High-Speed/Hypersonic Test and Evaluation … of Ground Test Working...High-Speed/Hypersonic Test...

American Institute of Aeronautics and Astronautics

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High-Speed/Hypersonic Test and Evaluation Infrastructure Capabilities Study*

Thomas Fetterhoff† Dr. Edward Kraft‡

Dr. Marion L. Laster§ Arnold Engineering Development Center

Arnold AFB, TN 37389

and

William Cookson Office of the Secretary of Defense, ATL-TRMC

The United States Department of Defense (DoD) has designated Hypersonics a transformational technology. This study is focused on the systems development test and evaluation (T&E) of air-breathing high-speed and hypersonic (HS/H) war fighting capabilities. The study includes consideration of T&E capability requirements for modeling and simulation (M&S), ground test, and flight test and addresses potential T&E science and technologies required to support future T&E requirements. The study also focuses on defining the HS/H weapon systems development capability requirements, where air-breathing propulsion is employed, necessary over the next 15 years to successfully develop and sustain weapon system and access to space capabilities currently emerging from HS/H technologies. In 2004 the National Aerospace Initiative (NAI) refocused Service and DARPA HS/H Science and Technology (S&T) spending to mature HS/H expendable and reusable weapons and space technologies at targeted “off-ramps” in 2010, 2015, and 2020. There is enough confidence in the potential of HS/H technology that mission applications ascribed to the NAI HS/H technologies clearly indicate HS/H weapon systems are emerging as viable and attractive solutions to a number of DoD capability requirements. The U. S. Office of the Secretary of Defense, Director of Operational Test and Evaluation (OSD, DOT&E), directed that a study be performed (1) to reexamine the ability of existing DoD and NASA infrastructure to support required engineering and systems development of HS/H technologies into weapon systems and (2) to produce an HS/H T&E capability requirements roadmap to guide investments in M&S, ground-test, and flight-test capabilities and related facilities studies/research needed. Not surprisingly, this study has reaffirmed the conclusions of scientists and engineers in numerous previous studies. The current U. S. national Research Development Test and Evaluation (RDT&E) infrastructure is inadequate to effectively and efficiently transform most emerging HS/H technologies into military flight systems capabilities. The modeling and simulation, ground, and flight evaluation infrastructure must be upgraded so that the products of S&T can be applied to the development of advanced weapon systems.

* The research reported herein was performed by the Arnold Engineering Development Center (AEDC), Air Force Materiel Command. Work and analysis for this research were performed by personnel of Aerospace Testing Alliance, the operations, maintenance, information management, and support contractor for AEDC. Further reproduction is authorized to satisfy needs of the U. S. Government. This paper is declared a work of the U.S. Government and not subject to copyright protection in the United States. † Chief, AEDC/XRS, Associate Fellow ‡ Chief Technologists, AEDC/CZ, Fellow § Consultant, ATA, Associate Fellow

14th AIAA/AHI Space Planes and Hypersonic Systems and Technologies Conference AIAA 2006-8043

This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

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Nomenclature CFD = Computational Fluid Dynamics DoD = Department of Defense HCM = Hypersonic Cruise Missile HS/H = High Speed/Hypersonic M&S = Modeling and Simulation NAI = National Aerospace Initiative OT&E = Operational Test & Evaluation RDT&E = Research Development Test & Evaluation S&T = Science and Technology SCM = Supersonic Cruise Missile T&E = Test and Evaluation

I. Introduction Hypersonics is one of the transformational technologies identified by the U. S. Department of Defense (DoD),

National Aerospace Initiative (NAI), a DoD planning activity that has established a technology roadmap designed to mature hypersonic technologies. The new class of high-speed/hypersonic (HS/H) weapon system capabilities will require the use of air-breathing hypersonic flight systems that operate largely within the earth’s atmosphere, in contrast to high-speed systems such as the Space Shuttle and re-entry vehicles that transit through the atmosphere, using rockets for launch and unpowered reentry. HS/H air-breathing weapon systems will typically fly an entire mission at altitudes between 15 to 50 km over extended ranges. Developing and operating highly integrated HS/H air-breathing systems for these flight regimes presents numerous technical challenges with respect to integrated aeropropulsion systems, materials, thermal protection, hot structures, flight control systems, and total aerodynamic systems integration.

Risk reduction in the development and acquisition of advanced air-breathing HS/H systems will require appropriate and timely application of modeling and simulation (M&S), ground test, and flight test. Failure to achieve the appropriate balance between these disciplines usually generates increased program cost and risk. The challenge for developing an integrated roadmap for HS/H engineering development and test and evaluation (T&E) capability requirements is to identify the capability requirements for each discipline – M&S, ground test, and flight test – and then leverage the individual capabilities to provide a comprehensive, but cost-effective, approach.

The challenges for applying M&S to hypersonic flight conditions encompass deficiencies in modeling turbulence, flow separation, aerothermochemistry, plasma interactions, and conjugate heat transfer. These deficiencies are intensified by a lack of sufficiently detailed measurements at hypersonic conditions to permit either improved fidelity in the models themselves or validation of the models. This lack of needed data is largely the result of shortcomings in existing test facilities and partly a result of the lack of a comprehensive approach to capturing needed validation data.

The flight condition simulation capabilities required for the transformational HS/H systems envisioned far exceed current ground-test capabilities with respect to: – Sufficient run times to achieve necessary thermal equilibrium conditions – Sufficiently high enthalpy conditions to properly simulate propulsion and/or heat-transfer phenomena – Flow medium and flow quality to provide a sufficiently accurate simulation for scale-to-flight conditions – Test facilities with sufficient scale to simulate a fully integrated airframe/propulsion system

In some cases, new technologies must be pursued to develop the advanced ground-test capabilities and testing methodologies required by the next generation of HS/H systems.

Flight testing of HS/H air vehicles, especially those which fly at Mach 4 and above, presents many new challenges. Flight-test resources have not kept pace with science and technology (S&T) research. The high-speed capability of these new classes of vehicles expands inland tracking capability and flight safety decisions in the areas of range control, airspace jurisdiction limits, and overall range safety. Offshore range improvements are also required to support successful hypersonic flight testing. Such shortfalls in the overall HS/H Research Development Test and Evaluation (RDT&E) capability of the U. S. are addressed in this report.

This initial study is focused on the requirements for engineering development and T&E of air breathing HS/H for military flight system capabilities. Subsequent studies will encompass operational T&E and interoperability issues. The study includes consideration of T&E capability requirements for M&S, ground test, and flight test, and defines potential T&E science and technologies required to support future T&E requirements. The study is also focused on

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defining the engineering development T&E capability requirements necessary over the next two decades to successfully develop and sustain weapon system capabilities currently emerging from HS/H technologies.

The lead time for development and acquisition of the T&E capabilities needed to support HS/H weapons development is as long or longer than for the HS/H technologies themselves. With the advent of hypersonics as a nationally mandated transformational program, the U. S. once again finds itself inside the lead time necessary for a number of the solution sets required. This will likely result in T&E capabilities funding requirements out to FY 2020 and beyond. Moreover, because of the dynamic nature of HS/H technological pursuits, the T&E solutions will need to evolve and be updated and revised with the progress of the HS/H technology developments.

II. History

A. Hypersonic Science and Technology Programs The U. S. has made several attempts over the past four decades to develop hypersonic technologies that would

permit sustained atmospheric flight. One measure of success has been in the identification of the technological challenges that must be overcome before such vehicles can be successfully developed. Few of the enabling technology gaps have been closed by past hypersonic programs, particularly for air-breathing propulsion systems.

Figure 1 depicts some of these HS/H “X-vehicle” programs. Note the periodic interest (and funding) for hypersonic S&T, as well as a seemingly reduced emphasis over time. The U. S. fielded major S&T programs in the 1960s, including the Aerospace Plane and DYNASOAR. Technology programs included innovative concepts such as a hypersonic air-breathing engine that would cruise in the earth’s atmosphere while gathering and condensing excess oxidizer to be used for rocket propulsion at higher altitudes. In the late 1970s, there were the X-24C and National Hypersonic Flight Research Facility (NHFRF) programs. Some of the more optimistic and highly advertised programs began in the 1980s, including the U. S. National Aerospace Plane (NASP), British HOTOL, and German Sanger II, as well as initiatives by the U.S.S.R. and Japan. Australia’s HyShot program was initiated in the 1990s and flew in 2001 and 2002. Many of these programs were directed primarily toward more economical space travel, with both single- and two-stage-to-orbit applications. However, some saw the potential for rapid passenger travel between cities (including President Reagan’s “Orient Express”). Figure 1 also shows that many of the early X-vehicles were rocket-propelled. Although the X7 successfully demonstrated a ramjet powered system, rocket-based systems were much easier to build and test than the fully-integrated, air-breathing systems required for future HS/H weapon system capabilities. Hence, T&E testing of the next generation of vehicles will be significantly more challenging than the T&E testing of the early X-vehicles.

In the late 1980s and early 1990s, the U. S. invested significant resources (~$3 billion) into the development of the National Aerospace Plane (NASP) (Ref. 1) – the first fully integrated, scramjet-driven flight system development. Although many advances in M&S as well as material development resulted from the NASP program, no flight vehicle was ever built. One of the major reasons for the demise of the ambitious NASP program, as stated by the Scientific Advisory Board (Ref. 2) in a postmortem analysis, was a lack of ground-test facilities to develop the needed system capabilities. This error will potentially be repeated if appropriate investments in RDT&E infrastructure to support future HS/H weapon system developments are not made.

