THE BOTTOM LINE
The committee believes that the National Aerospace Initiative (NAI) is an effective instrument for assisting the Department of Defense (DoD) and the National Aeronautics and Space Administration (NASA) in their pursuit of technologies for our nation’s future military systems and its future space launch needs, both crewed and uncrewed. The NAI goals directly address issues of national concern. NAI has fostered collaboration between the DoD and NASA in research and technology areas—hypersonics, access to space, and space technology—that can benefit both organizations. It has increased the visibility of the two agencies’ related research and technology development efforts and has made it easier for them to work together to achieve overlapping objectives. It has increased the probability of achieving synergistic results. It offers opportunities to achieve efficiencies that would not be possible if each agency were to work in isolation. The committee recommends that DoD and NASA, through NAI, continue to advocate, communicate, and facilitate the nation’s endeavors in hypersonics, access to space, and space technology.
The stated mission of NAI is to “ensure America’s aerospace leadership with an integrated, capability-focused, national approach that enables high speed/hypersonics flight; affordable, responsive, safe, reliable access to and from space; and in-space operation by developing, maturing, demonstrating, and transitioning transformational aerospace technologies.”1 For hypersonics and space access, NAI goals are stated as follows:
Hypersonics. Flight demonstrate increasing Mach number capability each year, reaching Mach 12 by 2012.
Space access. Demonstrate technologies that will dramatically increase space access and reliability while decreasing costs.2
DDR&E. 2004. National Aerospace Initiative. Mission Statement. Available at http://www.dod.mil/ddre/nai/mission.html. Last accessed on April 04, 2004.
DDR&E. 2003. National Aerospace Initiative. Sustaining American Aerospace Initiative. Available at http://www.dod.mil/ddre/nai/nai_brochure1.pdf. Accessed on December 23, 2003.
The study committee was asked to answer three general questions—Is NAI technically feasible in the time frame laid out? Is it financially feasible in the same time frame? Is it operationally relevant? The committee’s answers are presented in the paragraphs that follow.
Concerning the technical feasibility of hypersonics, the NAI roadmap for integrated high speed/hypersonics and space access ground and flight demonstration outlines a series of development and demonstration programs resulting in a Mach 12 air-breathing capability in the 2014 time frame. While the committee believes that Mach 12 air-breathing vehicles may be technically feasible in that time frame, it recommends a more comprehensive approach addressing all requisite activities, from fundamental research to critical technology development to flight demonstration.
The NAI phased approach to space access with rocket propulsion envisions that technology investments will result in increasingly ambitious potential system payoffs by 2008 and 2015. The quantified payoffs include short turnaround time; high sortie numbers for airframe, propulsion, and systems; low marginal sortie cost; high reliability; and improved payload performance. The committee believes strongly in the general goal of demonstrating technologies to dramatically increase space access and reliability while decreasing cost but does not believe that all the payoffs will be available in the time frames suggested by the NAI.
Concerning financial feasibility, the committee believes that both pillars are underfunded in relation to current NAI planning. It believes that near-term NAI funding for the air-breathing hypersonics pillar might suffice for a significant critical technologies program that could support near-term warfighting applications such as missiles. However, sharply higher budgets will be required to achieve the currently stated, long-term NAI objective of air-breathing hypersonic access to space. The access-to-space pillar faces a similar funding issue. The NAI envisions a multiphase demonstration program with increasingly capable reusable rockets available in 2008 and 2015. The development of these vehicles is not supported by current budgets. Clearly, neither the goals of NAI nor the needs of the military services can be met without significant additional funding.
Finally, the committee found that NAI is operationally relevant. All the DoD operational commands contacted by the committee believe that NAI technologies and capabilities, if realized, could support, to a degree, their stated capability goals and missions, such as Prompt Global Strike, Global Missile Defense, and Operationally Responsive Spacelift. However, non-NAI approaches can also support these missions, and the operational commands recognize that many NAI technologies have yet to be developed and proven.
The committee strongly agrees with the operational commands, which, while they support the capabilities offered by NAI, believe that NAI must be balanced with other research and technology development efforts, priorities, and investments to ensure proper trades between current, near-term, and future combat capability.
