NASA Technical Memorandum 107266

Cassini/Titan IV Acoustic Blanket Development and Testing

William O. Hughes and Anne M. McNelis Lewis Research Center Cleveland, Ohio

Prepared for the 42nd Annual Technical Meeting and Exposition sponsored by the Institute of Environmental Sciences Orlando, Florida, May 12-16, 1996

National Aeronautics and Space Administration

_AN IV ACOUSTIC BI,ANKEr DEVELOPMENT AND _G

Wmi_m O. Hughes, NASA Lewis Research Center Anne M. McNelis, NASA Lewis Research Center

BIOGRAPHY INTRODUCTION

William O. Hughes develops and directs the launch New and improved acoustic blankets were recently vehicle v_roacoustic environment activities at NASA developed and tested to support NASA's Cassini Lewis Research Center. He has defined acoustics and mission. Acoustic blankets are utilized in the payload v_ration requiremmts, specifications and test plans for fairing (PLF) of expendable launch vehicles (ELVs) to over 10 years. Mr. Hughes previously worked at reduce the fairing's interior acoustics and the subsequent Analex Corporation, U.S. Steel Research and Raytheon. vibration resp(msc of the s_ and its components. He received his B_. (1977) in Physics from Penn State Univemity and his ME. (1981) in Mechanical The CX im spacea wm be Launchedin Octa Engineering from rneg_Mellon Univcmity. 1997, by a Titan Iv/centaur launch vehicle, to explore Saturn and its moons. "[he electric power source for the Anne M. McNdiJ is a s_ dynamics engineer at Cassini mission are three mission cri_cal Radioisotope NASA I_zwis Research Center. For the past three years, Thermoelectric Gcncratom(RTGs). The RTG design she has performed vibroacousfic analysis to develop wm previously vibration qualified for the Space Shuttle acoustic and random v_ration test specifications. Ms. _t,mch cDvirotmactRand utilized on _c C.ralJlco McNelLs previously worked for Bailey Controls Ulysses spacecraft missions. Company. Her B.S. degree is in Systems and Contro! Eng0neering fzom Case Western Reserve University. However analysts at the JetPropulsion Lalx)ratory OPL), the spacecraft designer, preOiaed that acoustimlly driven vibration levels for the Cassini RTGs would exceed the RTGs' previous qualification v_ration levels. This cxceedence is primarily due to RTG mounting _CT differences along with differences in the hunch vehicle andspacecra . NASA Lewis Research Center recently led a multi- ot_nizgio_ effort to develop and test verify new To avoid an extremely costly reqtmlification of the acoustic blankets. These blankets support NASA's goal RTGs, a major acoustic blanket development and test in reducing the _tan IV payload faLrmginternal effort was initiated and funded by NASA Lewis acoustic environment to allowable levels for tl_ Cassini Research Center (LeRC), the latmch vehicle integrator spacecraft. To accomplish this goat a two phase for the Cassini mission. If successful the new acoustic acoustic test program was utilized. Phase One comisted blankets would provide a lower acoustic and vibration of testing numerous blanket designs in a fiat panel environment for the Cassini's RTGs than the configuration. Phase Two consisted of testing the most environment obtained when using the standard Titan IV promising designs out of Phase One in a full scale acoustic blankets. cylindrical payload fairing. This paper will summarize this highly successful test program by providing the BesidesNASA LeRC and JPL, other organizations rationale and resulLsfor each test phase, the impacts of involved in this joint effort included Lockheed Martin this testing on the Cassini mission, as well as lxoviding Astronautics (LMA, formerly Martin Marietta some general informationon blanket designs. Tectmologies Incorporated, MMTI), McDonneU Douglas Aer_pace (ME)A),_ Corporation,Analex Corporation,CambridgeCollaborafiveIncorporatedand KEYWORBS theRiverbankAcxmsticalI.zboratory(RAL).

