1
Overview

BACKGROUND

Study Tasks

Because rocket and air-breathing propulsion systems are the foundation on which planning for future aerospace systems rests, the Deputy Assistant Secretary of the Air Force for Science, Technology, and Engineering (SAF/AQR), with support from the Director, Defense Research and Engineering (DDR&E), asked the Air Force Studies Board (AFSB) of the National Research Council (NRC) to review and comment on the planning for propulsion development that is under way at the Department of Defense (DoD) and the commercial technical base for these air-breathing and rocket engines that allow access to space and for in-space propulsion systems (see Box 1-1 for the study’s statement of task). This full-spectrum propulsion study assesses the existing technical base in these areas and examines the future Air Force capabilities the base will be expected to support; it also defines gaps and recommends where future warfighter capabilities not yet fully defined could be met by current science and technology (S&T) development plans. The recommendations in this report may shape DoD engine development planning for the next 15 years and, possibly, military capabilities beyond that.



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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs 1 Overview BACKGROUND Study Tasks Because rocket and air-breathing propulsion systems are the foundation on which planning for future aerospace systems rests, the Deputy Assistant Secretary of the Air Force for Science, Technology, and Engineering (SAF/AQR), with support from the Director, Defense Research and Engineering (DDR&E), asked the Air Force Studies Board (AFSB) of the National Research Council (NRC) to review and comment on the planning for propulsion development that is under way at the Department of Defense (DoD) and the commercial technical base for these air-breathing and rocket engines that allow access to space and for in-space propulsion systems (see Box 1-1 for the study’s statement of task). This full-spectrum propulsion study assesses the existing technical base in these areas and examines the future Air Force capabilities the base will be expected to support; it also defines gaps and recommends where future warfighter capabilities not yet fully defined could be met by current science and technology (S&T) development plans. The recommendations in this report may shape DoD engine development planning for the next 15 years and, possibly, military capabilities beyond that.

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs BOX 1-1 Statement of Task The NRC will: Catalog anticipated military propulsion, spacelift, and in-space propulsion needs out to the year 2018. Review current and future planned civil, commercial, and defense S&T activities in the areas of propulsion, including turbine propulsion, spacelift, and in-space propulsion (2004-2018). Identify technical gaps and suggest rough order of magnitude (ROM), specifically applied S&T investments in these areas of propulsion. Identify specific opportunities for leveraging between the civil, commercial, and defense S&T activities in these areas of propulsion. Suggest strategies for future S&T activities in these three propulsion areas and the transition of these activities into potential military programs. Estimate the military capabilities that could be achieved at several different ROM levels of S&T investment in the areas of propulsion. The report will discuss (1) the potential range of warfighter capabilities that may need to be addressed by the propulsion technical base; (2) the programs/activities under way in the technical base; and (3) an initial discussion of perceived gaps, inadequacies, disconnects, and/or omissions. The report will provide the NRC recommendations for dealing with these issues and a rough order of magnitude estimate of the investment needed to address them. Capabilities-Based Planning The committee soon discovered that the capabilities-based planning currently in use throughout DoD is still quite immature and does not allow propulsion needs to be easily determined (Bexfield and Disbrow, 2005).1 1 Capabilities-based planning is a form of all-threats planning. It addresses growing uncertainty in the threat environment by using a wide range of possible scenarios to bound

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs Further, DoD’s S&T Reliance planning process has been modified to adapt to the capabilities-based planning process, interrupting the technology area reviews and assessments for 1 year. In addition, capabilities-based planning, which involves analyzing the alternatives for any given capability, does not specify system solutions until after the analysis is complete and a decision has been made. This methodology requires that the technical base programs funded within the S&T budget cover a broad spectrum of alternatives to enable potential future capabilities. Clearly, a technical base manager would seek maximum definition of the capabilities likely to be needed, while a capability definer, usually the warfighter, would like the technical base to be flexible and general enough to support any defined need. Unfortunately, at the present time, neither group can attain the clarity it would like, for a number of reasons. With this reality in mind, the committee sought to determine the extent to which future capabilities can be clearly defined and how the propulsion technical base can be structured to realize them. One would expect to see a propulsion technical base consisting of numerous programs at technology readiness levels (TRLs) of 2 or 3 awaiting orders to be matured to TRL 6 or 7. To do this successfully, realistic development roadmaps and funding profiles for crossing the gulf between TRLs 3 and 6 would be developed and kept up-to-date to create a basis for program objectives memorandum (POM) development. If this were the real-world case, the committee’s data-gathering efforts would have been relatively straightforward. However, the committee members assigned this task found, with a few exceptions, neither well-defined capabilities nor realistic technology transition planning. For the purpose of this report and in lieu of clearly stated needed capabilities, the committee’s analysis must be based on a great deal of informal and anecdotal information gathered through contacts with both capabilities planners and the technical base managers attempting to satisfy the planners and on briefings provided to the committee from the Services, DDR&E, the Defense Advanced Research Projects Agency (DARPA), the National Aeronautics and Space Administration (NASA), and various academic and requirements and thereby reduce the tendency to fixate on a certain threat, location, or set of conditions. DoD has shifted during the past 4 years from the threat-based model that dominated defense planning in the past to a model focused on capabilities—a model that places emphasis more on how an adversary might fight rather than on who the adversary might be or where the war might occur. This model is designed to plan for uncertainty—the defining characteristic of today’s strategic environment. A more detailed explanation of capabilities-based planning and processes is found in Chapter 2.

