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NASA Contractor Rep.ort 175320

VIBROACOUSTIC .STUDY OF THE

NASA GODDARD SPACE FLIGHT

CENTER 088-1 PAYLOAD

(B1SA-Ca-175320) VIEcoACCOSII: STUDY OF THR N85-224E5

lAS! GODCABC SPICE FLIGHT CENTER OSS-1

PAYLOAD (lockbe6d Missiles and Space Co.)

37 p HC 103/~F ~01 CSCL 22B unclas

G3/16 20245

Y. A. Lee

W. Henricks

Lockheed Mi"ilell & Space Compang Inc.

11j 1 Lockheed Wag

Bunnl/oale, Califomia,94086'

Contract NAS5·25156

January 1985

National Aeronautics and

Space Administration

GoddW Space flight t;enter

Greenbell, Maryland 20771

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NASA Contractor Report 175320

VIBROACOUSTIC STUDY OF THE

NASA GODDARD SPACEFLIGHT

CENTER 088-1 PAYLOAD

:1 ['

! ' I Y. A. Lee

I , W. Henricks I :

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Lockheed Mi.sile. & Space Company Inc.

1111 Lockheed Way .

Sunnyvale, California, 94086

Contract NAS5-25156

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January 1985

NJ\SJ\

Nallonal Aeronautics and

Space Admlnislrallon

Goddard Sp&ee flight Center

Groenbell. Maryland 20771
BIBLIOGRAPHIC DATA SHEET

..._-----~

GSFC 25-44 (10/77)

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For sale bv the National Technlcallnformallon Service. Sprongloeld. Virginia 22151.

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.

NASA CR~175320

4. Title and Subtitle 6. Report Date

VIBROACOUSTIC STUDY OF THE NASA January 1985

GODDARD SPACE FLIGHT CENTER OSS-l 6. Performing Organization Code

PAYLOAD

7. Author(s) 8. Performing Organization Report No.

Y• A. Lee, W. Henricks LMSC-D980796

9. Performing Organization Name and Address

I

10. Work Unit No.

Lockheed Missiles & Space Company, Inc.

1111 Lockheed Way 11. Contract or Grant No.

Sunnyvale, CA. 94086 NAS5-25156

13.TyPt of Report and Period Covered

12. Sponsoring Agency Name and Address . Goddard Space Flight Center

Greenbelt, MA 20771

Technical Monitor: Frank On, 'Code 731.1 14. Sponsoring Agency Code

15. Supplementary Notes

16. Abstract

A database management and prediction system named VAPEPS (Vibroacoustic

Payload Environment Prediction System) has been developed for the vibration and acoustic data obtained from Spac:e Shuttle payload components. The

software of this database management system is used to predict the environment of a. Shuttle payload. This prediction is then compared with empirical

observations made during an acoustic ground test. The study includes an

investigation of previous findings to the effect that flight induced ra.ndom

vibration response is more severe than that which occurs during ground

testing.

.

17. Key Words (Selected by Authorls)) 1B. Distribution Statement

Space Shuttle, Vibroacoustics, Database, VAPEPS, Environment, Vib...oacoustic Predictions, Payloads, 05S-1

.

19. Security Classif. lof this report) 20. Security Classif. lof this page) 21. No. of Pages 22. PriceUnclassified Unclassifled

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PREFACE

This report evaluates the possibility that the Shuttle payload flight

vibration environment can exceed the corresponding environment induced during

an acoustic ground test. Included is a study of an analytically predicted

versus the empirically observed random vibration response of a shuttle

payload; this study makes use of the software provided by the VAPEPS

(Vibroacoustic Payload Environment Prediction System) database management

system•

. .

