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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs 7 Strategies, Issues, and Funding Trends MAXIMIZING THE RETURN ON INVESTMENT The Department of Defense (DoD) has used long-term funding (10-15 years) of the Integrated High Performance Turbine Engine Technology (IHPTET) program—now the Versatile Affordable Advanced Turbine Engines (VAATE) program—and the Integrated High Payoff Rocket Technology (IHPRPT) program as its key strategy for advancing aerospace propulsion. This strategy—long-term, stable funding—has succeeded by enabling incremental advances. These advances notwithstanding, the committee has been asked to examine some alternative strategies. Using the Air Logistics Center to Enhance Technology Transition The component improvement program (CIP) for aircraft turbine engines has been utilized effectively to address safety, reliability, and materiel obsolescence in fielded engines. To improve technology transition and cycle time for incorporating new and emerging technology, a lean approach is required. Recommendation 7-1. Engine test capabilities at the Oklahoma City Air Logistics Center (OC-ALC) should allow for engineering changes of existing hardware to be accomplished by the cognizant engineering authorities and, after configuration control board approval, for demonstrating the approved technology-enhanced hardware or accessory on the government test stand at OC-ALC. This would shorten the cycle time for introducing minor engineering improvements into the current legacy fleet of engines and reduce the overall costs to accomplish the qualification. Additionally, it would provide a test bed on which to qualify non-original-equipment-manufacturer (non-OEM) repaired or reengineered parts, new sources of repair, or non-OEM suppliers of parts. Recommendation 7-2. DoD should change the way it manages, contracts for, and buys fuel for the existing fleet. Three years after a system enters into service, budgets for repairs, component improvement, and overall fuel cost should be transferred to the base that maintains the propulsion system. In addition, testing to qualify engine repairs and component improvements should be conducted at the facilities responsible for maintaining the engine. In addition, there are only a small number of OEMs for engines, and each OEM has its own very specialized technical support team. Not only does an OEM fund some of its own work—known as independent research and development (IR&D)—it also receives funding for exploratory or advanced development research from the Air Force Research Laboratory (AFRL) or other service laboratories. The applicability and transition of the technology developed, if not restricted by proprietary rights or licensing agreements, lags significantly from one OEM’s engine program to another OEM’s engine program.
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs Spiral Development History shows that spiral development has been applied to many of the Air Force and Navy fighter engines.1,2 For example, the propulsion systems for the F-16 and F-15 aircraft underwent spiral development to increase their thrust and reliability. Spiral development has proven to be a very cost-effective way to greatly increase the warfighting capabilities of these aircraft. The major derivative programs of these engines (e.g., the F100-220 and F100-229 versus the F100-100) bundled technology packages from IHPTET or IR&D programs to markedly improve performance. Currently, DoD is not leveraging the large F-22 and F-35 propulsion investments by providing spiral development programs to meet the requirements of these aircraft. For example, derivates of the F119/F135 or F120/F136 engines should be considered as prime candidates to power the Global Strike aircraft. Finding 7-1. History has demonstrated that the introduction of new technology into existing weapon systems—i.e., spiral development—can be a very cost-effective way to upgrade warfighting capability. Recommendation 7-3. The Air Force and DoD should apply spiral development to all weapons systems that are in service longer than it takes to develop a new generation of technology. GOVERNMENT AND INDUSTRY COLLABORATION The committee visited most of the aerospace propulsion companies to inquire about commercial best practices and technology capabilities and to observe and study how their strategic plans incorporated these technologies into their products to improve thrust and durability and to reduce fuel consumption and weight. In most cases, the engineering processes of these companies had standard tasks like risk reduction and design review that were more in depth than the Air Force’s current specification reviews—namely, preliminary design review and critical design review. A number of the companies had paperless manufacturing process sheets and paperless inspection process standards. In most cases, all of the tools were controlled in kit form, with each tool having its place in the kit, and the process could not move forward until the kit tools were used, placed back in the kit and accounted for. Again, in most cases, these processes and best practices were put in place to reduce cost and manpower and to allow the companies to be world-class competitors. Recommendation 7-4. DoD should adopt commercial best practices to reduce costs and exploit the technical expertise of its research laboratories to enhance the integration process in its product centers and depots. Shortening the Demonstration Time The committee and the presenters had different views on the 1-year engine demonstrator. Some of the presenters doubted that engines could be tested in 1 year simply because there would not be enough time to complete such testing. However, committee members argued that engines or engine components could be tested in 1 year if the effort was well focused, planned out (including contingency), and 1 In the mid-1980s, Barry Boehm, then a chief scientist at TRW, Inc., devised spiral development as a way to reduce risk on large software projects. Although Boehm devised it for software engineering, the DoD has adapted the spiral development technique as part of its evolutionary acquisition strategy to get newer technologies into large platforms, such as assault vehicles and computer systems, much more quickly. More information on the spiral development methodology may be found at the Carnegie Mellon Software Engineering Institute Web site, at http://www.sei.cmu.edu/cbs/spiral2000/february2000/BoehmSR.html. Last accessed on August 8, 2006. 2 Also known as “evolutionary acquisition,” spiral development is an acquisition strategy that defines, develops, produces or acquires, and fields an initial hardware or software increment (called a phase or block) of operational capability (OUSD AT&L, 2003).
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs executed. In the 1960s, 1-year testing programs were done routinely. In multiyear programs especially, frequent testing is an effective way to keep the program energized. Recommendation 7-5. DoD and major propulsion contractors should define the process changes needed to produce 1- to 2-year technology demonstrations. Decreasing the interval between demonstrations of technology in major propulsion systems will increase the rate of technology development. Reliance Program In response to the Deputy Secretary of Defense’s challenge to the services in 1989 to create a new approach that would increase efficiency in research, development, testing, and engineering (RDT&E), the Service assistant secretaries mandated the Defense Science and Technology Reliance Program (Reliance Program) to focus resources on propulsion requirements and capabilities (DMR 922). As mentioned in Chapter 2, the committee heard anecdotally from knowledgeable, informed sources that the Air Force was the lead service in propulsion for the Reliance Program. Since the Air Force has been by far the largest investor in the science and technology (S&T) arena in both aircraft propulsion and rocket propulsion, the committee felt this made sense. However, a review of the Reliance Program failed to identify a lead service for propulsion. In fact, the program divides propulsion into subordinate elements as reflected in the Defense Technology Area Plan (DTAP) panels: air platforms, nuclear technology, space platforms, and weapons (Ray, 2005). Finding 7-2. The committee believes that having propulsion segmented in different DTAP panels results in overlapping, unfocused efforts from one Service to the next and from one panel to the next. Further, the panels’ efforts do not produce a prioritized list of defense technology objectives. The Reliance Program, as presently structured, also does not give the panel chairs the necessary authority to enforce cooperation and discipline in program execution. Moreover, the program published its last Science and Technology Strategy in 2000. Overall, the present Reliance Program organizational construct tends to inhibit the maturation and coordination of funding for propulsion efforts from basic research to applied R&D and demonstrations across DoD. INNOVATIVE CONTRACTING MECHANISMS This section discusses the issues and opportunities associated with a large and growing portion— sustainment—of DoD expenses for aircraft propulsion systems. As shown in Figure 7-1, approximately $4.2 billion of the total $7.1 billion annual DoD gas turbine propulsion budget is spent on the sustainment of existing engines. In addition, fuel for the existing fleet (assuming a very conservative $1/gallon) is estimated from FY04 data to cost $4.7 billion annually. The projected weapon system force structures for the next 15 to 20 years indicate that current systems will dominate and that new systems will be acquired at slower rates and smaller numbers than the legacy fleets they replace. This will lead to ever-increasing aging of the DoD gas turbine fleet. By 2020 most of the existing gas turbine propulsion systems will have reached or exceeded their design life and will need service life extensions. Unless strong action is taken, the growing proportion of the DoD propulsion budget allocated to sustainment of and fuel for the existing fleet will become a death spiral, wherein the portions of budget allocated to technology and development budgets must be always reduced.
