REPRESENTATIVE MECHANICAL SHOCK TESTING FOR SATELLITE ELECTRONIC UNITS

Transcription

1 REPRESENTATIVE MECHANICAL SHOCK TESTING FOR SATELLITE ELECTRONIC UNITS B. Brévart, J. Poirier, S. Behar-Lafenêtre, N. Girault THALES ALENIA SPACE FRANCE 2 nd Workshop on Spacecraft Shock Environment and Verification ESTEC, November DOC-TAS-EN /11/2015 CONTEXT OF THE INVESTIGATION Shock testing is specified in terms of a base acceleration SRS and leave largely open the definition of the test bench (resonant plates/beams, pyrotechnic or mechanical shock source) 2 Numerous facilities are available All test methods do not induce the same level of stress in the equipment General equipment over-testing with test facility w.r.t. a realistic payload environment has been demonstrated and quantified (ECSSMET 2012) 12/11/2015 First investigation on representative shock testing presented at ECSSMET 2014

2 OVER-TESTING ISSUE TAS implemented two electronic units fully monitored with accelerometers, strain gages and 3D I/F force cells (TxTTC), exposed to different shock environments 3 Simplified pyrotechnic point source and payload structure Tx TTC Bac6U Pyroshock generator 12/11/2015 OVER-TESTING ISSUE Same electronic units recently exposed (2015 shock campaign) to a representative pyrotechnic mechanism (solar array release) 4 Representative Pyrotechnic Mechanism on TxTTC Bac6U 12/11/2015

3 OVER-TESTING ISSUE True in plane acceleration is difficult to measure and its level is low in the two considered cases (pyrotechnic point sources) Better estimation with a flat tri-axial accelerometer than a cube In plane specification should be distinguished from the out of plane specification 5 G 2013, Thales Alenia Space OVER-TESTING ISSUE Out of plane acceleration also sensitive to measurement method Excessive levels given by accelerometers on a bonded cube 6 Accélération (g) G Fréquence () T-LAZ-Z T6Z T8Z

4 OVER-TESTING ISSUE TAS test bench is a suspended resonant plate excited by a mechanical impact (pendulum // or dropping mass ) 7 Qualification Shock Environment In plane excitation Out of plane excitation OVER-TESTING ISSUE Maximum responses of the unit (X/Y/Z accelerations, stresses, I/F forces) are largely due to the out of plane excitation More than 20dB over-test on most responses above 1000 Half over-test or so is only due to the test bench configuration The rest of the over-test is due to the specification process 8 B3Z 26 db 16 db OVER-TEST OVER-TEST due to test bench configuration (Same Average Base Acceleration)

5 TAS SIMULATION PHASE Solution trends identified by shock simulation of the plate-unit coupled system Half sine point force tuned to meet I/F acceleration Sensitivity analysis to various parameters with the objective to get representative unit responses for a given I/F acceleration 9 F tuned F tuned TAS SIMULATION PHASE OUTPUTS Very sensitive model parameters Contact between the unit and the shock plate Suppress tool plate (between unit and shock plate) Add washers eventually Shock plate thickness Optimal value is 10mm (bending stiffness is the same as the sandwich panel) 10 Low sensitivity parameters Modification of the anvil shape/thickness Damping of the shock plate Possible plate damping solution to minimize low frequency interface acceleration dispersion

6 TAS SOLUTION: Z AXIS EXCITATION Suppression of the tool plate, 10mm shock plate on a foam 11 BEFORE 10mm AFTER TEST OF TAS SOLUTIONS Considering the same average base excitation, accelerations on the unit with the thin plate setup (Z axis excitation) are more representative of the pyrotechnic tests 10mm Shock Table 16 db Thick Shock Table 10mm Shock Table 12 Thick Shock Table 9 db G G TE3Z 8 db 10 db Thick Shock Table Pyroshock generator on simplified payload TE1X 10mm Shock Table BE6Y

7 TEST OF TAS SOLUTIONS Combined with X and Y axis excitation, the new test set-up for 13 Z axis (thin plate) yields the unit qualification The SRS of all the measured accelerations is fully covered Thick Shock Table Y axis Thick Shock Table Y axis Thick Shock Table X axis Thick Shock Table X axis G 10mm Shock Table Z axis G 10mm Shock Table Z axis BE6Y BE7Y TEST OF TAS SOLUTIONS Combined with X and Y axis excitation, the new test set-up for Z axis (thin plate) yields the unit qualification The SRS of all the measured strains is fully covered 14 10mm Shock Table Z axis Thick Shock Table X axis G G Thick Shock Table Y axis

8 TEST OF TAS SOLUTIONS TxTTC unit with 3D I/F force cells tested on the thin plate (without an additional tool plate) similarly 15 BEFORE AFTER TEST OF TAS SOLUTIONS With similar applied accelerations, normal I/F forces with the new test setup are more representative (amplitude, phase) of the pyrotechnic tests N Pyroshock generator on simplified payload 800 N Mechanical shock test Z axis New setup (10mm plate) 2600 N Mechanical shock test (Z axis Thick plate + Tool plate)

9 TEST OF TAS SOLUTIONS In plane I/F forces with the thin plate remain high The 10mm plate is much stiffer (//) than the inserts in the sandwich panel N Mechanical shock test Z axis New setup (10mm plate) 320 N 1550 N Mechanical shock test (Z axis Thick plate + Tool plate) TEST OF TAS SOLUTIONS A mass dummy is necessary for calibration of the 10mm shock plate even for small units 18 I/F Z acceleration average without the unit I/F Z acceleration average with the tested unit I/F Z acceleration average with the tested unit I/F Z acceleration average with the dummy unit Calibration without Dummy Unit Calibration using a Dummy Unit

10 TEST OF TAS SOLUTIONS With the thin plate (10 mm), calibration of a specification is not more difficult to achieve than it was with a thick one 19 Ref. ESA Shock Handbook: - Average acceleration respects tolerances - Less than 6 db between diagonal sensors Peak accelerations around 1000g for a 2000g SRS plateau! TEST OF TAS SOLUTIONS A 15mm plate behaves like the 30mm plate (+ tool plate) at high frequencies (above 1000 ) db 8 db Total Loss of HF Benefit Acceleration on Bac6U PCB with the 10mm plate (blue curve) vs other shock tests Acceleration on Bac6U PCB with a 15mm plate (blue curve) vs other shock tests

11 CONCLUSIONS Given the I/F average acceleration, the equipment response on a 21 10mm shock table is more representative of a pyrotechnic test (point source) on a simplified payload and Accelerations, normal I/F forces, stresses The representative test configuration for Z axis excitation is the one that reproduces the bending stiffness of the sandwich panel X and Y axis excitation still required to qualify an equipment w.r.t. a representative pyrotechnic mechanism Calibration of a shock specification with a thin shock table does not appear more complex than it is with a thick one A mass dummy is required A 15mm plate is not as representative of the payload environment regarding high frequency response in particular PERSPECTIVES The simulation phase has been efficient identifying the sensitive parameters of the shock test Coupled plate-unit configuration could be used for equipment shock response simulation 22 In plane excitation (thick shock table) remains severe In plane and out of plane shock specifications must be differentiated when justified