The X-43A program (Ref. 3) took a more structured and modest approach to the flight demonstration of an integrated scramjet powered vehicle. The X-43A was designed from the beginning to perform within the current RDT&E ground-test infrastructure test capabilities, and a systematic validation of the design tools was performed at each step of the demonstration vehicle development. The X-43A vehicle was conservatively designed to lower the risk of the technology flight demonstration, and thus was not designed to provide the type of information useful to

Figure 1. High Speed/Hypersonic X-Vehicles.

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the development and acquisition of a scramjet powered weapon system. After a failure of the booster system on the first attempt, flight tests were successfully conducted at Mach 6 and 9 demonstrating hydrogen/air combustion and system performance..

Outside the U. S., at least seven countries have been or are currently engaged in the development of hypersonic technologies. These include Britain’s HOTOL, Germany’s Sanger, India’s Hyperplane, Japan’s HOPE, France’s Hermes, Australia’s HyShot, and the Buran of the former Soviet Union. Some of these are discussed in Ref. 4. There is no evidence that any of these programs have resulted in breakthrough technologies, and it is noted that many have been put on indefinite hold or cancelled as of this writing. The Australian HyShot scramjet successfully demonstrated hydrogen/air combustion at Mach 7.8 in 2002. It is interesting to note that in the early 1990s, there was a push in both Europe and Japan to upgrade old or build new ground-test facilities that would provide them the independent capability to develop the necessary technologies and flight systems (Ref. 5).

B. Hypersonic Testing Resources Numerous U. S. government studies over the past four decades specifically point out the requirement for

improved hypersonic T&E capabilities and the need for research to support development of some hypersonic facilities and the associated instrumentation. Many of these studies have been conducted by the country’s most prestigious scientific organizations (e.g., Defense Science Board, National Research Council, Air Force Scientific Advisory Board). Some were directed by Congress, demonstrating their understanding that problems exist. Others have been sponsored by the tri-Services, DoD, or NASA and have included membership of the nation’s top experts from industry and government. The findings of these studies are consistent with those of other, similar studies conducted over the last 40 years. During these four decades, the lack of investment in hypersonic test technologies and facilities has prevented the testing community from keeping pace with the testing needs of hypersonic S&T programs and projected system applications.

Significant ground-based test facilities may take five to ten years or more to design and build. Some of the desired test facilities must themselves be supported by research to investigate new approaches for energy addition and materials/cooling techniques to permit containment of the required high-pressure, high-temperature test gases. Computational Fluid Dynamics (CFD) and flight testing are essential design and testing techniques, and they are complemented by ground-test facilities. However, computational methods to develop and verify codes are limited by lack of experimental data, and flight testing alone of experimental hypersonic aircraft returns only small quantities of very expensive data relative to what could be obtained if needed test facilities were available. Computational methods and flight testing must be present in any successful development program, but the lack of adequate ground-testing capability has severely handicapped hypersonic programs in the past and will continue to do so until the needed test resources are made available.

The hypersonic programs of the 1960s and early 1970s sponsored the nation’s most dedicated and well-funded hypersonic test facility development programs. Many facility technology advancements resulted from research, and several prototype test facilities were built and operated. If some of these more promising test capability concepts had been carried to completion, the hypersonic programs of the past few decades would have likely experienced a more successful outcome. Instead, few of the capabilities funded were completed or exist today.

Reasonably good hypersonic perfect gas aerodynamic wind tunnels exist today, but none simulate the real-gas and aerothermal effects encountered in flight at Mach numbers above 8. Aerothermal test capability is currently limited to perfect gas wind tunnels and nonequilibrium flow shock tunnels capable of gathering heat-transfer data. Small electric arc tunnels and vitiated air test mediums exist and can be used to conduct material testing of relatively small samples. The primary aeropropulsion hypersonic ground-test facilities available in the U. S. today consist of impulse facilities providing milliseconds of test time, blowdown vitiated facilities providing seconds to minutes of test time (but without a clean-air test medium), small research facilities with clean air, and small electric arc tunnels. None of these facilities are adequate for developing hypersonic weapon systems employing air-breathing propulsion. Also, there is not a capability to propulsion mode transition testing at supersonic and hypersonic Mach numbers.

III. Organization of the Study

A. Study Team Participants The study team participants represented a national cross section of experts in flight testing, ground testing,

modeling and simulation, science and technology development, and systems development from the Army, Navy, Air Force, DoD, Department of Energy, NASA, and independent consultants numbering about 30 people in all.

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B. Flight Systems – Requirements Basis for the Study Test capability technical needs and timing have been focused on potential flight systems that may result from the

S&T technologies being pursued by the NAI program plan (Refs. 6 and 7). Figure 2 lists seven HS/H vehicles representative of the technologies being pursued under the NAI roadmap. The time frames for maturing these vision concepts are also indicated. These seven vision vehicles are the basis for the test scenarios used in this study to determine RDT&E capability requirements.

Near Term Mid Term Far Term

Attributes

SCM HCM HS Aircraft Interceptor HS Aircraft HS Aircraft Space Access

Mach No 3-5 4-8 2-4 8-12 3-6 4-7 7-15 Range

(Nautical Miles)

400-700 1000 2300 1500 5000 12000 LEO

Payload 250-500 250-1000 10% Mass Fraction 2000

3% Payload Fraction

10% Mass Fraction

3000 25000 40000

Size L 168 in. D<24 in.

L 168 to 250 in. D<24 in.

L 100 to 150 ft.

? < L ~ 100 to 120 ft.> ?

L 100 to 150 ft. L ~150 ft. ? < L 150

to 200 ft.

Propulsion System

Turbine + (Ram) Fuel: JP-7/8/10

Boost to Ram / Scram, Fuel: JP-7/8/10

Turbine, Large D. (48 in.) Fuel: JP-7/8/10

Boost to Scram, Slush H2

Turbine + Ram / Scram, JP-7/8/10

Turbine + Ram / Scram, JP-7/8/10

AB: M 0 to Scram, or Boost to Scram, Slush H2

Figure 2. NAI Program Seven Visionary Systems.

The major attributes for each of these vehicles are listed in this figure. From left to right the near-term visionary systems are a Supersonic Cruise Missile (SMT), a Hypersonic Cruise Missile (HCM), and a High-Speed (HS) Aircraft. The mid-term visionary systems are a Mach 8 to 12 Hypersonic Interceptor/Attack missile and a Mach 3 to 6 High-Speed Aircraft. The far-term visionary systems are a Mach 4 to 7 High-Speed Aircraft and a Space Access vehicle.

IV. Approach Based on a number of HS/H S&T programs underway across the services as well as the NAI roadmap for HS/H

technology development, a set of seven vehicles, noted above in Section III.B, provide the basis for developing test scenarios. Scenarios for the developmental use of M&S, ground test, and flight test were established for each vehicle to assess the current capability versus future capability requirements. The study team analyzed these scenarios to determine gaps in needed T&E capability. The approach to establishing a national T&E capability in hypersonics was based on three concurrent steps:

1. Utilize Current Capabilities – Considering that some capabilities have evolved from other requirements and could be applied to support high-speed and hypersonic systems development, and because of some limited past investments to support hypersonic-specific T&E needs, some basic capabilities exist. Existing M&S, ground-test facilities, and flight-test ranges will be used, as long as they continue to be available, within the range of their limitations in the early stages of hypersonic development until other, more advanced, capabilities can be acquired.

2. Upgrade Current Capabilities Where the Technology is Available – Based on previous studies and technology developments, some knowledge exists to develop many of the needed capabilities to support hypersonic development. A systematic plan is required for those acquisitions, most of which are upgrades to existing capabilities, and funding must be acquired before any additional development can proceed. This approach is currently underway in a number of cases, helping to overcome recognized T&E gaps, and will provide the means to begin early development of several hypersonic systems.

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3. Invest in Test Capability Technology to Meet Weapon Systems Requirements – Some advanced test capability technology will ultimately be required to develop needed systems. This last, and most critical, step must begin now in order to respond to several of the NAI off-ramps and the NAI roadmap. In many cases, the technologies will need to be developed before the facilities can be built or M&S tools can be applied. The task is to identify such critical needs early and establish a path that will provide the capabilities when they are required.

The team formulated a comprehensive set of engineering development and T&E capability requirements to support the vision vehicles and technology off-ramps and then compared these requirements with available capabilities. Where deficiencies were found, a concise set of capability gaps and suggested solutions were defined.

V. Test and Evaluation Required to Develop and Deploy Hypersonic Systems Risk reduction in systems development is ideally achieved by the appropriate and timely application of each of

three complementary disciplines: modeling and simulation (M&S), ground test, and flight test. Without the appropriate T&E resources to develop system design data, system technology is compromised, and the costs of alternative approaches for design information can be prohibitive.

A. Integrated Test and Evaluation The concept of Integrated T&E (IT&E) used in this paper is a “system of systems” viewpoint directed at

providing the best value-added T&E support to the development and acquisition of aerospace systems. IT&E is a virtual integration of the major T&E processes and participants, keeping in mind the total system as opposed to individual T&E tasks. IT&E is a three-fold approach to streamline the weapon system acquisition process by integrating M&S, ground test, and flight test.

Application of IT&E to HS/H systems takes on even more importance because of the limitation each of the simulation methodologies has at the high-enthalpy, high-pressure conditions of hypersonic flight. None of the simulation methodologies alone will be able to overcome the challenges, so innovative approaches on integrating M&S, ground test, and flight test will be required. One of the key factors required for integrating M&S and testing are measurement capabilities, either in ground-test facilities or on flight vehicles. Ensuring the availability of appropriate instrumentation for HS/H systems development is one of the key T&E technology requirements.