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs industry representatives. This is not to say that there are no documents that help define potential future technology developments. There are. In fact, one excellent example is the Department of Defense Space Science and Technology Strategy, cosigned by the Air Force Under Secretary and the DDR&E and discussed in Chapter 4 (DoD, 2004). However, in informal discussions with Air Force Research Laboratory (AFRL) and Air Force Space Command (AFSPC) personnel, it became obvious that this strategy was not the determinant of their marching orders and was considered to be only one out of several strategies in play. The committee concluded that even when clear direction exists, it is not always followed. Air Force Vision 2020 Capabilities Review and Risk Assessments reviews the global strike, homeland security, global mobility, global persistent attack, nuclear response, and space and C4ISR tasks or missions. The capabilities required are (1) command and control; (2) intelligence, surveillance, and reconnaissance; and (3) force application and force projection. Based on its review of the Air Force Master Capabilities Library (USAF, 2005) and presentations made to it, the committee highlighted some of the missions for which propulsion capabilities will be needed in the 2020 time frame, along with particular requirements: Global or Long-Range Strike Achieve desired effect(s) rapidly and/or persistently, on any target; With little or no warning time; In any environment, including those where weapons of mass destruction may be located; and Having been denied contiguous areas from which to operate. Global Mobility and Airborne C4ISR Global mobility (airlift and air refueling) Robust, sustained, adverse weather capabilities for deployment, employment, and redeployment and Survivable in radio frequency, infrared, and directed-energy environments. Airborne C4ISR Ability to shorten the kill chain by achieving better situational awareness; Platforms that can persist for hours/days;

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs Ability to operate from long distances; and Platforms that are globally connected (node in a sensors, datalink, and fused intelligence network). Reliability and Maintainability Consider that 60 percent of present military aircraft inventories will still be in service in 2018; Use the Component Improvement Program (CIP) to replace low-reliability parts; Utilize evolutionary programs to develop reliable, efficient, low-cost turbine engines; and Minimize total life cycle cost. Cross-cutting Capabilities/Needs Stealth/survivability; Inlet/exhaust integration and flow control Increased ranges and payloads; Increased size of operational envelopes (missiles and air-breathing); Address power densities for sensor suites, directed-energy weapons; and Environmental factors (noise, emissions). Rotorcraft Military uses 1960s and 1970s technology DoD has elected to use commercial technology and Commercial rotor technology not designed for DoD operating environments. Future needs for Air Force: rapidly deployable, highly reliable, survivable, all-weather, long-range platforms; Special operations, combat search and rescue, medium lift (e.g., noncombatant evacuation operation); Miscellaneous support and force protection; Army: responsive, deployable, agile, versatile, lethal, survivable, sustainable, and dominant anywhere; More range and payload;

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs Reduced logistics footprint; and Low operational and support costs. Small Unmanned Aerial Systems Hovering/perching small unmanned aircraft systems (UASs) and micro-UASs Micro: 1-3 nm range/day/fair wx, 0.5 lb payload, and field supportable; Man-portable: 1-2 hr endurance, 1-2 lb payload, and field supportable; and Tactical class: 10-12 hr endurance, 100 lb payload, and multimission. Munitions Range of requirements from low speed, long endurance to high speed, long range; Small size, low observable; Long shelf life; and Increased power requirements (USAF, 2005). Finding 2-1. Space strategy is clearly defined by the DoD Space Science and Technology Strategy. However, it is not being followed except as part of a broader set of strategies deriving from other considerations. There appear to be no similar documents at the level of the Office of the Secretary of Defense (OSD) that set forth the strategies for developing capabilities in other important areas such as aircraft systems and UASs. Recommendation 2-1. DoD should develop strategy documents containing clear guidance on future required capabilities in all system development areas and should pursue funding to achieve those capabilities. With a clearer understanding of the capabilities that are needed, technical base managers can reassess their programs to identify the program elements that will allow them to draw up the necessary technology transition roadmaps and funding profiles. Service leaders would then be in a much better position to assess alternative capabilities. The committee’s judgments are based specifically on data gathered about propulsion technology devel-

