LAT-PR-01967Section 8.3 – Structural Design1 GLAST LAT Project CDR/CD-3 Review May Apr 2003 Martin With contributions from: Youssef IsmailJohn Ku Mike FossRich Bielawski Michael LoveletteJim Haughton Eric GawehnLarry Wai Gamma-ray Large Area Space Telescope LAT Structural Systems

LAT-PR-01967Section 8.3 – Structural Design2 GLAST LAT Project CDR/CD-3 Review May Agenda Design Overview –LAT design –Design and interface changes since Delta PDR –CCB actions, trade studies, and open issues Peer Review RFA’s and requirements Structural analysis model development Structural analysis results –LAT modal analysis –Distortion analysis –Interface loads extraction Environmental test plans –Integration and test flow –Modal survey testing –Sine vibe and sine burst testing –Acoustic testing –Optical and muon surveying Summary and conclusions UPDATE

LAT-PR-01967Section 8.3 – Structural Design3 GLAST LAT Project CDR/CD-3 Review May Mechanical Design Overview LAT Overview Anticoincidence Detector (ACD) Mass270.1 kg (Mar 2003 est) Size1806 mm w x mm h InterfacesGrid bolted joint, shear pins Electronics Mass199.3 kg (Mar 2003 est) Size1417 mm sq x 222 mm h InterfacesStand-off to CAL; thermal joint to X-LAT Plate Grid/X-LAT Plate/Radiators Mass329.3 kg (Mar 2003 est) Size1580 mm sq x 236 mm h InterfacesFour-point mount to SC flexures LAT Structural Design Parameters DesignSpec Mass kg<3000 kg Center of Gravity149.3 mm<185 mm Width1806 mm<1820 mm Height mm1100 mm LAT Mass Budget and Current Estimates (kg) EstimateBudget TKR CAL ACD Mech Elec LAT Total Source: LAT-TD “LAT Mass Status Report Mass Estimates for Mar 2003” Calorimeter (CAL) Mass kg (Mar 2003 est) Size364 mm sq x 224 mm h InterfacesGrid bolted friction joint Tracker (TKR) Mass504.9 kg (Mar 2003 est) Size372 mm sq x 640 h InterfacesGrid Ti flexure mount and Cu strap

LAT-PR-01967Section 8.3 – Structural Design4 GLAST LAT Project CDR/CD-3 Review May System Block Diagram TKR Module CFC tray, side walls Grid monolithic alum structure CAL Modules alum bottom plate Elec. Boxes alum electronics box MLI Insulation MLI surrounding underside of LAT ACD Base Elec Ass’y alum frame LAT Radiators on +/- Y sides of LAT Grid Spacecraft LAT mounting structure Spacecraft SC bus structure Solar Arrays S.A. mount MLI Surrounding ACD LAT Block Diagram X-LAT Plate monolithic alum structure Radiator Mnt Bkt Support Radiators at corners of Grid EMI Skirt Shields E-Boxes, supports X-LAT Pl Htr Switch Boxes Operate Radiator heaters Anticoincidence Detector Tracker Mechanical Systems Spacecraft Trigger and Data Flow Electronics Calorimeter Legend

LAT-PR-01967Section 8.3 – Structural Design5 GLAST LAT Project CDR/CD-3 Review May LAT Design Details Grid corner detail showing heat pipes and purge grooves; corner chamfer and bottom flange Radiator Mount at Grid corners. Note mid-side Grid Wing Reverse-angle view of VCHP S-bends and DSHP connection TKR mid-side and corner flexures Copper thermal straps

LAT-PR-01967Section 8.3 – Structural Design6 GLAST LAT Project CDR/CD-3 Review May LAT Interface Details Grid Wing with SC mount bracket EMI Skirt push-back around SC stay-clear LV fairing static stay-clear PAF, per Boeing PPG Flexure on top of octagonal SC volume

LAT-PR-01967Section 8.3 – Structural Design7 GLAST LAT Project CDR/CD-3 Review May LAT Underside Design Details Upside-down view of a Grid Y side, showing DSHP’s, Grid Wing, X-LAT Plate, and EMI Skirt Detail of TEM, TPS, and EPU box stack Empty boxes EPU boxes PDU box GASU box SIU boxes TEM/TPS (16x) LAT Underside View of Electronics Boxes

