GLAST Large Area Telescope LAT Pre-Shipment Review Mechanical Structure John Ku Design Integration and Analysis Stanford

1. Gamma-ray Large Area Space Telescope GLAST Large Area Telescope LAT Pre-Shipment Review Mechanical Structure John Ku Design Integration and Analysis Stanford Linear Accelerator Center Mechanical Test

2. Purpose / Contents • Demonstrate structural readiness to ship the integrated flight instrument to the spacecraft vendor • The LAT… • …is compliant with all structural requirements • …successfully satisfied all test objectives • …has no outstanding NCRs related to structural performance Mechanical Test

3. Changes since PER • Requirements / Design Update, i.e. Changes since PER • ACD-to-Radiator and ACD-to-blanket bar interface modified • Velcro patches did not line up and were incompatible (both sides were loop) • To solve this, kapton tape was used to attach the blankets to the ACD • Blankets are lower on ACD by approximately 12.7 mm, resulting in looser fit. • Interface to radiators and blanket bars are okay • The new attachment method successfully sustained all environmental tests and functioned properly • APPROVED: This change is documented in NCR#00942 Mechanical Test

4. Requirements compliant • All flight system design analyses have been successfully completed and demonstrate adequate margin • Mission System Spec  433-SPEC-0001 • LAT-SC Interface Requirements Spec  433-IRD-0001 • Mission Assurance Requirements Spec  433-MAR-0001 • LAT Environmental Requirements Spec  LAT-SS-00778 • LAT Performance Verification Plan  LAT-MD-00408-04c Mechanical Test

5. Structural VCRM Summary Mechanical Test

6. L L E EMI/EMC Successfully Passed Environmental Tests • The mechanical tests, highlighted in red boxes, are part of the environmental test sequence, shown below (see LAT-MD-02717): • No liens that require any retest at NRL! Baseline Ship to NRL C F S NRL Post-Ship at SLAC Sine Vibe Acoustic Receive, Mount C T Unpack Radiators L L L L L L Pre Post - Axis Final T - Bal T - Cycle Pre - TV Weight Ship to Remove Pack LAT CG Spectrum Radiators L C F C S S C S L TESTING IN THERMAL VAC CHAMBER F F L L LAT Functional and FSW Test Limited Performance Test Limited Performance Test C C T T TCS Functional Test TCS Functional Test Comprehensive Performance Test Comprehensive Performance Test S S EMI/EMC Emissions/Susceptibility Test EMI/EMC Emissions/Susceptibility Test E E SVAC Test SVAC Test Mechanical Test

7. Sine Vibration Test Objectives Met • Were the Sine Vibration Test Objectives met? • Verify the strength of the LAT and subsystem interfaces under PFQ loads and durations • Was this be accomplished? YES! Pre- and post-test signature overlays show identical structural behavior prior to and after PFQ loads • Measure primary natural frequencies (fn) of the primary modes of the LAT • Was this be accomplished? YES! The first mode of the LAT was measured to be 60 Hz, which agrees with predictions and verifies the design requirement to be above 50 Hz • Determine transmissibility (Q) of the LAT • Was this be accomplished? YES! Low level sine sweeps showed a primary mode amplification of ~15, corresponding to a damping ratio of ~3.3% of critical • Validate the math model used for coupled loads analysis • Was this be accomplished? YES! Data review shows that the math model accurately predicts hardware performance • Verify the workmanship and processes used in the manufacture and assembly • Was this be accomplished? YES! Pre- and post-test signature overlays show identical structural behavior prior to and after PFQ loads Mechanical Test

8. Sine Vibration Test Configuration Mechanical Test

9. Sine Vibration Test Anomaly • Y-Axis Sine Vibe Test, June 2, 2006 • During Run #11 at ½-level, an abort was experienced at 31.87 Hz • Immediately preceding the abort, three loud sounds (described as dull thuds) were noted by engineer on the floor • The abort itself was not so unusual, but the combination with the very unusual sounds, further investigation ensued • Investigation findings (see backup slides for details) • A thorough review of the data points to a high frequency shock at the strong direction flexures • Peak shock (unfiltered data) is ~60g while inertial acceleration (filtered at 50 Hz) was 1.4g. • Maximum shock (unfiltered) in LAT SS’s is ~6.67g while inertial acceleration (filtered) is 0.14g • 6.67g high frequency shock event has very little energy content • Problems are not expected due to these low shock inputs • NCR documenting this anomaly has been closed with some follow-up actions to be performed by the GPO Mechanical Test