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs opment and not on the broader aspects of technology development and transition. For example, specified propulsion capabilities for assured access to space—survivable, low-cost, and reliable launch systems to enable on-demand launch of payloads to any orbit and altitude required—would be sufficient to focus propulsion research and development. However, the committee fears that basing important analyses of alternatives on less than fully considered cost and schedule realities does not serve decision makers well. Propulsion Research It is clear to the committee that unless additional emphasis is placed on propulsion, the technological lead the United States has enjoyed for so long, and perhaps taken for granted, will cease to exist. This very complex issue will become obvious to anyone who reads this report, and the decrease in funding for propulsion research in this country and the narrowing of the technological lead this country enjoys over other countries cannot be ignored. The culmination of a number of events, some interdependent and others independent, has gotten us to this point. The demands for resources for everything from fighting the war on terror; responding to natural disasters like the tsunami in Indonesia and Hurricane Katrina at home; to modernizing our military forces, health care, and education have made it very difficult to maintain funding for propulsion research. That fact, coupled with reductions in industry investments in propulsion research, has created a near crisis. Engine original equipment manufacturers (OEMs) historically invested a percentage of their engine sales in research for the next-generation engine. Significant reductions in military engine acquisitions for many years and the downturn in commercial sales since 9/11 have contributed greatly to this situation. Compounding the situation is the above-mentioned change in how DoD determines its requirements, from a threat-based system to a capabilities-based system. Although this change was made in response to the uncertainty surrounding any given threat and the need to be able to respond to an increasing variety of threats, it makes the job of the research and development (R&D) community much more difficult. In the past, this community could develop a propulsion system for a given threat, or at least devote its resources to such an undertaking. Today, it must spread its resources over a number of systems that have the potential to provide a given capability. As a result, none of these systems may get the priority or funding they need to reach maturity and provide the capability needed.

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs S&T Funding 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.2 This number reflects funding for 6.2 and 6.3 research 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 overall DoD funding includes Army, Navy, and DARPA funding as well as funding for programs emanating directly from DDR&E. The Air Force funding in PR makes up between 66 and 75 percent of the overall DoD investment in this area. In FY04 and FY05, Air Force funding for PR was $291 million and $297 million, respectively, as the result of congressional add-ons to the Presidential Budget Requests (PBRs) of $251 million and $234 million. The Air Force projects increases in PBRs from $252 million in FY06 to $305 million in FY11. The overall DoD investment in PR from FY04 to FY07 remains fairly flat at around $400 million to $410 million except for a spike to $440 million in FY05.3 The flatness of the numbers does not give a true picture, however, particularly for 6.2 work, where the budgets in gas turbine technology from FY02 to FY06 were fairly flat but cover AFRL payroll and administration costs. While the amounts for in-house R&D remained fairly flat, the amounts for industrial R&D fell precipitously over the FY02-FY06 period. The committee finds that there has already been significant erosion of the U.S. lead in propulsion technology and that a flat budget will lead to further erosion. Because the investments projected 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 funded at the expense of existing programs or would require additional 2 Jim Engle, Deputy Assistant SAF/AQR, discussion with the committee on March 1, 2005. 3 The principal Air Force and DoD-funded PR programs include the Integrated High-Performance Turbine Engine Technology (IHPTET) program, the Versatile, Affordable, Advanced Turbine Engine (VAATE) program, the High-Speed Turbine Engine Demonstration (HiSTED) program, the Revolutionary Approach to Time-Critical Long-Range Strike (RATTLRS) program, the Hypersonics Flight Demonstration (HyFly) program, and the Force Application and Launch from the Continental United States (FALCON) program.