LAT-PR-01967Section 8.3 – Structural Design8 GLAST LAT Project CDR/CD-3 Review May LAT Design Changes Since Delta-PDR Subsystem changes affecting system performance –Re-designed TKR bottom tray: added titanium and CFC reinforcement to CC tray –Modified TKR flexure: accommodated updated bottom tray design and provided for stiffer cantilever mode for TKR –Increased ACD mass: accommodated larger tile overlaps and an increase in structural stiffness/strength LAT internal interface changes –Integrated Grid Wing into bottom flange Incorporated Wing into machined Grid (no longer a bolt-on part) Tapered the Wing into a full bottom flange around Grid perimeter to reduce stress concentrations at SC mount, heat pipe cut-outs, and CAL-Grid tab joints –Changed TKR thermal interface to thermal straps Copper straps provided an improved compliant joint to the Grid –Stiffened TKR flexure connection to Grid by eliminating the shimmed “diving board” This was part of TKR bottom tray re-design Effect was to increase TKR first-mode natural frequency –Moved Electronics Box structural mount to CAL back plate Boxes are now hard-mounted to CAL plate by way of moment-bearing stand-offs Cleaner structural design simplified analysis and test plans for CAL and Electronics groups Forces on the X-LAT Plate are reduced to just the inertial loads of the plate –X-LAT plate thermal connection changed to V-Therm cloth Test program underway –CAL-Grid bolted joint modified to include pins Development program underway to finalize pinned joint design Design incorporated into CDR analysis

LAT-PR-01967Section 8.3 – Structural Design9 GLAST LAT Project CDR/CD-3 Review May LAT External Interface Changes Since Delta-PDR Finalized Radiator dimensions and interface –Modified Radiator aspect ratio at request of Spectrum –Agreed on final width, based on reduction in spacing between Radiators that was requested by Spectrum –Agreed on final height, based on Spectrum’s positioning of the LAT and PAF stay-clear agreements with Boeing –Resulting radiator area has increased to 2.78 m 2, although its efficiency has decreased Finalized Radiator mount location to SC –Moved strut mounting location down at request of Spectrum –This reduced Radiator first-mode natural frequency, but margin to 50 Hz requirements is still large Modified LAT-SC mount region –Finalized bolt pattern and pad size to accommodate Spectrum’s flexure design –Agreed to final LAT and SC stay-clear geometry around flexure Increased LAT envelope around ACD –Increased enveloped by 10 mm around the base of the ACD to accommodate the lower ACD tile and connectors –Change was approved by GLAST PO and Spectrum, and is part of the LAT baseline

LAT-PR-01967Section 8.3 – Structural Design10 GLAST LAT Project CDR/CD-3 Review May Design Changes Since Delta PDR (cont) LAT Delta PDR Design July 2002 LAT CDR Design May 2003 Radiator panels widened and shortened, reducing thermal efficiency Panels cut-out locations fixed SC-LAT mount region finalized VCHP S-bends

LAT-PR-01967Section 8.3 – Structural Design11 GLAST LAT Project CDR/CD-3 Review May Change Control Board Changes Since Delta-PDR ACD mass growth (LAT-XR ) –Added structural mass to increase design margins –Added mass in scintillating tiles to increase size of tiles and overlap between tiles Mechanical Systems mass growth (LAT-XR ) –Added mass for Grid box additions: Grid Wing, bottom flange, EMI Skirt stiffening, X-LAT thermal straps –Added mass for slightly increased Radiator area Calorimeter mass de-allocation (LAT-XR ) –Decreased mass allocation to reflect reduction in size of CsI logs –Log size was reduced to accommodate tolerance stack-up within CFC box structure Power allocation update (LAT-XR ) –Updated power allocations based on current measured values –New allocations and hot-/cold-case bounds flowed to LAT-TD , “A Summary of LAT Dissipated Power for Use in Thermal Design.” –Updated allocations and bounds have been used for CDR thermal analysis