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs FIGURE 7-1 Investment in turbine engines by DoD. SOURCE: Burns (2005). Reducing the costs of sustainment and fuel therefore becomes a dominant issue. In many cases new business models may be required to capture the opportunities. However, the new business practices coupled with modest investments would have high leverage since approximately 60 percent of all DoD propulsion funding, not counting fuel costs, is dedicated to sustainment. Current business practices, with different funding sources for CIPs, depot maintenance, and support on the one hand and operational fuel cost on the other, create artificial roadblocks preventing maximum return from past S&T investments. An example of the need for innovative contracting is the TF33 upgrade program to reduce fuel consumption on the B-52. CIP funding is only able to provide a digital engine control, a fuel management unit, and a compressor gas path outer case seal, which together reduce the specific fuel consumption (SFC) by 1.5 percent. However, a 6 percent reduction in fuel consumption could be realized if other improvements developed by the engine OEM through completed S&T programs could be transitioned to the TF33 engine. Current CIP funding is inadequate to cover the cost of such transitioning. Under an alternative innovative contracting model, the engine OEM could be asked to produce the detailed design at no cost. The engine depot would purchase the parts by means of a performance-based logistics process, perform the engine upgrade, and test the engines to verify component improvement. In exchange, the Air Force would reimburse the OEM with 25 percent of the net fuel savings over the life of the aircraft. An additional 25 percent of the savings would be awarded to the S&T community, and the rest of the savings would be realized by the fuel community. This model could incorporate off-the-shelf improvements and produce great savings for DoD. An example of the need for incorporation of new technologies is the Air Force’s F108 engine in the KC-135. The F108 is the military version of the CFM56 and much older in configuration than the CFM56 commercial engine fleet. The commercial CFM56 engines have a utilization rate of 3,000 hours/year and are overhauled and upgraded to the latest configuration approximately every 3 years (at the life limit of 9,000 hours). These upgrades address items critical to flight-safety, unscheduled engine removals (UERs), durability improvements, and fuel economy. Since the Air Force’s utilization rate is 500 hours/year, the 9,000-hour life upgrade occurs only every 18 years unless driven by UER or safety items. Even when returned to the depot prior to the 9,000- hour limit, the engines are not upgraded to the latest configuration but are returned to service in their original configuration or with minimal upgrades to fix the source problem. A complete rather than partial upgrade to the latest commercial configuration anytime
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs overhaul is required would reduce the fuel burned and enable the engine to stay on wing longer, with improved safety and performance, thereby saving overall support cost. Recommendation 7-6. To reduce the cost of fuel burn and of sustaining the portion of the existing fleet that will be in service in 2020, DoD should develop innovative contracting methods to facilitate the incorporation of evolving technologies into existing engines. MITIGATING TECHNOLOGY RISKS Under the current DoD acquisition process for new big aerospace systems (i.e., aircraft of all kinds, missiles, launch systems, complete space systems of all types), the choice of concept approach—that is, how they propose to meet the top-level mission requirements and needs—is left entirely to the large prime contractors (e.g., Boeing, Lockheed-Martin, Raytheon, Northrop Grumman). There is very little incentive for these large companies to take additional risks by inserting significant new technologies. They would rather use as much commercial off-the-shelf hardware, software, and other equipment as possible so that they get to production as quickly as possible and start marking up their prices to make large profits on high volume sales. Developing new technologies to increase the probability of meeting mission requirements just increases the financial risks early in the program and presents the risk of cancellation (by Congress if no one else) if the developments issues and problems get too large during the DDR&E phase of the respective projects. There are numerous examples of risk aversion throughout the recent history of government procurements. The tremendous pressure to avoid the risk of developing new technologies to meet new mission needs (because of the potential financial risk to the contractor) has caused propulsion technology to atrophy. A remedy for this barrier to the use of new technologies to enable or enhance mission capabilities is to provide explicit financial incentives to prime contractors and to openly assume more of the early development financial risks (Jobo, 2003). The development and fielding of a new DoD space system might exemplify how this would work in terms of new procurements. Since all the launch vehicle capabilities are set for the next 15 or 20 years through the mandated use of evolved expendable launch vehicle (EELVs) in that time frame, the amount of mass injected into low Earth orbit (LEO) is therefore also fixed for that time frame. The only way to increase useful payload mass for accomplishing the mission with increased margins and reliability would be to incentivize the use of new spacecraft bus technologies such as structure, power and propulsion (which together make up 80-90 percent of the mass injected into operational orbit) so that the payload fraction can be increased to 50-70 percent of the injected mass. This would stimulate the development and insertion of new technologies that will achieve such as much higher specific mass (power/weight), more advanced power sources, and energy storage systems, and better-performing in-space propulsion systems such as high-power plasma accelerator thrusters. Government customers must offer these incentives if they wish to mature key new spacecraft technologies for important defense missions in a reasonable period of time without putting all the risk on the prime contractors. ADDITIONAL ISSUES This section describes various important topics not covered elsewhere in the report: (1) infrastructure needs for aerospace propulsion, (2) education requirements, (3) basic research requirements, (4) leveraging national resources for world-class aerospace propulsion, (5) foreign efforts in aerospace propulsion, and (6) related environmental issues.