10. Sine Vibration Data Excellent Correlation between test and analysis Mechanical Test

11. Acoustic Test Objectives Met • Were the Acoustic Test Objectives met? • The primary objective is to demonstrate that the fully integrated LAT is capable of withstanding acoustic noise loads, simulating launch conditions. • Was this accomplished? YES! Pre- and post-test signature overlays show identical structural behavior prior to and after PFQ loads. Additionally, performance testing showed no degradation due to acoustic loads • A secondary objective is to verify the acoustic analysis, i.e. that the LAT components were qualified to high enough levels of random vibration. • Was this accomplished? YES! The responses show subsystem test level specifications were conservative Mechanical Test

12. Acoustic Test Configuration Mechanical Test

13. Acoustic Data Mechanical Test

14. Mass Properties Test Objectives Met • Were the Mass Properties Test Objectives met? • Measure the overall mass and CG of the fully integrated LAT • Was this accomplished? YES, with caveat. The preliminary data analysis does not account for GSE tolerances. The adjusted CG calculation will be published in the mass properties report • Verify the following three IRD requirements: • LAT mass does not exceed 3000kg. Was this accomplished? YES! The mass properties test showed the LAT mass to be 2782 kg (2789 kg predicted) • By Analysis, show Zcg is a maximum of 185mm above the LAT Interface Plane (LIP). Was this accomplished? Not yet, but will be published in the test report. This is considered very low risk since prediction error is small when compared with measured quantities. • By Test, show X-cg and Y-cg are within 20mm of the LAT Coordinate System (LCS) Z-axis. Was this accomplished? YES! The measured CG is (-0.56mm, -1.27mm); the predicted CG was (-1.57mm, -1.2mm). • A secondary goal is to verify that the measured mass properties coordinate with the math model mass matrix Was this accomplished? Not yet, but the results will be published in the mass properties report. Mechanical Test

15. Mass Properties Test Configuration Mechanical Test

16. Readiness Statement • All Pre-ship related requirements are verified • Requirements still needing verification • Mass property requirements will be satisfied by 9/22/06 • Other requirements will be satisfied at Observatory Testing • Environmental tests executed successfully • Sine Vibration Test completed successfully, report pending • Acoustic Test completed successfully, report in review • Mass and CG Test completed successfully, report pending • The LAT structure is ready for shipment to SC vendor Mechanical Test

17. Gamma-ray Large Area Space Telescope GLAST Large Area Telescope LAT Pre-Shipment Review Back-up Slides John Ku Design Integration and Analysis Stanford Linear Accelerator Center Mechanical Test

18. LAT Margins of Safety • Current calculations for system performance are fully compliant with requirements • Completed analysis of current design demonstrate adequate margin for mechanical loads and stress from handling, test and flight environments (ECLA and FDLC2 used for flight loads) Mechanical Test

19. LAT Margins of Safety Mechanical Test

20. Appropriately tested at lower levels of assembly • LAT Instrumentation Plan  LAT-TD-00890-03 • Flight and ground instrumentation defined • LAT Dynamics Test Plan  LAT-MD-01196-03 • Sine Vibration, Acoustic, and Mass Properties tests described • All lower level flight system verification activities have been satisfactorily completed and all discrepancies are sufficiently understood to warrant proceeding • Engineering Test Unit testing since CDR are documented and the design reflects the results • Coupon Tests • Insert pullout and shear strength (keensert, helicoil, potted inserts, bare threads) • torque to preload ratios • http://www-glast.slac.stanford.edu/MechanicalSystems/Analysis/Testing/EM/ • Flight-like coupon tests • Grid wing corner • Grid EM1X4 Stiffness Verification Test  Complete  LAT-TD-02417 • http://www-glast.slac.stanford.edu/MechanicalSystems/Analysis/Testing/Component/ • CAL EM Vibration Test  Complete  LAT-TD-01888 • TKR EM Vibration Test  Complete  LAT-TD-04310 • SC Flexure Strength and Stiffness test  Complete  LAT-TD-07813-01 • Flight Subsystem tests  subsystem EIDP reports provide more detailed subsystem test data Mechanical Test