11
section

1.0

2.0

4.0

TABLE OF CONTENTS

INTRODUCTION

A STUDY OF OSS-l RANDOM VIBRATION RESPONSE DURING

LIFTOFF AND GROUND TEST

Comparisons of Liftoff and Ground Test rata

Evaluation Of Liftoff And Ground Test IBta Discrepancies

Design And Test Recommendations

Fu ture Studies

OSS-l PAYLOAD VIBRATION - PREDICTION VERSUS MEASUREMENT

Payload Modelling

VAPEPSPrediction and Comparison With Measurement

CONCLUSIONS

REFERENCES

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TABLE OF CONTENTS (Cont)

ILLUSTRATIONS

OSS-l Payload Configuration

Ground Test and STS Vibration Comparisons

Ground Test and STS Acoustic Comparisons

Comparisons of STS-3 Flight and Ground Test Data,

OSS-l Payload

Comparisons of Flight and Ground Test Data,

Another Payload

OSS-l Pallet Payload Transducer Locations

OSS-l Pallet Payload Transducer Locations

(Plan View)

Statistical Energy Analysis Model of Zone2 and

Zone4

VAPEPS Prediction and Measurement In Zone 2, OSS-l

Payload

VAPEPS Pr-ediction and Measurement In Zone 4, OSS-l

Payload

.TABLES

Structural Parameters of Equivalent Pallet Structure

Structural Parameters of Pallet Inner Panel

OSS-l Acoustic Test Level

VAPEPS Parameters of Zone2 and Zone4 Models

Normal Measurement DATE Transducers

In Zone2 and Zone4

Normal Measurement Non-DATE Transducers In

Zone2 and Zone4

Zone2 Prediction and Measured PSD Data

Zone4 Pr-ediction and l1easured PSD Data

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1.0 INTRODUCTION

This report presents a comparative evaluation of Shuttle liftoff and ground

test random response data that was obtained from the Office of Space Science

-1 (OSS-l) pallet payload (Figure 1.1) flown in the cargo bay of STS-3. This

stUdy was initiated by NASA Goddard Space Flight Center (GSFC) to evaluate

the possibility that the payload flight vibration response can exceed that

occurred during an acoustic ground test when the ground test acoustic

excitation is normalized to the flight acoustic environment. Included in

this study is a comparison of a VAPEPS (Reference 1) predicted environment

for the 033-1 payload with respect to that observed during ground test.

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2.0 A STUDY OF OSS-l RANDOM VIBRATION RESPONSE DURING LIFTOFF AND GRJUND TEST

This section of this report presents the results of an investigation into the

possibility, first noted in an earlier study (Reference 2) that: (1) Shuttle

payload components may be receiving a significant amount of mechanically

transmitted energy that appears to be originating at the orbiter-payload

interface and (2) If an exact simulation of the Shuttle Cargo Bay acoustic

spectrum is used during a ground test performed in a reverberant chamber, the

acoustic·induced random vibration response of payload components will be more

severe in flight than the corresponding response induced during the ground

test. This later situati~n is contrary to expendable launch vehicle

experiences. Further, it is undesirable with respect to existing ground test

philosophy that ground tests should induce payload/component responses at

least equal to that experienced during service. Recommendations are made as

to how a test program could be structured to partially accommodate this test

philosophy.

Included in this study is the result of a similar and confirming experience

of another payload flown on the Shuttle. While there exists a considerable

degree of uncertainty concerning the Shuttle vibroacoustic environment,

making it difficult to set perceptive tailored payload and payload component

design and test requirements, the experience to date does not suggest that

this environment is any more severe than that typicallY encountered by

expendable launch vehicle payloads.

2.1 COmparisons of Liftoff and Ground Test Data

The liftoff and ground test random vibration data used in the study were the

data from one-third octave band analyses as processed and supplied by GSFC.

The ground test acoustic data were also similarly processed and supplied by

GSFC, the Shuttle flight data, however, was processed and supplied by

Lockheed Missiles and Space Co. (LMSC).

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During data processing it was noted that the signal to noise ratio of the

data on the Shuttle flight tapes was very low at frequencies above

approximately 800 Hz. Corrections were made. However, because uncertainties

still remained, this high frequency data was not used.

The grounn test acoustic spectrum used in this study is the spatial average

of tt.e C:a~a obtained from the six microlX\ones that controlled the reverberant

chamber in which the ground test was performed, see Reference 2 for details.

The Shuttle flight acoustic spectrums that were used are the spatial average

and maximum values of the data obtained from microphones located in the

immediate vicinity of the payloads flown on Shuttle flights ST3-2 thrv. ST3-4.