1. The Case for Modeling and Simulation M&S is used throughout the entire product development process from concept development to operational test

and evaluation (OT&E) of the final product. Ground-test facilities and flight-test ranges especially benefit from M&S. The application of M&S is critical for ground test because the development of a ground-test facility, its measurement systems, and the need to correct for nonsimilitude relative to flight is necessary for reducing the cycle time, risk, and cost of developing a hypersonic flight system. M&S is likewise critical to flight test for planning, mission synthesis, flight and range safety, and analysis. Analysis particularly benefits since measurement density is never enough to preclude the need for the use of computation to select and locate instrumentation and to determine global results from sparse measurements.

With respect to the development of hypersonic flight systems, M&S spans: – Concept development – Configuration design and optimization (systems and subsystems) – Prediction of ground-test results – Ground-test and flight-test design (test article, instrumentation suite, experiment optimization, corrections to

experiment for nonsimilitude) – Analysis and evaluation of ground-test results – Prediction of flight-test results – Prediction of material response to aerothermodynamic environment – Flight-test optimization (instrumentation suite, communications system, flight profile) – Flight and range safety monitoring – Analysis of flight-test results – Prediction of OT&E results (plasma effects on the reaction control system [RCS], exhaust signature,

performance, stability and control, structural and thermal loads) – Mission profile and optimization

As shown above, M&S is used to support every step of the developmental test process. It is obvious that the better the M&S capability, the greater the potential for application. Whether a particular M&S capability is employed to best use will depend on the economics of the application and the opinion of the user as to how much

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reliance one can place on the results. The former speaks to the ease of application and the cost and speed at which the desired result can be obtained in comparison to the alternative. The reliance is clearly affected by the certification or validation of the M&S method, but it also depends on the user’s overall risk assessment.

Figure 3 (taken from Ref. 8) is a diagram of the M&S cycle applied to the development of a propulsion system concept. As flight Mach number increases and ground-test facility capabilities to accurately simulate actual flight conditions for long test durations become limited, CFD necessarily plays a larger role. Any lack of environmental simulation will result in data adjustment using CFD methods. Thus, it is most important to acquire validated analysis programs that can reliably support ground and flight testing for high Mach number vehicles.

Figure 3. M&S Notional Process for Propulsion System Design (Ref 8).

It takes exceptional computer performance to provide needed computational results in a timely manner. Codes must also be structured to take advantage of computational power. Depending on the problem, various codes and models are employed to provide needed simulations with adequate physics being modeled. When it is not possible to provide adequate computing power, compromises in the physics of the simulation may be made to achieve an answer in a timely manner. However, the ensuing answers become increasingly flawed as departure from the true physics of the situation increases.

2. The Case for Ground Test Ground-test facilities have been an essential component of flight system development since (and including) the

Wright brothers. Facilities that simulate the flight environment are used to evaluate performance, operability, durability, and component integration, thus providing a matrix of data that is used to design the initial flight system. Throughout the world, aviation and space vehicle developments have been paced by the availability of good ground-test facilities.

Historically, a new subsonic aircraft development program might include up to 20,000 hr of testing with scaled aircraft models in wind tunnels. A new turbojet engine will likely endure 10,000 hr of development testing in ground-test facilities, of which more than 1,000 hr will be at simulated flight conditions. Those aerodynamic and propulsion development programs do not involve new technologies, but refinement of proven technologies.

Ideally, hypersonic systems would be developed with the same testing rationale as today’s supersonic systems (e.g., development of systems technologies and major components in ground-test facilities that closely simulate actual flight conditions, with adequate testing time to evaluate performance, durability, operability, and component integration prior to flight). However, the higher the system performance Mach number, the larger the gap in the ability to test the system using today’s facilities. For the higher Mach numbers, it will likely be technically

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impossible to design and build ground-test facilities that will concurrently provide both adequate simulation of flight conditions and extended run time. Thus, it is clear that complementary ground-test facilities (none which fully satisfy simulation requirements) must be available to provide the total data set needed to produce system design and to reduce system risk. Consequently, M&S and flight testing assume an even more demanding role.

3. The Case for Flight Testing After more than four decades of investment in hypersonic flight programs, only recently have the technologies

matured sufficiently to permit development of a vehicle flight system, i.e., NASA’s X-43 program. NASA’s X-43 flight research program recently demonstrated successful free-flight of an airframe-integrated scramjet propulsion system at Mach 6.7 in March of 2004. This was followed by another successful free-flight and propulsion system operation at Mach 9.7 in November 2004. These research flights, though successful in proving scramjet operation at hypersonic speeds, have shown deficiencies in areas such as micro-instrumentation development and the difficulty in calibrating various instrumentation components to the vehicle’s operating speed. Over-water testing, with its deficiencies, was chosen to reduce cost and risk.

Future hypersonic vehicles must be flight tested to prove operational capability in “real world” flight environments. Although the goal of ground-test facilities is to duplicate flight environments as closely as possible, there have been no facilities developed, and none are expected to be developed, where the actual vehicle can be tested on the ground and still fully duplicate flight conditions.

Usually, unanticipated issues or deficiencies are encountered that must be fixed during the course of flight testing. Progressive design improvements usually have to be made. These improvements are identified during a buildup test approach where the least critical stressing flight conditions are first administered to the vehicle. Incremental increases in stressing conditions, such as higher Mach number and higher temperatures, are subsequently applied to the vehicle until the final design conditions have been demonstrated. This approach allows the flight-test engineers to define potential problem areas needing attention before a catastrophic failure can occur. The better the fidelity of ground-test facilities and their ability to adequately characterize vehicle development, the fewer development issues are found in flight. However, even the best ground facilities cannot fully duplicate a “real world” flight environment.

Hypersonic systems may well require a different approach to be examined for vehicles covering long distances at the fringes of the atmosphere. Issues of vehicle control, telemetry, position, and flight termination systems will need to be addressed. Some advanced hypersonic systems may require incremental improvements to existing test resources and methods, while other test scenarios may require major improvements to existing capability. Advanced hypersonic systems – well beyond the scope of current systems in complexity and capability – might likely require T&E resources that simply do not exist and may not be clearly identified at this time. Flight test needs to address several sets of initial objectives. The benefits of new research and development capability will be to advance operability (rapid turn times between launches, and thus reduced cost) for military (hypersonic strike), other government (space access), and commercial access to space.

Current technology involves extensive infrastructure that is not effectively integrated. This infrastructure typically consists of control systems, test and checkout equipment, mission planning systems, and flight safety planning and operations. Improved monitoring capability is needed. Sensors are a critical component not only for assessing health and status, but also for understanding a vehicle’s performance characteristics. Several drawbacks exist in today’s sensor systems. First, they are generally intrusive. Second, they are less reliable than the hardware that is being monitored. Third, most need manual calibration. Fourth, they are unable to detect when the output is degraded or has failed. Finally, they cannot detect off-nominal readings caused by the effects of failures in other parts of the system.

VI. Assessment of T&E Capability Requirements The NAI off-ramp vehicle concepts were adopted to develop scenarios against which T&E capabilities could be

evaluated. Gaps between current capabilities and required capabilities were the basis for determining a HS/H T&E capability requirements roadmap. The seven off-ramp vehicles that may evolve from NAI S&T are described in limited detail.

A. Vehicle Attributes Used for T&E Scenario Development The vehicle descriptions of the seven off-ramp technology vehicles are given in Fig. 2 of Section III.A. Included

in Fig. 2 is a list of the attributes that pertain to Mach number range, payload, size, and three types of propulsion systems, with a wide range in performance, vehicle size, and mission. There are three missile or interceptor systems

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ranging in speed from Mach 3 to 12 and three aircraft systems (probably manned, but future development in autonomous technology and communications could result in unmanned systems) that range in speed from Mach 2 to 7. The final vehicle supports space access, although the NAI only addresses an air-breathing carrier vehicle from Mach 7 to 15. The first stage might be either similar to the Mach 7 aircraft or rocket boosted. Rocket systems were not addressed in this study. For each concept vehicle, the team developed a detailed weapon system development scenario and assessed current capabilities versus needed capabilities for each vehicle.

B. HS/H T&E Requirements Assessment The insights gained from the assessment of the M&S and T&E scenarios for each of the study vehicles presented

in Section III.A were further processed to develop an integrated assessment of the key HS/H capability requirements. The HS/H capability requirements are summarized in this section.

1. T&E Requirements Summary A high-level notional assessment of the nation’s current integrated T&E capability to support HS/H weapon

system development is presented in Fig. 4. In this notional chart, color coding is used to provide a quick-look assessment of the ability of the T&E community to meet the required capabilities. Green indicates that the current T&E capability can adequately support the development and acquisition of the vehicle class of interest. Yellow indicates that some T&E capability exists, but some major facility capabilities are lacking, which can result in serious system design deficiencies. For example, an aeropropulsion test facility may exist that sufficiently covers the size, run time, Mach number, and altitude required for a selected vehicle propulsion system, but it may use a vitiated test medium. Since combustion can be very sensitive to the test medium gas properties, determination of the propulsion system performance to a sufficient confidence level required for flight can be significantly degraded.

Figure 4. Notional T&E Capability Requirements Summary.

Red indicates that no capability currently exists and that using an engineering work-around is done at great risk. Failure to develop the T&E capability will severely hamper the development of HS/H weapon systems in this class. In the chart, a color gradient within any box indicates one level of capability at the low end of the Mach number range for that scenario and a different level of capability at the upper end of the Mach number range. For example, for the Mach 2 to 4 High-Speed Aircraft, there is currently a comprehensive capability to test and develop a large turbine engine at Mach 2, but no capability exists above Mach 3.2. Hence, at the upper limit of Mach 4 there is no current capability. Since at Mach 4 the technical community would be pushing the limits of design and performance for a turbine engine, there would be significant risk in trying to extrapolate from Mach 3.2 to Mach 4 in terms of performance, durability, and operability.

