INSTRUMENTATION DEVELOPMENT

NASA Technical Memorandum 4505

Perspective on The NationalAero-Space Plane ProgramInstrumentationDevelopment

Rodney K. Bogue and Peter Erbland

MAY 1993

NASA Technical Memorandum 4505

Perspective on the NationalAero-Space Plane ProgramInstrumentation Development

Rodney K. Bogue

Dryden Flight Research FacilityEdwards, California

Peter Erbland

NASP Joint Program Office

Wright-Patterson Air Force Base, Ohio

National Aeronautics and Space AdministrationOffice of ManagementScientific and Technical Information Program1993

PERSPECTIVE ON THE NATIONAL AERO-SPACE PLANE

PROGRAM

INSTRUMENTATION DEVELOPMENT

Rodney K. Bogue*

NASA Dryden Flight Research Facility

P.O. Box 273

Edwards, California 93523-0273Peter Erbland**

NASP Joint Program Office

Wright-Patterson Air Force Base, Ohio

Abstract

This paper presents a review of the requirement for,and development of, advanced measurement technol-ogy for the National Aero-Space Plane program. Theobjective is to discuss the technical need and the pro-gram commitment required to ensure that adequateand timely measurement capabilities are provided forground and flight testing in the NASP program. Thepaper presents the scope of the measurement prob-lem, describes the measurement process, examines howinstrumentation technology development has been af-fected by NASP program evolution, discusses the na-tional effort to define measurement requirements andassess status of NASP technology; and summarizes themeasurement requirements. The unique features of theNASP program that complicate the understanding ofrequirements and the development of viable solutionsare illustrated.

OH

hydroxyl radical (a combustion intermediary)

P pressure

PdCr palladium-chromePLIF planar laser-induced fluorescenceq˙ heat transferRF radio frequencySBIR Small Business Innovative ResearchSSTO single-stage-to-orbitT temperature

Tech Mat Technology MaturationTMC titanium matrix composite

efficiencyhc combustion

hm mixing efficiency

Introduction

Instrumentation for the National Aero-Space Plane(NASP) program, is an enabling technology critical toaccomplishing the program goals. This paper provides:(1) an historical overview of the work within the NASPprogram to develop instrumentation technology in sup-port of the program objectives, (2) a discussion of thedevelopment process and activities, (3) an assessmentof the current development status, and (4) a perspec-tive on the features of the NASP program that con-tributed to the current state of instrumentation tech-nology readiness.

Nomenclature

BTU British Thermal Unit

CFD computational fluid dynamicsCW continuous wavedB decibel

FeCrAl iron-chrome-aluminumLIF laser induced fluorescenceLOS line of sightNASP National Aero-Space PlaneNDE nondestructive evaluation

*Aerospace engineer. Member AIAA**Aerospace engineer. Member AIAA.

Copyright © 1992 by the American Institute of Aeronau-tics and Astronautics, Inc. No copyright is asserted in theUnited States under Title 17, U.S. Code. The U.S. Govern-ment has a royalty-free license to exercise all rights under thecopyright claimed herein for Governmental purposes. Allother rights are reserved by the copyright owner.

Defining the Measurement Problem

In the NASP program, instrumentation developmentis seen almost exclusively as a problem in developingtransducers to measure the key parameters necessaryto confirm performance and research models of phys-ical phenomena. There are additional aspects to theinstrumentation task, such as data acquisition, system

interconnects (wiring or fiber optics), recording, andtelemetry. However, the program technology needswere thought to be concentrated on the development oftransducers that would operate in the extreme environ-ment characteristic of hypersonic atmospheric flight.Scope of the Measurement Problem

In this document, the measurement problem hasthree essential domains. These are quality, environ-ment, and application. These domains or dimensionsare illustrated in Fig. 1.Quality

The quality domain characterizes the quality of theinformation available. Defined here, quality is a multi-dimensional domain that includes the factors normallyassociated with the goodness of information. Typicalquality factors are repeatability, accuracy, precision,and frequency capability. Off-the-shelf systems pro-vide adequate measurement quality information underbenign environmental conditions. For new measure-ments, the measurement quality must be establishedfrom new concepts with new baseline standards definedsimultaneously. For example, when a thermographicphosphor technique is used for temperature measure-ment, the phosphor measurement repeatability, accu-racy, precision, and frequency response must be estab-lished by experiment. This capability then becomes thebaseline standard for thermographic phosphor temper-ature measurement.Environment

The environment domain encompasses all the envi-ronmental factors that influence the measurement. Inthe NASP program, the primary environmental fac-tors are severe temperature and high heat transferrates. Other environmental factors include: oxidizing–reducing atmosphere, ionized–plasma gas conditions,low temperature (liquid–slush hydrogen), high thermalgradients, and high-intensity acoustic fields.Application

The application domain includes the details of mak-ing a specific measurement in a specific situation. Theapplication domain is characterized by the need to in-tegrate transducers into the NASP systems, whetherstructural, propulsive, or aerodynamics. Often, the in-tegration requires that the transducer be small. Inothers, it may need to be chemically nonreactive, orthe transducer installation may require matching somephysical parameter, such as thermal conductivity orspecific heat, so the parameter being measured is notdisturbed. Most situations require a combination ofthese factors to meet the specific need. The location ofthe test in either the ground or flight environment isalso a factor in the application domain. The following

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examples illustrate the application domain; however,these examples are not fully representative of the broadspectrum of unique applications in the NASP program.The first example is making a heat transfer measure-ment on the surface of a highly curved wing-leadingedge of a vehicle in hypersonic flight. This measure-ment must be performed without adding surface rough-ness, and without disturbing the surface heat conduc-tivity or thermal capacity. This application requiresthat the transducer be integrated into the leading edgeand the means for transmitting the information awayfrom the transducer (wiring or fiber optics) must beimbedded into the supporting structure. The sensingfor this application may also be possible through re-mote, nonintrusive techniques. This application is farmore difficult to implement than a ground test involv-ing heat transfer measurement from a flat surface, forexample.