LAT-PR-01967Section 8.3 – Structural Design12 GLAST LAT Project CDR/CD-3 Review May LAT Mechanical System Schematic Diagram LAT Schematic Diagram Anticoincidence Detector Tracker Mechanical Systems Spacecraft Trigger and Data Flow Electronics Calorimeter Legend

LAT-PR-01967Section 8.3 – Structural Design13 GLAST LAT Project CDR/CD-3 Review May Trade Studies Since Delta PDR Moved Electronics Box structural mount to CAL back plate –Trade issues Hard-mounting the Electronics Boxes to the X-LAT Plates vastly increases the complexity of the structural design, and makes verification testing of the CAL difficult De-coupling the Electronics Boxes produces a stiffer, more testable structural design, at the cost of a lower-conductance thermal design –Trade conclusion Boxes now hard-mounted to CAL plate by way of moment-bearing stand-offs The cleaner structural design simplifies analysis and test plans for CAL and Electronics groups Forces on the X-LAT Plate are reduced to just inertial loads of the plate –Open issues X-LAT Plate to Electronics Box thermal interface is still under development V-Therm is the baseline design, but its implementation is still under development More on this during the Mechanical Subsystem talk Radiator panel top profile –Trade issue Prior to spacecraft selection, and rectangular hole was baselined at the top of the Radiator, to allow for integrating the VCHP’s and accessing the LAT-SC bolted joint This design was structurally adequate, but afforded poor access to the CDR VCHP connection design and limited access to the SC-LAT bolted joint –Trade conclusion Modified the Radiator panel design to include a stepped top profile Radiator area is only marginally impacted The stepped design allows good access along the entire top of the Radiator, under the bottom of the ACD

LAT-PR-01967Section 8.3 – Structural Design14 GLAST LAT Project CDR/CD-3 Review May Structural Interface Open Issues CAL-Grid structural joint –Issue: joint has recently been changed from an all-friction joint to a pinned joint, but analysis and development testing are not yet complete –Closure plan Structural analysis underway  CDR analysis results will be used to finalize joint limit loads Joint testing is underway  Coupon tests will establish joint allowables Process development work underway  Pinned liquid-shim application processes (and the impact on the joint design) are understood; final process qualification is underway X-LAT Plate to Electronics box thermal joint –Issue: thermal strap design was recently abandoned in favor of V-Therm carbon fiber cloth, with much testing yet to be done –Closure plan Materials testing Contamination studies and testing Thermal properties testing Joint design and tolerance study Radiator-SC strut angle –Issue: Spectrum has proposed to change the IRD baseline and angle support struts holding the bottom of the Radiator –Closure plan

LAT-PR-01967Section 8.3 – Structural Design15 GLAST LAT Project CDR/CD-3 Review May Structural RFA’s from Peer Review

LAT-PR-01967Section 8.3 – Structural Design16 GLAST LAT Project CDR/CD-3 Review May Structural RFA’s from Peer Review (cont 1)

LAT-PR-01967Section 8.3 – Structural Design17 GLAST LAT Project CDR/CD-3 Review May Structural RFA’s from Peer Review (cont 2)

LAT-PR-01967Section 8.3 – Structural Design18 GLAST LAT Project CDR/CD-3 Review May Structural RFA’s from Peer Review (cont 3)

LAT-PR-01967Section 8.3 – Structural Design19 GLAST LAT Project CDR/CD-3 Review May LAT Requirements Flow-Down

LAT-PR-01967Section 8.3 – Structural Design20 GLAST LAT Project CDR/CD-3 Review May Key LAT Configuration and Structural Requirements

LAT-PR-01967Section 8.3 – Structural Design21 GLAST LAT Project CDR/CD-3 Review May LAT Integrated Structural FEA Model LAT structural model moved to NASTRAN –Changed FEA software from ANSYS to NASTRAN to make it more compatible with GLAST project office –Re-built model to improve dynamic analysis capabilities –Model is used to generate system structural response and interface limit loads Subsystem models updated –New TKR model from Hytec—including bottom tray and flexure design modifications –Updated ACD model from GSFC—with new mass baseline –Incorporated reduced CAL model from NRL –New Radiator model from LM— including size and mount point modifications –Re-built electronics—new model based on current E-Box and interface designs –Grid Box model modified—integrated Wing and X-LAT Plate modifications have been included LAT Finite Element Model NEW Picture