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Figure 2.1 is typical of the twelve one-third octave data sets that were

received from GSFC for analysis. Clearly there are a number of points within

the frequency spectrum between 31.5 Hz and 2000 Hz where the measured flight

data is higher than that measured during the ground test. It should be noted

that the flight and ground test measurements were made at identical locations

on the OSS-l structure. The corresponding acoustic excitation that produced

this response is presented in Figure 2.2. An examination of the figure

indicates that the spatial average ground test acoustic excitation levels are

at least 5dB higher than the corresponding excitation encountered in flight.

In fact, the maximum acoustic excitation believed to have been experienced in

flight by the OSS-l payload is significantly less than the spatial average

value of the ground test .reverberant chamber acoustic field. This latter.

statement is true except between 50 Hz and 100 Hz where these acoustic

spectrums are about the same value. Based on these comparisons it appears

that an exact simulation of the Shuttle cargo bay acoustic field during a

ground test would not produce the desired random vibration response and would

represent an under test with respect to the flight conditioll. The question

then is, just how much of an under test does testing with a reverberant

acoustic field represent; and, knowing this, how should test requirements be

specified to cater to this situation?

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2.2 Evaluation Of Liftoff And Ground Test Data Discrepancies

The magnitude of the under test described above was quantified in the

following manner: (1) The ground test one-third octave response spectra

processed from each random vibration measurement was normalized to account

for the differences between the acoustic ground test spatial ~verage acoustic

levels and the corresponding spatial average levels of flight. (2) A flight

to normalized-ground-test ratio was then obtained for ea~h one-third octave

reponse spectrum value. This was done for each measurement made. This

operation resulted in twelve such ratios for each one-third octave value

between 31.5 Hz and 800 Hz. (3) The average value of these one-third octave

ratios was then obtained and expressed as a dB value; a posi~ive value

indicates the magnitUde of the under test involved. The results one obtains

concerning the magnitude of this under test does depend on the acoustic

spectrums used to normalize the response data. Therefore, to obtain a

measure of the minimum discrepancy between liftoff and ground test reponse

valuesf the above operation was repeated by normalizing to the maximum

acoustic excitation believed to have been encountered in flight by the OS3-1

payload. The results obtained from these analyses are shown in Figure 2.3.

Presented in Figure 2.4 are the results of a corresponding analyses performed

on another payload.

The,data s~own in, Figures 2.3 and 2.4 confirm the general finding of the

Reference 2 study; namely, an exact simulation of the Shuttle c~rgo bay

acoustic field during a ground test will not excite a response of payload

structure/components as high as that expected to be encountered in flight.

The reason(s) for this situation is not well understood ac present. It could

be due in part to differences in the coherence characteristics between the

two acoustic fields; or, possibly due in part to mechanical energy being

transmitted from the side rails and trunnion fittings of the Shuttle. This

latter energy source was not simulated in either of the ground test studied;

and therefore, at the present ti~e is considered the meet likely source of

the noted discrepancies. Whether the source of this energy is due to the

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liftoff inertial loads, or the external acoustio fi~ld coupling with the

eargo bay structure/skins, and then mechanically transmitting this energy to

the payload was not and could not have been investigated as part of this

study using the data supplied. However, because of the launch time period at

which most of this data was obtained, it is believed that the response due to

the liftoff inertia excitation has decayed to an insignificant value.

Therefore, the response data used in this study represents that due to

acoustic coupling of one form or another.

2.3 Design And Test Recommendations

It is recommended that system level ground acoustic tests be performed using

the best simulation possible of the internal cargo bay acoustic field

expected to be encountered in flight. Trying to account for the higher

response levels expected in flight by increasing the system level ground test

acoustic levels is not recommended for the following reason. At present it

is suspected that it is the mechanical energy being transmitted by the cargo

bay side rails that is causing the higher response levels observed in

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It is observed in Figures 2.3 and 2.4 that while all the data is positive,

indicating an under test, the general magnitude and trends of the data are

not really that similar. Not enough was known about the dynamic

characteristics, among other things, of the two payloads to account for the

differences shown. Also, it should be noted that other than being positive,

the 033-1 trends shown in Figure 2.3 are not too similar to the corresponding

trends reported in Refe~nce 2. As previously mentioned, the results one

obtains regarding the ma~nitude of the discrepancies between flight and

ground test acoustic induced random vibration response will depend on the

flight spectrum used to normalized the ground test data. The approach used

in this and the referenced study was not quite the same which probably

accounts for the difference in trends. The appropriate normalization

procedure would depend on understanding the acoustic versus mechanical

coupling characteristics within the 035-1 payload which was not sorted out in

either study.
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flight. If so, then the payload structure/co~ponent response charact~ristics

due to this type of excitation will appear as due to a distributed inertia

loading. The response due to distributed inertial loads can be totally

different from the forced loading of an acoustic pressure field. ' Therefore,

aooustic ground test where the excitation levels have been arbitrarily

inoreased to try to account for the higher response levels expeoted in flight

may cause unwarranted problems with payload structure/components only

susceptible to direct acoustic excitation.