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs Infrastructure Gas Turbine Research The lead organization within DoD for the development of advanced aerospace propulsion technologies is the AFRL, which maintains key research facilities and technical expertise necessary for the development of advanced turbine engines. As with access-to-space and in-space propulsion research, AFRL may leverage NASA research activities related to gas turbine engines (NRC, 2006a). The gas turbine industry has progressively decreased its experimental infrastructure over the past two decades, relying on AFRL to support the complex experimentation necessary to overcome key technical barriers. Many of the AFRL’s research facilities are 20 or more years old and need major improvements to meet the development needs of future warfighters. Infrastructure improvements will be needed in terms of increased airflow and temperature; increased drive horsepower, fuel supplies at maximum pressure and temperature; common adaptive hardware to accommodate transient inlet temperature, pressure, and velocity profiles; and quick-response, real-time nonintrusive (laser) instrumentation and data acquisition. Technology facilities that are among the candidates for construction or upgrade to meet future warfighter needs are listed here, along with some cost estimates. Compressor Research Facility and an aeronautics laboratory. A national facility for full-scale demonstration of innovative compressor designs would provide low-cost proof-of-concept tests. Estimated operation and ongoing upgrade cost: $4.5 million per year. National combustor development facility. AFRL and Arnold Engineering Development Center (AEDC) have jointly indicated a desire to perform the validation for VAATE combustors for propulsion systems for future warfighter systems such as Joint Strike Fighter (JSF), long-range strike, and Joint-Unmanned Combat Air System in an efficient, affordable, common national facility to be located at AEDC. Estimated cost: $6 million per year. National Aerospace Fuels Research Complex. AFRL has the only aircraft fuel system simulator in the United States that is used for fundamental research, exploratory development, and in-house development of advanced fuels, additives, and fuel system components. This versatile facility is in need of annual upgrade. Estimated cost: $900,000 per year. Aerothermal Research Facility. This facility is critical for studying turbine blade loading, testing high-temperature blade designs, and studying blade heat transfer. Estimated upgrade costs: $1.3 million per year. Turbine Engine Fatigue Facilities. Used for structural evaluation and life assessment of hot section components. This facility is a key asset for achieving predictions of turbine airfoil life. Estimated costs: $300,000 per year. Fuels Research Jet fuel costs have more than doubled since 2004, and this rising cost of jet fuel is a large expenditure for DoD. Estimates show that the DoD fuel bill is $6.8 to $9.4 billion per year higher (compared with 2004) due to fuel price hikes and the additional cost of transporting fuel to the battlefield. Finally, DoD needs to operate with a smaller variety of fuels for better logistics, and it needs advanced fuels for the thermal management of aerospace vehicles. To develop advanced fuels requires state-of-the-art analytical chemistry laboratory facilities, small-scale, well-controlled engineering test apparatus, large-scale extended duration facilities, and smaller-scale aircraft fuel system simulators. Most fuels research facilities have been closed or mothballed recently, and the AFRL fuels research facility is over 20 years old. Suggested gaps are these: Fuels analysis facility. The successful development of advanced fuel and sensor technologies requires analysis of chemical and physical properties of fuel. Quantitative analysis facilities need
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs upgrading to maintain state-of-the-art capabilities. Annual investment in this activity would be $3.2 million. Equipment for synthesizing additives. Synthesis of novel chemical additives that improve the operating characteristics of hydrocarbon fuels requires the ability to study wide ranges of chemical functionalities. Equipment such as standard reaction/distillation system hardware and oligomer and polymer synthesis hardware is required for synthesizing smart additives. Annual investment in this activity would be roughly $3.0 million. Fuel thermal stability studies. Test facilities and instrumentation are required to study the thermal stability of high-temperature aerospace fuels for thermal management and characterizing nanotechnology-based sensors. Establishing a modeling and simulation facility composed of a Beowulf Cluster would significantly enhance current capabilities for developing and using computational tools. Annual investment in this activity would be about $1.8 million. Hypersonics Research Only a few hypersonic high-enthalpy facilities exist in the United States. They all suffer from various limitations. Facilities used to test scramjet engines for relatively long duration are vitiated (impure) air tunnels in which the free stream contains combustion products and in which the enthalpy is limited to below Mach 8. The shock tunnels and expansion tunnel at the Calspan-University of Buffalo Research Center, Inc., the Caltech T5 shock tunnel, and the General Applied Sciences Laboratory expansion tube range in enthalpy up to Mach 20, but are all short-duration facilities (1 to 10 msec) and also have other limitations, including free stream dissociation. An example of a successful and ongoing collaborative hypersonic test facility is the 1-MW radiatively driven hypersonic wind tunnel/MARIAH II (Mansfield et al., 2005). MARIAH II partners the AEDC with other groups to develop a long-duration, true-enthalpy, clean-air, high-Mach-number hypersonics testing capability. The enabling concepts under development for this capability include cold air storage at ultrapressure with energy addition downstream of the throat to obviate containment of high pressure and hot air via high-energy electron beams to Mach 12 with subsequent magnetohydrodynamic acceleration for Mach 15. Finding 7-2. Detailed measurements in the free stream and in the flow fields of tested articles, particularly in the engine combustor, could provide essential data for validating simulation methods. A further technology shortfall is an inadequate knowledge of reaction rates, in particular the coupling of vibrational excitation, dissociation, and surface chemistry. Ground testing using hypersonic high-enthalpy facilities is needed to develop numerical simulation tools that take proper account of high-enthalpy effects. Such tools can then be used with greater confidence in the design and preparation of flight tests. Recommendation 7-7. AFRL should maintain a core competency in propulsion technologies by strengthening its unique infrastructure to meet future warfighter needs. Over 3 years, $13 million per year should be added to the AFRL propulsion and power 6.2 budget for gas turbine facilities, $8 million per year for fuel research, $8 million per year for a hypersonics research facility, and $2 million per year for numerical simulation tool development to achieve the critical additions and improvements to AFRL infrastructure identified in this study. Education The current and planned levels of DoD science and technology (S&T) programs are greatly reducing the number of trained propulsion workforce in the United States (NRC, 2001). Planned DoD S&T funding is one-half to one-third of FY00 levels, but when Air Force fixed costs are taken into account, the effect on university and contractor manpower is magnified.