Acoustics, Acoustic Blankets, Blankets, Cassini, Payload Fairing, Spaoect_ Acoustic Environment, Spacecraft Acoustic Testing, Titan IV, Vibroacoustics ACOUSTIC 'lEST PROGRAM OVERVIEW Phase One consisted of evaluating new blanket designs by acoustic testing of fiat panel blanket samples. Flat A_ousticblanbt clcsigntcc_zology for aerospace panel testing had the advantage that numerous designs applicationshas seen tittle clcvclopmcntin the past could be quickly evaluated at a relatively low cost. By twenty-five years. DeveJ.oping an acoustic blanket to proper interpmati_ of the absorpti¢_ and transmission meet the needs of the Cassini mission necessitated loss test data obtained, the leading candidate designs developing advanced blanket tedmology. Not only did ¢xmld then be ch=en for further testing in Phase Two. the blanket have to reduce the acousticfield sLon_fu'_ntly, but it bad to do so in the Phase Two would test the leading candidate blanket frequency range of 200 to 250 Hz. Typicany acoustic designs=ci the baseline Titan IV blanket design in a blankets are most effective at frequencies of 400 Hz and _dl scale cylindrical payload fairing. A]though this type above. of testing is expensive, the effect of the blankets on redudng the PI.Fs interior acoustics would be measured Specifically, our goal was m design and test a new withthe ight-like and acoustic blanket which woukl reduce the expected geometry, for oaly the few lxom_ng candidates. acoustic envirmm=t for the Cassini RTGs by 3 dB at 200 and 250 Hz, when compared with the baselim Titan This two phase t=t approach was dx=a beca=e it was IV blanket system environment. ozsid=ed _lc and risky to test m unproven new design in an expensive full scale test. Likewise the "Ihe apFoach taken was to develop a two-phase acoustic geometry and size of the flight payload fairing made it test program that would provide confidence that the new unwise to baseblanketselectionsolely on the basisof blanket would x=ult in an optimal, feasible system that testing of flat panel samples. had a high probability of performing we. in the flight co_figuration. Toe two phase test program which was foUowed is ilh_trated in flow_ format in F'_qa'e 1.

PHASE ONE Acoustic Panel Tests at Team Eflort led by Riverbank Acoustical Laboratory l_IcOonnell Douglas (parameter opUmizallon on barrier March 28 - April 29. 1994 rnatedal, location, weighl, etc.)

I 9 Configurations Tested Verification Conliguralions Design of Experiments Techniques Used (including some outside of Design ol Experiments Limits)

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! PHASE TWO Stop: Casslnl Payload Fairing Acoustic Tesls [ Team Effort led by No BJanket J Marlin Mariella 7 full-scale Acoustic Tests al I .Jan 10 - Feb 14. 1995 Redes gn Martin Marietta's Acoustic Chamber V10 and V5 Compared tO Baseline Configuration A Effects Quantified I

Both V5 and Vl0 Blankets _ el Design Goal of 3 dB Acoustic I Reduction at 200 & 250 Hz .J

lqliure 1. Overdew ottbeTwo PhaseAcousdc Blanket Test _ FLAT PANEL TESTING DEVELOPMENTAL SERIES OVERVIEW

The testing of the new blanket designs in a f_t panel configuration ocaLrred in March-April 1994 at the _ MLLI_ WJUJ. Rivaba_ Acousticm Laboratory(RAL), Geneva, PAN m t IH_4_KH_rS NO1' -- IIEVl[R_IU4ilr Hlinois. Absorpdon values for the blankets were IIOUmCE SlOE obtained from reverberation time tests per ASTM CA23. Blanket transmission loss(TL) values were obtained from testing per ASTM Eg0. Figure 2 illustrates the TL test configuration. Umi_ng the absorption and "IT,test data, analytical predictions were made to calculate the effect of each new blanket design in redudng the PLF's intmor acoustics, at the frequencies of interest.

A total of 19 different blankets (18 new designs and the /" Titan IV baseline blanket) were tested for absorption mw_ --,e"_m'-" and TL characteristics. "Fnese designs are illustrated in F_n'e 3. Additionally, a isogrid panel sample, fi'om a Transmission _ Test Configuration Titan IV PLF wall, had its TL measute_ separately and Figure 2. for Flat Paad Testing (Chamber walls was also used for all the blanket TL testing. (The Titan are cut away to show isogrid panel and IV PLY is a cylindrical aluminum isogrid structure, [mer mm) (Fr_ mterenee L) mnsisting of a geometric pattern of machined out triangular pockets.) Each blanket tested was an 8 foot by 9 foot _aangular sample. As a material constraint, all blanket materials utilized in the new designs had to be already qualified for spaceflight. The DOE part of the development tests looked at three main parameters of a 4 inch thick blanket design. Fust, Testing was divided into two series of tests known m the density of the blanket's fiberglass batting was varied the development tcsts and the verification tests. The from 0.6 to 2.4 pounds per cubic foot (pcf). Second, development test series will be explained first. As part the density of the internal barrier was varied from 0.0 of the development tests, the isogrid panel and the Titan (no internal barrier) to 0.44 pounds per square foot IV baseline blanket wcrc tested. Also the Design of (pso. Third,the locationof the internalbarrierwas the Expcdmcnts (DOE) tcctmiquc was utilized to maximize varied from 0 to 3 inches fi'om isogrid paneL the amount of meaningful test information while running a minimum number of tests. From this DOE technique it w_ cxpected that one could determine the infl_noe FLAT PANEL TESTING of various factors on the response and determine which DEVELOPMENTAL SERIES RESULTS combination of these factors would optimize the response. Each development testwas run twiceto The results from the devck>pmcntal test series were check forreasonablemeasurement repeatabilityand surprising and somcwlmt disappointing. With regards to insurethatthetestwas recordingmeaningfuldataand the absorption data it was discovered that the Titan IV blanket not just backgn3und variation. baseline was already optimized for our frequcndcs of interest. The absorption peak of the 'I'ne Titan IV baseline blanket is 3 inches thick, with a Titan IV baseline blanketwas previously thought to 0.6 pounds per cubic foot deasity fiberglass batting, occm" between 400 and 5(]0 Hz. The flat panel test of with no internal barrier. It was believed that blanket the baseline blanket showed this peak to be at 250 Hz. improvements cadd be obtained by optimizing both the Increasing the blanket(batting) thickness, such as in absorption(i.e.thickerblanket)and TL (i.e.heavier DOE 1, improved the absorptionat 125 Hz, but aauaUy blanket) characteristics forour Cassinimission critical made the absorption worse at 200 - 250 Hz, as shown frequencies of 200 - 250 Hz. Therefore in order to by Figure 4. Thus our new intent was to try to keep reach our acoustic goal either a thicker (four inches) our baseline blanketabsorption values and to reach our blanket and/or a blanketwith an internalbarrier would goal by increasing the "IT, at 250 I-Iz. be needed. hmrme DOE 1 DOE 2 DOE 3