LAT-PR-01967Section 8.3 – Structural Design22 GLAST LAT Project CDR/CD-3 Review May Subsystem FEA Model Quality Checks Subsystem model evaluation –Review model—units, orientation/coordinate system, size, mesh resolution –Review delivery report—do the report and model agree FEA model check-runs –Free-free modal analysis—check model for mechanisms –Translation check—check model for inadvertent grounding –Gravity check—check that inertial loads are reacted only at boundaries –Temperature check—check that structure is free to expand/contract Analysis comparison runs –Mass, center of mass—compare with subsystem estimate –Modal analysis—check against subsystem detailed model and report UPDATE

LAT-PR-01967Section 8.3 – Structural Design23 GLAST LAT Project CDR/CD-3 Review May LAT FEA Model Boundary Conditions Accelerations –Used LAT center-of-mass accelerations from LAT Environmental Spec. for structural load cases SC mount boundary condition mimics flexure-type connection –X-Side SC mount Restrained in the Y- and Z-directions Free in all 3 rotational DOF’s and X –Y-Side SC mount Restrained in the X- and Z-directions Free in all 3 rotational DOF’s and Y Radiator mounting –Radiators mounted to Grid through Radiator Mount Bracket –SC boundary condition fixed in Y- direction (out-of-plane) only LAT F.E.A. Properties and Current LAT Estimates Source: LAT-TD “LAT Mass Status Report, Mass Estimates for Mar 2003,” 7 Mar 2003 LAT Static-Equivalent Design Accelerations Source: LAT-SS “LAT Environmental Specification,” March 2003 LAT F.E.A. Model Metrics UPDATE

LAT-PR-01967Section 8.3 – Structural Design24 GLAST LAT Project CDR/CD-3 Review May LAT FEA Model Quality Checks FEA model check-runs –Free-free modal analysis—check model for mechanisms –Translation check—check model for inadvertent grounding –Gravity check—check that inertial loads are reacted only at boundaries –Temperature check—check that structure is free to expand/contract Analysis comparison runs –Mass—compare model mass with LAT estimate –Center of mass—compare model center of mass with LAT estimate –Modal analysis—compare subsystem modes in LAT model against fixed-base results UPDATE

LAT-PR-01967Section 8.3 – Structural Design25 GLAST LAT Project CDR/CD-3 Review May Launch and On-Orbit Load Case Definitions Launch Structural Load Cases On-Orbit Thermal Load Cases

LAT-PR-01967Section 8.3 – Structural Design26 GLAST LAT Project CDR/CD-3 Review May Integration and Test Load Case Definitions Integration and Test Structural Load Cases Integration and Test Thermal Load Cases

LAT-PR-01967Section 8.3 – Structural Design27 GLAST LAT Project CDR/CD-3 Review May Modal Analysis Results 10 modes below 75 Hz –1 significant LAT modes –Multiple ACD panel, BEA vibration modes –Multiple Radiator modes and mode combinations LAT drumhead mode – Hz at 2679 kg estimate – Hz at 3000 kg allocation Significant LAT Modes LAT Drumhead Mode UPDATE

LAT-PR-01967Section 8.3 – Structural Design28 GLAST LAT Project CDR/CD-3 Review May Summary of Key Deflections Due to Launch Loads Grid Deflection –6.8 g thrust load at MECO produces maximum Grid bowing –Grid max deflections Center: mm Corner: mm TKR Gap closing –Dishing of the Grid tends to tip TKR modules together Max gap closing: mm Budget: mm Radiator distortion –In-plane max motion: mm –Out-of-plane max bowing: mm LAT Deflected Shape Plot UPDATE

LAT-PR-01967Section 8.3 – Structural Design29 GLAST LAT Project CDR/CD-3 Review May Interface Deflections Deflections and relative motions extracted directly from integrated FEA model Relative motions at interfaces are part of LAT Environmental Spec interface loads definition UPDATE

