterly Review of the GLAST/LAT Project, August 14, 2001 Martin Nordby9 Interface Design CAL joint –Prototype testing underway: Grid, bolt, joint design strength OK  Interface looks solid, with no surprises in view TKR interface –Flexure design in place and TKR is prototyping joint for EM tests  Design looks good, but testing needs to resolve thermal, structural questions (how to align flexures; affect of thermal gasket on structure) ACD –Conceptual design in place, thermal interface design in-progress  Interface may need modification if ACD tile coverage is modified Spacecraft –Interface development held up due to export-control issues –Legal hurdles recently cleared, and progress is now re-starting  Will not be able to baseline an interface design with SC before PDR

GLAST LAT ProjectQuarterly Review of the GLAST/LAT Project, August 14, 2001 Martin Nordby10 Technical Issues List Spec’s and ICD’s –Issue: level 4 spec’s and ICD’s are not yet complete –Response: expect completion of 90% of drafts by PDR Thermal systems development –Issue 1: Radiator design is immature for PDR –Response 1: Contractor is ramping up on personnel to develop conceptual design –Issue 2: Electronics thermal design is very immature –Response 2: Handling thermal transients by shunting power to Radiator is being baselined. Planning EM test and analysis of this Spacecraft interface design –Issue: Design has not matured adequately for PDR –Response: Export-control issues have been resolved, and progress is re-starting. We will miss PDR, but expect conceptual baseline by early CY2002

GLAST LAT ProjectQuarterly Review of the GLAST/LAT Project, August 14, 2001 Martin Nordby11 Mechanical Systems Schedule Scheduling –Mechanical Systems schedule is being final-checked for baseline Check links to I&T Find and resolve budget phasing discrepancies between budget and cost-loaded PMCS schedule Status –In general, we have slipped with respect to the schedule Short staffing of budgeted positions Late start of thermal contract –Expect to make up schedule variances during EM development, since this program is being scaled back New I&T Manager and Engineer will unload Mech Systems personnel from double-duty work Thermal contract in-place (possibly approved today)

GLAST LAT ProjectQuarterly Review of the GLAST/LAT Project, August 14, 2001 Martin Nordby12 Cost Issues Budget vs proposal estimate –Current budget of $RYM8.5 is high by $RYM3.5 –Areas where cost grew Corrections for lost system-level analysis, reserve, and overhead Addition of EM test program, Qual. Grid test program Issues in investigating de-scoping options –Engineering model Current budget includes ~$700k for EM thermal-vacuum testing We are planning to scale this back to a minimal EM program with moderate additional risk –Qual Grid Qualification test of Grid and Radiators (thermal, mass models) Budget includes ~$800k for Qual Grid fabrication This reduces technical and schedule risk of qual testing flight hardware at the end of the program