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Not surprisingly, as Mach number increases, it becomes more challenging to provide the needed T&E capability. All three disciplines (M&S, ground test, and flight test) become stressed with increasing Mach number. M&S models lack sufficient detail of the physics of turbulence, flow separation, conjugate heat transfer, and aerothermochemistry at high Mach numbers. Coincidentally, the lack of physical understanding is exacerbated by the difficulty of providing good experimental data for model validation at the high Mach numbers. Ground-test facilities are challenged to produce and contain the tremendous flow energies associated with hypersonic flight. The pressures and temperatures required to duplicate these flight conditions challenge existing materials and restrict the amount of time such high-performance facilities can operate. Open-air ranges are challenged to provide a safe footprint for high-speed vehicles; track, measure, and record the vehicle performance; and provide a timely flight termination system.

An integrated T&E concept utilizes the most suitable combination of M&S, ground, and flight tests to accomplish the T&E mission. Their function is to reinforce each other so that their ultimate joint product fulfills its proper function in the development of a flight system. The high-level view of the M&S capability assessment is characterized as modeling maturity and as model validation. Even though a modeling capability might possess all of the desired attributes, unless it has been validated for the needed use, it is not likely to be of use. At the very high Mach numbers (e.g., Mach 10 to 15) a paradigm shift in development testing may occur. Since ground-test facilities cannot produce the desired flight simulations, they may concentrate more on producing information that validates M&S codes.

Clearly, it will require an integrated use of all three disciplines to develop the higher speed systems. Knowledge gained from the application of T&E capabilities to each vehicle will have to be leveraged and used to build confidence to move to the next higher Mach number vehicles. There will also be a requirement to introduce new T&E technologies and capabilities to address the higher Mach number systems. Fortunately, the most challenging flight systems are further in the future, thus providing some time to develop the T&E capability required. However, significant technology development is required, and the time required to develop such advanced capabilities requires the necessary investments to create these capabilities to commence in the very near future.

VII. Gap Descriptions

A. Modeling and Simulation Model Maturity – There is a range of opinions regarding model maturity among the candidate solution

assessments. The color coding in Fig. 4 represents the median view. Specific comments relating to aerodynamic and propulsion model maturity and related issues are enumerated in the following summary. 1. Aerodynamic/Aerothermodynamic Related – In lieu of faster and/or more computers working on a problem, it is customary to break the components of the

system level CFD models into smaller, processable elements to be “postintegrated” at a global level. This almost universally meets with the introduction of model-merging errors, and the correction time that is consequently introduced increases risk to accuracy and schedule. A “new” look at the aeroflow-field physics processing methods – or even the rudimentary programming language to make the models more readily processable – might be a good pursuit in the near term.

– Dynamic staging/store separation is done rather routinely using today’s technology. – Boundary-layer transition has a low probability of being accurately simulated within the next 20 years. 2. Propulsion Related – Modeling of the chemical kinetics of hydrogen is much more mature than for heavy hydrocarbons. – Operability is harder to model (and more of an issue) for dual-mode scramjets. – Assessing performance is more difficult as velocity increases because net thrust is the difference of two large

numbers. – Turbulence modeling, like operability, is more difficult (shock/boundary-layer interaction) and more important

for dual-mode scramjets. – Stealthy inlets cause distortion patterns that could easily reduce engine surge margin. Successful performance

calculations of these stealthy inlets are a validation issue and will need to be demonstrated on a regular basis and compared to experimental results.

– Inlet and propulsion systems will need to be finely tuned to operate as a system and not as individual components passing information back and forth at the aerodynamic interface plane (AIP). M&S will need to advance in the area of compression system modeling to the point where the inlet and compression system work in tandem so that aerodynamic information is correctly passed and the inlet-engine can be designed as a system rather than as individual pieces.

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– Any aircraft designed to fly above Mach 4 conditions will have to transition to some form of propulsion other than a gas turbine engine. Transition to a ramjet will require understanding the transition process, the aerodynamic distortion that may be produced, and the effect on the inlet. CFD codes need to simulate the transition process. Once the propulsion system has transitioned, the system will need to operate as a ramjet, and resultant combustion issues will likely become significant. A methodology will need to be developed to handle the transitory nature of transitioning from turbojet to ramjet.

– Conjugate heat-transfer modeling is required to simultaneously solve the flow path aerodynamic and coolant heat transfer instead of paring a three-dimensional (3D) flowfield solution down to one-dimensional (1D) or two-dimensional (2D) boundary conditions for thermal analysis.

– Transient modeling is required to provide time-accurate solutions to unsteady flow fields such as inlet unstart and combustor dynamics.

– Physics-based, high-fidelity modeling that can be rapidly executed/analyzed and potentially tied into “optimization” solvers is needed to provide rapid convergence on best solutions to minimize the “build-and-test” environment of current flow path/inlet nozzle integration design methodologies in use today.

B. Ground Test 1. Aero-propulsion Ground Test

For ground-test facilities, an attempt is made to expose the test article to an environment that duplicates the environment encountered in flight. There will nearly always be compromises, but the better the flight simulation, the more likely the development of a successful flight system. Many of the critical ground-test facilities expose the test article to airflow (as in a wind tunnel or engine test facility). Figure 5 shows the reservoir temperatures and pressures that must be generated in the test facility in order to simulate flight velocity and altitude. The flight dynamic pressure (200 to 2,000 lb per square foot) shows the general envelope in which many flight systems with air-breathing propulsion will fly. Note the very rapid increase in required facility total temperature and pressure with advancing Mach number. The ability to generate and contain the heated, high-pressure airflow challenges flight simulation in ground-test facilities.

Figure 5. Wind Tunnel Reservoir Pressure and Temperature.

The ideal test facility (note Table 1) would accept a full-scale test article and expose it to the flow environment it would experience in flight for mission-duty, cycle run durations. It will be noted that some types of testing, such as aerodynamic testing, permit relaxation of some environmental simulation parameters, thus permitting use of scaled test articles and smaller, less costly test facilities. However, testing of aeropropulsion systems offers much less relief, since combustion processes require duplicated flow conditions and cannot be scaled in time or space, and thus presents the most difficult testing challenge. Since the propulsion system is such a critical systems component, the adequacy of propulsion test facilities is critical to the development of flight vehicles.

As discussed previously, aeropropulsion ground testing requires simulation of the pressures and temperatures of flight. Today, capabilities for heating air to duplicate flight conditions are somewhat limited. Two basic concepts are known for adding energy to the flow: thermal acceleration and magnetohydrodynamic (MHD) acceleration. Table 1 displays various known thermal energy addition concepts that are in use or have been demonstrated in the laboratory.

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12American Institute of Aeronautics and Astronautics

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a. Turbine Engine Testing – High-speed turbine engines will be used for a number of the concept vehicles. A turbine engine will be the propulsion system for the Mach 2 to 4 High-Speed Aircraft and the lower speed component for the Mach 3-6 and 4-7 aircraft. Hence, turbine engine testing is critical to HS/H system development. Turbine engines and associated testing facilities have existed for at least six decades. It might be rationalized that the technology should be so familiar that new turbine engines could be designed with little risk. However, experience shows that even the smallest change in an engine can require a new development program. Furthermore, the engine cannot be developed as a small-scale test article, as noted earlier. They must be tested at full scale. Turbine engine testing cannot typically be accomplished in a wind tunnel designed for aerodynamic testing. Both the inlet and exhaust airflows must be independently controlled. The turbine engine test facilities usually have compressors and either heaters or coolers to treat the pressurized air to match flight temperature requirements. On the exhaust side, the pumping system must handle the total volume flow at the low pressure of the altitude being simulated. Thus these test facilities are large and expensive. The necessity and usefulness of such test facilities was first demonstrated by the Germans in WWII. The U. S. has used world-class turbine engine test facilities since that time. The newest U. S. facility for altitude testing is the DoD Aeropropulsion Systems Test Facility (ASTF), designed and built in the 1970 to 1985 time period. This facility has a replacement cost of at least $2 billion and has been a major contributor to all DoD (and most commercial engine) development programs in the last two decades.

In Fig. 4, the High-Speed Aircraft (Mach 2 to 4) shows some green and red. The large engine test facilities are limited to Mach 3.2, yet turbine engine R&D programs predict future engine performance to Mach 4 and above. Therefore, development of new, high-performance turbine engines will incur considerable increased risk without testing to these speeds. All of the three large, high-speed aircraft propose use of turbine engines as either primary or first-stage propulsion. The Access-to-Space vehicle could possibly do the same. Clearly, this test facility performance gap must be addressed.

b. Ramjet/Scramjet Testing – Air-breathing propulsion above a flight Mach number of about Mach 4 requires ramjet propulsion to about Mach 6 and scramjet propulsion at speeds above that. Most of the off-ramp systems use ramjet/scramjets and require their testing at flight conditions. The Hypersonic Interceptor/Attack Weapon requires boost to about Mach 6 and scramjet propulsion at speeds up to Mach 12. The Access-to-Space vehicle uses air-breathing propulsion to Mach 15. These are the systems with the highest flight Mach number requirements.