The second example is making a measurement of thegas species in a scramjet propulsion system. This mustbe done in the limited volume available in a flight ve-hicle while providing optical access for the laser beamprobe in the extreme thermal environment. A simi-lar measurement in a laboratory test facility would notimpose the severe size constraints on the measuringequipment, although the quality and environment do-mains would be nearly the same for both situations.For the NASP program, measurement technology isadequate to satisfy the quality domain requirements forbenign environments. However, the environmental andapplication domains are inadequate, and developmentis continuing to establish improved capability. Thissituation is shown in Fig. 2. The quality domain iscoupled to the environmental and application domainsin the sense that adequate technology for benign envi-ronments is not adequate technology for extreme envi-ronments and special application situations.

Quantifying the Measurement Domains

The three measurement domains provide useful stan-dards to gauge current measurement capability anddetermine instrumentation development requirements.However, to use these standards, it is first necessaryto quantify each of the three domains. The qualitydomain is more difficult to quantify than others be-cause the quality requirements are determined by theobjectives of a particular test, whereas, the environ-ment and application requirements are determined bythe test article and test conditions. This link betweenmeasurement quality and test objective is less intuitivethan the connection between either environment andtest conditions or application and test article.

Uncertainty analysis defines the relationship betweentest objectives and measurement quality. Uncertainty

analysis takes the specific, quantified, test objectives

and establishes the type, location, and quality of mea-surements needed. For example, a ramjet combustortest is planned to determine combustion efficiency fora new fuel injection concept. To be successful, the com-bustion efficiency must be determined to an accuracyof ±5 percent. An uncertainty analysis examines theequations used to calculate combustion efficiency (hc)from measured facility and test data. This allows thesensitivity of hc to each measurand to be defined. Sub-sequently, the expected accuracy of each measurement(P, T, q˙) is propagated through the performance equa-tions to determine the expected accuracy of the com-bustion efficiency. The accuracy required of the var-ious measurements can then be adjusted to meet therequired accuracy in combustion efficiency. This anal-ysis allows a quality requirement to be established foreach measurement, and justifies that quality as beingnecessary and sufficient to accomplish the objectives ofthe particular test. Unfortunately, uncertainty analysisis complex, time consuming, and difficult to generalizeand for this reason, the measurement quality dimensionis difficult to bound.

Thermal Effects

The thermal environment amplifies the intensity ofthe other responses in addition to inducing its owneffects. Change in physical characteristics of mate-rials is a major effect of temperature. Temperaturechanges affect stiffness, yield strength, and creep. Thefollowing example shows how the other responses areintensified. At room temperature, the chemical effectsof oxidation on the sensor and installation are negli-gible for the operating lifetime of most installations.At elevated temperatures, oxidation may shorten theuseful lifetime to a few hours and require special re-calibration procedures to accommodate the change inchemical composition. Another example is the ther-mal environment that precipitates changes (reversibleor irreversible) in the physical state of transducer com-ponents. Examples of state changes include changesin physical strength because of temperature changesor because of the formation of new compositions (suchas alloys) created by nearby components. The effectsfrom new compositions tend to be irreversible.Chemical Effects

The chemical environment precipitates chemicalchanges in the makeup of a transducer and its instal-lation. These changes cause degraded performance. Acommon example of this effect is the oxidation of criti-cal materials that irreversibly change the physical char-acteristics over time to produce “aging”. Besides oxi-dation, chemical interaction between transducer com-ponents is a factor that must be considered especiallywhen the device is operated at elevated temperature.Special coatings can sometimes be used to separate re-active materials and alleviate the effects of chemicaldegradation.

Electro-magnetic Effects

The electro-magnetic environment introduces spuri-ous signals into the transducer outputs through electro-magnetic fields near the transducer. Sources of thesefields include power wiring, power conversion compo-nents, and various radio frequency (RF) transmissions.In hypersonic flight, the local flow field about the vehi-cle reaches temperatures where ionization and dissoci-ation create a conductive plasma condition, the effectsof which are not well understood.Mechanical Effects

The mechanical environment includes the absoluteand differential physical motions to which the trans-ducer is subjected. These motions include accelera-tion, velocity, and displacement as well as differentialversions of these same parameters. Mechanical strain is

For the NASP program, the quality domain is espe-cially difficult to bound because of the diversity of testobjectives, the rapid evolution of test techniques, andthe lack of uncertainty analyses for specific tests withinthe program. Consequently, the quality domain, whereit has been bounded, is a somewhat general and artifi-cial estimate of the expected quality requirements. Theenvironment domain is bounded by the thermal, chem-ical, mechanical, and acoustic environments in whichthe vehicle is designed to operate. The application do-main is bounded by the variety of material systems andstructural concepts under development as well as theoverall weight, volume, and power limitations for theinstrumentation on the X-30. These issues will surfaceagain when the challenge of requirements definition isdiscussed.

Measurement Process

Measurements are made by using a physical phe-nomenon to transform information into a usable form.The transducer is subjected to the effects of a measur-and of interest and the transducer output provides theuseful information (Fig. 3). “All transducers respondto all aspects of their environment in all ways of whichtransducers are capable of responding...”1 For exam-ple, the transducer responds to the thermal, electro-magnetic, chemical, and mechanical environment. Thechallenge of measurement is to enhance the desired re-sponse(s) and to suppress the undesired responses. Anexample of a strain transducer is shown in Fig. 4.

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a common example of a differential displacement being

experienced by a transducer. The effects of transducerssubjected to mechanical strain may include changes inoffset, scale factor, and linearity. If the transducer isnot irreversibly damaged by the strain, recalibration isusually required at a minimum.Transducer Example

The typical strain transducer uses piezo-resistive ef-fects and sensor distortion to provide an output thatchanges resistance in response to mechanical strain in-puts. Figure 4 illustrates the transducer response situ-ation with several environmental stimuli being appliedto the strain transducer. A useful strain transducerwill enhance the response to the mechanical environ-ment and suppress responses to all other environmentalstimuli.