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs This finding strikes to the very heart of the country’s technical advantage and is not easily reversed. S&T programs are the main training ground for all levels of propulsion engineers and scientists. The major reductions in S&T programs since FY00 are negatively impacting not only the rate of development in basic areas such as materials, computational fluid mechanics, structures, controls, health monitoring, and prognostics, but also the number and the quality of people who are attracted to these fields. Reduced government support in S&T has resulted in the downsizing of university programs in the propulsion area that will eventually result in an unacceptable shortage of well-trained young engineers. The committee believes this loss in number and quality of people to be the worst long-term effect of the current DoD funding profile. The committee urges DoD to aggressively pursue strategies to reduce sustainment and other recurring costs so that more funding can be applied to investing in the technology base that supports the future and return the S&T funding to world-class levels. The Commission on the Future of the United States Aerospace Industry (Walker et al., 2002) recommended that the federal government significantly increase its investment in basic aerospace research. The commission went on to say that investment “enhances U.S. national security, enables breakthrough capabilities, and fosters an efficient, secure and safe aerospace transportation system.” The committee’s concerns are further supported by the statistics below and reinforced by some recent studies (Gibbons, 2004; NRC, 2004, 2006b): Over 26 percent of the aerospace workforce will be eligible for retirement in 2008. The proportion of aerospace workers 30 years old or younger dropped from 18 percent in 1987 to 6.4 percent in 1999 (NRC, 2004). Aerospace engineering degrees awarded during 2003-2004 were as follows: B.S., 2,232; M.S., 915; and Ph.D., 210. The share of doctorates awarded to U.S. citizens declined from 54.4 percent to 42 percent between 1999 and 2004. Further, to continue the development of young propulsion professionals, the studies cited above put forward a set of objectives (Walker et al., 2002; Gibbons, 2004; NRC, 2004, 2006b): Develop, fund, and implement a mentoring program for young engineers. Provide scholarships and fellowships to pursue advanced degrees in aerospace propulsion. Sustain robust S&T projects in basic and applied research to attract, train, and retain highest caliber young engineers and scientists. Increase the recruitment of young U.S. citizens educated and trained in mathematics, science, and engineering disciplines into propulsion engineering. Finding 7-3. It is critical that the government provide the resources needed to maintain and improve university education and research programs that train undergraduate and graduate propulsion engineers. Funds are needed for developing innovative educational programs, such as distance learning, in the area of propulsion. Additionally, the government should provide fellowships for promising students in graduate school, fund a robust, long-term S&T propulsion program that will employ graduating engineers, and maintain and upgrade university propulsion research facilities. Recommendation 7-8. DoD should increase S&T funding levels to support warfighter needs. It should ensure that significant portions of propulsion S&T funds continue to support research at universities. This has the additional benefit of training a cadre of future government and industry S&T professionals as well as supporting research facilities at those institutions. Basic Research Technology is an enabler for advances in aircraft engines and missiles capabilities, and much of the technology is underpinned by basic research. Examples of basic research advances that have made the
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs transition into design include computational procedures for the design of complex three-dimensional turbomachinery, directionally solidified turbine blades leading to single crystal airfoils and blades, and the software and hardware for full-authority digital electronic engine controls. Basic research, conducted not only at AFRL and the main DoD laboratories but also at many world-class academic institutions and at a smaller number of industrial R&D laboratories, provides the essential foundation on which to develop and validate component and propulsion system design. According to the AFRL, for turbine engines to provide the capabilities needed by future warfighters, basic research should undertake the following (AFRL, Undated): Need better life prediction for components Do not have a full understanding of heat transfer in turbines Do not have validated life prediction tools Do not have control strategies for improved life Need to identify robust turbine engine component loading limits and establish the potential for flow control to exceed those limits Compressors, turbines, combustors Need for studies to be completed in compressible flow environments Need to address thermal management for high Mach applications Need bearing thermal management capabilities high Mach engines Need clean-burning, nonfouling, high-heat-sick fuel technologies Need to establish the potential for pulse detonation technology to improve propulsion system affordability and meet performance goals Need 6.2 funds for industry development of technologies for VAATE II and III Need turbine engine approaches to drive airborne megawatt power systems Need to establish role of advanced turbine engine technology for small weapon system propulsion Need to consider technologies that could have impacts beyond 2017 To address these challenges, research on high-impact technology research programs are under way in-house at AFRL/PR. The research falls in three VAATE focus areas—durability, versatile core, and intelligent engines (AFRL, Undated): Durability Turbine engine structural dynamics, and Turbine high-stage loading and heat transfer. Versatile core Combustion research and diagnostics development, Compact core technologies, Pulsed detonation technology development, Emissions reductions via fuel additives, High-heat-sink fuels, Enhanced low-temperature fuel performance, Smart fuel technologies, and Ultimate liquid lube system for large turbofan/turbojet engines. Intelligent engines Assessment of advanced turbine engine technology, Mechanical systems prognostics for intelligent engines, Innovative aero approaches for compressor high-stage loading, Bearing performance and model validation, and Augmentor high-impact technologies (AFRL, Undated). This research is accomplished through individual projects with three key elements:
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs Fundamental approach to long-term technical challenges; Modeling and simulation to reduce costs and to promote a scientific approach; and Critical experimentation to validate and refine models. These projects focus on enabling high-risk, high-payoff concept development along with basic research investigations to overcome technical barriers that hinder breakthrough technology development. However, enabling research efforts such as these (see Box 7-1) have been declining over the last decade because the available funding cannot support them. It is critical that industry be provided 6.2 (applied research) funding to pursue high-risk, high-payoff technology programs if far-term, game-changing capabilities are to be provided to the warfighter. Key areas for basic research on propulsion technologies, such as the technologies for gas turbine engines (GTEs) discussed in Chapter 1, are the following: Modeling and simulation. New methods for using modeling and simulation not only in design but also in development. The goal is to have more effective processes both to get from idea to actual system development and to enable root cause diagnosis and the addressing of problems that occur later in the development cycle. Intelligent components and intelligent engines. These include not only smart components that improve performance but also enhanced capabilities in health monitoring and prognostication (including sensors and actuators) that will improve safety and reduce ownership cost. Ensuring robustness to variability. This includes designing engines and components to tolerate variability, either from the manufacturing process or from field usage. Potential benefits include enhanced durability and operability and decreased cost. Materials. A quantum jump in the operating temperature of turbine blades above 2300F will require a new base material other than nickel; to date, only platinum has the balance of properties required for operation at higher temperatures. Future propulsion materials requirements include improved material systems for disks and airfoils together with coatings that will withstand the operational stresses and degradation modes at these high temperatures. Coatings are important to protect the underlying material from environmental degradation, but these coatings may be prime-reliant, which means that failure will imminent after loss of