LAT-PR-01967Section 8.3 – Structural Design30 GLAST LAT Project CDR/CD-3 Review May Interface Load Recovery The LAT Environmental Specification is the collection point for interface loads for subsystem design and test Current load tables in the LAT Environmental Specification contain results from the Delta-PDR structural model (also being used for the current CLA cycle) –Some interface limit loads were generated by LAT static-equivalent analyses –Some limit loads were gleaned from the preliminary CLA, completed in December, 2001 The goal of CDR analysis is to generate updated loads, based on the CDR design, and compare with Delta-PDR design values –Include results for all load cases to assure that worst-case loads have been captured –Identify interfaces and load cases where CDR analysis shows higher predicts than earlier analysis  develop action plan to resolve these issues –Identify interfaces where loads have come down considerably  investigate reducing limit loads in the Environmental Specification, to increase design margin LAT Mech PDR Structural Analysis Aug, 2001 LAT PDR Structural Analysis Jan, 2002 Prelim CLA Results Out Dec 2001-Mar, 2002 Deliver Mech PDR LAT FEA (Sep, 2001) LAT Delta-PDR Structural Analysis Aug, 2002 Deliver Delta- PDR LAT FEA (Sep, 2002) LAT CDR Structural Analysis May, 2003 LAT Env Spec Mar, 2003 SC Study II Struc Models Deliver CDR LAT FEA (Jun, 2003) Spectrum Proposal Struc Model Mission PDR CLA Results Out May, 2003 LAT Env Spec Jun, 2003 Spectrum PDR Struc Model Mission CDR CLA Results Out Sep, 2003 LAT Env Spec Oct, 2003 LAT Structural Analysis Flow-down Schedule

LAT-PR-01967Section 8.3 – Structural Design31 GLAST LAT Project CDR/CD-3 Review May SC-LAT Interface Load Recovery Loads shown are the maxima for all 4 mount points, for the static- equivalent load cases shown Environmental Spec loads are the result of the preliminary CLA UPDATE

LAT-PR-01967Section 8.3 – Structural Design32 GLAST LAT Project CDR/CD-3 Review May Radiator Interface Load Recovery Loads are derived from the LAT static- equivalent analysis, using LAT center-of- gravity accelerations The preliminary CLA of the LAT/Radiators on a generic spacecraft predicted a maximum strut load of only 365 N, so the CLA does not produce the limit load for this interface Acoustic analysis predictions could alter these limit loads for the interface to the SC mount struts UPDATE

LAT-PR-01967Section 8.3 – Structural Design33 GLAST LAT Project CDR/CD-3 Review May TKR Interface Load Recovery TKR Flexure joint –Flexures isolate the carbon-fiber TKR structure from thermal strains of the Grid –All flexure normals point to the center of a TKR module –The 8 flexures are not a kinematic mount TKR Flexure force recovery –Nodal forces are retrieved by isolating nodal forces at the TKR Flexure beam elements –Design limit loads are the maxima of the TKR module loads Limit loads identified for peak compressive, tensile, and shear load Peak loads all occur in corner bays UPDATE

LAT-PR-01967Section 8.3 – Structural Design34 GLAST LAT Project CDR/CD-3 Review May CAL Interface Load Recovery CAL-Grid tab joint –Pins carry all shear load at joint –Bolts carry pull-out and prying loads Load recovery –Tab loads separated into 2 types Shear tabs Bolted tabs –All tabs designed to peak limit loads UPDATE

LAT-PR-01967Section 8.3 – Structural Design35 GLAST LAT Project CDR/CD-3 Review May ACD Interface Load Recovery ACD Base Electronics Assembly (BEA) to Grid Joint –Bolted connection at 4 corners of BEA carry z-direction (thrust) loads only –Bolted and pinned connections at the center of each of the 4 sides Interface load recovery –Interface loads evaluated by retrieving nodal forces at rigid extension from Grid to BEA –Loads shown are design loads for each bolt/pin Mid-Side Mounts –Shear: RSS of X, Z shears in plane of Grid wall –Tens/Compression: normal to Grid wall Corner Mounts –Shear: assumed to carry no shear –Tens/Compression: parallel to LAT Z-axis UPDATE