The typical strain transducer response to the previ-ously mentioned environments will be assessed in thefollowing paragraphs. If the response is manifest asa change in the basic transducer characteristic (resis-tance), the response will be termed intrinsic. Extrinsicresponse is the result of effects associated with attach-ment to the structure. When the strain transduceris installed, the effects of this installation modify thetransducer behavior and the strain at the installationpoint. Strain transducers respond to the thermal envi-ronment with a change in intrinsic resistance becausethe electrical resistance of most materials changes asthe temperature changes. Over wide temperature ex-cursions, many materials exhibit phase changes in theircrystal lattice structure. A phase change often inter-jects a step change in resistance at a critical temper-ature. When a transducer material is an alloy at ele-vated temperatures, one of the alloy constituents maysublime and change the transducer makeup therebyaltering the intrinsic electrical resistance and the re-sponse to the applied strain. Constituent sublimationis seen as a drift in the intrinsic resistance.

Thermal effects also appear in the gauge attachmentto the measured structure. When the structure andthe strain transducer have different thermal coefficientsof expansion, a strain will be induced into the trans-ducer because of a differential expansion as tempera-ture changes. This effect is in the extrinsic responsecategory and is often conveniently combined with theintrinsic responses previously noted into a term calledapparent strain. A strain gauge installation can betemperature cycled to calibrate the response to tem-perature and the calibration used to suppress the ef-fects of temperature during actual strain measurement.Figure 5 shows that the magnitude of this effect forcommercial gauges employed under NASP can be ashigh as 14000 µ strain for anticipated temperature cy-cles. Through the use of temperature compensation

techniques, this 14000 µ strain may be reduced to lessthan 4000 µ strain (also shown in Fig. 5). These tech-niques were developed as a part of the NASP instru-mentation development activity. This gauge outputvariation must be applied as a correction factor to themeasured strain value which may be typically between100 and 2000 µ strain. For quality measurements, theapparent strain variation with temperature must behighly repeatable.

The chemical environment affects the intrinsic andthe extrinsic responses of the strain transducer. Theintrinsic response is caused by changes in the chemicalmakeup of the transducer itself (usually experiencedas oxidation). Often an alloy constituent of the trans-ducer will oxidize at high temperatures and change thebasic gauge resistance and the basic response to strain.These effects are similar to those experienced when analloy constituent evaporates. This response would beseen as a slow change in gauge characteristics that arecombined in a term called drift or aging.

When the strain transducer is installed, the installa-tion modifies the strain transfer and the strain at theinstallation point. The gauge installation modifies thestrain when the structure lacks stiffness and the gaugeinstallation adds stiffness at the point of measurement.This situation frequently occurs when the strain mustbe measured in a thin skin.Development Time and Resources

Substantial work is required to transform a new mea-surement concept into a useful research tool. This worktranslates into significant time and resources. Experi-ence has shown that this process requires several mil-lion dollars and between 5 and 10 years to accomplish.

Program History

To understand the state of NASP instrumentationrequirements and technology development it is nec-essary to first understand the history of the NASPprogram and the evolution of the instrumentationprogram.

Copper Canyon (1983–1985)

The NASP program began in 1983 with the “CopperCanyon” phase which concentrated on vehicle concepts.This stage of the program was completed at the endof 1985. There is no evidence that any measurementdevelopment work was done during this program phase.Technology Maturation (1986–1990)

Phase 2 of the NASP program began in 1986. Theearly years of this phase were marked by competitiveengine and airframe development efforts and the forma-tion of the Technology Maturation (Tech Mat) programto develop critical technology required by the NASP

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program. Technology teams were formed to direct tech-nology advancement in the following seven disciplin-ary areas: aerodynamics, computational fluid dynamics

(CFD), high-speed propulsion, low-speed propulsion,structures, materials, and flight systems. Governmentstaff provided the direction for these teams with par-ticipation and periodic review by contractor and othergovernment and academic representatives. Respon-sibility for instrumentation development was placedwithin these seven teams. Two teams (structures andlow-speed propulsion) identified funding to supportmeasurement technology development.

Shortly after the teams were formed, an instrumen-tation task force was established. Near the end of theTech Mat program the Instrumentation Task Force wasformally chartered as an instrumentation team and re-sources were provided for additional development cov-ering multidisciplinary instrumentation problems suchas high-temperature optical fibers and optical fiber-based sensing. By the end of the Tech Mat program,five of the original seven teams had initiated mea-surement technology development primarily concernedwith ground test measurements.

Consortium–National Team (1990 to present)In 1990, the five NASP prime contractors formedan instrumentation consortium. This group focusedon developing needed technology to support NASPflight measurements. Shortly after the consortium be-gan work, competition ended, and the five prime con-tractors formed the national team. Consortium ac-tivities and the Tech Mat program ended about thissame time. When the national team was formed, workwas allocated to each of the participating contractorsas work packages. Several contractor work packageswere identified to continue instrumentation develop-ment, however, because of resource allocations, onlythe three airframe contractors participated in this de-velopment. Coincident with this teaming, the gov-ernment work package process was created to comple-ment the contractor’s activity and to continue the gov-ernment contribution within the technology program.Work package oversight was provided by a consoli-dated government–contractor review team.

and technical features of the NASP program that haveparticularly complicated the definition of measurementrequirements.