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]Rigure 3. Blanket Destgm Tested in Phase One

4 To maintain this baseline absorption required a FLAT PANEL _G minimum of 3 inches of fiberglass ba_ng on the VERIFICATION SERIES OVERVIEW inboard side (side opposite PLF isogrid wall) of the barrier. The presence of an intemat _n'ier not only The original intent of the verification series was to test increases the TL but itaffectsthe blanketabsorlXio_ verify the optimum blanket candidates as identified by characteristics by creating a double peak (and a valley the DOE technique. Although much useful information between the peaks) in the absorption spectrum. "t_nus it cbtzined in the developmentalseries, there was no also became important to avoid sttifting the absorption design tested which met our goals nor did the DOE valley into the critical frequency range of interest. analysis point to any combination of the tested blanket Hgurc 4 illustrates these points. parameters which would meet our goals. The name "verificationseries" remained but thisseries now With regards to TL, it was found that the barrier needed became an effort to use the previous test data to to be either heavier or plac_l further away fxum the analytically brainstorm to a solution within the allowable PLF isogrid walL Analysis of the test data showed that budget, blanket materials and test facility time a 4 inch blanket would not meet our goats. Both the constraints. _tion and TL requireds_n_c_t tlncknc_ and therefore even thicker blankets would be nccdcd to A few verification blanket designs were tested with reach our goal mixed, but non-satisfactory, results. As indicated earlier a thicker blanket would be needed. Relief came from the LMA Cassini Project Office who indicated that a 5 inch thick and even a 6 inch thick blanket would be allowable and stilt meet the necessary mission clearance reqttirements.

Figure 4. Absorption Flat Panel Test Data

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Figure 6. Transmission Loss Flat Panel Test Data

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=--,7--- BASELINE _ ISOGRID ""4---" V5 -.--o-.-- VIO