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs funding. Funding for 6.1 and 6.2 research is vital to the warfighter since such research is the source of new ideas and technologies and educates new engineers and scientists in aerospace propulsion. The Committee’s Judgment The study statement of task required the committee to “identify technical gaps and suggest rough order of magnitude (ROM), specifically applied S&T investments in these areas of propulsion.” The committee based its ROM estimates on its collective judgment, which, in turn, was based on the members’ extensive experience and expertise in aerospace propulsion. By definition, these estimates are rough; however, the committee believes each is reasonably within the correct order of magnitude. In its recent budget requests, the Air Force did not project changing its investment in propulsion S&T in future years much from its current level. The committee believes this investment needs to be increased if technical gaps are to be filled. The Reliance Program The DoD Science and Technology Reliance program (the Reliance Program) was originally mandated by the Service Assistant Secretaries to focus resources on propulsion requirements and capabilities (DMR 922) as part of the 1989 Deputy Secretary of Defense challenge to the Services to increase efficiency in research, development, testing, and evaluation (RDT&E). As discussed in Chapter 2, the committee heard anecdotally from informed sources that the Air Force was the lead service in work on propulsion for the Reliance Program. Since the Air Force has been by far the largest investor in the S&T arena in air-breathing propulsion and rocket propulsion, the committee felt this information made sense. However, when the committee reviewed the Reliance Program it found no mention of a lead service for propulsion. In fact, the Defense Technology Area Plan (DTAP) divided responsibility for propulsion among four panels: air platforms, nuclear technology, space platforms, and weapons. The committee believes that having propulsion spread over different DTAP panels results in overlapping, unfocused efforts on the part of the various Services as well as the panel subject areas. Further, the panels’ efforts do not set any priorities for DoD technology objectives. The Reliance Program, as presently structured, also does not give the panel chairs the authority they need to achieve cooperation and discipline in Reliance

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs Program execution. Overall, the present Reliance Program organizational construct tends to inhibit the maturation of propulsion efforts, from basic research (6.1) to applied R&D (6.2, 6.3) and demonstrations (6.2, 6.3), and the coordination of their funding across DoD. AIR-BREATHING PROPULSION SYSTEMS Challenges Facing Air-Breathing Propulsion Systems The Air Force is transitioning to a capabilities-based planning model. DDR&E presented capabilities requirements for the 2020 time frame for four warfighting scenarios: traditional, irregular, catastrophic, and disruptive (Sega, 2005). The propulsion challenges are discussed in Box 1-2. The committee looked at DDR&E’s capabilities requirements and the capabilities of the current operational systems that will still be in service in the 2020 time frame to define the technology requirements, the opportunities for technology improvement, and opportunities to leverage different business approaches to meet the needs of 2020 warfighters. Characteristics of Aircraft Needed by Warfighters in 2020 From the information it had gathered, the committee was able to paint an overall picture of the 2020 warfighter’s fleet powered by air-breathing propulsion systems: First, over 60 percent of the aircraft that will be used by the 2020 warfighter are in service today. If the Joint Strike Fighter (JSF) F-35 is included, then it would mean that over 80 percent of the 2018 fleet exists or is under development today. Additionally, the costs of sustaining and fueling this fleet are the two most expensive items in the budget and are growing rapidly. Second, time-critical targets and the expected decrease in the number of forward bases make high-speed aircraft a requirement for the 2020 warfighter. Two main types of propulsion systems not in operation today will be required to provide this speed capability: gas turbine engines (GTEs) that operate in the Mach 3.6 to 4.2 range and ramjets/scramjets that operate in the Mach 4.0 to 16 range. In fact, some capabilities may require combining cycle propulsion

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs BOX 1-2 Propulsion Challenges Future U.S. armed forces must address an array of challenges that far surpass those faced in the past. Numerous security studies have described the evolving and transformational nature of the U.S. security environment. In response to these challenges, aircraft propulsion systems must evolve more rapidly than ever before. The four propulsion challenges are traditional, irregular, catastrophic, and disruptive: “Traditional” challenges require continued improvements in legacy performance metrics for GTEs. Some of these metrics are propulsion system thrust-to-weight (T/W) ratio, fuel consumption, life-cycle cost, and durability. Continued improvement of these metrics will allow the United States to maintain its technical superiority in GTEs and will provide an opportunity to reduce the cost of maintaining, supporting, and fueling currently fielded engines. “Irregular” challenges require improvements in propulsion system stealth, survivability, austere basing (e.g., short and vertical takeoff and landing), and greatly improved fuel economy for long loiter times. Propulsion systems optimized for UASs will also play a major role in this area. “Catastrophic” challenges require propulsion systems that power vehicles to high Mach numbers to counter time-critical targets. Propulsion systems for long-range strike missions must power manned vehicles, which cruise between Mach 2 and Mach 3.5. Hypersonic vehicles, which cruise between Mach 4 and Mach 16, are required to stand off and strike time-critical targets or to protect the homeland from incoming weapons. “Disruptive” challenges require propulsion systems to power vehicles for directed-energy weapons or to counter directed-energy weapons. Propulsion technologies such as integrated thermal and power management, high-heat-sink fuels, and large electrical generating capacity are required to meet these threats. These propulsion systems will also be required to power miniaturized, autonomous, networked sensor and/or weapon systems (adapted from Sega, 2005).