Programmatic Challenges

The development of measurement requirements forNASP has been complicated by several programmaticfactors. These factors include cooperation from thedisciplines, program organization, evolution of the ve-hicle design, competing program objectives (researchvs. demonstration), schedule fluctuations, and the lackof clear payoff toward achieving program goals.Disciplinary Cooperation

Since the disciplinary engineers (structures, aero,propulsion) represent the customer, their cooperationis essential to development of credible measurement re-quirements. Obtaining a clear set of requirements fromthe disciplines, i.e., what they must measure, as op-posed to what they desire to measure, has been diffi-cult. The disciplines have for the most part, only iden-tified measurement requirements that could be satisfiedwith off-the-shelf instrumentation.Program Organization

In the beginning, the program was not organized toadvocate and address measurement requirements. At-tempts were made to improve requirements definitionas the program gained momentum. This included char-tering the instrumentation task force, the subsequentformation of an instrumentation team, and the forma-tion of the instrumentation consortium.Evolution of Design

The evolution of the NASP design also contributedto the problem of defining valid requirements. Thewide range of structural concepts, material systems, en-gine concepts, and ground test methods created manyenvironments and applications within which measure-ments could be required. For example, a measurementsuch as heat flux had to be considered for each ofthe possible material systems with their correspondingunique thermo–chemical environments and structuraldesign concepts [copper alloys, graphite–copper com-posites, refractory metals (coated or clad), cobalt andnickel superalloys, titanium matrix composites, beryl-lium and beryllium composites, carbon–carbon, andcarbon–silicon carbide]. This situation has improvedbecause the number of material systems and designconcepts have been reduced as the program hasevolved.

Competing Program Objectives

Measurement requirements definition has been af-fected by the uncertainty over whether the X-30vehicle is a research test bed or a demonstration vehiclefor single-stage-to-orbit (SSTO). This competition

The Challenge of Requirements

Definition

From the outset of the NASP program, developmentof measurement requirements has been a significantchallenge. The reasons for this are programmatic andtechnical, yet the results are the same; a more gener-alized definition of measurement requirements, a moregeneral statement of measurement deficiencies, and aless focused technology development program. Thefollowing paragraphs briefly relate the programmatic

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extends to the ground test program wherein many of

the tests must be a balance between research, to under-stand the behavior of a component, and demonstra-tion to prove that a given technical approach will work.Satisfying the research community implies higher mea-surement accuracy and more difficult measurands (e.g.,wall shear, flowfield properties, and surface strain) ver-sus the demonstration community whose primary mea-surands are those required for system control and safety(e.g., surface pressures, and temperatures). In pro-grams of this type, it is important to establish early onthe emphasis (research, demonstration, or some bal-ance between) which will guide the test objectives andconsequently the test requirements.Schedule

The aggressive, success oriented program schedulecreated the dichotomy that if the instrumentationneeded by the program took more than 1 to 2 yearsto mature, it was already too late for development; onthe other hand if the development only required 1 or 2years, then it could be delayed until the next phase ofthe program. Thus, a serious effort to define the mea-surement requirements and provide for development ofthe needed technology could be delayed.Lack of Payoff

Clear requirements are necessary to understand defi-ciencies, which in turn will show the payoff of invest-ing in measurement technology. In particular, the lackof data quality requirements made advocating devel-opment work substantially more difficult. If this dataquality assessment were accomplished, the payoff in un-derstanding measurement requirements and the bene-fits derived from instrumentation development wouldbe clear.

Technical Challenges

In addition to the programmatic challenges, thereare unique technical features of the NASP programthat have complicated the definition of measurementrequirements. The most important issues include par-allel technology development, differences in ground andflight requirements, the variety of applications and en-vironments, the complexity of the transducer integra-tions, collective severity of the measurement environ-ments, and the lack of sensitivity–uncertainty anal-ysis. Each issue will be discussed in the followingparagraphs.

Parallel Technology Development

The basis for these factors is the parallel technologydevelopment required to satisfy NASP design goals.Figure 6 illustrates the number of technical fields underdevelopment by NASP and compares this with earlier

experimental hypersonic vehicles. By way of exam-ple, the NASP program is conducting basic research tocharacterize the thermal and mechanical properties ofseveral advanced materials. Concurrently, the manu-facturing processes for these new materials are underdevelopment to understand the optimal methods for fab-ricating cost effective materials of uniform quality.In addition, the NASP program is developing advancedstructural concepts using these materials. This paral-lel development increases the scope of the measurementrequirement (measurement capability for multiple can-didate material systems and structural concepts) andcomplicates the solution of any single measurementproblem.

This increased complexity is shown by taking a sin-gle material–structural concept (titanium matrix com-posite (TMC) hot structure) and considering a singlemeasurement (strain). We define the measurement en-vironment as a silicon-carbide fiber reinforced b-21S ti-tanium composite material system, consolidated usinga hot isostatic press process, joined using either spotwelds or brazed joints and intended for operation to1500 °F. The measurement of strain on such an arti-cle is complicated by (1) the poor behavior of conven-tional strain gauges between 700–1500 °F (nonlinear,nonrepeatable apparent strain; temperature dependentdrift and gauge factor; and immature attachment tech-niques), (2) lack of maturity of the TMC thermophys-ical properties database, (3) batch-to-batch variabil-ity of the fabricated materials, (4) complex, thermal-cycle-dependent, residual stress state of the composite(a function of its processing and lay-up), and (5) thevariable performance of the developmental structuralattachment–assembly processes.

The resulting complexity of strain measurementgiven this host of problems seems obvious whenseen collectively from the instrumentation perspective.However, it is often overlooked when viewed from theisolation of any single discipline. This is only one of themeasurement problems presented by the parallelism inNASP technology development. Clearly defining themeasurement problem for each measurement given thevariety of NASP materials and structures presents adaunting challenge.

Ground versus Flight Requirements

The need to define the unique measurement require-ments for ground and flight testing further compli-cates the requirements development process. Althoughthe measurands required are similar, the constraintsimposed on meeting those requirements can be dif-ferent (Fig. 7). Thus, clear definition of these con-straints is necessary to structure an adequate develop-ment program.