21. Appropriately tested at lower levels of assembly (cont.) • Notable fabrication discrepancies and resolution • Subsystem EIDP reports provide more detailed subsystem manufacturing discrepancy information • Shear plates are held in place by a captive stud and nut. Substandard nut manufacturing caused galling which could lead to stud failure during attempted nut removal. • Resolution: do not remove defective nuts unless necessary. If necessary, split nut to preserve stud. • This anomaly affects 8 out of 64 studs and 4 out of 16 Calorimeters • Additional information can be obtained from a tech note written by J.Ku: “Use of Subtandard Nut,” dated 6 Feb 2006. Mechanical Test

22. GLAST LAT Sine Vibration TestY-Axis Anomaly John Ku June 2, 2006

23. Problem Statement • Y-Axis Sine Vibe Test, June 2, 2006 • During Run #11 at ½-level, an abort was experienced at 31.87 Hz • Immediately preceding the abort, three loud sounds (described as dull thuds) were noted by engineer on the floor (C. Fransen) • The abort itself was not so unusual, but the combination with the very unusual sounds, further investigation ensued • The input spectrum was not as expected. The expected and tested spectra are shown below • Visual Inspection initiated at approximately 2pm • A connector saver (on –X side) was found disconnected from the flight hardware • A washer used for lifting was found loose in the inner bag (accidentally left in bag) • A stone (sharpening stone) was found on the shaker armature • These findings do not explain the sound that was heard • No other anomalies were found via visual inspection • A thorough review of the data showed that the anomaly was most likely caused by LAT/SC interface slippage, which will be explained in the following slides Mechanical Test

24. Anomaly Caused by LAT/SC Interface Slippage • A review of the unfiltered time histories showed that there was a shock-like event at the +X and –X flexure / LAT interface. • The peak responses observed for the +X and –X interfaces were 59.34 and 58.94g’s, respectively. • Filtered results for the same accelerometer channels showed maximum content of 1.347 and 1.362g’s, enforcing the theory that this is a high frequency event. Unfiltered  Peak = ~60 g Filtered  Peak = ~1.3 g +X Flexure Unfiltered  Peak = ~60 g Filtered  Peak = ~1.3 g -X Flexure Mechanical Test

25. Energy Release Observed • Further examination of the time-phased data of the “event” shows a strain reduction, i.e. energy release, immediately prior to the shock event (~ 1.5 milliseconds). • This enforces a sudden slippage theory. energy release observed here Mechanical Test

26. Energy Release Observed • Zoomed-in data showing sudden energy release. energy release (slippage) observed here Shock (Impact) observed here Mechanical Test

27. Mechanical Joint Design • This theory is plausible because • There is clearance in the pin to LAT bushing • Bushing: LAT-DS-02554: ID = 0.564 +0.002 / -0.000 • Pin: OD = 0.5625 +0.0000 / -0.0010 • Max Clearance = 5.660 – 5.615 = 4.5 mils • Expected clearance ~3 mils to be confirmed by Marc Campell • There is clearance in the pin to SC Flexure • Undertermined amount • Friction holds the joint in static equilibrium, but is not reliable as lateral accelerations increase. • We observed slippage at approximately 1.76 g’s at the LAT CG. • According to this, the joint coefficient of friction would be ~0.26 (plausible). • 64 ft-lb torque * 4 7/16 bolts + static weight = ~41237lbf normal force • 1.76 g * 2780kg = ~10787 lbf total • This sounds like a major design flaw, but in reality, the LAT vibration test subjects the suspect interface to significantly more severe loads than at the observatory level, so the design may be adequate • Additional investigation should be performed to ensure linear performance at the observatory level • Manual notching at the LAT first natural frequency is okay because the responses will still be significantly higher than the observatory analysis shows • 0.3g MIN @ 32.5 Hz @ LAT CG based on Observatory analysis • 0.7g @ 32.5 Hz @ LAT CG already experienced at te ½ level notched run Mechanical Test

28. Conclusions and Path Forward • Conclusions • All the above findings point to a high frequency shock at the strong direction flexures • Peak shock (unfiltered data) is ~60g while inertial acceleration (filtered at 50 Hz) was 1.4g. • Maximum shock (unfiltered) in LAT SS’s is ~6.67g while inertial acceleration (filtered) is 0.14g • 6.67g high frequency shock event has very little energy content • Problems are not expected due to these low shock inputs • Path Forward • Conduct “intermediate” LL sine vibration test and overlay with pre-test signature • Cable up EGSE and perform LPT over the weekend to confirm LAT function • Before resuming test on Monday, have an 8am EDT tag-up (Ken to send dial-in info) • Marc to provide as-built data • If intermediate and pre-test signatures are okay, AND LPT results are favorable, then continue testing Monday morning Mechanical Test