LAT-PR-01967Section 8.3 – Structural Design36 GLAST LAT Project CDR/CD-3 Review May Electronics Interface Load Recovery Electronics Box joints –Rigid stand-offs to the CAL carry z-direction (thrust) loads, and lateral loads and moments –Flexible connection to the X- LAT Plates allow transverse motion while providing compressive pre-load CAL interface load recovery –Limit loads extracted from model –Loads shown are at the base (CAL side) of the stand-off X-LAT Plate interface load recovery –Lateral, shearing loads defined to be zero: connection allows lateral motion –Tension/compression loads arise from deflection of the Grid UPDATE

LAT-PR-01967Section 8.3 – Structural Design37 GLAST LAT Project CDR/CD-3 Review May Structural Analysis Summary and Further Work Summary –Subsystem structural models have been updated to reflect CDR designs –Model quality checks have been completed Further Work UPDATE

LAT-PR-01967Section 8.3 – Structural Design38 GLAST LAT Project CDR/CD-3 Review May Verification Test Outline Integration and Test flow Qualification and verification flow –Strength qualification test flow –Vibro-acoustic test flow Dynamic test plans (see LAT-MD-01196, “Dynamics Test Plan”) –Modal survey –Sine vibration –Sine Burst –Acoustic LAT survey plans (see LAT-MD-00895, “LAT Instrument Survey Plan”) –Optical survey –Cosmic-ray muon survey

LAT-PR-01967Section 8.3 – Structural Design39 GLAST LAT Project CDR/CD-3 Review May Integration and Test Flow LAT Integration and Test Flow UPDATE

LAT-PR-01967Section 8.3 – Structural Design40 GLAST LAT Project CDR/CD-3 Review May Strength Qualification Test Flow Grid Box static loading –Without Radiators, TKR’s, and ACD –Includes 16x CAL Plate STE’s –TKR joints tested one bay at a time –SC-LAT tested one joint at a time –Grid Box distorted to strength-qualify CAL joint and Grid Box assembly TKR, CAL, TEM/TPS sine burst –Fixed-base strength qualification of subsystem module and interface design ACD Shell and Base Frame Assembly –Fixed-base strength qualification of internal flexures, subsystem, and interface design LAT sine burst –LAT mounted on vibe test stand –Completes strength qual of Grid and TKR joint ACD Sub-Ass’y Sine Burst A TKR QM Sine Burst, Static Load Q ACD Shell + BFA Sine Burst Q CAL QM Sine Burst Q TEM/TPS QM’s Sine Burst Q E-Box PF QM’s Sine Burst P Grid Box Ass’y Static Load P Radiator Static Load P LAT Ass’y Sine Burst P GLAST Obs Sine Burst P Subsystem Qual Tests Subsystem Acceptance Tests

LAT-PR-01967Section 8.3 – Structural Design41 GLAST LAT Project CDR/CD-3 Review May Vibro-Acoustic Test Flow LAT and GLAST vibro-acoustic test plan –LAT modal survey—without Radiators, while at SLAC –LAT sine vibration—without Radiators; includes sine sweep signature –LAT acoustic—without Radiators –GLAST Observatory sine vibration—with Radiators but without solar arrays (TBR); includes sine sweep signature –GLAST Observatory acoustic—with Radiators but without solar arrays (TBR) –GLAST Observatory shock—shock event applied at PAF separation plane ACD Sub-Ass’y Sine Vibe, Random Vibe A ACD Sub-Ass’y Acoustic A TKR Qual Module Sine Vibe, Random Vibe Q TKR Flt Modules Sine Vibe, Random Vibe A ACD Shell + BFA Sine Vibe, Random Vibe Q ACD Shell + BFA Acoustic Q CAL QM’s Sine Vibe, Random Vibe Q CAL FM’s Random Vibe A TEM/TPS QM’s Sine Vibe, Random Vibe Q TEM/TPS FM’s Random Vibe A E-Box PF QM’s Sine Vibe, Random Vibe P Grid Box Ass’y P Radiator Sine Vibe P Radiator Acoustic P LAT Ass’y Modal Survey, Sine Vibe P LAT Ass’y Acoustic P GLAST Obs Sine Vibe P GLAST Obs Acoustic P Subsystem Qual Tests Subsystem Acceptance Tests GLAST Obs Shock P