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Variety of Applications

A given measurement must accommodate many ap-plications. For example, Fig. 8 shows that the problem

of defining heat transfer measurement requirements iscomplicated by the need to make these measurementsin seven different materials for four different structuralconcepts, each of which constitutes a unique applica-tion. Each application is designed to accommodate adifferent vehicle thermal, mechanical, and chemical en-vironment. In addition, several transducer conceptsmust be considered to identify the approach that willbest satisfy the measurement quality, environment, andapplication requirements.

Complexity of the Transducer Integrations

The complexity of NASP structural designs, theseverity of the test environments, and the difficultyand risk associated with transducer integration havehampered the development of measurement require-ments. The vehicle design must be tailored to accom-modate critical instrumentation installations. For ex-ample, when a critical structural member has an uppertemperature limit beyond which failure is highlyprobable, a means must be provided to measure andmonitor that temperature even though it may requirea design modification. In this situation, there are noworkarounds. A high degree of design integration isrequired to ensure that a transducer installation ap-proach will satisfy the measurement requirement yetnot compromise the structural integrity.

The complexity of the transducer integration prob-lem coupled with the rapidly evolving structural designspace has resulted in the first priority being placedon the demonstration of survivable structures. Theadditional complications presented by embedded in-strumentation will be addressed only after survivalis demonstrated. This approach significantly compli-cates the application dimension of the measurementrequirements. Figure 9 illustrates the type of cooledpanel structure required for an SSTO vehicle. Clearlypressure, temperature, heat flux, and wall shear mea-surements within a 0.020-in. wide structure presentformidable sensor integration challenges.Diversity of Measurement Environments

The NASP program has a significant range of en-vironments within which measurements must be ac-complished (Fig. 10). These environments are di-rectly related to the maturity of the vehicle designand database. Thus, as the design (geometry or ma-terials), target operating conditions (dynamic pres-sure), or fidelity of the test and analysis databasechange, the measurement environments change. Forexample, as the understanding of shock-enhanced heat-ing has evolved, the projected peak heat transfer

rate, where the bow shock intersects the engine cowlleading edge, has spanned the range from 50,000 to90,000 BTU/ft2-sec. Similarly, the peak acoustic lev-els predicted for the vehicle have varied from 170 to200 dB. This variability forces the generalization of themeasurement environment requirements to have stableobjectives for the measurement development activities.Sensitivity and Uncertainty Analysis

The development of credible measurement require-ments has been made more difficult by the lack of sensi-tivity and uncertainty analyses. The objective of theseanalyses is to understand the type of measurements andthe measurement quality required to satisfy the objec-tives of a test. The alternative is to gain this insightempirically by the costly process of trial and error. Theimportance of this point is shown by the decision todevelop hydroxyl radical (OH) nonintrusive diagnosticsystems for high-speed combustor testing.

The NASP program has invested substantial re-sources to develop two nonintrusive systems to measureOH. This decision was based on several logical premisesall of which strongly suggested that OH was a viable in-dicator of combustor performance. When the systemswere used in combustor testing, the OH images weredifficult to interpret, could not be quantified, and mostimportantly, could not be used to establish or absolutecombustor performance. Therefore, this diagnostic waslimited to providing qualitative insight into combustorflows.

A numerical sensitivity analysis was conducted forthe combustor after it was found that the data pro-duced by these systems were not providing the requiredinsight. Mixing was varied ±10 percent that produceda +14-percent/–11-percent change in the combustionefficiency. The various surface and flowfield quanti-ties were examined to determine their relative changecompared to that seen in the mixing and combustionefficiency. Figure 11 shows the measurands that areuseful for determining combustion efficiency for a dataplane at the combustor exit. It is clear that OH is nota change-sensitive indicator for combustion efficiency,because it decreases from the nominal value whetherthe mixing is increased or decreased. Conversely, themass flux of water and the line-of-sight (LOS) averagedwater number density vary in direct proportion to thecombustion. Note also that oxygen mass flow is a sen-sitive indicator of combustion efficiency for the caseanalyzed. An important fact not revealed by this datapresentation is that for this analysis, less than 5 per-cent of the original oxygen remains in the flow at theexit plane. Therefore, a moderate change in combus-tion efficiency produces an unusually large percentagechange in oxygen mass flow. The accuracy of the mea-surement is a critical consideration if changes in small

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quantities must be resolved, as would be the case formeasuring oxygen in a stoichiometric or rich combustorwith high-combustion efficiency.

The conclusions drawn from this sensitivity analysisare (1) water and oxygen are better indicators of com-bustor performance than OH for high-speed combustortesting, and (2) sensitivity analysis should be followedby an assessment of the accuracy with which each of thecandidate parameters must be measured. Thus, sensi-tivity and uncertainty analyses are key tools in definingand validating measurement requirements, and in thecreation of instrumentation development programs toaddress measurement deficiencies.Requirements Status

It is difficult to delineate specific measurement qual-ity, environment, and application requirements for thelarge number of unique measurements required by theNASP program. Measurement requirements, like anyother requirements, must be supported in the manage-ment process by a spokesperson backed by substanti-ating information derived from test objectives. Testobjectives cannot be solidified until the evolution rateof the design reaches the point where the environmentaland application requirements are bounded. Measure-ment quality requirements for the ground and flighttest activities must then flow from uncertainty and sen-sitivity analyses.

Despite the uncertainties and generalities inherentin the development of measurement requirements forthe NASP program, several major efforts have beenmounted to understand these requirements. These ef-forts were made by the Instrumentation Task Forceand the Instrumentation Consortium which were in-troduced earlier.Task Force Assessment

The instrumentation task force assessed the mea-surement requirements for structures, propulsion, flightsystems, and aerodynamics disciplines. The measure-ment needs were evaluated based on priority, schedule,and measurement technology maturity. Within eachcategory, the task force provided a separate evaluationfor ground testing and flight testing. This evaluationidentified 26 areas requiring development emphasis, 20specific measurands and 6 broadly defined technolo-gies (Fig. 12). This assessment guided the early in-vestments in instrumentation development and was thebasis for the next requirements assessment.