Reference 3 is a study to develop a procedure accounting for the structural

borne vibration received by Shuttle payload components. This stUdy found

that this excitation could be accounted for by keeping payload component

random vibration design and test requirements at or above .03 G"2/Hz below

180 Hz. It is recommended that payload components be designed and tested

accordingly except that the heavier payload components/ subassemblies,

~pproximately 50 lbs or heavier, be assumed to have a response limit of .1

G"2/Hz~ This response limit value is cons~dered appropriate based on a

review of the data provided in Reference 3.

The above recommendations pertain to low frequency structural borne vibration

which may be generated at the Shuttle side-rails/trunnion fittings and

transmitted to payload components. How to account for the higher frequency

aspects of this environment, even if it is necessary at all, remains to be

establishea. Also, added to· the random vibration levels given above should

be the payload dependent environment due to direct coupling with the internal

acoustic field of the cargo bay.

2.4 Future Studies

Studies are required to develop a measurement program that will provide data

to understand the differences observed between the random vibration induced

in Shuttle payloads during ground test and the corresponding environment·

observed in flight. These studies must first include the development and

investigation of analytical models of one or more plausible physical

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situations that would support the phenomenon obser'red. Such studies are

necessary to: (1) determine the appropriate/best location of the acoustic

and vibration transducer used in any measurement scheme and (2) support the

interpretation of data obtained from these measuremen~s. An empirical

program without such analytical support will not provide data to understand

the phenomenon, except to know what occurred on a given flight, on a given

payload, etc. The desired extrapolation to other Shuttle flights and

payloads will not be possible. This 1s the situation that the aerospace

community now finds itself in with respect to the Shuttle vibroacoust1c

measurement program as it has been structured to date.

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3.0 OSS-l PAYLOAD VIBRATION - PREDICTION VERSUS MEASUREMENT

The OSS-l payload has been modelled for Statistical Energy Analysis (SEA).

The SEA computation is performed with the VAPEPS prediction software. The

predicted vibration are compared with the measured data obtained during the

system level acoustic tests performed in the 40,000 cubic foot test chamber

at the NASA/GSFC in Greenbelt, MD (Ref 4 and 5). The comparinon are made for

different zones on the payload, as defined by Ref 2.

3.1 Payload Modelling

Figures 3.1 and 3.2 show the OS5-l payload configuration. Various

experimental hardwares are mounted on the pallet. During the system level

acoustic test, the pallet is suspended in the air with cables from an

overhead crane. There is no mechanical energy transmitted into the pallet

payload. The acoustic field around the payload is the only energy source.

The pallet is a structure with a frame and face panels. It is a good

acoustic energy receiver. Appropriate SEA models are made for different

"zones" of the pallet payload in order to make meaningful comparison with the

measurement. The zones are classified in page 15 of Ref 2. Zone 1 is

defined as the payload primary structure within the proximity or the

payload-orbiter vehicle separation plane. ZOne 2 is the payload primary and

secondary structure (exclusive of mounting brackets) not included in zone 1.

Zone 3 is the payload structures specifically designed for mounting of

components such as shelVing, platforms, or brackets. Zone 4 1s the payl0~d

large surface area, lightweight structures at outboard areas which respond

primarily to acoustic pressure forces. Due to the availability or structural

parameters, Zone 2 and Zone 4 are modelled as shown in Figure 3.3. Because

the random response .predictions are made in the normal direction, only normal

measurements or high-frequency accelerometer's are of interest.