As described in the preface, this study was undertaken in response to a request by the U.S. Air Force that the National Research Council (NRC) of the National Academies provide an independent evaluation of the feasibility of achieving the science and technical goals outlined by the NAI. To conduct the study, the NRC appointed the Committee on the National Aerospace Initiative under the auspices of the Air Force Science and Technology Board.
To answer the three general questions the study committee was asked—Is NAI technically feasible in the time frame laid out? Is it financially feasible in the same time frame? Is it operationally relevant?—the committee was asked to perform several tasks, including evaluating NAI in terms of warfighter capabilities and baselining the readiness of NAI technologies. The committee was also asked to recommend technologies that should be emphasized over the next 5 to 7 years as well as specific efforts to advance hypersonics and access to space over the next 20 years. In
addition, the committee was asked to consider two Air Force budget scenarios—one assuming that no additional NAI funds are allocated and one corresponding to optimal NAI development timelines. Finally, the committee was asked to suggest initiatives to ensure a more robust aerospace science and engineering workforce.
THE NATIONAL AEROSPACE INITIATIVE
The National Aerospace Initiative is a joint technology initiative begun in 2001 by the DoD and NASA. The goals of NAI are to renew American aerospace leadership; push the space frontier with breakthrough aerospace technologies; revitalize the U.S. aerospace industry; stimulate science and engineering education; and enhance U.S. security, economy, and quality of life. The initiative focuses on science and technology advances in three areas, or “pillars”—high speed/hypersonics flight, access to space, and space technologies. The high speed/hypersonics flight goal is to demonstrate Mach 12 by 2012. The access-to-space goal is to demonstrate technologies to dramatically increase space access and reliability while decreasing costs. Leveraging the full potential of space is the goal of the space technology pillar, an area that, by agreement with the sponsor, the committee did not address.
Air-breathing hypersonic vehicles have potential application as missiles, cruise missiles, long-range strike aircraft, and/or space launchers. Technology development and demonstration are required to mature critical hypersonic technologies to the point where a decision could be made to fund any or all of these applications. The technical challenges of air-breathing hypersonics increase dramatically as the speed of the vehicle increases, through scramjet speeds that could reach Mach 4 to Mach 14. The military departments and NASA have ongoing technology development and demonstration programs in air-breathing hypersonics. The Army and Navy programs are directed toward missile applications. The Air Force is interested in nearer-term missile applications and is also working with NASA to pursue the longer-term possibilities of reusable launch vehicles for space access.
During the past 45 years, space access capability has been developed for low-launch-rate applications from low Earth orbits to beyond the solar system. Rocket-based vehicles have operated as missiles, long-range strike missiles, or space launchers for 50 years. The Air Force and NASA are both investing in technology for rocket-based, reusable launch vehicles. While their final systems may be very different, they share many common technologies, for which NAI is facilitating related collaboration. The Air Force has credible emerging needs for a rapid rate, operationally responsive spacelift capability that might utilize a reusable rocket-powered vehicle. NASA needs a replacement for its Space Transportation System (the space shuttles) that might be implemented in the next decade using reusable, rocket-based propulsion. Both DoD and NASA are planning new rocket-based systems for the near term but are at the same time working on capabilities in air-breathing hypersonics for possible application to launch vehicles in about two decades.
Advances in space technology are desired to provide national security decision makers with the most current and complete information made available through on-demand intelligence, surveillance, and reconnaissance. In addition, space technology advances are desired to benefit other warfighter mission areas such as navigation, weather, communications, missile warning, space control, and force application. Satellite systems using advanced space technologies are seen by NAI participants as a vital element of space, air, and ground systems that are so well networked and integrated that they provide revolutionary capabilities. The nonmilitary benefits of advanced space technology include the scientific study of Earth, leading to improved capabilities for predicting climate, weather, and natural hazards.
During 2002, workshops and meetings were held to further develop NAI definitions, goals, and plans. Planning teams were formed around the three NAI pillars. They included participants from
the three military departments, NASA, and staff of the Director of Defense Research and Engineering (DDR&E). The teams used a structured process to go from the high-level NAI goal statements to project-level technology roadmaps. The process combined layered analysis (goals were analyzed to determine objectives, which were analyzed to determine technical challenges, and so on) and planning (projects were identified and roadmaps developed to address the challenges). By the time of this study, NAI participants had undergone the first iteration of this process and had developed initial roadmaps that included project-level details. The initial roadmaps included many DoD and NASA NAI-related projects that had already been under way or planned when NAI was established.