Instrumentation Consortium Assessment and Flight Measurement List

Instrumentation development conducted under theNASP Tech Mat program was primarily aimed at

ground test measurement deficiencies. However, flightinstrumentation deficiencies were seen as potentiallylong poles in the X-30 development path and therefore,more effort was needed to attack the most critical ofthese problems. In response, the five competing NASPcontractors formed the instrumentation consortium tocollaborate in the development of required flight in-strumentation. The contractors revised and prioritizedthe instrumentation task force measurement list into18 measurement areas. Eleven of these measurementareas were selected for treatment in the consortium.The first task in the consortium program was to eval-uate the flight measurement requirements for each ofthe eleven measurands. This assessment provided de-tailed information on the measurement quality and themeasurement environment and application. Each tech-nical discipline at each contractor site was solicited fortheir measurement needs. These inputs were evaluatedand summarized into specifications of required mea-surement capability. Figures 13 and 14 illustrate thebreadth of responses and type of detailed data con-tained in the consortium requirements. The consor-tium effort provided much detail regarding the specificmeasurement requirements, yet it also lacked the ad-vocacy from the technical disciplines to program man-agement that was experienced during Tech Mat.The second task in the consortium program was toassess the most promising measurement techniques foreach measurement need. Where the technology wasdeficient, a technical approach and development pro-gram were recommended. Figure 15 summarizes therecommendations from this task. With the exceptionof control position sensing, all of the measurement ar-eas required substantial development. Unfortunately,at this point the consortium was terminated becauseof lack of funding and the end of competition in theNASP program.

There have been no subsequent refinements to themeasurement requirements. These requirements led toseveral development efforts which will be discussed inthe following section.

Instrumentation Development Status

and Accomplishments

After the instrumentation consortium, the NASPprogram supported instrumentation developmentthrough contractor work packages, government workpackages, the Small Business Innovative Research(SBIR) program, and the NASP Test Directorate. Thiswork took place through a centralized instrumentationeffort as well as through the disciplines.

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In the centralized instrumentation program, the con-tractor and government efforts were structured to becomplementary in addressing the measurement prob-lems. Unfortunately, funding limitations had adverseimpacts on the scope and the depth of the develop-ment activities. There has been a progressive reduc-tion in the scope of the development work from 11measurement areas to 8. Figure 16 shows this de-crease in scope from the initial work to the present.In addition, the funding was so severely limited thatfor a given measurement area only a small portion ofthe actual measurement deficiency could be addressed.For example, in the case of heat flux (Fig. 8), the is-sues of transducer compatibility, installation technique,measurement fidelity, and data analysis method mustbe addressed for each of these seven measurement ap-plications. However, with the existing funding onlytwo measurement techniques are being investigated forone material-structural system. Clearly, this increasestechnical risk to the program.

Limited additional development has been supportedby the technical disciplines. This includes work toapply nonintrusive flow measurement techniques toNASP tests, investigation of nondestructive evaluationtechniques, and development of skin friction measure-ment techniques for extreme environments.

For many technical disciplines, making measure-ments is considered an adjunct to the normal technicaltask. Many experimenters design instrumentation sys-tems to support their own testing and usually rely onoff-the-shelf hardware to accomplish the measurementrequirements. When conducting parallel technologydevelopment in extreme environmental conditions, themeasurement needs often exceed the capability of off-the-shelf equipment. Acquiring reliable test informa-tion from an extreme environment requires design andengineering from a measurement perspective not unlikethat needed for technology advancement in a nonmea-surement discipline. The same challenges exist withregard to thermal, chemical, electrical and mechanicalenvironments to which is added the need to minimizedisturbances to the measured parameters. In this en-vironment, the only way that instrumentation can re-ceive appropriate emphasis, visibility, and resources isfor it to be recognized as the unique discipline that ittruly is.

•Measurement technology development must pro-ceed in parallel with other disciplinary devel-opment to assure testability of technology testarticles. When validating the performance of test articles, thelack of critical measurement capability can precludethe ability to conduct meaningful tests. In spite of thesoft requirements definition, it is possible to identifyand mature measurement concepts early on and waitfor specific measurement applications to be done whenthe design is mature. Running fast is good, but startingearly is better.

•Sensitivity and uncertainty analyses are requiredto validate requirements.Program requirements must be validated using crit-ical sensitivity and uncertainty analyses. Otherwisevaluable resources may be expended in the develop-ment of measurement capability that does not addressreal program needs.

Development Progress

Despite the limited funding, some importantprogress has been made in addressing NASP measure-ment deficiencies. The following table summarizes thework accomplished during the current phase, and isorganized by parameter development area.Further Work

Despite this progress, much development remainsto be done. A particularly pressing need is in thearea of off-surface, nonintrusive measurements. High-temperature strain measurement is another area inneed of improved measurement capability. Proof-of-concept development must advance in parallel withother disciplinary technology to assure that meaningfultesting can be accomplished.

Lessons Learned

This section highlights several important lessons gar-nered from the NASP program regarding the under-standing of measurement requirements and the devel-opment of instrumentation.

•Instrumentation must be treated as a discipline fortechnology development programs organized on adisciplinary basis.