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs All electric propulsion thrusters at any power level need PPUs having greatly reduced mass per kilowatt. One promising approach to this is a solar-electric drive that uses a high-voltage solar array to provide power directly to a Hall thruster. A larger industrial base than presently exists is required for assured production of complete electric propulsion systems (thrusters, feed, and PPUs). For Hall electric thrusters there appear to be two sources: Aerojet Redmond and Northrop Grumman/Busek. For ion thrusters the future is uncertain, because Boeing has sold its Torrance, California, electric propulsion facility to L-3 Communications. PROPULSION SYSTEMS FOR STRIKE AND TACTICAL MISSILES This section addresses propulsion technologies applicable to military airborne, extended-range strike and tactical missiles. Such missiles include surface-to-surface; surface-to-air; air-to-air; air-to-ground, extended-range global strike; and air-to-near space. Currently, almost all these missile types use standard Class 1.3 hydroxyl-terminated polybutadiene/ammonium perchlorate (HTPB/AP) propellant solid rocket motors. Very little new work has been conducted over the last 10-15 years to improve solid rocket motor propulsion systems for missiles by the S&T elements of the Services or by the OSD. Most of the IHPRPT funding for solid rocket technology has been for strategic sustainment to maintain some level of capability and industrial base. For one reason or another, none of the few advanced propulsion technologies that have demonstrated significant improvements has been transitioned into an operational system to date. IHPRPT Goals for Improving Missile Propulsion Most of the IHPRPT goals for improvements in propulsion systems for tactical missiles are proving to be somewhat unrealistic for the medium term. People talk about higher combustor operating pressures (>2,000 psia) and high-energy propellant formulations, but they cannot demonstrate them with acceptable margins. Solid propulsion technology has run into a ceiling dominated by throat erosion for the best materials that experts have devised. This same limit has prevented using a number of new high-energy propellants. By their very nature, tactical missiles have higher chamber tem-

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs peratures and higher throat velocities, and in many cases their products of combustion are chemically incompatible with nozzle materials, all of which results in unacceptable throat erosion. The Army has done considerable work to demonstrate missile trajectory and energy management using storable gelled liquid propellants and pintle-in-the-throat throttleable solids. This work has achieved reasonable success in increased missile range, accuracy, and real-time retargeting. For example, using gelled propellants for energy-managed propulsion systems, the Army was able to flight demonstrate doubling the range of a tube-launched, optically tracked, wire-guided antitank missile from 4 to 8 km and hit the intended target. However, as already stated, these technologies have not yet been transitioned into any operational system. Current IHPRPT Research Missile propulsion technology work under IHPRPT is divided into three categories: solid propellant motors, hybrid rocket motors, and gelled propellant motors. Solid Propellant Motors Solid propellant technology work in-house at AFRL in solid motor design and hardware demonstrations appears to be minimal. Basic research in a number of very advanced areas is of high quality, however. An important IHPRPT project contracted to both Aerojet and Alliant TechSystems is to develop and validate advanced computational tools. The intent is to replace empirical models with more physics-based models. AFRL is also working on a demonstration solid propellant motor that incorporates a desubmerged lightweight nozzle, reduced part counts and fewer interfaces, a carbon-carbon exit cone, a wet-wound graphite/resin system, the elimination of dome reinforcements, strip-wound Kevlar ethylene propylene diene monomer (EPDM) rubber insulation, a Class 1.3, 90 percent solids HTPB/cyclotrimethylene trinitramine/royal demolition explosive (RDX) propellant, a consumable igniter, and a smaller electromechanical thrust vector assembly (EMTVA). At the U.S. Army Missile Command, Huntsville, Alabama, solid propellant missile propulsion technology is focused on three high-leverage areas: controllable thrust propulsion (CTP), insensitive munitions (IM),