LAT-PR-01967Section 8.3 – Structural Design42 GLAST LAT Project CDR/CD-3 Review May LAT Modal Survey Test goals –Validate the LAT structural finite element analysis (FEA) model by correlating with test results –Measure all primary modes of the LAT/Grid structure. –Measure the first mode, and all modes predicted to have high mass participation, for every subsystem –Measure as many natural frequencies of the LAT up to 150 Hz as practical –Test results will be used to evaluate the predicted expected modal frequencies and mode shapes, and used to modify the structural FEA, if needed. –Finalize test environments and notching plans for sine vibration testing Configuration –Fully integrated, except the Radiators are not mounted –Supported off of its spacecraft (SC) mount brackets, –+Z-axis point vertically up –LAT powered off during testing Specialized test equipment requirements –LAT supported by the Vibe Test Plate which provides a rigid support of each mount point –Vibe Test Plate sits on a massive base-isolated table, to damp high-frequency base noise being transmitted to the structure –Excited using two stingers, located under the LAT

LAT-PR-01967Section 8.3 – Structural Design43 GLAST LAT Project CDR/CD-3 Review May LAT Modal Survey (cont) Instrumentation –High-precision accelerometers mounted to the LAT and test stand Outstanding technical issues –Establish excitation levels –Finalize accelerometers for test, based on predicted test levels Source: LAT-MD , “LAT Dynamics Test Plan,” March 2003 ACD Accelerometer Placement CAL Bottom and E-Box Accelerometer Placement TKR, CAL, and Grid Accelerometer Placement

LAT-PR-01967Section 8.3 – Structural Design44 GLAST LAT Project CDR/CD-3 Review May LAT Sine Vibration / Sine Burst Tests Test goals –Verify the LAT’s ability to survive the low frequency launch environment –Test for workmanship on hardware such as wiring harnesses, MLI, and cable support and strain-reliefs which will not have been fully verified at the subsystem level –Interface verification test for subsystem structural interfaces to the LAT Grid Configuration –Fully integrated, except the Radiators are not installed –Supported off of its spacecraft (SC) mount brackets, on the Vibration Test Stand –The LAT is tested in all three axes, X, Y, and Z independently, requiring re-configuration between tests –The LAT is powered off during sinusoidal vibration testing, and the E-GSE cable harnesses removed Specialized test equipment requirements –The Vibe Test Stand must support the LAT at the SC interface with flight-like connections –The Stand must allow for reconfiguration to alternate axes, with the LAT attached, to avoid unnecessary handling

LAT-PR-01967Section 8.3 – Structural Design45 GLAST LAT Project CDR/CD-3 Review May LAT Sine Vibration / Sine Burst Tests (cont) Instrumentation –Accelerometers mounted to the LAT and test stand, to cover the entire dynamic range predicted for the LAT and subsystems Outstanding technical issues –Accelerometer sensitivity—pre-test dynamic analysis will indicate the level of precision and dynamic range needed for this test –Finalize LAT degrees of freedom at STE connection (simulating a “fixed” connection or a flexure) –Establish test levels based on Observatory CLA, without exceeding interface limit loads Source: LAT-MD , “LAT Dynamics Test Plan,” March 2003 TKR, CAL, and Grid Accelerometer Placement Radiators Accelerometer Placement LAT Sine Vibration Minimum Test Levels