Concluding Remarks

Instrumentation technology must be advancedon a broad front to meet the demanding re-quirements of the National Aero-Space Plane pro-gram. Further development work is needed to mea-sure performance of critical propulsion and struc-tural systems to the accuracy required for success-ful development of an airbreathing single-stage-to-orbit vehicle. Important breakthroughs have beenachieved in many disciplinary areas, however, similar

9

advances have not occurred in instrumentation tech-nology. All research programs begin and end withdata, and the quality of the data is constrained by thestate of the art in measurement and instrumentationtechnology.References1 Stein, Peter, “Measurement Engineering, Vol. I:Basic Principles,” Fifth Edition, Imperial Litho,Phoenix AZ, 19.TableDevelopmentareasStrainObjectivesDevelop PdCr and FeCrAl resistance gauges for operation to 1500 °F and characterize behavior on NASA materials.Develop fiber optics measurement approach-es using sapphire fibers.Characterize performance of fiber optic dis-tributed temperature measurement system at 1000 °F.Develop techniques for attaching optical fibers to NASP materials and structures.Demonstrate techniques for fiber optic tem-perature measurement at 2000 °F.Develop fiber optic dual temperature meas-urement approach for cooled panel structures.Develop thin film differential thermopile and apply to NASP material.Develop and evaluate 2-D inverse thermal analysis tools for application to NASP structures and materials.Validate parameter estimation codes for determining thermal properties of NASP materials.Develop 2000 °F fiber optic microphone with frequency response up to 100kHz and dynamic range of 130–190 dB.Develop a pneumatic line analysis and com-pensation tool for analyzing small diam-eter pressure lines with high-temperature gradients.Develop multicomponent nonintrusive meas-urement system for application to high-enthalpy combustor testing in im-pulse facilities.–planar LIF of OH–double pulse and double plate holo-graphic interferometry–high-speed schlierenAccomplishmentsSuccessful compensation of FeCrAl and PdCr gauges has reduced apparent strain by an order of magnitude.Work just initiated.Identified and solved optical fiber/measure-ment system compatibility problems.Identified preferred techniques for attaching optical fibers to TMC and superalloy materials.Work terminated.Sensor fabricated and characterized.Installation techniques evaluated.Ready to install and test.Prototype devices calibrated and tested on ceramics and metals. Starting trials on NASP materials.Code used to analyze sensor installation approaches for cooled panels. Performance of embedded T/C approach quantified.Work just initiated.1000 °F sensors fabricated and in test.2000 °F sensor fabricated, testing to begin soon. Model evaluated using low-temperature data shows good agreement. High-temperature test facility under development.System fabricated and tested in Cal Tech T-5 facility as part of high-speed com-bustor test.System undergoing modification to upgrade PLIF cameras, improve ability to quantify OH, and improve schlieren camera.TemperatureHeat fluxPressure/microphoneGasdiagnosticsystemdevelopment10

Table Concluded.DevelopmentareasGasdiagnosticsystemdevelopmentObjectivesApply diagnostics to NASP combustor tests.–OH PLIF–O2 PLIF–O2 LOS absorptionApply diagnostics to NASP aerodynamic tests.–Raman in Mach 6 tunnel–Rayleigh in Mach 6 tunnelDevelop resonant holographic interferom-etry for OH including laser source and recording techniques.Develop low attenuation 2000 °F silica fiber. Develop low-loss sapphire fiber for use in microphone and temperature sensing.Develop low-loss sapphire silica splice.AccomplishmentsSuccessful measurements within shock layer of NASP model.Feasibility demonstrated in lab with CW tunable lasers.Evaluation of pulsed laser source underway.Ni/Cr/Pt coated silica fiber fabricated and tested-identified problem with coating integ-rity. Modifying coating process.Low-loss sapphire (2, –4, dB/m) fabricated using laser heated pedestal growth.Low-loss splice (1.4 dB) fabricated using alum-inosilicate glass jumper.Floating element sensors fabricated and test-ed in Mach 2 and 3 combustor flows with heat fluxes to 400 BTU/ft2-sec.Thermal diffusivity, magneto-optical imag-ing and shearography techniques have been evaluated for NASP materials and structures.ResonantholographyHigh-tempopticalfiberSkinDevelop sensors for operation in high heat flux combustor tests.Develop and evaluate advanced NDE tech-niques for analyzing NASP materials and structures.Nondestructmethods920703

Fig. 1 Dimensions of instrumentation requirements.

11

Fig. 2 Technology capability.

Fig. 3 Making a measurement.

12

Fig. 4 Strain transducer responses.

Fig. 5 Temperature effects on strain gauge performance.

13

X-15MaterialsStructural conceptsThermal control conceptsAirframe conceptsEngine conceptsFlight control conceptsSubsystemsInstrumentationAnalytical toolsTestingXXXXXXAssetXXXXXXXShuttleXXXXXXXNASPXXXXXXXXXX920708Fig. 6 Parallel technology development.Ground testsensorsShort life (1 hr)Large, heavyAllow complexBroad funding baseRepairable/replaceableHigh performanceCan isolate effectsFlight testsensorsLong life (100 hr)Small, light, low powerDesire simpleNarrow funding baseNonrepairableLower performance?Must treat combined effectsRequirements are broad enough that one solutionwill not solve both problems920709Fig. 7 Typical ground v. flight requirements.14

Fig. 8 Scope of the typical measurement problem.Fig. 9 Typical actively cooled panel configurations.15

LocationActively cooled panelsEngineAirframeLeading edgesEngineAirframePassively cooled panelsCarbon/carbonMetal matrix compositeCryogenic tankageTemperature,°F–200/1,800–200/1,200–200/2,000–200/1,2001,800/3,0000/1,800–430/150Heat flux,BTU/ft2-sec2,00030010,000/50,0002,00060151dT/dt,F/sec1,0001,0001,0001,000250100500Acoustic,dB200190190170190180150Vibration,g50035020035030030030920712Fig. 10 Extreme measurement environments.- 14% increase in combustion efficiency- 11% decrease in combustion efficiency7060504030Parameters evaluated atcombustor exit planeMeasurandsindicative ofcombustionchange fromnominal value(%)20–20–30–40–50–60–70hcH2OH2OmassLOSflownumberdensitypeakOHQ dotOHLOSavgnumbernumberdensitydensitypavgO2massflow920713Fig. 11 Combustor parameter sensitivity.16