6 FLAT PANEL TESTING FULL SCALE I'LF _G OVERVIEW VERIFICATION SERIES RESULTS Having chosen the most promising blanket candidates Configuration 3/5 was the first 6 inch thick bla_ct (Vl0 and VS) out of Phase One testing, Phase Two tested. V5 also had a heavy internal bamer (0.44 psi) testing could now begin. Phase Two testing was a fun and was the first new blankct design which stxJwed scale test series with a cylindrical PLF, which would significant promise in meeting the original test goaL simulate the flight boundary ox_litions and geometry. Phase Two testingoccurredin January-February1995 at C_xx_guration V10 was the first test configuration to LMA's Rot¢_'ant Acoustic Laboratory (RAL), have the "super" heavy barrier (0.88 _ and was 5 Dearer, Colorado. inches thick. ARhough this blanket would weigh about 6 timesthe Titan IV baselineblanket,thisweight was The test hardware consisted of a 60 foot high section of allowed by thc Cassiniprogram. a Titan IV PLF, along with a Cassini spa_ simulator and a Centaur simulator. "1_¢ lower lx_t'tion Thinner (4 inches)and thicker(6 inchcs)varimionsof of the spacecraft simulator was a high fidelity thesuper heavy barrierwere alsotestedin developmental test model ('DTh0 suppliedby YPL configurationsV12 and Vll, V13 respectively. Inc.ludcdittldswas one RTI3 dynamic simulatorand two RTG mass simulators.The upper portionof the From all19 new blanlmtconfigurationstemed,VIO, simulator and the large High Cain Antenna Vll and V13 configurations,allwith the superheavy (HGA) at the top of the s[mcccraR were simulators barrier,were analyzedto reduce the PLF's acousticthe [xovided by LMA to represent the proper geometry and best at 200 - 250 Hz. V5 was the only configuration volume effects. Figure 7 is a photograph which shows without the super heavy bamer which was analyzed to the Cassini spaog:rafl simulator and the aft section of o.r goaL the Titan IV PLF in LMA's acoustic chamber. Figure 8 is a photograph which shows the acousticblankets the intm'io¢ isogrid IV Figur_ 5 illmtra_ the fiat panel absccption test data for mounted on wall of the Titan the Titan IV baseline,, V5 and Vl0 blankets. Similarly, PLF. F'_n-e 6 illustrates the TL test data for these same blankets and the isogrid pan©l by itself. Phase Two testing consisted of a series of seven acoustic tcslsto determine the acoustic cnviromncnt and vibrationc_ent It should be noted that the impact of the increased "IT, the RTG for three diffca-ent values seen in the fiat panel test rcsulls is scvgndy blanketconfigurations(3" baseline, 5" vto and 6" VS). lessened when prediaing PLF ao0ustic noise reduction. F'_,urc 9 shows the test matrix. This is because the flight PLF does not have 100% full blanketcoverage,but is insteadonly partiallycoveredto In the test matrix, the term "full coverage" does not allowforaccess,doocs,splitrails,wiringharnesses,etc. imply 100% blanl_ o_erage but is meant to convey that the tested configuration had similar blanket Using the measured _ and TL flat paneltest covet-age to thax expected for the actual C.assini flight- data,MDA performed acousticanalysisusingtheir Partial ooverage was a test condition equal to 75% of PLFNOISE so_ to ixedia the noise reduakm the full coverage. Two pardal coverage tests were done, which would be obtained for the T'R_ IV PLF with the one for the baseline and one for a bamer blanket, to appropriate flight blanketcoverage. Based on this imp¢ove our _ and pcediction of the effeas analysis,itwas decided to choose VlO as theleading of blank_ coverage oQ the tK.F's inte¢ior acoustics. blanket candidate fex furth¢_ testing in the full scale The remflls of these tests are outside the scope of this PLF oonfiguration. V5 was also chosen for this additional testing because its rmulls also looked 'me testmatrix also shows testing with and without promising and itsdesign (barrierweight)was TVAs. TVAs are tuned vibrationabsorberswhich were significantly different Rom VlO. attached to the lower portionof thc spacecraRin an attemptby JPL to reduce thevibration theRTGs. A complae summary of the flat panel test results may of be found in Rcfetctm_ 1. Again theseresultsare outsidethispaper'sscope of intere_ however JPL's Cassiniprogram officehas decxied not to utilizethe TVA design for tl_ C.assini flight. Figure 7. Cassini Spacecraft Simulator in Aft Section of 23tan IV PLF (From Reference 2.) Figure 8. Interior View of Acoustic Blankets Mounted on Titan IV PLF's Isogrid Wall (From Reference 2.) A PLF Station "--" Equivalents Zones/ Blankets Coveraqe P/L Simulator 701 _/R 1 3-in Std Full No 641 2"//13-intor= 2 3-in Std Full Yes, w/TVAs 2"21' i Casesa,, ._ 3 3-in Std Partial Yes, w/TVAs 552 7 4 5-in V-10 Full Yes. w/TVAs 492 f 8 3-in, V-1 5 5-in V-10 Full Yes, wloTVAs 432-- and V-5 9 Blanket 6 5-in V-10 Partial [Yes. w/oTVAs 370-_ 'Options I 7 6-in V-5 Full Yes, w/oTVAs 312 I 263 11 t

]Rip=re 9. Test Matrix for Full Scale PLF Testing

The Pbmc 1_o test _ was demB_ed to mcasBr¢ the dctta effect of the ¢m, Lmc_cms using new barrier blmdccts when compared to the ¢mrkOmnem using tb¢ bascfin¢ blankets. S_¢¢ the rcvcttcrant acoustic field of the test chamber is different than the travcliag acoustic wave at a launch pad, it was felt that delta / measurements would be most meaningful as opposed to M2 the absolute measurements. M4 113 0 ® To properly quantify this delta effect a number of microphooes were u_ to measure the PLF's interior acoustic field, as shown in Figure 10. A large number 3 Ext Mics of these micmphon_ were located in Zones 9 and lOof every 120" 4 M9.10 the PLF, which was the mB_m of high interest for the , t RTGs. Other microphones wcr¢ kx:a_d to measure the acoustic field in other zones of the PLF and to reflect past and futu_ "['RanW flight locations and past test locations by JPL. One of the microphon_ is visible in Ill F'_na'e & A small number of accelerometers were mounted on the simulatot_ to ensure that the simulators were behaving normany. Although not shown here, JPL aad MDA also bad a large amount of instrdmentatlon to measure the vibration response of the Cassixd spacea_ and PLF resIxct_ely.

