LAT FSW System Checkout TRR

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

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 NCR00942

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

5
Structural VCRM Summary
6
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
F
C
S
NRL Post-Ship
at SLAC
Sine Vibe
Acoustic
Mount
Receive,
C
T
Radiators
Unpack
L
L
L
L
L
L
Pre Post
-
Axis
Final
T
-
Cycle
T
-
Bal
Pre
-
TV
Weight
Ship to
Remove
Pack LAT
CG
Spectrum
Radiators
L
C
L
C
S
S
C
S
F
TESTING IN THERMAL VAC CHAMBER
F
F
L
Limited Performance Test
L
Limited Performance Test
LAT Functional and FSW Test
Comprehensive Performance Test
C
T
TCS Functional Test
Comprehensive Performance Test
C
T
TCS Functional Test
SVAC Test
S
E
EMI/EMC Emissions/Susceptibility Test
SVAC Test
S
E
EMI/EMC Emissions/Susceptibility 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

8
Sine Vibration Test Configuration
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 SSs 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

10
Sine Vibration Data
Excellent Correlation between test and analysis
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

12
Acoustic Test Configuration
13
Acoustic Data
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.

15
Mass Properties Test Configuration
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

17
GLAST Large Area Telescope LAT Pre-Shipment
Review Back-up Slides John Ku Design
Integration and Analysis Stanford Linear
Accelerator Center
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)

19
LAT Margins of Safety
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/MechanicalSyste
  ms/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/MechanicalSyste
  ms/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

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.

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

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 58.94gs, respectively.
• Filtered results for the same accelerometer
  channels showed maximum content of 1.347 and
  1.362gs, 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
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
26
Energy Release Observed

• Zoomed-in data showing sudden energy release.

energy release (slippage) observed here
Shock (Impact) observed here
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 gs 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 _at_ 32.5 Hz _at_ LAT CG based on Observatory
  analysis
• 0.7g _at_ 32.5 Hz _at_ LAT CG already experienced at te
  ½ level notched run

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 SSs 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