Many test facility requirements and constraints described for turbine engines also apply for ramjet/scramjet testing, but now the required temperatures and pressures for flight simulation are more demanding, as can be seen in Fig. 5. The propulsion systems should be tested at full scale since scaling laws do not exist. However, module or partial module testing may be possible. In addition, scramjet propulsion systems tend to be highly integrated with the vehicle, and the complete vehicle must eventually be tested as an integrated system. It becomes impractical (both technically and financially) to provide a continuous airflow for high-Mach simulated flight conditions. Although short run times may be useful for evaluating performance at discrete design points, seconds, minutes, or tens of minutes of run time will be required for operability and durability testing. Blowdown testing facilities provide seconds to minutes test time, and they usually store high-pressure air in storage tanks over a period of time and release the air for the duration of the test. For clean air testing to about Mach 7, heat can be stored in a ceramic matrix that releases heat to the high-pressure air. For combustion-heated vitiated air, a fuel is burned in the high-pressure airflow, and the test medium becomes a mixture of air and combustion products. Oxygen is added to the vitiated airflow to replenish the vitiated airflow consumed in the combustion heating process. This type of vitiated air test capability is limited to about Mach 8 simulated flight total temperature. Various uncertainties arise regarding the data by testing in combustion-vitiated air test facilities. The existing primary DoD and NASA test facilities use combustion-vitiated air. It is unknown, in general, whether engine ignition limits and performance reproduced flight well enough.

The primary propulsion test capability that exists above Mach 8 currently is relatively small impulse (shock) tunnels where the test time is of the order of milliseconds and the test medium is usually not clean air. The air is usually in a thermal and chemical nonequilibrium state and may contain metallic contamination from facility nozzles. Electrical arc-heated facilities, which usually produce contaminated air, have also been used for propulsion research testing on a limited basis.

The effects and limitations of combustion-vitiated testing, development of clean air test facilities below Mach 8, definition of needed facility run times, and definition/development of test capabilities above Mach 8 are all test facility technology gaps that must be addressed.

In Table 1 three new facility concepts are displayed: the Radiantly Driven Hypersonic Wind Tunnel (RDHWT) that uses beamed energy into the supersonic air flow in the nozzle, the RDHWT with radiant energy beamed into the plenum, and MHD acceleration employing electron beams to sustain electrical conductivity in low-density, low-temperature supersonic flow. All three of these concepts require development and demonstration .

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c. Propulsive Mode Transition Testing – Several of the off-ramp vehicles change propulsive mode as they accelerate or decelerate. Consider that a transfer from turbine (or rocket) to ramjet to scramjet will usually involve a flow-path change while maintaining thrust. It is not likely that the vehicle can carry three independent propulsion systems, so there will necessarily be engine components and fuel systems that have multiple uses. It is anticipated that development of such a combined-mode propulsion system will require many hours in an engine test facility with a free-jet nozzle and perhaps a clean airflow. This propulsion concept is a requirement for all hypersonic vehicles that operate throughout the flight envelope from takeoff to cruise.

d. Ramjet and Scramjet Engine Acceleration Testing – Most of the off-ramp vehicles will require a ramjet or scramjet engine to change thrust output as the vehicle accelerates or decelerates. This will require a test facility with a variable Mach number test capability. Development of a programmed accelerating and decelerating hypersonic propulsive system is considered to be a challenge for both the engine designer and the test facility designer. Conceptual approaches to multimode propulsion systems need to be defined to assist test facility designers. 2. Aerodynamics

a. Aerodynamic Ground Testing –For HS/H vehicle development, aerodynamic wind tunnel testing is needed for the complete range of flight speeds – i.e., subsonic, transonic, supersonic, and hypersonic. (See Fig. 6 for the overall assessment and evaluation.)

Three NAI systems are aircraft that take off and land on conventional runways and need the subsonic and transonic test capabilities as well as the supersonic and hypersonic test capabilities. The three missile systems are to be launched from the ground, a ship, or a carrier aircraft and may be rocket boosted to high-speed flight conditions while passing through several flight speed regimes. Thus, this study considers the ability of the U. S. to test all these future systems in the HS/H regimes but also considers the low-speed, transonic, and supersonic wind tunnel test capabilities and needs for development of these systems.

In aerodynamic development testing the need nearly always is to duplicate flight Mach number. Simulating Reynolds number (for scale and viscous effects) is highly desirable but not always practical for large vehicles such as aircraft-size systems because wind tunnels for this purpose become large, often technically impractical, and very costly. This problem is usually addressed by making Reynolds number corrections either empirically or analytically (thus a modeling and simulation issue and need). Since missiles are usually much smaller than aircraft, the flight Reynolds number is usually much less and subsequently more closely simulated in the wind tunnel although not always duplicated.

In the hypersonic flight speed regime (above about Mach 8 to 10), changes in air chemistry occur that produce a “real gas” effect that is technically difficult and often impractical, if not impossible, to simulate in wind tunnel testing. Thus, “real gas” corrections to aerodynamic data are needed and often best addressed with analytical corrections. This procedure, however, does require validation of the analytical models. The categories of aerodynamic development testing considered in this study for the NAI off-ramp systems are listed in Fig. 6, which shows an assessment of aerodynamic test capabilities by these categories for each of the seven NAI off-ramp systems. The aerodynamic test capabilities for the near-term NAI off-ramp systems are generally adequate, as also illustrated in Fig. 4. However, improvements in inlet airframe integration and nozzle after-body test capabilities are needed, especially for large-scale (aircraft size) testing where geometric fidelity is needed and can only be achieved at reasonably large scale. A minimum of 25-percent scale is recommended for inlet airframe integration. This is also true for the mid-term and far-term aircraft and Access-to-Space systems.

Hypersonic wind tunnels that simulate velocity as well as Mach number require significant amounts of energy addition to the air to achieve the high velocities in the nozzle flow expansion process. At energies required to achieve about Mach 8 velocities and above, the air ionizes, dissociates into atomic species (O and N) in the wind tunnel stagnation chamber, and often forms some NOX. These species and ions can chemically freeze in the nozzle flow expansion process, producing a nontrue air test medium. Some recombination does occur in the nozzle, but increased amounts of nitrogen oxides can be produced. Whenever these dissociation, ionization, and abnormal recombination effects occur, the effects on the aerodynamic data must be taken into account because the “real gas” effects of flight usually are not simulated. These dissociation and recombination phenomena are also important for aerothermal testing, as will be discussed later.

Perfect-gas, relatively cold-flow, wind tunnel test capability exists in the U. S. to about Mach 16. Impulse tunnels provide some real-gas effects, but these effects often do not necessarily simulate flight real-gas effects as mentioned above. Thus, there is a need for real-gas flight simulation test capability, and/or analytical procedures are needed to correct data taken from perfect gas and nonreal-gas wind tunnels to predict flight results. It may be impossible or at best very difficult to build the desired real-gas test facility, so M&S data corrections are expected to be necessary.

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Hypersonic wind tunnel productivity is an issue, especially above Mach 10. For production development testing, thousands of data points are typically needed to support aircraft design. Existing blow-down wind tunnels provide seconds to minutes of test time. Impulse tunnels operate for milliseconds, and only a limited number of these facilities exist. One set of data points per run is generally available in these cases. Productivity must be a major consideration when selecting a solution.

b. Specialty Testing Requirements – Aero-Optic – The types of aero-optic testing needed are listed in Fig. 6. The need exists to evaluate the optical

distortion induced by the flow field over the sensor window and thermal effects on the window itself. At present, aero-optic testing is limited to cold-flow (perfect gas) and impulse wind tunnels. The impulse wind tunnels are the only high-enthalpy (energy) wind tunnels available for this type of testing. As with the case of aerodynamic testing, test time is an issue and a gap for any testing above Mach 10, which is needed for the Mach 8 to 12 Hypersonic Interceptor/Attack Missile.

– Jet Interaction –The Mach 8 to 12 HI/AW is identified as needing a jet interaction test capability. As the name implies, jet interaction (JI) is an interaction between a control jet and the free-stream airflow around a flying vehicle. The purpose of JI is to provide aerodynamic stability and control, generally under transient conditions. For aerodynamic stability and control testing, conventional wisdom calls for the creation of a very large experimental database for vehicle development in a relatively short period of time. This implies that highly productive test facilities are needed. Additionally, flight duplication is desired and must be achieved at least in a number of baseline tests. Adequate run duration must be available to fully establish the jet interaction flow field. In general, existing hypersonic test facilities do not satisfy these productivity, flight duplication, and run time criteria. For hypersonic speeds, Mach 6 to 15 aerodynamic facilities (perfect gas facilities) do exist, but they are generally of modest size and do not provide flight duplication enthalpies. Developers of missiles favor a full-scale test in highly productive facilities and will acquiesce to flight duplication enthalpies that can be provided only by very short run time facilities (shock/impulse wind tunnels). This, of course, provides a limited database with flight duplication enthalpies without the benefit of testing for transient effects. A facility with flight enthalpy duplication capabilities and run times of the order of seconds does not presently exist, but such a facility would provide added transient testing capability at flight enthalpies. The need for highly productive cold-flow facilities will continue to exist as before.