FULL SCALE PLF TESTING gJF,S-_3[S

The z_xtts from the full scale PLF testing were very successful Referring again to the test matrix of Figure 9, the key tests were Tests 2, 4and 7. Test2 estabtished the baseline measurements using the Titan IV baseline blanket, whereas Tests 4 aad 7 would allow ]Rlpm_ 1@. Full Scale PLF Test the cakndatioa of the delta effect of the new blanket ImWffimmt_tim (From Rd'_ 2.) dcsigas abo_ tbc bas¢l_. (I'c_s 4 aad 5 ate essenti_y repeals from an acous_c point of view. The

10 pcesence of the TVAs might affea the spacecra_ levels below those provided by the baseUne blankets. v_ratien response but does not affect the PLF's interior Also whereas this improvement is largest at 200 to 400 acoustics. Tests 1 and 2 were used to confirm that the I-Iz, it is a positive improvement at all frequencies. presence of the spacecraft simulator did not cause anything abnormal to ocoar within the PLF.) Figure 12 illustrates the delta improvement for the V10 and V5 blankets. This figure shows that both the V10 "Ihe acoustic excitation on the external side of the PLF and the V5 blankets were suocessf_ in reducing the simulated the Titan IV flight external spedficafion and RTG acoustic environment by 3 dB at 200 and 250 Hz. was based on the average of six control microphones. For the Vl0 blanket this improvement is 3-5 dB at 200 The test to test repeatability of this external excitation Hz and 4.0 dB at 250 Hz. For the V5 blanket the was extremely good (range of 0.4 dB over an 7 tests at improvement is 3.2 dB at 200 Hz and 4.6 dB at 250 Hz. 200 and 250 Hz). However to account for even these small variations all test data was a_usted to represent Similar values are reached when the test data is the level which would be obtained if the acoustic evaluated at the t'95/50 statistical leveis, instead of at excitation was exactly the Titan IV external the mean value. specification. Of course, the ultimate goal was to reduce the RTG Figure 11 illustrates the main results of Phase Two vibration response to prevent a v_ration requalification test of the RTG. The 8nalys_ of the RTG response is testing. The external specification is the desired PLF external specification. Test 2 data shows the average of outside the scope of this paper, but an indication of the 10 microphones in zones 9 and 10. This represents the vibration reduction achieved is shown in Figure 13. average PLF interior level in the RTG region when the This figure shows the acceleration PSD (power speetral Titan IV baseline blankets are utilized. Similarly the density) response at the base of the RTG dynamic Test 4 and Test 7 data represent the same miorophone simu_tor for the baseline blanket and for the (6") V5 blanket. One can see substantial improvement, average when the VI0 and V5 blankets are substituted for the baseline blankets in zones 8, 9, 10 and 1I. particularly in the 200 and 2.50 Hz frequencies. From Figure 11 one can see that the new blankets were very stxxxss_ in reducing the PLF interior acoustics to A complete summary of the full scale cylindrical PLF testing may be found in References 2 and 3.

Figure !1. PLF Zone 9-10 Mlerephone Averat,e for Baseline, V$ and ViO BlanketLq

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12 BLANKET SELECTION FOR CASSINI MISSION LESSONS LEARNED

The tectmical assessment of the Phase Two test data is The two phase test approach used to solve the Cassini that both of the new barrier blankets ('/5 and V10) mission's problem was extremely successful Numerous exceeded the goal of reducing the acoustic environment candidateswere quickly evaluated in the fiat panel by more than 3 dB and significantly reduced the RTG testing and when they were found to be --_t_factory, v_ration response, at the 200 and 250 Hz critical additional candidates outrode the original limits were fxequencies. No detrimental effects were seen at any found to be promising. These promisingcandidates frequency or in other PLF zones. were then tested in the full scale PLF testing and found to exceed the original goals of the blankettestprogram. The technical assessment of the test data is also that If the initial lx'oposed new blankets were not first tested both of the new barrier blankets had _filar acoustic as flat panel samples but instead tested only in the full performances and that other programmatic scale test and there found to be unsatisfactory, a large considerations could lead to the selection of the final amount of time, money and effort would have been blanket design for the Cassini mission. wasted in pe_orming the full scale tests on these blankets. NASA LeRC's Cassini Project Office has selected the v5 (6"thickblankets)fortheupcoming Cass_ Knowing that there is a difference between a small flat mission. Factorsweighed in the decision,in additionto panel sample and a flight cylindrical PLF, is it possible the acoustic improvement, were the added weight of the to use the results from a flat panel test to predict the barrier blanket systems, and contamination, separation, results in a full scale PLF test? thermal,venting,and clearancefactors.With most of theseconsiderationsbeing nearequal the weight of the Analytical software codes, such as PLFNOISE and blanketsystem became the decidingfactorand the VAPEPS, can [xedict acoustic levels within the PLF "lighter"V5 blanketwas chosen over the heavierVI0 using the blanketcharacteristicsalong with the PLF blanket.The %'5blanketisstillapproximatelyfour structural and geometric properties. To obtain even times the weight of the Titan IV baseline blanket. quicker ptedicn'ons during the flat panel testing, a relatively simple method was developed by Cambridge Because of the success of this blanketdevelopmental Collaborative and NASA LeRC. This method enables test program, vibration rcquafificafion of the RTGs for one to predict the delta improvement of a new blanket the Cassinimissionwillnot be necessary.The design over a baseline blanket design for a PLF _rion of the new V5 blankets to reduce the acoustic configuration using the fiat panel sample test data. excitation and the subsequent vibration of the RTGs eliminates the need to manufactm'e additional RTG units Using dynamic power balance and assuming steady state for a requalification test program, thus saving conditions and that the energy absorbed by the blanket approximately $20-25 million in manufacturing cost and is much greater than the energy absorbed by the $5 million in testing cost. unblanketed PLF isogrid wall and by the spacecraft, then the following equation can be derived:

