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THEMIS MISSION PRE-ENVIRONMENTAL REVIEW VIBRATION & ACOUSTICS David Pankow

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THEMIS

MISSION PRE-ENVIRONMENTAL REVIEW

VIBRATION & ACOUSTICS

David Pankow

University of California – Berkeley

…with help from: Terry Scharton (NC State) & Mike Sholl (UCB)

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

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)

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

Themis PER: Vibration & Acoustics

PYRO SHOCK Test Data from Probe 2 Test at JPL

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

Themis PER: vibro-acoustics – 5s peaks

BaseForce Time History for the X Axis -3 dB Random Vibration Test

1069/213 = 5 s

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)

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

Themis PER: vibro-acoustics – 5s peaks

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.

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

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

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

Themis PER: Vibration & Acoustics

PCA MODAL MASS vs. FREQUENCY

NON- FUELED PROBES

OUR TEST CONFIGURATION

FUELED PROBES

FOR REFERENCE ONLY !!

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

- Scott Gordon (542) & Alan Posey (543) recommend dropping this test !

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)

Themis PER: Vibration & Acoustics

- PCA Acoustics Test
- TEST PLANS
- Thm-mint-proc-061
- Same Accel. List used in Vibration
- PSS brackets will be included

- Same Accel. List used in Vibration
- SAI-plan-0740
- JPL: 144-D-A-100000, Rev. E
- Same setup as GSFC - PC Test
- (7/14/05)

Themis PER: Vibration & Acoustics

PCA Acoustics Test Levels

Themis PER: Vibration & Acoustics

BACKUP SLIDES

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

Themis PER: Vibration & Acoustics

Themis PER: Vibration & Acoustics