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Zone 2 Model

The overall pallet payload is modelled as an equivalent plate with all

payload experiments as the non-structural mass loading. The pallet structure

consists of inner panels, outer panels and many stiffeners in-between. The

equivalent plate has the same surface width and length,. structural stiffhess

(EI), surface mass density, and structural longitudinal wavespeed, as those ~.

of actual pallet. The critical frequency is therefore matched. The

derivation of equivalent plate is obtained by using the computer program

PLATE which is a part of VAPEPS software (Ref 1). The derived equivalent

pallet properties are shown in Table 1.

There are 24 inner panels of the pallet. The average dimension of each panel

is 38.1 inch by 27.5 inch. It is of honeycomb construction with aluminum

face sheets. Table 2 shows the structural parameters of the honeycomb panel

and those of the equivalent panel. From Table A-2 of Ref 4, the total weight

of pallet primary .f~ttings, secondary fittings, hardpoints. and keel fittings

are 290 Ibm. If we assume this weight is non-structural mass uniformly

distributed on all 24 inner panels, then the surface mass density of

equivalent panel is increased from original 1.382 x 10-5 to 4.369 X 10-5

Ibf - sec2/in3• Based on this value and other equivalent parameters

listed in Table 2, the panel fundamental frequency with simply supported

boundaries is calculated to be about 90 Hz. This is the (split) frequency in

our model. Below this frequency, the whole pallet structure vibrates as a

unit. The eqUivalent pallet parameters in Table 1 should be applied. Above

this frequency, the individual panel of pallet vibrates independently with

the stiffeners as the boundaries. The parameters of the inner panel. in Table

·2 are used as the pallet parameters in this frequency range.

All payload instruments and components are modelled as non-structural .mass

attached to the equivalent pallet. From Table A-2 of ref 4, the total

integrated pallet weight is 6807 Ibm. From Table 1 of this report, the total

mass of the equivalent pallet structure is 418 Ibm. The difference of 6389

Ibm is considered as non-structural mass.

17
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Table 1 STRUCTURAL PARAMETERS OF EQUIVALENT PALLET STRUCTURE

size = 228.6 inch x 110.0 inch

-6 2 4 Pm =2.025 x 10 Ibf -sec lin

H = 20.01 inch

Ps =4.052 x 10-5 Ibf -sec

2/in3 (skin and stiffeners)

Ps =2.821 X 10-5 Ibf -sec2/in3 (skin only)

E = 7.820 x 104 psi

Total mass = 418'1~m

..., -,--,..,---•...........•._-_..._---..

, i

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Table 2 STRUCTURAL PARAMETERS OF PALLET INNER PANELS

. ..~..• ":'.-~_._~ __...__.-,",_,","_ -...!r"'1..... _

, ..."'.... ......,.......~,.-, ..........~- - .~

.73' I I

I }

= 107 pai

-4 2 4 = 2.59 x 10 lbr - sec lin

=0

= 9.562·x 10-6'~br - sec2/in4

E

E

Face sheet

Honeycomb

....--.

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Equivalent parameters

-5 2 4 Pm = 1.644 x 10 lbr - sec lin

H = .8409 inch,

Ps = Pm x H = 1.382 x 10-5 lbf - sec

2/1n3

E = 6.346 x 105 psi

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19
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The sound pressure level (SPL) around the OS3-l pallet payload is measured by

the control microphones. The averaged SPL in ll3-octave bands can be found

in ref 2 and listed in Table 3. During the acoustic test, both inner panels

and outer panels of the pallet structure are exposed to the acoustic field.

Double-sided excitation must be appl:i.ed to the equivalent pallet structure.

The VAPEPS' prediction software is applied in response calculation. A

two-element Statistical Energy Analysis (SEA) model is used, with the test

chamber acoustic field as the EXTA-element and th~ equivalent pallet

structure as the SKIN-element (see Figure 3.3). The parameters of both

elements are listed in Table 4. The pallet damping loss factor is assumed to

be inversely proportional to frequency, wi th value of 0.1 at 250 Hz. Because

the VAPEPS software assumes the EXTA-element to be coupled with the

SKIN-element on a single side, the coupling loss factor between th~se two

elements must be doubled to account for dOUble-sided excitation.