The NAI executive office, staffed by DoD and NASA personnel, acts as an advocate and facilitates collaboration in the development of goals, plans, and roadmaps for the three pillars.
Late in the budget cycle, DDR&E succeeded in having new NAI funding (in addition to that for existing or planned projects) included in the President’s budget request (PBR) for fiscal year (FY) 2004. No new NAI funding was included in the PBR for FY 2005 and beyond; however, DDR&E expected the FY 2005 PBR to add new out-year funding.
THE NAI ROADMAPPING PROCESS
The committee believes that DoD and NASA have made a positive start; however, it also noted some weaknesses in what has been done so far. It was not clear to the committee that the process used to develop the NAI roadmaps was effective in defining a comprehensive and compelling technology development program that would mature all of the critical enabling technologies in time to meet the various NAI schedule goals, one of them being a milestone decision in 2018 on hypersonic access to space. For example, NAI brought together essentially all existing U.S. programs and attempted to use them to lay out a high speed/hypersonics technology roadmap. However, this roadmap is more a collection of existing programs than a logical and complete plan to achieve military strike, global reach, and space access objectives. Each of the collected programs has elements that address some portion of the critical technologies, and each program, owing to its very existence, has a funding line. The collective funds, if properly applied, perhaps are sufficient in the near term for a significant critical technologies program; however, as configured, it is not clear that the collected programs cover all critical hypersonic technologies. The low level of basic and applied research in the NAI plan is also conspicuous.
The committee recommends that, starting with a defined and articulated vision, DoD and NASA use a top-down process based on sound system engineering principles to determine the objectives, technical challenges, and enabling technologies and to plan the fundamental research, technology development, ground testing, and flight demonstrations required to mature the enabling technologies to levels sufficient for application. The result should be a comprehensive, integrated roadmap that ensures all technologies are sufficiently matured to support the multitude of decision milestones scheduled during the NAI time frame of interest. This roadmap may include preexisting projects; however, the roadmapping process should closely examine how each project contributes to achieving NAI goals and assess the trade-offs with other needed technology efforts. The roadmap should include detailed plans for fundamental research and clearly defined exit criteria for each of the critical technologies. The committee recommends that DoD and NASA clearly communicate the plan, once it is complete, to decision makers and stakeholders, including the public.
The committee recommends that DoD and NASA complete an end-to-end cost estimate for the top-down program through the period of interest and then work to secure funding commitments consistent with this cost. This plan and its funding estimates should then be exposed to competition from other DoD and NASA requirements to see if they are realistic. For example, if the national plan to complete and begin initial operational capability of a multibillion-dollar new and revolutionary two-stage-to-orbit, reusable launch vehicle is achieved in 2015-2018, how likely is it that at
the same time Congress and the nation will be willing to approve an even more expensive follow-on air-breathing hypersonic launcher?
To help assess the realism of the resulting roadmaps, the committee recommends that DoD and NASA set up their planned NAI advisory panels, steering groups, and revolutionary concepts panels to review the NAI program on a continuing basis. The committee believes that the progress NAI has made in facilitating coordination of activities among participants would benefit from periodic oversight by independent groups of experts.
The committee identified four critical enabling technologies for air-breathing hypersonic flight that must be matured: air-breathing propulsion and flight test; materials, thermal protection systems, and structures; integrated vehicle design and multidisciplinary optimization; and integrated ground test and numerical simulation and analysis.
Propulsion is foremost among the critical technologies that will enable air-breathing hypersonic flight, both for the dual-mode ramjet/scramjet engines that will achieve hypersonic speeds and for the lower speed engines that will accelerate the ramjet/scramjet to takeover speeds (typically Mach 3-4). Several challenges exist for scramjet engines, among them performance and operability across a broad range of operating speeds, especially above Mach 8; management of the extreme thermal environment encountered by such engines; and durability of engine structures and systems for long life and low maintenance. Challenges for low-speed engines include thrust-to-weight ratio (i.e., high thrust at low weight while maintaining high efficiency), thermal management, and integration with both the airframe and the high-speed propulsion system.