LAT-PR-01967Section 8.3 – Structural Design46 GLAST LAT Project CDR/CD-3 Review May LAT Acoustic Test Test goals –Verify the LAT’s ability to survive the acoustic launch environment –Test for workmanship on LAT hardware, especially that hardware which responds to acoustic loading –Validate the acoustic analysis Configuration –LAT is fully integrated, including the Radiators –Mounted to STE using the flight-configuration bolted joint –LAT +Z-axis vertical, and with Radiators integrated to the Grid as well as to the STE at the SC strut mount points –LAT is powered off during acoustic testing, and the E-GSE cable harnesses removed Specialized test equipment requirements –The Vibe Test Stand must support the LAT in the same degrees of freedom as the SC flexures, to avoid over-constraining the Grid and Radiators –The STE fills the volume between the Radiators, so must approximate the acoustic behavior of the SC Instrumentation –Accelerometers mounted to the LAT and test stand –Microphones mounted around the LAT

LAT-PR-01967Section 8.3 – Structural Design47 GLAST LAT Project CDR/CD-3 Review May LAT Acoustic Test (cont) Outstanding technical issues –Establish acoustic fill and response requirements of STE to adequately bound response of SC –Define post-test modal signature test to verify that LAT dynamic response matches baseline –Finalize accelerometer and microphone placement –Perform pre-test acoustic analysis LAT Acoustic Test Levels Source: LAT-SS , “LAT Environmental Specification,” March 2003

LAT-PR-01967Section 8.3 – Structural Design48 GLAST LAT Project CDR/CD-3 Review May LAT Surveying Survey program goals –Verify as-integrated interface stay-clears –Verify LAT alignment requirements –Verify science performance requirements Validate analytical thermal-mechanical analysis models Develop correlation functions for thermal-mechanical distortion Predict the expected on-orbit precision of the instrument Survey program description –Optical surveying Subsystem inspection measures position of survey retro-reflector balls with respect to physical features and active elements of subsystem module After integration, laser tracker measures bearing and distances to balls on the LAT and in the integration room Data reduction of measurements produces position location information for all balls relative to room coordinate system, and prediction of measurement precision This will establish location of subsystem surfaces and features in their as-integrated positions, providing a verification check during integration –Muon surveying Uses naturally-occurring cosmic-ray muons Muons generate straight-line tracks through TKR modules Mis-alignments between modules will show up as a step in the reconstructed track With muons generating enough cross-tower tracks, the relative locations of tower can be measured This will be used to precisely establish the locations and attitudes (and changes) of TKR modules

LAT-PR-01967Section 8.3 – Structural Design49 GLAST LAT Project CDR/CD-3 Review May LAT Surveying (cont 1) LAT Optical and Muon Surveys During Integration and Test Source: LAT-MD “LAT Instrument Survey Plan”

LAT-PR-01967Section 8.3 – Structural Design50 GLAST LAT Project CDR/CD-3 Review May LAT Surveying (cont 2) Instrumentation –Laser tracker—measurement precision of instrument is less than 10 microns, but actual precision is more a function of room temperature stability, reflector ball location precision –Tracker—measurement precision and instrument calibration will be verified with Calibration Unit beam tests at SLAC Specialized test equipment requirements –Room temperature controlled to within 5 o C (TBR) –LAT and GSE/STE temperature stable to within 2 o C (TBR) –Support stands allow for leveling the LAT to within 0.2 degrees to ensure proper functioning of heat pipes –Chill plates provide a heat sink for the Grid during in-air testing Outstanding technical issues –Investigating the use of inclinometers during thermal-vacuum testing –Thermal-mechanical model of LAT in test configuration has not yet been done—this is needed to establish precision and stability requirements for STE

LAT-PR-01967Section 8.3 – Structural Design51 GLAST LAT Project CDR/CD-3 Review May Summary of Structural Test Issues and Closure Plans

LAT-PR-01967Section 8.3 – Structural Design52 GLAST LAT Project CDR/CD-3 Review May Summary and Conclusions UPDATE Structural Analysis Summary Verification Test Summary Conclusions Summary –LAT Dynamics Test Plan has been written and is ready for initial release –LAT Thermal Test Plan has been written and is ready for initial release –LAT Survey Plan has been written, with final pieces coming together for release before CDR –Test instrumentation and levels are understood Further work –Perform pre-test analysis to finalize instrumentation and STE requirements –Expand test plans with results of pre-test analysis –Complete test implementation plans