Zone 4 fudelitlg

The pallet inner panels are modeled as ~le SKIN-element in the SEA model for

Zone 4 (see Figure 3.3). Both equivalent pallet parameters in Table I and

inner panel parameters in Table 2 are ~till applicable for the frequency

~ange,b~low and above 90 Hz, respectively. Because the accelerometers used

for comparison are on panels, we cannot apply all the non-structural mass

used in Zone 2 to these panels. As a matter of fact, only the actual items

mounted on these panels should be considered. Based on the information

available to· us, either none or very little mass are mounted. Therefore zero

non-structural mass is assumed in VAPEPS calculation.

During the acoustic test, only one side of pallet panel is exposed to the

full test t'Jhamber SPL. The acoustic level on the other side is much lower

'., .'(:. .

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and assumed to be negligible.

Zone 4 calculation.

No double-sided excitation is reqUired in this

20
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Table3 OSS-l ACOUSTIC TEST LEVEL

1/3-octave Center

Frequency (Hz)

31.5 124.5

40 125

50 123

63 125.5

80 125.5

100 126

125 128

160 129

200 129

250 130.5

315 130

400 130

500 130.5

630 131.5

800 1~9.5

1000 12(.5

1250 127.5

1600 125

2000 124

21
•

Table 4 VAPEPS PARAMETERS OF ZONE 2 AND ZONE 4 MODELS

SKIN

Low Frequenoy (below 90 Hz) High Frequonoy (above 90Hz)

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TYPE :: 1

ROW :: 1.12x10-7

4 CO :: 1.32x10

V :: 6.912Xl07

AP =S.619X105

AAC = .02

TYPE :: 1 TYPE It 1

ROW -6 ROW :a 1.644xlO-S :: 2.025x10

CL :a 2XI05 CL II 2xlO5

H :: 20.0 H It .8409

AP 4 AP 4

:: 2.515xlO II 2.515x10

ALX :: 38.1 ALX =38.1

ALY =27.51 ALY =27.51

DLF :: .1 DLF :: .1

4 5 E :: 7.820x10 E II 6.346x10

PATA :: 677.5 PATA :: 6299

.. / -5 ROWS:: 1.382XIO-5 ROWS :: 4.05xlO

A5MS :: 16.53 (Zone 2) ASM3 :: 16.53 (Zone 2) . I

ASMS 0 (Zone 4) ASM3 :: 0 (Zone 4) IIJ

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I 3.2 VAPEPS Prediction and Comparison With Measurement

•

..

The acceleration data uaed to oompare with the VAPEPS prediction are selected

from the PSD data set obtained during the GSFC system level acoustio test

(ref 5). The VAPEPS predictions represent the spaoe-time averaged

acceleration in the direction normal to the struotural surfaces. To make a

fair oomparison, 26 normal transducer data in Zone 2 and Zona 4 are seleoted

out of the total 158 accelerometer measurements. The DATE and Non-DATE

transducers of this data set are listed in Table 5 and Table 6,

respectively. The transducer numbers of these transduoers are those used in

refs 4 and 5. There are 20 PSD in Zone 2 and 6 PSD in Zone 4. Using these

PSD data samples, the averaged PSD in G"2/Hz and its associated 95%

confidence limits are calculated by using VAPEPS commands and based upon

log-normal distribution. Table 7 and Table 8 list the averaged value,

confidence limits, and VAPEPS prediction for Zone 2 and Zone 4,

respectively. They are also plotted out in Figure 3.4 and Figure 3.5,. The

comparison between data and prediction are good.

23

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. : SO'7'm or 55Z2 n , ..., .1.
.. Table 5 NORMAL MEASUREMENT DATE TRANSDUCERS IN ZONE 2 AND ZONE 4

2

4

Measurement Description

Aft side of thermal canister base (Z)

Side of cold plate (normal)

Panel No. 4 central insert (normal)

Measurement No.

V08D9297A

V08D930lA

V08D9293A

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24

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Table 6 NORMAL MEASURE~~NT NON-DATE TRANSDUCERS

IN ZONE 2 AND ZONE 4

Freon line, panel 19 (Z) V 66

Panel 4 quarter span (normal) V 61

Panel 9 (normal) V 83

Panel 18 (normal) V 63

Freon' line standoff, panel 19 (normal) V 68

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Measurement Description

(Zone 2)

Box beam at HP (Z)

SUbsystem MSFC CPSS (PCB) base (Z)

Experiment CPSS (normal)

HSFC CPSS FMDM (Z)

Iowa Base

HP No. 6 (OL) ( Z)

HP No. 5 (OL) (Z)

HP No. 2 (OL) (Z)

HP No. 4 (OL) (Z)

HP No.1 (OL) (Z)'.