The committee focused on three important areas of materials technology: thermal protection systems, actively cooled combustor panels, and cryogenic tanks. The silica foam tiles used for thermal protection on the space shuttle are fragile and require extensive maintenance between missions; they are not suitable where rapid response is a requirement. More rugged thermal protection systems are needed that are passive (uncooled) or active (cooled). In the combustor section of a hypersonic propulsion system, active cooling is necessary, even at modest Mach numbers. Although extensive testing of various candidate designs has been accomplished, no single solution to all the operational requirements has emerged. Cryogenic tanks have received considerable attention in recent years, but no fully reusable tank has been adequately tested in the flight environment. The remaining step is to produce and flight test a full-scale, reusable tank through many cycles.
Air-breathing hypersonic vehicles will consist of highly integrated systems that will require multidisciplinary design optimization to obtain robust vehicle designs that satisfy all constraints. At hypersonic Mach numbers, much of the airframe must act as the inlet and nozzle for the propulsion system. The shape of the vehicle will determine the vehicle structure, the type of integrated thermal protection system and its material, the control system, the flight mechanics, and the flight trajectory. The flight trajectory, in turn, will determine the aerodynamic heating loads, which will influence vehicle aeroelastic behavior, performance, and empty weight. The empty weight of the vehicle is directly related to the structural shape, and the vehicle airframe will also affect the fuel and payload volume since, unlike conventional aircraft, the greater part of a hypersonic vehicle’s volume must accommodate fuel. Several capabilities needed for multidisciplinary design optimization are not yet mature.
Integrated ground test and numerical simulation and analysis is another critical and enabling technology area that must be matured. The number of parameters that must be simulated in a vehicle development program is increased substantially when the Mach number goes from 3 to 8 or more. Computational techniques, while largely successful in many low-Mach-number flow applications, suffer severely at hypersonic speeds, yet, owing to test facility limitations, they are essen-
tial for supplementing ground testing. Ground test facilities that can provide longer test times (seconds versus milliseconds) and more diagnostics are needed. Though a number of facilities exist for hypersonic and hypervelocity testing, they must be enhanced, along with diagnostics. One or more new facilities will also probably be required to meet the full needs of hypersonic system development.
Over the next 5 to 7 years, the committee recommends that, through NAI, DoD and NASA should continue to support programs for developing and flight testing small-scale hydrogen and hydrocarbon engines and should begin to develop a mid-scale scramjet engine and to demonstrate scramjet operation at the highest anticipated operational speeds (approximately Mach 14). For the long term, along the path to meeting the objective of a full-scale, air-breathing, hypersonic launch vehicle, the committee recommends that engine development proceed by increasing engine scale in at least three steps: small scale, medium scale, and large scale. The committee believes that DoD and NASA need to better coordinate and agree on their readiness definitions and assessments for high-temperature materials and that a reinvigorated basic and applied research program is needed to push these materials along. The committee believes that development of multidisciplinary design optimization specific to hypersonic vehicle design is long term and will require several more years of adequate, sustained funding. As for combined research in ground testing and computation, the committee believes that the DoD and NASA NAI roadmap should include benchmarking experiments at different facilities; external flow testing at the correct enthalpy and covering the parameter space in combination with application of validated tools; ground testing of missile-scale engines at all designed-for operational speeds; subscale testing of engines for hypersonic vehicles larger than missiles; and a 10-year research program on hypersonic flows, emphasizing high-enthalpy effects.
The committee studied a variety of inputs and reference sources pertaining to the NAI access-to-space pillar. Although NAI is chartered as a technology development effort, the access-to-space pillar goals are expressed in terms of future operational system characteristics. This approach allows NAI to cast its net across a broad range of possible contributing technologies but necessitates the translation from system characteristics to technology objectives—a process open to some interpretation. Furthermore, without a clear understanding of the eventual system configuration, the specific system characteristics specified in the three-phase pillar could be difficult to justify and might result in expending resources on low-payoff technologies.
That said, the committee found that many areas of research require attention under the NAI access-to-space pillar. Near-term and long-term technologies must be pursued, with appropriate weighting between the two. The technologies most likely to contribute to achieving the near-term goals of NAI are advanced materials for use in propulsion and thermal protection systems; integrated structures; electrical/hydraulic power generation and management technologies; software transportability; and error-free software generation and verification. Furthermore, the development of computational analysis tools and methodologies should be emphasized—especially when coupled to test analysis and ground test facilities.