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs and new materials. Controllable thrust has the potential for significant system benefits. It can provide extended range and shorter time to target at mid-ranges in a single system. Controllable thrust systems also can reserve propellant energy for end-game performance. Thrust profiling for either ground- or airborne-launched missiles can be provided by using solid propellant motors with a variable area nozzle, hybrid solid fuel with gelled storable oxidizer, or gelled storable liquid propellants. Hybrid Rocket Motors Lockheed Martin Michoud Operations has worked on hybrid propulsion technologies since 1989. Because the fuel is inert, launch vehicles or missiles that use these propellant combinations can achieve good performance and gain the benefits of having a nonexplosive propellant combination. Controllable thrust hybrid rocket motors are being investigated by the Army. Two types of hybrid rockets have been considered: (1) a conventional hybrid rocket in which liquid or gelled oxidizer is injected into the port(s) of the solid-fuel grain or the fuel-rich propellant grain for combustion and (2) a gas-generator type of hybrid rocket in which the fuel-rich solid propellant grain burns in its own combustor and the discharged products are further burned with the oxidizer-rich gases in a postcombustor. In some special but rare cases, an inverse hybrid can be considered in which the solid grain is made of oxidizer-rich material and the injected liquid is a fuel-rich material. In the past, hybrids suffered from significant instability problems because of low regression rates. Recently, there have been several significant breakthroughs in hybrid technology at Lockheed Martin Michoud, Stanford University, and Orbitec. These hybrid technology advances with their inherent safety should greatly advance hybrid propulsion applications for space and missile systems. Gelled Propellant Motors Gelled propellants can meet field and aircraft operational and handling requirements. They have the potential of being inherently insensitive to IM threats because the fuel and oxidizer are stored in separate tanks. A throttling gel engine using a passive pintle demonstrated a turndown ratio of 12:1 while maintaining greater than 98 percent Isp efficiency. Design criteria for gelled propellant propulsion systems for missiles of almost any size have been validated at Northrop Grumman Corporation. The critical

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs design element is a central injector with a single sleeve that permits throttling, no dribble face shutoff, and restart. Recommendation 5-4. DoD should ensure that the development of advanced tactical missiles, responsive global-reach missiles, and ABMs satisfies four key requirements: effective energy/trajectory management, higher-energy-density performance, minimum smoke exhaust, and insensitive propellants. The S&T part of the DoD/Air Force strategic plan for missiles should focus on the technologies and design criteria necessary to meet these goals. The committee’s estimate of annual funding that would be required to make reasonable progress in establishing advanced capabilities in these areas is $20 million to $30 million. Two Potentially Transformative Concepts There are a couple of potential opportunities for transforming how certain tactical, responsive global reach, and ABM missions could be achieved. One system concept utilizes self-contained ABVL modules. Another would make use of a multimission modular vehicle (MMMV). Both airborne launch concepts could transport rocket-powered missiles to high-altitude launch points at optimum geographic locations, enabling broad flexibility with respect to launch time, azimuth, orbital inclination, and time to target for missiles used for ABM missions, tactical support, or long-range global strike. Such concepts could provide a rapid response capability beyond what is available today to counter emerging threats. Launching missiles from a flying aircraft platform can dramatically improve both missile performance and time to target. High-altitude air launch allows the rocket to bypass the initial parts of a ground-launch trajectory, where combined negative effects can result in a velocity loss of around 3,500 feet per second. Recommendation 5.6. The Air Force and DoD should sponsor a detailed system engineering study of using the MMMV air-based launch system for medium-sized missiles in combination with the air-based vertical launch study for various types and sizes of missiles called for in Recommendation 5.5, thereby ensuring that both studies are focused on the Air Force/DoD optimization criterion “mission success.” The studies would identify the propulsion technologies (modifications or new concepts) that should be evolved in order to take full advantage of such air-based launch platforms for operationally responsive missions.

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs OUTLOOK FOR ALL ROCKET PROPULSION SYSTEMS: ACCESS TO SPACE, IN-SPACE OPERATIONS, AND AIRBORNE MISSILES As shown in Tables 4-10 to 4-14, funding for technology programs such as IHPRPT and for sustaining improvements in propulsion engineering on various weapon systems now accounts for a much smaller fraction of the overall research and engineering (R&E) funding line. This limits the accomplishments of propulsion improvement efforts and minimizes the opportunity to train the next generation of designers and production specialists. Personnel demographics indicates that many individuals with critical skills in the development and production of large missiles and launch vehicles will retire in the same time frame. One outcome will be to limit the capabilities and flexibility of U.S. space assets that are crucial to support the warfighter and without which the national defense will be compromised. The consequences of this funding situation have been eroding U.S. aerospace capability for many years. Unless there is a serious commitment to reversing this trend, the ability of industry to provide the high-quality engineering and production capability for realizing the Air Force’s medium- and far-term transformational in-space and missile goals will be at risk. Cross-cutting Technologies Fuel Jet fuel costs have risen by a factor of 2.2 since 2004, and this rising cost of jet fuel is a major expenditure for warfighter support. Estimates are that the DoD fuel bill was $6.8 billion to $9.4 billion higher in 2005 than in 2004 due to fuel price hikes and the additional cost incurred in transporting fuel to the battlefield. Further, DoD is increasingly dependent on foreign sources of refined fuels and relies on supplies from refineries that are vulnerable to terrorist attacks. Finally, DoD needs to use fewer varieties of fuels to simplify logistics, and it needs high-thermal-stability fuels to facilitate the thermal management of aerospace vehicles. Materials The propulsion industry today, air-breathing and rocket, is taking advantage of materials and processing investments spurred by the ManTech