HP No. 3 (OL) (Z)

Pallet HP No. 1 (OL) (Z)

HP No. 12 (IL) (Z)

HP No. 7 (IL) (Z)

HP No. 10 (IL) (Z)

HP No. 14 (IL) (Z)

,HP No., 8 (IL) (Z)

Pallet HP No. 17 (IL) (Z)

(Zone 4)

Acce1. No.

V 45

V 74

V76

V 27

V 15

VI06

VI03

V100

V 51

V 48

V 21

V 6

V133

Vl09

V112

V 57

V 54

V 3

PSD No.

71

53

55

19

10

105

161

99

39

36

13

61

132

108

111

74

42

3

90

75

93

87

47

, .

25

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Table 7 ZONE 2 PREDICTION AND MEASURED PSD DATA

•

1I3-OCt. 95% 95%

Center VAPEPS Measurement Confidence Confidence

Freg Prediction (Average) Lower Limit Upper Limit

<Hz) 2 (g 1Hz) <l/Hz) <l/Hz) (l/HZ)

31.5 ~.2382E-04 2.6648£-04 1.0819E-04 2.9'956-0'

'0 2.6471£-04 1.5911£-04 8.6'56E-05 1.97386-0'

50 1.4234£-04 1.0933E-04 6.9462E-05 1.5502£-04

63 1.7098E-04 3.73296-0' 2.6077E-04 5.4394E-04

80 1.2756E-04 5.3594E-Oll 2.7977E-04 7.19366-0'

100 1.1869E-04 6.6920E-04 3.1I1BlE-04 9.2425£-04

125 8.0557E-03 1.6281E-03 8.9242E-04 2.6228E-03

160 5.117JE-03 3.30986-03 1.75526-03 5.8310£-03

200 3.0525E-03 4.4911£-03 2.7830£-03 8.'3956-03

250 '.'8'56-03 3.5'316-03 2.1106E-03 5.'7226-03

'.29836-03 2.q7166-o3 1.42500-03 3. q82JE-03 i ' 315 • __ J

qoo 5.7688E-03 lj .1116 3E-O3 2.0412£-03 6.542lE-03 '--1

500 1.2929E-02 5.0606E-03 2.619 BE-03 8.65576-03 ,_."

630 5.33986-03 S.0953E-03 3.2145E-03 8.83346-03

800 I

1.6979E-03 3.15116-03 1.6260E-03 5.32926-03 I

1000 6.0996E-04 2.01l13E-03 9.8'86E-0' 3.1601£-03

1250· ·5.4112E-04 2.8940E-03 8.91726-0' 3.66136-03

1600 1.9829E-04 7.3839E-04 3.68656-0' 1.1753£-03

2000 1.3619E-04 3.96568-04 2.~573E-04 8.6464E_04

•

•

26

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Table 8 ZONE 4 PREDICTION AND MEASURED PSD DATA

l/3-0ct. 95% 95%

Center VAPEPS Measurement Confidence Confidence

Freq Prediction (Average) Lower Limit Upper Limit

<Hz) <i/Hz) <i/HZ) (i/Hz) (i/Hz)