coating integrity; this poses operational constraints, which may, however, be obviated to some degree by prognosis. The conventional screening of new material chemistry needs to be replaced by analytical materials modeling tools whose results can be verified by targeted experiments (NRC, 2006a). The direction in advanced technology for ceramic materials is away from monolithic structural ceramics to ceramic matrix composites (CMCs) that have inherent toughness. Much research is taking place on these materials. Distributed propulsion. This includes research on arrays of propulsors highly integrated into, and synergistic with, the airframe flow, to provide incremental changes in aircraft performance. Box 7-1 Example of Breakthrough Basic Research: Positron Propulsion There is an exceedingly revolutionary, far-term fuel/energy source on the horizon: positrons. Research on the main enabler of this concept, the long-term storage of positrons as positronium, is in progress. In terms of energy density, positrons are eight orders of magnitude more energetic than chemical fuels. The energy density of chemical sources is approximately 50 MJ/kg. Nuclear energy densities are 10 million times those of chemical energy. Antimatter energy density is 180 MJ/μg. This unprecedented energy density could be utilized for a wide spectrum of applications, military as well as commercial and industrial. The technology could enable deep space propulsion using positron thermal
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs rockets to replace the proposed nuclear thermal rockets. One key aspect of positron energy is that when an electron and positron annihilate, the gamma photons produced are too weak to cause photonuclear effects, so positron annihilation would produce no nuclear residue. The basic technologies for conducting positron research are production, moderation, storage, and conversion. The most common way to make positrons is to accelerate a beam of electrons into a heavy metal target (e.g., tungsten), generating the positrons by bremstrahlung and pair production mechanisms. Another way is to use a deuteron accelerator and a diamond (carbon) target to make radioactive nitrogen, which decays to produce positrons. Personnel at the University of California at Riverside are proposing a modification of the deuteron accelerator approach that promises a significant increase in the positron production rate. Most methods of positron production produce them at very high energies. To be useful, positrons need to be slowed or moderated. A popular way to moderate positrons is to impact a positron beam into a heavy metal target and let elastic and inelastic scattering slow the positrons. Typical efficiencies of this process are approximately 10-5 (one out of 100,000 positrons survives). The energy is typically reduced from 1 MeV to 1 to 10 eV. These slow positrons are electromagnetically manipulated into various forms of positron traps. An alternative method of moderation, which uses solid neon, has a moderation efficiency of 5 × 10-3 (0.005), nearly a hundredfold improvement. AFRL Munitions Directorate personnel are building an experiment using solid hydrogen that promises a 10- to 100-fold improvement over neon (i.e., an efficiency of between 5 × 10-2 and 5 × 10-1). These experiments are projected for the 2006 to 2007 time frame. Positrons are usually stored as a bare, positively charged plasma in electromagnetic devices called Penning traps. However, one of the most exciting facets of positron research is storing neutral positronium atoms. The neutrality of positronium solves the problem of Coulomb repulsion. A positronium atom is a bound state of an electron and a positron. Its structure and physics are much like those of a hydrogen atom with the proton replaced by a positron. Positronium atoms left to themselves will annihilate in less than 142 nsec. Chiueh (1997) and Shertzer et al. (1998) say that long- lived positronium may be possible by applying large crossed (perpendicular) electric and magnetic fields to positronium. They indicate that positronium may be stabilized for up to a year with 10-T magnetic fields and 104 V/cm electric fields. Recently, government contractors have found very long stabilization times at field strengths of 3 T and approximately 103 V/cm. Positronics Research LLC and AFRL are working with DARPA to fund and perform experiments that will store energy at densities 15 times that of chemicals. This effort will be in collaboration with the Chemical Division of Argonne National Laboratory, which will modify its linear accelerator to provide positrons for DARPA’s positron storage and production program.1 1For additional information, see http://www.nasa.gov/mission_pages/exploration/mmb/antimatter_spaceship.html. Last accessed on June 4, 2004. Finding 7-4. It is the view of the committee that basic research is not a linear process. Thus, it sees opportunities for basic research as not limited to resolving problems at low technology readiness levels (TRLs) but also possibly present at system levels (TRL 6, for example). To capitalize on these opportunities, there needs to be substantive engagement between researchers (university, company, or government) and the development community. In addition, since these problems are likely to span disciplines, multidisciplinary research teams rather than the traditional academic single investigators are increasingly becoming the most effective way to attack important research issues. Recommendation 7-9. DoD should restore 6.2 and 6.3 technology development funding to levels that give buying power equal to that which prevailed when the United States had held an undisputed lead in engine technology—i.e., the time when the F100 and F110 engines were being developed. DoD should aggressively pursue strategies to reduce sustainment and other recurring costs. It should increase 6.1 funding commensurately.
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs efforts. Some of this waste of financial and intellectual resources could be avoided by making accessible the results of past projects, even ill-fated ones. Finding 7-5. A focused effort, probably by DDR&E, to catalog and make accessible the findings of past technology programs would be highly useful. Recommendation 7-10. The Director, Defense Research and Engineering (DDR&E), should focus on cataloging and making accessible the findings of past technology programs. It could perhaps combine the databases of VAATE, Integrated High-Payoff Rocket Propulsion Technology (IHPRPT), and Integrated High-Performance Turbine Engine Technology (IHPTET) at the lower taxonomy levels to enhance technology cross fertilization. DDR&E should also establish a feedback process and cross-cutting flow of technology development that comprises the S&T, development, acquisition, and sustainment phases. Finding 7-6. The technology maturity steps conceived by the Air Force seem to proceed in one direction from 6.1 research through sustainment. Rather they should form a closed loop. The committee sees a tremendous advantage in having open and active communication between S&T through acquisition and sustainment, as shown in Figure 7-2. For example, S&T researchers, who are some of the brightest engineers and scientists in this country, could certainly contribute to the optimization, redesign, or modification in the development, acquisition, and sustainment phases of the ideas they converted into technologies in the first place. In the past, the Air Force had a design team that drew up the system configuration requirements for the technologies the Air Force would pursue. This capability has been lost, and today it is the contractors that put together the system architecture. Recommendation 7-11. The Air Force should establish within each major program office an in-house design group to bring it better overall insight into the systems it is acquiring and guide it in directing its resources from S&T through sustainment to meet the system requirements it has laid out. The Air Force would execute the active closed-loop communication between the technology steps. The discussion above deals with the benefits of leveraging to the military. Leveraging can also benefit the commercial sector. NRC (2001, p. 8) states as follows: Commercial aerospace exports, which are dependent in large measure on the technology base that is in turn supported by the Air Force, are traditionally by far the largest positive contributor to the U.S. balance of trade. Cutting-edge aerospace products will continue to be essential to U.S. dominance of the twenty-first century battlespace…. [However,] the overall positive aerospace trade balance has fallen by about 35 percent since 1998 (Douglass, 2000a).
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs FIGURE 7-2 Proposed flows of technology development and product development. SOURCE: Schafrik (2005). Figure 7-3 further illustrates the positive balance of trade that the aerospace industry enjoys. In good times, leveraging is wise. In the current S&T climate, leveraging may not be sufficient but is nonetheless necessary. FIGURE 7-3 Balance of trade by industry, 1998. SOURCE: Douglass (2000b).