MeasurandsAirdataAltitudeCatalycityDeflectionDensity profileFlow velocitySlush hydrogenHeat fluxControl positionPressureSurfaceFree streamShock positionSpecies profileStrainStructural integrityMeasurands (cont.)TemperatureSurface (skin)StructuralFlowTransition/skin frictionVibrationTechnologiesFluorescence flow measurementMaterial propertiesNondestructive evaluationOptical sensorsMeasurement standardsHigh-temperature wiringRecommended investment $33.6 M920714Fig. 12 Instrumentation task force measurement priorities.X-30 Heat Flux Measurement RequirementFunctionNo.LocationPurposeControl/safetyDesignvalidationResearchPerformance RequirementsNo.PurposeAccuracyFrequencyTimeconstantOthersNotes/specialconsiderationsEnvironmental RequirementsNo.TempPressOperatingVibAcousticShockTempNonoperatingPressVibAcousticShock920715Fig. 13 Application requirement detail for NASP heat flux measurement.17

X-30 Heat Flux Measurement RequirementsLocationA/C areas LEInletNozzleAcreageC-CMetal matrixControl surfacesInlet rampEngine cowlNozzleChineInternal structureWing boxLanding gearPrimary structureOtherCombustorCryo tanksCryo linesMisc engine4,105PurposeRI4,6,7,84,6,104,7,8,96,7,86,7,87,86,7,8,9,107,8,97,8,9,10311332211No of contractor requestsMD22111222GD111RD111111111PW1117655525TotalCode456710PurposeCoolant controlPropelant boiloff &insulationValidate CFDValidate aeroheatingmethodsDefine boundary layertransitionObtain aerodynamicand plume heatingEngine performance71111121020716Fig. 14 Application requirement detail for a NASP heat flux measurement.Strain•Develop Pd-13 Cr foil gauge•Prepare user guide for favorable available gaugesTemperature & heat flux•Define concept for wide field optical hybrid IR/thermographic phosphor system (T&q)•Demonstrate granted fiber optic distributed temperature sensor (T)•Demonstrate dual phosphor typed fiber optic point sensor (T&q)Pressure•Develop high-frequency/high-temperature surface mounted fiber optic sensor•Perform calculation to establish feasibility of standoff transducersAcceleration•Demonstrate fiber optic based accelerometer020717Fig. 15 Consortium development recommendations for contractor activity in phase 2D.18

Instrumentation andTask Forceairdata consortiaPhase 2DStrainHeat fluxStrainStrainGas diagnosticsDeflectionGas diagnosticsGas DiagnosticsAirdataMass flowAirdataSurface pressureSlush H2 gaugingSkin frictionSurface pressureSurface temperatureSurface pressureCatalycityTemperatureHeat fluxShock positionStructural integrityControl positionSurface temperatureTransitionAccelerationAcoustic noiseControl positionAcoustic noiseHeat fluxSkin frictionStructural temperatureH2 leaksMass flowStructural integrityAccelerationAcoustic noiseHydrogen leaks18 Measurement11 Measurement8 MeasurementareasareasareasGround and flightFlightGround and flightfocusfocusFig. 16 Decreasing scope of NASP instrumentation development.19

920718REPORT DOCUMENTATION PAGEForm ApprovedOMB No. 0704-0188Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering andmaintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information,including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington,VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.1. AGENCY USE ONLY (Leave blank)2. REPORT DATE3. REPORT TYPE AND DATES COVEREDMay 19934. TITLE AND SUBTITLENASA TM5. FUNDING NUMBERSPerspective on the National Aero-Space Plane Program Instrumentation Development6. AUTHOR(S)763-21-41 RXRodney K. Bogue and Peter Erbland7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)8. PERFORMING ORGANIZATION REPORT NUMBERNASA Dryden Flight Research FacilityP.O. Box 273Edwards, California 93523-02739. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)H-191610. SPONSORING/MONITORING AGENCY REPORT NUMBERNational Aeronautics and Space AdministrationWashington, DC 206-000111. SUPPLEMENTARY NOTESNASA TM-4505Prepared as AIAA paper at the Aero Space Planes Conference, Orlando, FL, Dec. 1–3, 1992.12a. DISTRIBUTION/AVAILABILITY STATEMENT12b. DISTRIBUTION CODEUnclassified—UnlimitedSubject Category 0613. ABSTRACT (Maximum 200 words)This paper presents a review of the requirement for, and development of, advanced measurement technologyfor the National Aero-Space Plane program. The objective is to discuss the technical need and the programcommitment required to ensure that adequate and timely measurement capabilities are provided for ground andflight testing in the NASP program. The paper presents the scope of the measurement problem, describes themeasurement process, examines how instrumentation technology development has been affected by NASPprogram evolution, discusses the national effort to define measurement requirements and assess the adequacy ofcurrent technology to support the NASP program and summarizes the measurement requirements. The uniquefeatures of the NASP program that complicate the understanding of requirements and the development of viablesolutions are illustrated.14. SUBJECT TERMS15. NUMBER OF PAGESAircraft Combustion; Heat transfer; High temperature instrumentation; Laser-induced fluorescence; National Aero-Space Plan; Scramjet; Strain17. SECURITY CLASSIFICATION OF REPORT18. SECURITY CLASSIFICATION OF THIS PAGE19. SECURITY CLASSIFICATION OF ABSTRACT1916. PRICE CODEAO320. LIMITATION OF ABSTRACTUnclassifiedNSN 70-01-280-5500UnclassifiedUnclassifiedUnlimitedStandard Form 298 (Rev. 2-)Prescribed by ANSI Std. Z39-18298-102Available from the NASA Center for AeroSpace Information, 800 Elkridge Landing Road, Linthicum Heights, MD 21090; (301)621-0390