– Impact/Lethality – Impact/lethality testing is not a type of aerodynamic testing, but for convenience it is included here as a specialty testing item. Requirements for improved impact/lethality capabilities using ballistic ranges include higher impact velocities, “soft launches” (launches at acceptable acceleration loadings), higher fidelity test articles, improved instrumentation, diagnostics, and computational capabilities. “Soft launch” capabilities are needed to permit the launching of extremely high-fidelity missile simulations at hypervelocity speeds. As missiles have grown more complex, the fidelity of the simulation has become more important. For gun-range lethality testing, high-fidelity, geometrically scaled projectile test articles are required that match

the axial and radial mass distribution of the actual missile, yet possess adequate integrity to withstand the acceleration loads experienced during gun launch. Current software permits engineers to analyze proposed projectile designs in the dynamic launch environment. The analysis simulates stress wave propagation through the projectile body, characterizing stress concentrations that exceed material yield. With marginal areas identified, design changes are incorporated that minimize the probability of projectile failure during launch. High-speed impact testing has been limited to speeds of less than 7 km/s by performance limitations inherent in the two-stage light-gas guns, which are generally used to accelerate impact models. Since space debris encounters and exo-atmospheric kinetic-energy-weapon intercepts occur at much higher velocities (approaching 17 km/s), considerable risk has been associated with extrapolating existing lower speed impact test results during the design of various space systems. In the counter-fire technique, a target model is launched at up to 7 km/s from one launcher, and the projectile is fired in the opposite direction at up to 8.5 km/s with impact velocities exceeding 15 km/s. Following the impact event, the target model is recovered for posttest analysis and evaluation. Other techniques are being pursued for the simpler, single-fire approach.

Sled tracks can test larger full-scale test items that are higher fidelity but cannot achieve the highest speeds needed. Sled track velocity limits are currently Mach 9.4. Test article throw weight, velocity, and fidelity are inadequate for the projected weapon systems. Sled tracks are limited in velocity, while gas guns are limited in weight and scale. 3. Aerothermal/Structural

HS/H vehicles that fly in the atmosphere are exposed to severe thermal environments produced by the very high flight velocities. These vehicles are exposed to temperatures produced by air friction and stagnation heating that range up to several thousand degrees. Thus, thermal protection is required for HS/H vehicles that fly in the

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atmosphere for minutes to hours, as do all off-ramp systems. These vehicles must be built of materials that will withstand the thermal and pressure loads and/or employ some method of active cooling. Also, subsystems of the vehicle are required to reliably operate in this severe flight environment. This means test methods must be employed to simulate the aerothermal environments for materials, structural, and operational subsystem developments that normally require using both aerothermal flow and static structural test facilities – both discussed further in this section.

a. Aerothermal – The aerothermal environment is composed of the aerodynamics, the enthalpy (or velocity), and the density effects. Around Mach 8 to 10 in the air-breathing propulsion flight corridor, air will begin to chemically dissociate (oxygen initially) when passing through the initial shock system produced by the vehicle. At Mach numbers greater than 12, the gases begin to ionize. Dissociation and recombination can continue to occur in the flow boundary layer resulting in significant effects on the vehicle heating.

Existing ground-test facilities can provide partial simulation. Perfect gas wind tunnels are used to measure heat- transfer coefficients (up to about Mach 16) although they do not provide the enthalpy required for the full heating rates. Impulse tunnels can provide the correct Mach number and enthalpy but for very short test times.

Ballistic ranges can provide the correct environment but for short test times. Electric arc heaters can provide high enthalpies but incorrect aerodynamics. All of the above may have scale shortcomings.

There is no significant gap in test capability to obtain first-order heat transfer data. However, there is a gap in providing the correct flow chemistry, which may be addressed with M&S. There is also a gap in providing sufficient scale for testing. If gaps are filled for air-breathing propulsion, the aerothermal gaps will also be closed.

b. Static Structural – HS/H aircraft systems that operate within the atmosphere for minutes and hours will require an entirely new type of testing with associated testing capability. It is common for new aircraft structures to be subjected to simulated flight loads reproduced via mechanical means. With the high-speed aircraft, not only will the flight loads be increased, but also the structure will experience internal loading produced by thermal stresses. The vehicle’s cooling system must accommodate the very high aircraft leading-edge temperatures and the propulsion system. These temperature extremes will defy analytical solution in the complex structures. It will be necessary to test major full-scale aircraft components in nonflow ground-test facilities that produce both external and internal loading. Such a facility, which was being planned in the NASP program prior to program cancellation, is critical for production of manned long-range hypersonic aircraft.

C. Flight Test Flight testing of subsonic and supersonic aircraft and missiles are presently conducted in low-density populated

areas of the U. S. and over water expanses such as the Gulf of Mexico and the Pacific Ocean. Hypersonic flight testing of NAI-type vehicles will require larger ranges than those currently available over land. Consequently, new and upgraded range tracking and instrumentation will be needed. This section discusses in detail the new capabilities and resources that will be needed for hypersonic flight testing. 1. Range Space/Safety

To fulfill the purpose of national space policy and national space transportation policy, suitable hypersonic corridors for air-launched, generic, combined-cycle, and hypersonic vehicles need to be identified. Re-entry corridors are instrumental to the development of low-cost, second-generation space transportation vehicles and weapon systems. The hypersonic vehicles must be flight tested in a realistic operational environment (flight corridor) to develop and demonstrate critical technologies needed for vehicle cruise and recovery. The air-launched, generic, hypersonic vehicle needs to be tested through all flight regimes that could occur during its launch, cruise, and landing/terminal phases without compromising public safety, unduly interfering with commercial and private aircraft, or adversely affecting the environment in the proposed hypersonic corridors. Establishing hypersonic corridors and completing the programmatic environmental documentation based on generic configurations will reduce the time required for environmental process approval for a specific hypersonic vehicle configuration.

Formally establishing hypersonic test corridors enables hypersonic testing in large, open-air ranges while enhancing over-land, over-water range integration. Closing the gap in open-air range capability will require formalizing the physical range attributes, including environmental assessments/impact statements; applicable regulatory, statutory, and legislative requirements; necessary Interservice/agency/state agreements; geosociopolitical consequences; and mitigation criteria associated with public safety.

For advanced hypersonic vehicle demonstrators, some shortfalls exist in our range infrastructure to adequately validate their applicable technologies. Significant questions will have to be addressed concerning many tangible flight-test support issues. Because hypersonic flight-test events will involve extended flight corridors, capabilities for a hypersonic or global test range (permanent data acquisition range) will need to be developed. Hypersonic

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vehicles, by their nature, will push the envelope of test range resources. Environmental impact analysis will need to be extended to cover a larger test range.

Over-land flight capability is critical for the viability of future HS/H testing and operations for military access to space and hypersonic vehicles. This requirement becomes especially critical for reusable systems that require contingency and abort options for the vehicle in the case of vehicle anomaly, both manned and unmanned. (The X-15 made ten emergency landings to dry lake beds during its flight-test program, each time saving the aircraft to fly again.) Approved corridors are required for flight-test vehicle technology demonstrations as well as operational weapon systems. These vehicles are being designed to develop advanced combined cycle air-breathing engines that will be critical for efficient flight test of weapon systems or first-stage-to-orbit for future reusable launch vehicles (RLVs). Testing this propulsion technology on flight vehicle demonstrators is a prime national focus. A subset of proposed solutions includes providing for augmenting the ongoing environmental analysis for hypersonic flight test corridors. To obtain final environmental approval for the envisioned initial test vehicles, analysis of many additional trajectories are required to support an incremental flight-test program. Initial flights for manned/unmanned aircraft would begin at low Mach numbers, with subsequent flights expanded into higher Mach numbers at further ranges. To safely support the flight test, a series of emergency landing sites should be investigated and approved in the environmental analysis effort. There is a gap in the ability to cost-effectively recover expendable hypersonic vehicles for data analysis of flight vehicle and propulsion system materials for vehicles launched over the water. For vehicles over land, range safety is a concern. A proposed solution would still look at developing a land/sea range capability for hypersonic air vehicles, as well as developing viable recovery system (e.g., chute) options – a gap that still exists.

Additionally, large-distance ranges for hypersonic vehicles would still require full-mission coverage, especially for a flight termination system (FTS). Present test ranges have limited FTS transmitter coverage because present vehicles under test have limited flight profiles, although high-altitude flights might still provide some line-of-sight coverage. A proposed solution would be to continue to analyze and develop an Over-the-Horizon Flight Termination System (OTH FTS). The goal will be to provide effective provision for public safety over any place on the globe, including satellite systems that may be more cost-effective than other systems considered. The future of range safety will rely heavily on the next generation of flight safety systems, the integration of vehicle health/monitoring management systems, and real-time flight performance prediction models associated with hypersonic vehicle design and operation. The evolution towards a more autonomous “space-based” type range is the most significant issue associated with current flight safety paradigms. Also, the ability to confidently use Global Positioning System (GPS) to conduct real-time vehicle tracking and trajectory assessment is a key enabling technology to protect the safety of the public and of property. Specific vehicle systems comprising or interacting with vehicle-based safety systems that will be of concern during flight activities are highlighted as follows:

a. Command & Control Link/Software – The goal for command and control would be to move from the present mostly-manual system through semiautomated and automated systems to an eventual autonomous system to improve interoperability, responsiveness, and flexibility. (Automation refers to machines taking over physical tasks from humans; autonomy refers to the ability to act without human control – i.e., the shift of decision-making from human to machine.) The command and control system is comprised of the following functions: monitor range asset health, status, and configuration; configure range assets; and execute command and control of range assets and flight vehicles to include flight termination systems (FTS). The eventual goal is to affect autonomous FTS (meaning flight destruct systems [FDS]) with manual override.

b. Flight Termination – Although an autonomous FTS is technically feasible, system performance requirements must be defined, development and validation costs must be accurately estimated, and issues of public acceptability (domestically and internationally) must be addressed to determine whether a fully autonomous FTS would be practical and cost-effective. The successful deployment of semiautonomous systems that would provide operational benefits, even if a fully autonomous system is never developed, would help resolve these issues. A first step would be to develop computerized simulations of vehicle dynamics and FTS responses to determine system requirements. These simulations could be followed by validation testing using sounding rockets or other low-cost test vehicles.