Propulsion research work should focus on all technologies contributing to engine reusability and reliability, including (but not restricted to) the development of high-strength, liquid-oxygen-compatible materials and new engine materials that can support combustion of both hydrocarbon and hydrogen fuels. In addition to research on engine materials noted above, generic materials research should be focused on technologies contributing to reusability, such as lightweight thermal protection materials, and structural materials that would be useful in reducing the dry weight of highly integrated airframe designs. Durability should be a prime consideration in the development of these materials. Additional materials research should focus on reusable propellant tanks. The
committee recommends that DoD and NASA support basic and applied materials research programs and their application to highly integrated structures.
Both DoD and NASA will benefit by leveraging the work being done by the Department of Energy for electrical power management and control. In this general area, advances in intelligent sensors and component thermal control are ready for attention from the NAI. Multiple programs supported by DoD and other agencies could also be applicable.
Software is one of the most demanding and expensive aspects of any modern aerospace vehicle. Delays in software development ripple through the entire development process and significantly increase the cost of the overall project. The committee recommends that DoD and NASA, through NAI, support a robust research effort devoted to lowering the costs of aerospace software production. This research should concentrate on the safety-critical nature of aerospace software.
The coupling of high-performance computing (numerical analysis) with the emerging capabilities of ground test facilities (analysis tools and methodologies) appears to show great promise of reducing the cost of vehicle development. Additionally, advances in vehicle health management technologies would pay dividends in safety, in engine life extension, and in reducing the scheduled maintenance burden. Although these technologies are often considered outside the core of traditional aerospace research, their advancement is a legitimate goal and should receive appropriate attention from NAI.
The committee recommends that DoD and NASA develop time-phased, reusable, rocket-based flight demonstration programs to move near-term, unproven technologies through flight test; specify and disseminate the technology readiness levels and specific exit criteria necessary to support operational decision points; ensure that research is directed toward obtaining the specified data and that the demonstrations—both flight and ground—are structured to obtain the required information/ data; and concentrate on technologies that contribute to reusability.
The goals of NAI—renewing American aerospace leadership, advancing aerospace technologies, revitalizing the aerospace industry, stimulating science and engineering education, and enhancing U.S security and the economy—are both affected by and concerned with the state of the U.S. science and engineering aerospace workforce. The ability to achieve NAI technical goals depends on this workforce. This workforce, in turn, can be enhanced through pursuit of these goals.
Fueled by what appear to be negative indicators, concern about the state of the U.S. aerospace workforce has been the subject of much discussion in recent years. These indicators show reductions in the number of persons employed in the aerospace industry, the decreasing U.S. share of the world aerospace market, the increasing average age of aerospace workers, decreasing undergraduate and graduate enrollment in science and engineering, and declining mathematics and science performance of U.S. students relative to that of students from other countries. If there is a direct relationship between the state of the aerospace workforce and national security, as some have argued, then one might also argue that national security is threatened. NAI goals explicitly address this concern.
The committee found that NAI participants are focused mainly on achieving the initiative’s technical goals. It is mainly through the pursuit of these goals that the NAI affects the aerospace workforce; however, the committee also found some NAI efforts specifically aimed at stimulating aerospace education and workforce development. Two university research, engineering, and technology institutes (URETIs) have been jointly funded by DoD and NASA and included in NAI. They perform research in reusable launch vehicles and aerospace propulsion and power by bringing together students, faculty, NASA and DoD researchers, industry, and facilities. Student research symposia, scholarships and fellowships, K-12 outreach, outreach to women and underrepresented
minorities, and researcher exchange are included. The NAI-affiliated URETIs are funded at about $3 million per year.
The committee recognizes that NAI alone cannot allay all concerns about the U.S. aerospace workforce; however, it believes that NAI can assist in a national effort to address those concerns. The committee believes that efforts to achieve NAI technical objectives can help the aerospace workforce by providing the most important component—stable and predictable funding. Despite finding several drawbacks to the current URETI model that should be addressed, the committee believes that the NAI URETIs are stimulating aerospace education and the workforce. The committee believes that pursuit of NAI’s workforce-related goals can and should be strengthened. The committee recommends that DoD and NASA establish an aerospace workforce pillar along with the existing hypersonics, access-to-space, and space technology pillars.