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs program of the past. In retrospect, the Services and DoD/DARPA funding spawned the entire aerospace materials supply chain that is in place today. As we look to the future with very limited and restricted ManTech, such investments are being driven by commercial engine needs and DoD is just tagging along. More of the advanced work will migrate offshore. For instance, SiC fiber used in highest temperature ceramic matrix composites (CMCs) is supplied from Japan, and TiAl processing is rapidly advancing in Europe. Since the DoD production base is not large, these new material technologies only become economical if there are commercial applications. This presents an opportunity for realistically planned ManTech programs that will provide baseline manufacturing technology for high-performance defense systems and also leverage requirements of the nondefense aerospace sector (DSB, 2006). Recommendation 6-2. The Air Force should fund ManTech at a level sufficient to enable future advances in materials for propulsion technology. Investment Strategy Options The range of challenges facing the U.S. military over the next 15 years requires that the United States field air-breathing propulsion systems that cover the Mach number range from 0 to Mach 16 and rockets that provide cheap, reliable, and ready access to space. These requirements, which are greater than the United States has faced since World War II, come at a time when existing equipment is demanding an ever-increasing share of the DoD budget for fuel and sustainment and when S&T is receiving less than 1.5 percent of the DoD budget. Clearly, this situation calls for DoD to define and then implement an optimal investment strategy for its limited resources. The committee examined a number of strategies and found that while no single strategy was right for all programs, several did allow DoD to optimize the impact of its investment. VAATE, like its predecessor IHPTET, utilizes and focuses all government and contractor independent R&D (IR&D) money and resources on the achievement of a common goal. No other DoD technology program has the reach or leverage of the VAATE program, whereby contractor IR&D funds are applied to extend government technology funding. An aggressive VAATE program is needed to meet the warfighter’s capability requirements.

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs The focus and leverage of the IHPTET program allowed the United States to field the most advanced fighter engines (F135 and F136) in the world. The IHPTET investment strategy had three main characteristics: (1) it gave all government and contractor technology funds and resources a common set of goals, (2) it had a relatively stable funding profile consistent with the time frame for developing and demonstrating new technologies, and (3) it tracked investment versus achievement of the technical goal. VAATE improves on the IHPTET investment model: Not only does it maintain the three IHPTET characteristics, but it also focuses on system solutions (high-impact, integrated solutions) as opposed to specific gas turbine improvements and makes affordability a key metric. A small share of the savings in sustainment and fuel costs of existing aircraft generated by IHPTET could be allocated to properly fund VAATE, which requires approximately $300 million per year focused on warfighter needs if the United States is to maintain its lead in gas turbine propulsion. The legacy fleet, which will make up over 80 percent of the 2018 warfighting capability (if the Joint Strike Fighter is included), needs drastic attention. In FY04, the cost to sustain the legacy fleet was $4.2 billion, and assuming a fuel cost of $1 per gallon, fuel amounted to an additional $4.7 billion. In other words, in FY04 the cost of operating the legacy fleet was approximately two-thirds of the total DoD propulsion budget. These costs will continue to increase, because the DoD fleet will grow older and the true cost of fuel will be much, much higher than the assumed $1 per gallon in FY04. Unless strong action is taken, the growing proportion of the DoD propulsion budget allocated for sustainment of the existing fleet and fuel for it will become a death spiral, with the portions of the budget allocated for procurement, development, and technology always decreasing. See Figure 7.1 for additional detail. The committee found that the breakdown of the DoD budget for fuel, maintenance, and product improvement for different commands and Services is wasting potential opportunities to decrease the cost of sustainment and fuel (see Chapter 3 for examples). To illustrate: An engine program office that has money to improve an engine is disconnected from the budget for maintenance cost of the engine and also from the budget that buys fuel to operate the engine. The committee found many cases where this lack of connecting authority and responsibility was causing poor decisions on trade-offs that were meant to reduce the costs of sustainment and of fuel burned.

