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

2. P-2 Test “look back”: The ~ 5 sigma extreme peaks
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. BACKGROUND Information
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. “PATHFINDER” PROBE 2 TESTS @ JPL, 27-31 MARCH
Themis PER: Vibration & Acoustics
“PATHFINDER” PROBE 2 JPL, MARCH
3 Axis Hz Sine Sweep
Rigid Body Motion – 1st Z mode was  100 Hz, Lateral was  60 Hz
3 Axis 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. PYRO SHOCK Test Data from Probe 2 Test at JPL
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 ∫area nature” of stated Grms values “GI-GO” = garbage in → garbage out

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

8. X axis random vibration – single largest FORCE peak in this test
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 ∫s X*(t) Y( t+s) dt …where X* is the complex conjugate
0.002 sec
( as ½ sine → 250 Hz)
sec
( as ½ sine →700 Hz)
Force ‘Time Lag’
 sec.
( ~36 250 Hz)

9. Summary of the Themis Probe Test Extreme Peaks
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. Wide-band Input or Response
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 5s is 60 * 20,000*6 E-7 = 73% This may explain why one sees more extreme peaks than predicted by a Rayleigh distribution.

12. 5s Extreme Peaks Conclusions
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. } TEST REQUIREMENTS Environmental Test Matrix ( SAI-SPEC-1164, Rev. A)
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. PRE-TEST of PC (fm) + QM PSS + Mass Dummies → Separation
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. PCA MODAL MASS vs. FREQUENCY OUR TEST CONFIGURATION
Themis PER: Vibration & Acoustics
PCA MODAL MASS vs. FREQUENCY
NON- FUELED PROBES
OUR TEST CONFIGURATION
FUELED PROBES
FOR REFERENCE ONLY !!

16. PCA (with 5 flight probes) Vibration Testing
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
TEST SEQUENCE
Pre- / Post- Sine Signatures
3 Axis 5-50 Hz (CLA-2) Sine Sweep (¼, ½, full)
Z Axis 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. Lateral Axes (T.L.L. = 4.31 G’s)
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. PCA Acoustics Test Themis PER: Vibration & Acoustics TEST PLANS
Thm-mint-proc-061
Same Accel. List used in Vibration
PSS brackets will be included
SAI-plan-0740
JPL: 144-D-A , Rev. E
Same setup as GSFC - PC Test
(7/14/05)

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

20. Themis PER: Vibration & Acoustics
BACKUP SLIDES

21. PCA (with 5 flight probes) Vibration Testing
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