÷ l-S*

+ lOLogto + l-S" T _ow blaake¢ -- S"

where,

A = Improvement (dB) of New Blanket above Baseline Blanket tg = Measured Blanket Absorption Coefficient z = Blanket Transmission Coefficient = i0 _--_-6=) TL = Measured Transmission Loss (dB) A TL = TL of Blanket with PLF Isogrid - TL of PLF Isogrid s" -- I B2_et_ suzzace_____ea__oz_£LF k Total Surface Area for PLF ]

13 "Ibis equation also assumes that no acoustic energy is PREDICTING BI.ANKET PERFORMANCE lest m-ucUa_y through damping or v_ration mechanisms and that the power balance is valid within All predictions given are delta impmv_mmts above the each _ band. 'I_tan IV base,linc blank_ (3 inches tlnc_ w_h no barrier). That is, the interiora,zuuics (sound pressure The delta improvement is due to two facto_ The first level, SPL) of the PLF will be reduced when the factor is the ch_ge due to the new abscrpti_ Ixedicted delta imgovement is positive. characteristics. The second factor is the chan_e due to the new trammimion Ires dmwact_ As stated Figure 16 shows the effect of increasing the blanket earlier, in develop/rig the new Cassin_ blanket, we had batting thickness and introducing a ban'icr that is to minim_ our decrease in the tim fact_ (keep the centered in the blanket Refer to Figure 3 for details of base/ine absoqX_) and maxim/ze our increase in the the blanket designs. The DOE 1 a_rve shows that second factor (increase transmis_'on loss). adding one mote inch (4 inches) of batting results in a small improvement. A 0.24 psf barrier has been "[he measuxed data from the fiat panel tests for the Titan introduced in this 4 inch thick blanket in DOE 4. This IV basetine, V5 and vl0 b_ekets can be used wit), tim tesu]_ in an imlxovement around 500 Hz, but is _ltmt_a to ix_lict tl_ imlXOVcmcat_ for V5 actually less than DOE 1 (no barfie0 below 315 Hz. and V10 blankets. Tais [xe_ctkm can then be _ the ban-letdmsity up to 0.44 psf f_ the 4 compared with the actual imgovement (SPL re_x:tion) inch thick blanket further imlxcves the blanket measured in the full scale PLF tests for the V5 and V10 performance as shown by the V1 prediction. F'mally, blankets in the PLF zones 9 - 10. for V5, the barrier remains 0.44 psf, but now the blanket thickness is 6 inches, with I inch being added F'_Lre 14 shows the lXedicted verses test data on each side of the barriex. This helps impt'ove both the imlxovement over the baseline blanket for the V5 absct'ption and transmission Ices and results in blanket. In tl_ case, the ixedicu'on methodology results substant_ improvement. in an un_ctim at all frequencies. "[he shape of the lxediction spectrmn does follow the actual test F'_ure 17 shows the effect of the location of the ban'ier. spectrum wen, with both the _ and actual test The V1 curve shows the prediction when the 0.44 psf data peaking at 250 Hz. bazrier is oentetedin the 4 ind3 blanl_L Moving the 0.44 psf barrier one inch toward the PLF's interior, A _ comparisoo for the improvement due to the results in the _ given by the DOE 7 curve. V10 blanket is shown in Figure 15. This comparison is Some _ in tram_ loss is more thnn offset better, however now the prediction tends to be a slight by the reduction in _ for this design fn>m 225 ovezixedicfion at the f_gluencfies of greatest interest to 630 Hz. The curve predicted for when the 0.44 (20o-25o Hz). Aga_ the mape of the prediction barrier is moved one inch outward toward the PLF spectrum follows the actual test spectrum well, with isogrid waU is shown in the DOE 8 curve. O"hebatting both spearums peakingat 250 I-tz. dmsity has also changed.) At the frequencies of interest (200 - 250 Hz) the wansmission loss factor is now It is not clearly _tood why the pt'ediction significantly smaller and the increase of the absoqXion methodology results in an _ction for V5 and an does not overcome this, resulting in a negative ch,mge,. overlXedicfion for Vl0. The answer may lie in the If the barrier is left in this position but is made heavier inhezent assumlXiam of the methodology. Or it may be (0.88 ps0 the _ission loss factor improves and the because the Vl0 blanket rcsulls depend more on the absorption factor remains the same. Tais is slmwn in tmnsmi_on loss fa¢_ than the V5 blanket results and the V12 lxediction curve. (Again, the batting density that the flanking paths may have differed slightly in the has cringed.) Phase One and Phase Two test setups. The flat panel test dam _ in _ Onc testing is Nevertheless these com_ showing reasonable valuable information. The _ methodology magnitude and frequency corre_on with test data, illustrated in this sectkm is one way of using this data to gives us amfide.nce that this pt-ediction methodology undcmm_ some of the coocepts of blanket design may be used to give a first order approximation on how which were learned during this program. a blanket design would perform in a full scale PLF test. For all the bl_ket predictions, the fiat panel p_sented in Reference 1 are used. When a blanket was