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs FOREIGN AEROSPACE PROPULSION EFFORTS Gas Turbine Engines A GTE industry is both a military and economic power enabler.3 Four countries currently design and build large modern GTEs: France, Russia, the United Kingdom, and the United States. While the United States is generally dominant, Russia’s GTE industry is reemerging. The United Kingdom and France, and indeed the European Union are heavily investing in GTE research and could achieve parity with the United States in one or two decades. China and India are rapidly evolving. China in particular is making great strides and appears to have a long-term strategy to become a propulsion power. They should have the resources in terms of both skills and funds to achieve this goal. Several countries have limited capabilities, such as component design, including the Czech Republic, Germany, Italy, Spain, Sweden, and Japan. Many others have some limited manufacturing capabilities, including Iran and Serbia. The dividing line is the difference between world-class, high-temperature military and commercial GTEs and throwaway, small GTEs. Entering the market for small throwaway engines is much easier with widespread proliferation of the necessary technologies. Russia is relying on life cycle cost as a critical and major technology driver, a marked difference from the Soviet era, when the engines could not run very long between overhauls. It is also teaming with others (China, Europe). Teaming with Russia could help China realize its ambitions. Russia has the capability, but it may take 20 years to attain parity with the United States. Its economy is strengthening, particularly due to its oil and other energy reserves, and its technology could spread to other countries. The United Kingdom is emphasizing GTE R&D. Rolls-Royce develops large world-class commercial engines on a par with those of GE, in particular the GE 90. The U.K. military programs tend to be cooperative ventures. France appears to place more emphasis on military engines, for which it has an indigenous design and development ability. The M88 is France’s most advanced production fighter engine. Aside from SNECMA, Turbomeca, Microturbo, and ONERA (the French aeronautics and space research center) are strong entities. A large portion (80 percent) of French research works on life-cycle cost, noise abatement, fuel consumption improvement, and emissions reduction. SNECMA is teaming with GE on CFM56 (a program of the U.S. and French governments), and Pratt & Whitney is teaming with Japanese and European companies on the successful V2500 engine. In many cases it is difficult to distinguish national borders, because programs cut across countries and corporations. While some laws prevent technology export, such laws are generally weakening. Moreover, it is difficult to limit the export of know-how as people become more mobile. China is working hard to develop its own industry. The national objective is to become world class. There is evidently a comprehensive plan in place. China has completed its first indigenous development program and transitioned an engine to production. China has growing resources—in terms of both people and funds—and a long-range vision. The United States maintains a lead of a decade (or more) in R&D. Europe poses a current threat in the commercial arena. The United States is a leader in some emerging fields, such as fuel cells and more electric aircraft, but others are catching up. It is unclear if VAATE is the whole answer. It certainly does not cover the environmental technologies that are arguably the key to winning the commercial race. The European Union is seeking pre-eminence in aerospace. Commercially, it is either there or close. It has an articulated and well funded program, the Advisory Council for Aeronautics Research in Europe (ACARE), and clear goals. By contrast, NASA is floundering in aeronautics. The impact on military GTE capabilities of losing (or, arguably, of having already lost) commercial leadership in GTE (and commercial aircraft in general) is unclear. It is likely that we will not know this for decades. Probably 3 This section is based, in part, on discussions with representatives of the National Air and Space Intelligence Center at the University of Dayton on October 20, 2005.
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs owing to a combination of workforce and marketing requirements, several U.S. multinational companies—among them, GE and Pratt & Whitney—have set up centers of excellence in the European Union, Russia, China, and India. These centers employ the best brainpower available in those countries and are training the future aeropropulsion workforces. In the long term, this will sharpen competition for U.S. exports and shrink the U.S. lead in commercial aeropropulsion. Finding 7-7. The committee found that the United States still maintains a lead in military GTE—probably about half a generation. In commercial GTEs, the United States has parity, but this position is eroding. The United States is on a par with the rest of the world for scramjets, solid rockets, electric propulsion, and pulse detonation engines (PDEs). It lags behind other countries in ramjets and liquid rockets. Pulse Detonation Engines and Rockets No one has an operational pulse detonation engine (PDE) or pulse detonation rocket (PDR), but they are a hot topic for research, with some 19 countries at least somewhat involved. The cost of PDE/PDR research is lower than the cost of research on GTEs. PDEs and PDRs still have many technical hurdles to overcome but are a promising new technology for some applications. Russia’s research in this arena is more fundamental (basic) than that in other countries. France, Japan, and Russia are developing applications. The French seem to be moving toward development and are collaborating with the Russians. They are arguably the most likely to have the first operational PDE. They have a plan and resources. The Japanese are also heavily into PDE research. PDEs are a serious possibility for low-cost missiles, and the French and Chinese are traditionally missile exporters. The committee expects that PDEs could be deployed in 10-20 years, probably on swarms of unmanned aerial systems (UASs) and missiles. The United States is nominally at par with the rest of world in PDE research. The Europeans dominate in the somewhat related area of internal combustion aero engines. Ramjets More than 13 countries are working on ramjets. The key players are China, France, Germany, India, Japan, Russia, Taiwan, and the United States. The Europeans are the world leaders—especially the French in liquid fueled ramjets. The Russians are key players in other areas. There are operational systems in India and many other countries. The Germans have boron-fueled versions. India is developing systems based on Russian technology. The Chinese have an indigenous program based on Russian designs. The Japanese have efforts on liquid-fueled ramjets and are working on a hydrocarbon-fueled air turborocket. Taiwan has a world-class research institute and is working on a system. Others, including Iran, Israel, Netherlands, South Africa, South Korea, and the United Kingdom, are also pursuing capabilities. As many as five new systems could become operational within the next 10 years. The United States does not have operational parity in ramjets. The AA-12 ramjet derivative is an answer to the United States advanced medium-range air to air missile. Hypersonics There are a number of hypersonic systems in R&D, but nothing is near deployment. Options include hydrogen and hydrocarbon scramjets, rocket-based combined-cycle engines and turbine-based combined-cycle engines. Russia is the leader, with France next in line. Australia, China, Germany, India, Japan, and are also coming along. The United States is arguably on a par with or somewhat ahead for hydrogen and hydrocarbon systems.
