THEMIS MISSION PRE-ENVIRONMENTAL REVIEW VIBRATION & ACOUSTICS David Pankow

1. THEMIS MISSION PRE-ENVIRONMENTAL REVIEW VIBRATION & ACOUSTICS David Pankow University of California – Berkeley …with help from: Terry Scharton (NC State) & Mike Sholl (UCB)

2. Themis PER: Vibration & Acoustics • AGENDA TOPICS • Probe 2 Test Results • P-2 Test “look back”: The ~ 5 sigma extreme peaks • JPL-2 Test Requirements • PC + Mass Dummies + QM PSS → Separation (a pre-test) • PCA Vibration Testing • PCA Acoustics Test

3. Themis PER: Vibration & Acoustics • BACKGROUND Information • Vibration tests have been performed on all boxes by UCB & Swales (various) • Sine Burst - Strength Qualification of ALL Probes performed by Swales. (SAI-RPT-0627 rev.C) • Sine Burst & Qualification of PSS (probe sep. system) by Swales. (SAI-RPT-0643, SAI-RPT-0720) • Modes, Burst, & Acoustic Test of PC with mass simulators by Swales (SAI-RPT-0705) • Probe 2 “Pathfinder” Vibration Test at JPL (SAI-TM-3025)

4. Themis PER: Vibration & Acoustics • “PATHFINDER” PROBE 2 TESTS @ JPL, 27-31 MARCH • 3 Axis - 5-50 Hz Sine Sweep • Rigid Body Motion – 1st Z mode was  100 Hz, Lateral was  60 Hz • 3 Axis - 20-2000 Hz Random(tests were at -3 dB to avoid the ~5s overloads) • Z Axis behaved like a “Brick”, all Q’s were less than 10 • X & Y Axes were a more Interesting ! • Pre- / Post sine signatures identified no significant changes • Vibration data has now been thoroughly reviewed by Berkeley & Swales • CLA-2 validation by Swales has been provided to code 542 • PAF Shock Test was Performed after Vibration – very benign ! • Post-Test Probe CPT was OK

5. Themis PER: Vibration & Acoustics PYRO SHOCK Test Data from Probe 2 Test at JPL

6. Themis PER: Vibration & Acoustics PSD’s of the Control Accelerometers and Base Force (-3 dB test)Force Limiting “C” was REDUCED from 2.0 to 1.4 (-6dB test) to stay within Test Limit Loads- in traditional log-log plot format→ “GI-GO” “REAL” “GI-GO” This Linear Scale plot reflects the“true ∫areanature” of stated Grms values“GI-GO” = garbage in → garbage out

7. Themis PER: vibro-acoustics – 5s peaks BaseForce Time History for the X Axis -3 dB Random Vibration Test 1069/213 = 5 s

8. Cross-Correlation of Base Force and Control Accelerometers X axis random vibration – single largest FORCE peak in this test CC [Xi Yi ] = Sj Xj* Yi+j … or ∫sX*(t) Y( t+s) dt …where X* is the complex conjugate • 0.002 sec ( as ½ sine → 250 Hz) • 0.0007 sec ( as ½ sine →700 Hz) Force ‘Time Lag’  0.0004 sec. ( ~36 phase @ 250 Hz)

9. Themis PER: vibro-acoustics – 5s peaks Summary of the Themis Probe Test Extreme Peaks • DATA BASED OBSERVATIONS • The largest Force and input Acceleration peaks were NOT concurrent • The active Mass (above) is NOT be confused with Modal Mass in FEM results • The Modal Mass (sine) does not compare well with this Active Mass (random) • Force peaks, as compared to acceleration, seem to load a larger fraction of the mass • Corresponding force and acceleration “local peak frequencies” estimates differ

10. Themis PER: vibro-acoustics – 5s peaks

11. Themis PER: vibro-acoustics – 5s peaks • Wide-band Input or Response • Distribution of Peaks tends toward Gaussian. • As the bandwidth of a Gaussian process increases, tending toward white noise, the distribution of peaks moves from Rayleigh to Gaussian (See for example: Lutes and Sarkani, Random Vibration, Elsevier Press, NY, NY, p. 493) • For a Gaussian probability distribution, the probability of |x| > 5s is 6E-7. If one has 60 seconds of white noise digitized at 20,000 points per sec. The probability of a point exceeding 5sis 60 * 20,000*6 E-7 = 73% This may explain why one sees more extreme peaks than predicted by a Rayleigh distribution.