14 Figure 14. Predicted versus Test Measured SPL Reduction for PLF Zones 9-10, Utilizing V5 Blankets.

5.00 •

4.00, 350,

3.00'

*_ 2.50

I_ 2.00

I._ / _L. "

I,_

O.SO I I I I I I I I I I 800 1000 100 125 160 2(]0 250 315 400 500 630 Frequency (Hz)

I _ V5 Prediction 1.4..-- V5 Measun_d I

Figure 15. Predicted versus Test Measured SPL Reduction for PLF Zones 9-10, Utilizing VI0 Blankets.

5OO T

450

400 I 3,50

_ 3.00

_ 2.50

_ 2.OO . I I I N i.m L \ I 1 \,l

I I ! 0.50 [ I I I I I 0.00 I I 200 250 315 400 500 _ 1000 100 125 160 FI't_luenc'y(Hz) m --o-- YlOPRd_ction ----°--"YlOMe_,med I I

15 F'qgure 16. Predicted SPL Reduction for Various Blanket Designs showing the Effects of the Birrier's Presence and Density.

g

-0.50 .4. 100 125 160 250 315 400 5(}0 630 800 10130 Frequency (Hz)

-='0"-- V5 _DOEI _r'_" DOE4 "--"¢---- Vl

Figure 17. Predicted SPL Reduction for Various Blanket Design showing the Effects of the Barrier's Location.

4O0

160 200 250 315 400 500 630 10{X) Frequency (Hz)

_DOE7 _DOE8 "_°'Vl2 oVI

]6 REFERENCF_ retested,a straightnumericalaverageof the datafrom the two runs were used in the pt'ediaion.A valueof 0.765 was used forS* in allpredictions,which istypical I. Armel, T.L, July 1994, _I'itan IV Payload Fairing S/N 000036 Acoustics Flat Panel Tests," M_onnett of the Cassiniflightblanketcoverage in thePLF zones of intcrest. Douglas Aerospace - Space Systems Report MDC 94H0067.

CONCLUSIONS 2. Bradford, L, October 1995, "Cassini Payload Fairing (PLF) Acoustic Bla_et Test, Part B: Test Report," A multi-organizational effort, led by NASA Lewis Locktmed Martin Report IQAS3-00014. Resea_ Center, to develop and test verify new acoustic blankets has been sts3cessfully completed. Two Right . Bet'gen,T.F.,July28, 1995, "CassiniPartial- DTM/Titan IV Payload Fairing(PLF) Acoustic viable blanket candidates, configurations V5 and VI0 Test have been found which meet the goal of reducing the Report,"JetPropulsionI.zboratoryInteroffice Memorandmn 325D-95-1ff2. PLF's interior acoustics in the zones of interest by 3 dB or more at the Cassini mission critical frequencies of 200 and 250 Hz. The V5 blanketshave been selected ACKNOWLEDGEMENTS by the Cassiniprogram to be utilizedforthismission. Because of thissuccess, the Cassini'sRTGs do not have The authot_ would like to acknowledge the contributions to be vibration requafified, resullmg in $25 - 30 million dollars in savings for NASA. of the following people who contributed to the success of this test program: Pat Symons, Bill Taylor, James Robinson and Kuan Lee of the NASA LeRC Launch The two phase test program followed in this effort was critical in meeting the objectives of the test program. In Vehicle Project Office who provided the funding and Phase One, numerous blanket candidates were quickly project guidance for this ambitious test program; IAlo BradRx_l, Bob Foster, Abe Jack, Tom Sayuk, Tom evaluated by fiat panel testing to arrive at potential blanket candidates. In Phase Two, theseselectblanket States and the entire LMA team who performed the candidates were then tested in a full scale cylindrical Phase Two testing and analysis; Theresa Atmel, Bob Kessler, Mary Long, Mike Seely,George Smuffex and payload fairing to determine tbcir performance in a the entire MDA team who designed the blanketsand realisticflightenvironment. directed the Phase One testing and analysis; Even Ht_t A wealth of acoustictestdatawas obtainedduringthis of Analex _ and Dr. Jerome Manning and Ben Hebert of Cambt'idgc Collaborative, Inc. for their testpv3gram. A methodology forusingfiatpaneltest data to obtain a first order lXediction of the pedofmance trem_ test support and data analysis throughout the of an acoustic blanket in a PLF has been _. test program; ThornBergen, Pan1Hardy,Harry The information lxesented in this paper may be u_Jzed Himelblau, Dennis Kern, and the JPL test team for their for other space missions and their own special insight on the Cassini spacecraft design and their test applications which may differ from the Cassini data analysis; Don Wong and Norm Lagerquist of the mission's. The barrier blanket tecimology developed for _ for their Titan IV vchJde and this program may also have non-space applications for knowledge and support; John Kopec and Peter Strauss from the Riverbank Aamstical Laboratory for cre_ding quieter acoustic environments for automobiles, ships, airplanes, homes, offices and indusWial settings. performing the PhaseOne testing.