31.5 7.3017E-03 1.1705E-03 3.4650E-04 5.2433E-03

40 4.5606E-03 1.5445E-03 4.0243E-04 1.147lE-02

50 2.4523E-03 1.1165E-03 3.08l8E-04 1.6654E-02

63 2.9457E-03 4.0249E-03 1.2279E-03 3.8768B-02

80 2.1977E-03 9.6107E-03 2.8512E-03 1.7284E-01

100 2.0448E-03 1.5852E-02 4.6532E-03 4.7497E-01

125 3.9105E-01 3.7130E-01 1.10 62E-Ol 5.5369E+01

160 2.484lE-01 3.1660E-01 9.2616E-02 1.4213E+01

200 1.4818E-ol 1.3704E-01 3.6327E-02 2.6095E+Ol

250 2.1770E-01 1.2622E-Ol 2.3454E-02 2.9895E+OO . 315 2.0865E-01 1.8772E-Ol 5.2077E-02 6.8599E+OO

400 2.8004E-Ol 1.5196E-Ol 4.3191E-02 1.8248E+00

500 6.2762E-01 1.3116E-01 3.2126E-02 1.8850E+OO

630 2.5921E-01 1.5309E-01 3.5525E-02 2.5003E+00

800 8.2422E-02 5.8768E-02 1.4796E-02 3.9342E..Ol

1000 2.9610E-02 2.7426E-02 8.1786E-03 1.267lE-Ol

1250 2.6268E-02 2.0523E-02 5.0739E-03 1.7428E-ol "

1600 9.6256E-03 9.6162E-03 2.2423E-03 1.0896E-Ol

2000 6.6113E-03 1.8319E-03 6.2288E-04 5.5840E-03

27

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00

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055-1 PALLET PAYLOAD ZONE 2 PREDICTION

x -VAPEPS PREDICTION, 0 -OATA CAVSl

+ -95% CONF LO'llER LIMIT,*'-95% CONF' UPPER LIMIT

,

¥...>.. It/?

/ tl"'\ '/'ik. .... /

//i'... er ./ r-./'\\

I rt/ ".,/ ~, '\

"- \'-

~,t\ '/; t- \ .....

Nf1 ") 'l-H

....

o

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c1 D. 100. 1000.

1/3 OCTAVE CENTER FREQUENCY CHZ)

VAPEPS Prediction and Measurement in Zone 2, OSS-1 Payload

"

\ \

" \ , . \ . \

10000.

I

-----. ,
~:

!/.-. ~../.

'. . --,

\

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u

U- <0Q

os S - 1 PAL LET PAY LOA 0 Z 0 N E. 4 PRE 0 Ie T ION

X -VAPEPS PREOlCTlON, 0 -DATA CAVGl

+ -95% CONF LOWER LIMIT,*-95% CONF UPPER LIMIT

"

, .-

f , ....

v___

" '\I f f I I

I I "" ~~

/ "+" I I ,

v l-l "\..\ ~._x·~

'" It""-' / -....; 0/ \

1 o. 100. 1000.

1/3 OCTAVE CENTER FREQUENCY (HZ)

10000.

Fig. 3.5 VAPEPS Prediction and Measurement in Zone 4,.03S-1 Payload

'.

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4.0 CONCLUSIONS

-"

/

/

,

,

/

An exact simulation of the shuttle cargo bay acoustic level during a ground

test may not excite payload components to response as high as that can be

expected to be encountered in flight. The exact reason that this situation

exists is unknown. Mechanically transmitted energy from the shuttle

side-rails/trunnion, Which has not been simulated in any of the acoustic test

performed to date, is presently considered the most likely source of this

problem. If accompanied by appropriate analytical studies, it is expected

that a flight measurement program could be designed that would resolve this

flight versus ground test discrepancy.

Based on sample size considerations, the present VAPEPS prediction software

appear to provide reasonable results. As VAPEPS is used, updated and

improved by the aerospace community, it is expected to provide a very useful

analytical tool for establishing the vibroacoustic environment for shuttle

. and expendable launch vehicle payload components.

30

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REFERENCES

1. NASA CR-166823, "Vibroacoustic Payload Environment Prediction System

(VAPEPS)," Y. A. Lee and W. Henricks and et. al.; June 1984.

2. NASA TM-85089, "Comparative Evaluation of Space Transportation System

(STS)-3 Flight and Acoustic Test Random Vibration Response of the OSS-l

Payload" by Frank J. On, dated September 1983.

f ./ f

...

31

April 1984.

ATM 83(3493~31)-3, "Structural Borne Vibration Input to Shuttle p~yloads"

by C. S. Tanner of the Aerospace Corporation, El Segundo, Ca., dated

5 May 1983.

NASA TM-86087, "Development of Baseline Random Vibration Environment

Criteria for Shuttle Pallet Paylbad Subsystems," by Frank J. On, dated

dated April 1982.

NASA Memorandum Report 731-0001-82, "DATE/OS3-l Payload-Related Acoustic

and Vibration Data from GSFC System Level Acoustic Test," by Frank J. On,

4.

5.

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