c. Flight Control Systems – Verification of the flight-control systems/hardware and the vehicle structure to physically withstand the launch, recovery, and in-flight abort environments should be done through independent analysis as well as through assessment of an applicant’s analysis. If certain abort modes are shown to place undue stress on the flight control hardware such that its functioning cannot be guaranteed (or the vehicle’s structural integrity guaranteed), then the instantaneous impact predictor (IIP) of the vehicle or the instantaneous impact zone (IIZ) of the vehicle’s debris field should be considered appropriately.

d. Guidance and Navigation (G&N) – The capability of the vehicle G&N systems to operate throughout the flight envelope and abort-regime should be verified. Like other data links, any attitude that could cause an inability

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for the vehicle’s G&N systems to receive pertinent data (e.g., vehicle blocking of GPS signals) should be accounted for in the mission planning and flight termination plans. It is likely that all classes of hypersonic vehicles will have some sort of internal navigational capability, such as an Inertial Measurement Unit (IMU), as a minimum. This will need to be tested and verified according to some standard of verification methodology. 2. Propulsion & Fuel

The consideration of the starting of the vehicle’s propulsion system during nominal atmospheric flight will be considered during vehicle safety review activities. However, the ability of the propulsion system to start and to operate during an abort scenario (especially a launch abort) should be verified. Since initiating a “test” abort during an actual launch is not feasible, the verification will have to rely on independent analysis of the propulsion system. Any previous flight experience in a flight regime similar to or equivalent to the vehicle’s abort flight regime by the vehicle under consideration of any other vehicle would be applicable (though probably rare). For some vehicles, fuel dumping may be an action called for by some flight-safing modes. If so, the ability of the vehicle to dump fuel will need to be verified. Fuel dumping will be part of the environmental impact study and should be assessed relative to routine commercial aviation fuel dumping activities. As with the propulsion system, flight-testing of this ability would cause its verification to be straightforward; otherwise, independent analysis, assessment, and commonality with extant systems already used will have to suffice. 3. Other Support Needs

Standardization Decision Support Tools – The development of improved suites of tools is required to aid in the decision making process. The current tools are mostly stand-alone and are not necessarily standardized across the ranges. The vision would be to have an automated suite of tools integrated with flight prediction models, IIP models, debris dispersion models, and flight simulators. Thermal Protection System (TPS) – Average surface temperatures of hypersonic aircraft can reach greater than

2,000ºF. Pressure or shock waves can cause some areas to exceed 4,000ºF or higher. If the vehicle enters orbit, the surface (or near-surface) temperatures may drop close to absolute zero (about -459ºF). The back face of the aircraft skin, where sensor processing takes place, can reach 300ºF for older style cold structures and 800ºF for newer style hot structures. Engine flow path temperatures are also a concern. Furthermore, thermal conditions throughout the airframe may affect structural integrity and flying performance. This becomes even more of a concern if cryogenic fuels that would create extreme differences of temperatures throughout the vehicle are used. Also, utilization gages for cryogenic propellants must be able to endure very low temperatures. The main concern is the ability of the thermal protection and thermal control systems to protect the vehicle’s systems in the case of an off-nominal flight trajectory. The temperature at which vehicle systems (including structure flight control hardware wiring) start to fail should be known for each system. If the vehicle undergoes an off-nominal trajectory and is then indicating – either through its performance or through sensor readings – that it is not healthy, the proper steps should be taken, up to and including vehicle recovery system (VRS) deployment. If the VRS is suspected of being impaired, then the vehicle should be commanded (or should execute an autonomous flight-safing mode) to fly to a nonpopulated area for attempted VRS deployment or “ditching.”

VRS – Some HS/H vehicles may choose to have a VRS. Other vehicles may have a nominal landing system that doubles as a VRS. It is not likely that an applicant will conduct a full test of the VRS during flight testing. Therefore, verification will have to depend on independent analysis, applicant assessment, and system test. The effect of the trajectory environment and the launch-abort environment should be considered so that the VRS parachutes will deploy. The actual parachute deployment systems and, if applicable, airbag deployment systems should be bench tested, and the command logic that invokes the VRS should be tested in mission simulations. The following steps, along with analysis and assessment, should verify the VRS to the maximum extent possible: • Develop requirements, interoperability • Refurbish fixed/upgrade technology - Integrate M&S capability • Determine requirements, design architecture, acquire hardware, install, and checkout.

4. Range Infrastructure a. Mission Planning – The next generation of hypersonic vehicles (missiles and aircraft) will require a new

generation of hypersonic flight-test tools and test methodology to support full spectrum flight-test and mission planning. Currently, insufficient in-house technical expertise and analysis tools are available to support hypersonic flight-test planning and engineering analysis activities. These activities include test engineering, test operations, and M&S capabilities over diverse flight regimes and test environments.

A proposed mission planning solution includes conducting initial studies to determine modeling and simulation test support requirements to include M&S systems, displays for acquisition data, and interconnectivity with flight-test ranges. Further test infrastructure development would then acquire and validate M&S capabilities. To close the

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gap, legacy test methodologies and associated technologies must evolve via these studies concurrently with virtual global range requirements definition.

b. Flight-Test Data Management – Data management is central to advancements in multiple areas. Supporting mission planning will require a capability for data processing of increased quantities of mission data, as well as an increase in data quantity processing speed. Advanced hypersonic weapon systems will drive an increased need for near-real-time data and availability of quick-look analysis. Legacy systems cannot handle required data formats and processing. Current data storage media will not support future HS/H system requirements, and data distribution requirements for future hypersonic missions will exceed the capability of current distribution networks.

Closing this gap will require developing increased data processing capabilities in mission control rooms and data centers, transitioning from legacy data storage media to dynamic, interactive data transmission control and display systems, and reconfiguring data transmission methodologies. Proposed solutions will need to determine data processing and management requirements, including data rates, data formats, data storage amounts, data storage configuration, and data storage media. A proposed solution will investigate potential industry solutions, determine standards, specify requirements, develop prototypes and technologies, and develop baseline capabilities that can be augmented to meet customer needs. The long distances required for flight test of hypersonic vehicles will require the capability to acquire mission data along the length of the hypersonic corridors. Presently, hypersonic corridors are not populated with data acquisition tracking sites. Metric tracking of hypersonic platforms will require increased data speed and outputs, without dropouts and degradation of data quality. Metric tracking of platforms flying at hypersonic speeds are limited by present tracking system slew rates and response times, which are too slow to maintain track. Also, acquisition of flight data shall require installation of additional sites capable of transceiving and processing of aircraft telemetry (TM), time-space-position information (TSPI), and GPS data. Of course, environmental, range safety, and risk mitigation to the public are primary concerns.

c. HS/H System Telemetry Tracking – In general, the current tracking capability relies on fixed-location, ground-based metric radars with C-band beacons aboard flight vehicles and inertial measurement unit (IMU) data in the telemetry stream. The long-term goal is to interface with other space and air traffic management systems and to have seamlessly integrated global operability for GPS and IMU metric tracking. The key step here (for tracking) in the near- and mid-term is to evolve to using GPS and IMU as part of a space-based range. The use of other mobile range assets such as high-altitude airships (HAA) and unmanned aerial vehicles (UAVs) to supplement space-based coverage is also envisioned. Regarding surveillance (surveillance of the restricted launch and downrange areas), it must be ascertained that members of the public are not placing themselves at risk.

The near-term desire is to automate the collection, transfer, and integration of surveillance data. The long-term goal is to include integrated, space-based surveillance and real-time situational awareness within selected regions worldwide. This is in contrast to the current capability, which involves manual data collection, data relay via voice, and table-top-and-tokens display.

Currently, telemetry is obtained via fixed or mobile ground-based receivers with a limited number of deployable space-based and airborne assets. The goal is to eventually have global coverage via the space-based range, supplemented by mobile assets as needed. Telemetry is probably the area of next-greatest interest – and perhaps of greatest concern – because of the loss of spectrum as a resource and the growth of the data-streams being transmitted. Closing the gap in data acquisition capabilities will require new and innovative methods of mission metric data tracking and application of the technology, including understanding requirements for telemetry, flight termination, and integrated M&S. This will likely require researching new technology for telemetry data acquisition and developing communications infrastructure architecture for extended range to include enhanced TSPI, utilizing GPS for better geometry and time correlation, global coverage utilizing/integrating space-centric range and mobile range assets, and utilizing the global information grid for distributed/integrated networks. A proposed study will look at different possibilities for tracking, including satellite tracking, platform-less tracking, and wireless tracking.

d. Interoperability and Data Exchange – A central theme in large-range/multirange operations for hypersonic vehicles is interoperability and data exchange capabilities. Hypersonic systems will require test ranges to provide a scalable and interoperable enterprise architecture system capability to acquire and process flight-test data and test simulation. Ensuring commonality and interoperability during flight test will reduce risk, processing, scheduling, and distribution costs. Flight-test data will be processed at the source and distributed in near- or real-time via common middleware such as TENA/HLA/DIS, common format, common data rates, and encrypted (if required), time stamped, minimized latencies. Flight-test data will meet accepted protocol data exchange standards and interfaces.

Presently no other compatible alternatives exist other than using legacy multirange specific data acquisition and reduction and distribution systems not adhering to data exchange standards and interfaces. Multiple data streams from a spectrum of sensor sources and interfaces transmitted via various formats will lead to data rates with little or

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no commonality. Critical-flight test data could be lost because of an inability to streamline and perform real-time distributive processing to critical destinations for flight safety display applications and further data analysis.