17 FormApproved REPORT DOCUMENTATION PAGE OMBNo.0704-0188

pul_c mpmlin9 IxJclenfor thls ¢oilo¢lkm of InlonmlJon Is mtknmed to rage 1 hourpw mq)onee, Includkl0_e _ne ior mvievdn0instnclJo_, seamh/_g ,--blino dala soumm, 9athldno and _lno the dals minded, and ¢xxqlM(J_ and mvwwmg Ihe coitec_n of InfocmalJon.Send ¢_rmmlS _ this bu_en esttmale or any ottw asped of mis coCec_Jonof _. indudinO suggmUms for mdudno mlsburden, m WahlnOton _ 8eMms, Otmcmmmf_x Irdorms_n OpenCom and Repor_ 1215_ Davls Highvmy. Suite 1204, Argn_ VA 2220_-43(_. and to 1heOffice of Mana_ 4m¢1Bud_ Pa_ Reductlo_ Pro_ (0704-01U). Wash_, DC 20503.

1. AGENCY USE ONLY (Leave blam*) 2. IEPORT DATE & REPORT TYPE AND DATES COVERED July 1996 Technical Memorandum 4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Cassini/Tilan IV Acoustic Blanket Development and Testing

WU-256-4X)-_ eL AUTHOR(S)

W'dliam O. Hughes and Anne M. McNelis

7. PERFORMINGORaMgZATK)NNAME(S)ANDADDRESS(ES) I 8. PERFORllI_ ORGANIZATION REPORT NUMBER National Aeronautics and Space Adminiswation Lewis Research Center E-10331 Cleveland, Ohio 44135-3191

9. SPONSORINGRBONn'ORINGAGENCYNAME(S)ANDADDRESS(ES) 10. SPONSORING44ONITORING AGENCY REPORT NUMBER National Aeronautics and Space Administration Washington, D.C. 20546-0001 NASATM-107266

11. SUPPLEI_NTAI:W NOTES Prepared for the 42nd Annual Technical Meeting and Exposition sponsored by the Institute of Environmental Sciences, Orlando, Florida, May 12-16, 1996. Responsible person, W'llliam O. Hughes, organization code 4310, (216) 433--2597.

12L DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

Unclassified *Unlimited Subject Categories 71, 18, 15, and 39

publication is available from the NASA Center for AeroSpace Informafi(m, (301) 621-(}390. 13. ABSTRACT (Maximum 200 movie) NASA Lewis Research Center recently led a multi-organizational effort to develop and test verify new acoustic blankets. These blanketssupport NASA's goal in reducing the Tilan IV payload fairing internal acousticenvironment to allowable levels for the Cassini spacecraft. To accomplish this goal a two phase acoustic test program was utilized. Phase One consisted of testing numerous blanket designs in a flat panel configuration. Phase Two consistedof testingthe most promising designs out of Phase One in a full scale cylindrical payload fairing. This paper will summarize this highly successful test program by providing the rationale and results for each test phase, the impacts of this testing on the Cassini mission, as well as providing some general information on blanket designs.

14. SUBJECT TERMS 15. NUMBER OF PAGES 19 Acoustics;Acousticblankets;Blankets;Cassini,Payloadfairing;Spacecraftacoustic 16. PRICE CODE environment; Sw.ecraft acoustic tesdng; Titan IV; Vibroacoustics A03 17. SECUmrvCLASmRCXnON 18. SECURffY CLASSU=ICA_ION 19. SECURITY CLAS_FICATION 20. UMITATION OF ABSTRACT OF REPORT OF THIS PAGE OF ABSTRACT Unclassified Unclassified Unclassified

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