12. Themis PER: vibro-acoustics – 5s peaks • 5s Extreme Peaks Conclusions • Extreme peaks in the base force & acceleration responses are a very real threat • Extreme single peaks in the input acceleration are less of a concern because they do not appear to produce near-resonant amplification of the response • The curve fit (slide 9) of the ‘Top 100’ base force and control accelerometer peaks indicate that both distributions were Gaussian in our Themis testing • Given the frequent observance of five sigma test peaks in time histories of responses in random vibration tests, three sigma design strength requirements, such as those in NASA-STD-5002, appear inconsistent. • The options are to increase mission limit loads, or to decrease test margins

13. Themis PER: Vibration & Acoustics TEST REQUIREMENTS Environmental Test Matrix( SAI-SPEC-1164, Rev. A)       X JPL-2    JPL-2  X JPL-2          X JPL-2 JPL-2 X -“Random Vibration is a POOR Substitute for Acoustics”Scott Gordon, code 542 } JPL-2

14. Themis PER: Vibration & Acoustics • PRE-TEST of PC (fm) + QM PSS + Mass Dummies → Separation • Based on a standing AETD concern • PSS Qualification used rigid interfaces • There is a concern for PCA petal flexing • Missing fuel mass may not adequately load the petals & PSS • This may cause “unknown-unknowns” in the Probe Sep. System • Worst Axis, or both Lateral Axes (if analyses are not conclusive) • Restrained PSS release with Probe Dummy on PC

15. Themis PER: Vibration & Acoustics PCA MODAL MASS vs. FREQUENCY NON- FUELED PROBES OUR TEST CONFIGURATION FUELED PROBES FOR REFERENCE ONLY !!

16. Themis PER: Vibration & Acoustics • PCA (with 5 flight probes) Vibration Testing • TEST PLANS • Thm-mint-proc-060 vibration tests • Thm-mint-proc-045 launch electrical configuration • SAI-spec-1164, Rev A • CLA-2 Sine update in SAI-TM-3005 • JPL: 144-D-V-100261 • TEST SEQUENCE • Pre- / Post- Sine Signatures • 3 Axis 5-50 Hz (CLA-2) Sine Sweep (¼, ½, full) • Z Axis 20-500 Hz Random at Probe Levels ← a placeholder • Scott Gordon (542) & Alan Posey (543) recommend dropping this test ! • PCA acoustics is an accepted “workmanship” substitute

17. Themis PER: Vibration & Acoustics 5-50 Hz PCA Sine Sweep (CLA-2 Predicts by SAI) NOTCH if needed for Limit Loads Lateral Axes(T.L.L. = 4.31 G’s) Thrust Axis(T.L.L = 5.81G’s)

18. Themis PER: Vibration & Acoustics • PCA Acoustics Test • TEST PLANS • Thm-mint-proc-061 • Same Accel. List used in Vibration • PSS brackets will be included • SAI-plan-0740 • JPL: 144-D-A-100000, Rev. E • Same setup as GSFC - PC Test • (7/14/05)

19. Themis PER: Vibration & Acoustics PCA Acoustics Test Levels

20. Themis PER: Vibration & Acoustics BACKUP SLIDES

21. Themis PER: Vibration & Acoustics • PCA (with 5 flight probes) Vibration Testing • BRIEF TEST PLAN HISTORY • PLAN 1 contained first probe random, then 2 x 2 (as delivered) probe random • The 2 x 2 random was viewed as “risk mitigation” for the later PCA acoustics • Our plans have evolved to 1 x 4 testing as delivery dates changed • Scott Gordon noted there wasn’t much risk if acoustics follows probe random • 2nd- 5th Probe random tests were deleted • Hallway “kibitzing” at JPL lead to “PCA random” as a surrogate ‘workmanship test’ • Scott Gordon observed that acoustics is a recognized workmanship test

22. Themis PER: Vibration & Acoustics

23. Themis PER: Vibration & Acoustics