A proposed enterprise architecture system solution will investigate a real-time distributive processing system with an asynchronous front end capability to acquire flight-test data inputs from multiple field sensors and output data synchronously. This feasibility study would determine project viability and desired capabilities. Specific features might include network-centric connectivity, optimized performance, scalable throughput performance, a standard-based architecture system, and native (embedded) encryption technology with minimized latency effects.

e. Onboard Sensors and Nonintrusive Instrumentation – A critical component for hypersonic vehicle flight test data acquisition is the capabilities of onboard sensors. Specifically, for development of air-breathing ramjet/scramjet engines, in-stream measurements on hypersonic flight vehicles are needed to better validate aerodynamic and combustion models. At present, measurements for pressure, temperature, and heat flux are available. Proper validation of the vehicle models requires more detailed measurements in the flow field (e.g., boundary-layer, free-stream, and across-the-combustor flow path). Use of conventional surface measurements to validate models will result in models that will not be adequately validated, so large uncertainties in modeling will remain. These uncertainties will then require operational vehicles to be built to accommodate these uncertainties, resulting in heavier and slower vehicles. A proposed solution would need to determine the feasibility of nonintrusive instruments to measure products of combustion and/or velocity, as well as set up a feasibility study of more advanced nonintrusive instruments to measure in-stream products of combustion and/or velocities. How effective this approach will be in closing the gap depends on how precisely and accurately the measurements that the model developers require can be made. It may still prove impossible to measure on a flight vehicle all, or a portion, of what the model developers require.

f. Plasma Effects – A further potential concern presented by hypersonic systems data acquisition involves plasma effects. It is generally viewed that plasma effects may not be manifested by all hypersonic vehicle configurations. However, depending on vehicle configuration (especially thermal protection materials), the plasma effect may be extremely important. Plasma-generated attenuation denies the capability to pass data between hypersonic vehicles operating at Mach 10 and above and mission control facilities. A proposed solution would involve a scientific study to reduce plasma-generated attenuation for better data reception.

g. Flight-Test Data Encryption – Another concern for data acquisition and analysis for hypersonic vehicles is the potential requirement for encryption of flight-test data for weapon systems development. The Intercontinental Ballistic Missile (ICBM) flight-test community has been transmitting its telemetry data without encryption for 30 years, so that capability and technology exist today. However, DoD policies for future hypersonic weapon systems may require encryption. Unclassified data acquisition removes onboard processing of test data and also removes encryption devices from the vehicle. This saves weight and reduces valuable instrumentation system space requirements while reducing overall system cost. A proposed solution would look at redesigning how data are “encrypted” to meet security standards. Raw unannotated/nondescriptive data are unclassified. Unless the parameter name and scale factor to apply to each measurement are known, the data cannot be comprised. Whether data are encrypted, the hypersonic test ranges are still faced with the problem of efficient use of the telemetry spectrum to support requested mission requirements. Insufficient spectrum bandwidth exists to continuously support multirange test activities. Continuing loss of RF spectrum impacts quality and quantity of data transferred and impedes data processing speeds. Furthermore, competition with other customers for data frequency spectrum, data bandwidth, and data configuration has compounded this situation. Existing systems are currently incapable of passing data at increased data rates. 5. Data Transmission and Frequency Spectrum Management

Proposed solutions would need to include alternate modes of data transportation, expanding TM coverage along hypersonic corridors, and transition of data to new frequency bandwidth to compensate for lost spectrum. These solutions would involve increasing inter- and intra-range transmission bandwidth, and potentially wireless data transmission using innovative and future technologies to better manage the frequency spectrum. Further study would determine the feasibility of other methods of wireless data transmission, study different wireless transmission possibilities, and determine the best alternative(s) such as directed energy, satellite relay, high-altitude relay, or others. The result would be to develop an interoperable strategy for transmission of data between Major Range and Test Facility Bases (MRTFBs) and further refine an investment program to update/replace legacy wireless data transmission systems.

a. Optical Tracking/Sensor Systems – A valued component to hypersonic flight test data acquisition will be optical systems. These systems can be extremely valuable in supporting flight-test data analysis. A real-time imaging tracking instrumentation system capability is required to acquire and track airborne vehicles that are air/ground launched with the capability of achieving hypersonic velocities at exoatmospheric altitudes. Existing

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instrumentation capabilities may have to be correlated to the test requirements to ensure data fidelity and satisfy customer objectives. However, there will still be a need to develop a more extensive distributive architecture enterprise capability. A proposed solution would be to develop design requirements for a suite of instrumentation avenues capable of addressing specific capability requirements. These capabilities might be comprised of fused radar, TM, GPS, Multiframe Blind Deconvolution (MFBD), and Infrared (IR) Technology sensor technology.

A potential support capability for long-range coverage may be provided by airborne data platforms that would augment ground-range systems for data acquisition, relay, optics data, etc. This capability could provide a research test bed for the DoD with a long-term capability for efficient test of HS/H flight experiments. Several aircraft options exist, such as Navy P-3 aircraft or joint Air Force-NASA Dryden C-20 aircraft. Proposals would continue engineering development for self-contained embedded systems, providing automation for configuration setups to reduce the required engineering support for each mission, and provide for easy upgrades and add-on systems for expansion. These systems upgrades will be necessary to be compatible with ground systems for high-speed data acquisition for hypersonic vehicles.

b. HS/H Vehicle Air Launch Support – A flight-test gap exists in the capability to air-launch the heavier hypersonic missile systems, support technology demonstrations, and provide flight-test support for hypersonic and Access-to-Space vehicles. This capability will provide viable airborne launch platform support for a wide range of experimental test vehicle concepts. This modification of test capability can further be used for test and operational missions (hypersonic vehicle operational demonstration). The Air Force Flight Test Center (AFFTC), in partnership with NASA Dryden Flight Research Center (DFRC), has acquired and modified a B-52H for test and evaluation of aerospace research vehicles weighing up to 25,000 lb. A proposed solution provides for the design, development, and modification of the B-52H so that it is capable of carrying aerospace flight test vehicles of up to 75,000 lb. 6. Advanced Ground Support Systems

A major cost-reduction gap lies in advanced ground support systems for hypersonic vehicles. Responsive ground operations for hypersonic/space access vehicles include rapid launch integration systems, rapid cryogenic propellants loading, preflight checkout, and preparation for launch-on-demand. There is currently a gap in the capabilities for testing hardware in the loop, including needs to have communication links to the launch and landing sites, control room, and range for checkout and validation of communication links prior to launch. This capability would develop the ability to simulate a complete launch-to-landing profile for either autonomous or pilot-controlled vehicles. A proposed solution provides for systems development similar to the former X-33 launch site (now owned by the AFFTC) that could provide a cost-effective test site for test and evaluation. This project would re-generate and/or upgrade ground support systems focusing on future capability needs as an operations and test complex. A dedicated facility will be required to house the necessary generic computers, displays, and software workstations to integrate the vehicles’ software. The initial model updates utilizing flight data would be performed here and subsequently transmitted to other ground-test facilities.

VIII. Conclusions A comprehensive study has been conducted by the U. S. DoD to identify shortfalls in test and evaluation

capabilities for the development of hypersonic weapon systems that employ air-breathing propulsion in the hypersonic speed regime. The flight systems baseline for the study was based on seven missile, aircraft, and space access systems identified as core hypersonic vehicles in the NAI.

The study shows that inadequacies exist in M&S and ground- and flight-testing capabilities, which must be addressed and solved before the various hypersonic systems can be developed with reasonable risk. Furthermore, technology developments must be pursued in the near term to ensure that infrastructure capabilities can be developed in time to meet proposed “off-ramp” technology schedules proposed in the NAI program that will allow systems developments.

References 1Schweikart, L, The Hypersonic Revolution – Case Studies in the History of Hypersonic Technology, V. III, The Quest for the

Orbital Jet: The National Aerospace Plane Program (1983-1995), Air Force History and Museums Program, 1998. 2Hilliker, Harry, “Report of the Ad Hoc Committee on Hypersonic Air-Breathing Vehicle Technology,” Air Force Scientific

Advisory Board Report, June 1992. 3NASA News Release 04-59, “NASA’s X-43A Scramjet Breaks Speed Record,” November 16, 2004. 4Buffo, M., “Technical Comparisons of Seven Nation’s (sic) Space Plane Programs,” AIAA 903674, AIAA Space Programs

and Technologies Conference, September 25-28, 1990, Huntsville, AL. 5Decoursin, D. G., “A Summary of European and Japanese Hypersonic Facility Activities,” Proceedings of the 1990

JANNAF Propulsion Meeting, Johns Hopkins University, Volume 1, pps. 203-210, 1990.

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6Kraft, Ed, “High Speed/Hypersonic T&E Infrastructure Roadmap,” Presentation to the 2005 Annueal International Test and Evaluation Association Annual Technology Review, Nashville, TN, July 2005.

7Committee on the National Aerospace Iniative, Air Force Science and Technology Board, Division on Engineering and Physical Sciences, “Evaluation of the National Aerospace Initiative,” National Research Council, The National Academies Press, Washington, D.C., 2004.

8McClinton, C. R., Hunt, J. L., Ricketts, R. H, Reukauf, P., and Peddie, C. L., “Airbreathing Hypersonic Technology Vision Vehicles and Development Dreams,” AIAA Paper 99-4978, 9th AIAA International Space Planes and Hypersonic Systems and Technologies Conference, Norfolk, VA, Nov 1-5, 1999.

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High-Speed/Hypersonic Test and Evaluation … of Ground Test Working...High-Speed/Hypersonic Test...

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