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs Rockets From the 1990s until today, many players have entered the field, including India, Iran, North Korea, and Pakistan. When the United States is compared with the rest of world in rockets, it can be seen to be largely still in the 1970s, and the Russians have been and remain ahead. The United States routinely purchases Russian designs, components, and whole engines. It has parity in deployed systems and is doing research on solids, but it is not doing well on propellant design (the United States has 35 propellant chemists who can be put to work on this problem versus thousands in China). In liquid rockets, the United States is lagging and could continue to lag. The U.S. programs were turned on and off while the Russians kept moving ahead. For liquid boost and hydrogen systems, the United States and Russia have very similar levels of technology. Russians systems represent the state of the art in LOx/HC. In upper stage rockets, the competition is a little bit ahead of the United States. If IHPRPT Phase III is accomplished, U.S. capabilities will greatly improve. But it is unlikely, with present investments, that it will achieve Phase II before 2015, and it is unlikely to even get to Phase III. With IHPRPT investments, the United States will get close in solids but have a shortfall in tactical systems. This is an area that requires serious study and committed investment. Space Propulsion For in-space propulsion, the United States abandoned Hall thrusters and the Russians took over. The United States has now pursued the technology for 10 years and has achieved parity in thrusters and has surpassed in power processing units. Overall, it has parity for in-space electric propulsion. ENVIRONMENTAL ISSUES Historically, DoD has invested little in engine emissions technology, deferring to NASA investments and expertise in this area. However, in recent years, much concern has been expressed over emissions from high-performance military aircraft. While DoD aircraft equipped with afterburners do meet the latest International Civil Aviation Organization (ICAO) standards, the ICAO threshold may not be sufficient, because military bases are required to meet National Ambient Air Quality Standards. Thus, research into clean fuels, fuel additives, and emissions of nitrogen oxides (NOx) is required. Some key technical challenges remain, including (1) increased engine performance without higher NOx, (2) increased combustor loading without affecting ignition and combustion stability, and (3) decreased combustor cooling without impacting durability and life. Also of note is the issue of compliance with the numerous international environmental laws and regulations on aerospace fuels. Finding 7-8. Environmental restrictions require the military to have a national security exemption for the use of JP-8 fuel in tactical vehicles in the United States. Additives and F-T type fuels that lack aromatic content have the potential to reduce soot and particulate emissions in a number of aircraft and engines in a cost-effective manner. Aircraft signature can be significantly decreased by soot-reducing additives, and the life of thermal barrier coatings can be significantly enhanced. The Environmental Protection Agency set particulate matter 2.5 (particles smaller than 2.5 μm in diameter) standards in 1997. A key technical barrier is the lack of knowledge about which processes can control soot formation and the effects of additives. Warfighter aircraft performance improves at higher cycle temperatures and pressures, both of which increase NOx emissions. For example, increasing the cycle temperature to achieve 10 percent higher thrust can increase NOx emissions as much as eightfold. Modeling of turbulent combustion processes and active control is required to study the effects of pressure, temperature, and lean blowout on carbon monoxide (CO), unburned hydrocarbon, and NOx emissions.
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs Recommendation 7-12. DoD should add $2 million per year to the combined 6.1 and 6.2 funding in environmental issues to perform research into clean jet fuels, fuel additives, TBC life, and gaseous and particulate emissions. PAST AND PROJECTED FUNDING FOR S&T The United States has the technical capability to field the most advanced gas turbine engines in the world for both fighter and transport aircraft. However, the U.S. technology lead has decreased in the last 20 years and, in the committee’s opinion, now amounts to only 10 years or so. Development costs grow and qualification schedules slip when key technologies are not in hand at program launch. The adage “technology must lead the commitment” was coined over 40 years ago after several major engine development programs suffered serious setbacks. The National Aerospace Plane vehicle, which has so far cost $2 billion, is a good example of a development program launched without the supporting technology in hand. Advanced technology demonstration has slowed down in the military. The DoD S&T budget for propulsion has been cut to the point that the technology demonstration cycle time has lengthened from 2 or 3 years in the 1990s (which led to the F/A-22 and F-35 engines) to between 5 and 7 years in the VAATE program. This longer time between technology demonstrations will greatly slow the rate of technology incorporation into gas turbine engines and place the U.S. technology lead at grave risk. DoD investment leads and leverages outlays by the U.S. industrial base for turbine engines. Without substantial DoD long-term investment, industry is likely to invest only in turbine engine S&T that maximizes its near-term profits. Of all the services, the Air Force has the highest stake in maintaining turbine engine superiority and therefore contributes about 80 percent of the DoD S&T funding for turbine engines. Yet, of the approximately $7 billion FY04 DoD investment for turbine engine acquisition, sustainment, development, and S&T, Air Force S&T funding was only 1.8 percent—$138 million (burdened) in FY03. In discussing funding, one must distinguish between Air Force funding and overall DoD funding. The latter includes Army, Navy, and DARPA funding as well as funding for programs emanating directly from (DDR&E). The Air Force funding in PR accounts for roughly two-thirds to three-quarters of the overall DoD investment in this area. Within the Air Force, work related to aerospace propulsion is also conducted in materials and manufacturing and air vehicles. The Deputy Assistant Secretary of the Air Force for Science, Technology, and Engineering (SAF/AQR) told the committee at its first meeting that the Air Force annual S&T investment in propulsion and power (PR) was about $300 million and was not likely to change much in future years.4 This number reflects 6.2 and 6.3 funding only. Any 6.1 propulsion-related funding is accounted for separately as part of basic research, which is administered by the Air Force Office of Scientific Research (AFOSR). The propulsion budgets for FY04 onward are shown in Table 7-1. In FY04 and FY05 the Air Force PR funding levels were, respectively, $291 million and $297 million as the result of congressional add-ons above the Presidential Budget Requests (PBRs) of $251 million and $234 million. The Air Force projects outyear increases in PBR from $252 million in FY06 to $305 million in FY11. On the other hand, the overall DoD investment in PR over FY04 to FY07 is fairly flat, at $400 million to $410 million except for a spike of $440 million in FY05. The principal differences between Air Force and DoD funding are in turbine engine technology—IHPTET, VAATE, a high-speed turbine engine demonstrator, and revolutionary approach to time-critical, long-range strike (RATTLRS)—and in hypersonics—e.g., hypersonics flight demo (HyFly), and Force Application and Launch from the Continental United States (FALCON). 4 Jim Engle, Deputy Assistant Secretary of the Air Force for Science, Technology, and Engineering (SAF/AQR), discussion with the committee on March 1, 2005.