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs Connecting the authority to make small investments to improve legacy propulsion systems with the responsibility for reducing sustainment and fuel costs for the same systems would allow good investment decisions to be made. Today, since no one person or command is responsible for the total cost and investment, no such trades are made, or they are very infrequent. Budgets spent on sustainment and fueling of the legacy fleet leave no room for the acquisition of new aircraft or the development of technology. 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. History shows that spiral development has been applied to the important Air Force and Navy fighter engines. For example, propulsion systems for the F-16 and F-15 aircraft underwent spiral development programs to improve their thrust and reliability, a very cost-effective way to increase their warfighting capability. The main derivative programs for these engines (e.g., F100-220 and -229 versus the F100-100) bundled technology packages from IHPTET or IR&D programs to markedly enhance performance. Currently, DoD is not leveraging the major F-22 and F-35 propulsion investments by providing spiral development programs (e.g., EMDPs) to meet the requirements for other aircraft. For example, derivates of the F119/F135 or F120/F136 engines are candidates to power future global strike aircraft. Spiral development is the most cost-effective way to maximize the effectiveness of long-lived weapon systems. Commercial experience has demonstrated that the government is a very high-cost integrator. DoD has made progress over the past several years in adopting commercial best practices. Commercial best practices clearly set requirements and then contract with suppliers to meet those requirements. 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.

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs The idea of a 1-year engine demonstrator program is a good one. The current trend is to move from IHPTET, where a major technology demonstration occurs every 1 to 2 years, to VAATE, where a major technology demonstration is planned once every 5 to 7 years. This long time between major technology demonstrations will accelerate the demise of the U.S. technology lead in propulsion systems. 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. 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. 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. DDR&E should undertake a focused effort on cataloging and making accessible the findings of past technology programs, perhaps even combining the IHPTET, IHPRPT, and VAATE databases at the lower taxonomy levels to enhance technology cross-fertilization. It should also set up a feedback process and facilitate a cross-cutting flow of S&T during the development, acquisition, and sustainment phases. REFERENCES Published AFSPC (Air Force Space Command). 2003. Air Force Space Command Strategic Master Plan FY06 and Beyond. October 1. Available online at http://www.cdi.org/news/space-security/afspc-strategic-master-plan-06-beyond.pdf. Last accessed on October 31, 2006. Bexfield, James, and Lisa Disbrow. 2005. MORS Workshop on Capabilities-Based Planning: The Road Ahead. Washington, D.C.: Military Operations Research Society. December. Available online at http://www.mors.org/publications/reports/2004-Capabilities_Based_Planning.pdf. Last accessed on August 9, 2006.

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs DoD (Department of Defense). 2004. Department of Defense Space Science and Technology Strategy. Washington, D.C.: Defense Research & Engineering. July 31. DSB (Defense Science Board). 2006. The Manufacturing Technology Program: A Key to Affordably Equipping the Future Force. Washington, D.C.: Office of the Under Secretary of Defense for Acquisition, Technology and Logistics. February. Available online at http://www.acq.osd.mil/dsb/reports/2006-02_Mantech_Final.pdf. Last accessed on August 9, 2006. NRC (National Research Council). 2003. Materials Research to Meet 21st Century Defense Needs. Washington, D.C.: The National Academies Press. Available online at http://newton.nap.edu/catalog/10631.html. Last accessed on August 11, 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 31, 2006. NSPD (National Security Presidential Directive). 2005. U.S. Space Transportation Policy. NSPD-40. January. USAF (U.S. Air Force). 2005. Master Capabilities Library. Unpublished Hampsten, Ken, Jim Ceney, and Gus Hernandez. 2005. “ARES subscale demo Phase I,” Presentation to HLV Industry Day on March 7. Space and Missile Center. El Segundo, Calif., LAAFB. James, Larry D. 2005. “ARES Industry Day AFSPC,” Presentation to HLV Industry Day on March 7. Space and Missile Center. El Segundo, Calif., LAAFB. Sega, Ron. 2005. “Department of Defense propulsion science and technology,” Presentation to the committee on May 24. Smith, Scott. 2005. “Air-based vertical launch,” Presentation to committee member Gerard Elverum on December 19.

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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs Chapters 2-7 and Appendixes A-E are reproduced on the CD-ROM that contains the full report but are not included in the printed report.