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs TABLE 7-1 DoD and Air Force Propulsion S&T Budgets for FY04 to FY07 (thousands of dollars)
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs The flatness of the numbers, however, is not indicative of the true picture, particularly in the 6.2 budgets. For example, Table 7-2 shows the breakdown of 6.2 funds in the gas turbine technology budgets from FY02 to FY06. Funding for 6.2 is the seed funding for the advancement of game-changing technology readiness prior to engine demonstration. The totals for lines 62203F/3066 plus 62203F/3048 taken together are fairly flat. However the 6.2 budgets also cover AFRL payroll and administration costs as well as additional internal taxes. The lowest three lines in the table show what is left for R&D. In-house R&D totals again are fairly flat, but the amounts for industrial R&D fall precipitously over the FY02 to FY06 period, as also shown in Figure 7-4. At this reduced level it is impossible to achieve the advances in capabilities that the Air Force needs to maintain air superiority. This confirms the statements to the same effect in Chapter 3 of this report. A consensus of the committee is that there has already been a significant erosion of the U.S. lead in propulsion technology and that a flat budget will lead to further erosion if these trends are not immediately reversed. Since the projected investments through FY07 are flat—they do not even cover inflation—one can expect only incremental improvements in technology over this period. Anything revolutionary would have to be at the expense of existing programs or would require funding above the projected levels. Research funding (6.1 and 6.2) is vital to the warfighter since it is the source of new ideas and technologies and promotes the education of new engineers and scientists in aerospace propulsion. It is painful to contemplate the consequences of further budget reduction from the present marginal levels of investment. In the event of budget reduction, funding priority in the 6.2 and 6.3 programs will be directed to warfighter needs. Again, 6.1 funding is extremely important for the reasons stated above. TABLE 7-2 6.2 Funding for Turbine Engine Technology Development (millions of dollars) Budget Item FY02 FY03 FY04 FY05 FY06a 62203F/3066 43.4 38.7 32.2 32.7 33.5 Payroll/administration 17.6 18.9 17.5 18.9 19.5 Taxes to Air Force, AFRL, and PR 2.6 2.3 2.3 3.7 4.5 In-house R&D 4.6 5.0 4.2 4.9 6.4 Industry R&D 18.6 12.5 8.2 5.3 3.1 62203F/3048 9.7 15.3 14.7 12.5 14.4 Payroll/administration 6.0 6.5 7.9 7.5 7.7 Taxes to Air Force, AFRL, and PR 0.7 0.8 0.9 1.3 2.0 In-house R&D 3.1 4.8 3.2 3.0 3.8 Industry R&D 0.0 3.2 2.7 0.7 0.9 Total 6.2 for in-house R&D 7.7 9.8 7.4 7.9 10.2 Total 6.2 for industry R&D 18.6 15.7 10.9 6.0 4.0 Total 6.2 for R&D 26.3 25.5 18.3 13.8 14.2 aIn FY06 $1.2 million for technicians no longer covered as part of AFRL taxes.
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs FIGURE 7-4 Technology development funding (6.2) for industry R&D on turbine engines. SOURCE: AFRL. REFERENCES Published Chiueh, Tzihong. 1997. Exotic atom: Double-helix positronium. Chinese Journal of Physics 35(4): 344– 352. Douglass, John W. 2000a. President, Aerospace Industries Association. 106th Congress: Industry tallies major gains on aerospace issues. AIA Update 5(6):2. Gibbons, Michael T. 2004. The Year in Numbers. American Society of Engineering Education. Available online at http://www.asee.org/about/publications/profiles/upload/2004ProfileIntro2.pdf. Last accessed on March 29, 2006. Jobo, Ronald. 2003. Applying the lessons of “Lean Now” to transform the U.S. aerospace enterprise: A study guide for government lean transformation. Cambridge, Mass: Massachusetts Institute of Technology. August 23. Available online at http://lean.mit.edu/index.php?option=com_docman&task=doc_view&gid=244. Last accessed on August 9, 2006. Mansfield, D.K., P.J. Howard, J.D. Luff, R.B. Miles, G.L. Brown, I.G. Girgis, R.J. Lipinski, G.E. Pena, L.X. Schneider, J. Grinstead, and R. Howard. 2005. The 1-MW Radiatively Driven Hypersonic Wind Tunnel Experiments Final Report. Arnold Air Force Base, Tenn.: Arnold Engineering Development Center. NRC (National Research Council). 2001. Review of the Future of the U.S. Aerospace Infrastructure and Aerospace Engineering Disciplines to Meet the Needs of the Air Force and the Department of Defense. Washington, D.C.: National Academy Press. Available online at http://www.nap.edu/books/0309076064/html. Last accessed on June 16, 2006. NRC. 2004. Evaluation of the National Aerospace Initiative. Washington, D.C.: The National Academies Press. Available online at http://www.nap.edu/catalog/10980.html. Last accessed on March 29, 2006.
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs NRC. 2006a. Decadal Survey of Civil Aeronautics: Foundation for the Future. Washington, D.C.: The National Academies Press. Available online at http://newton.nap.edu/catalog/11664.html#toc. Last accessed on August 21, 2006. NRC. 2006b. Rising Above the Gathering Storm—Energizing and Employing America for a Brighter Economic Future. Washington, D.C.: The National Academies Press. Available online at http://fermat.nap.edu/catalog/11463.html. Last accessed on March 29, 2006. OUSD AT&L (Office of the Secretary of Defense for Acquisition, Technology, and Logistics). 2003. Manager’s Guide to Technology Transition in an Evolutionary Acquisition Environment. Washington, D.C.: Office of the Secretary of Defense for Acquisition, Technology, and Logistics. January 31. Available online at https://www.dodmantech.com/pubs/MgrGuideToTechTrans.pdf. Last accessed on August 9, 2006. Schafrik, Robert. 2005. Materials Modeling and Simulation: Pathway to Radical Innovation. International Workshop on Accelerated Radical Innovation, March 10-12. Toledo, Ohio: College of Engineering, University of Toledo. Shertzer, J., J. Ackermann, and P. Schmelcher. 1998. Positronium in crossed electric and magnetic fields: The existence of a long-lived ground state. Physical Review 58(2): 1129-1138. Walker, Robert S., F. Whitten Peters, Buzz Aldrin, Edward M. Bolen, R. Thomas Buffenbarger, John W. Douglass, Tillie K. Fowler, John J. Hamre, William Schneider, Jr., Robert J. Stevens, Neil deGrasse Tyson, and Heidi R. Wood. 2002. Final Report of the Commission on the Future of the United States Aerospace Industry. November. Available online at http://www.ita.doc.gov/td/aerospace/aerospacecommission/AeroCommissionFinalReport Unpublished Larry Burns. AFRL/PRT overview/introductions. Presentation to the committee on April 5, 2005. Karen Ray, Defense science and technology reliance: Reliance planning process John Douglass. 2000b. Briefing to the Committee on the Future of the U.S. Aerospace Infrastructure and Aerospace Engineering Disciplines to Meet the Needs of the Air Force and the Department of Defense, on January 27, 2000.
Representative terms from entire chapter: