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GAO/NSIAD-92-5 -- page 58
Chapter 4
Development of Enabling Technologies
Although U.S. leadership and superiority in aeronautics face
increasing competition from Japanese efforts to develop aerospace
vehicle technologies, the United States is ahead of Japan in
hypersonic technology. The United States, through the NASP
Program, is advancing hypersonic technology further than Japan.
The United States is ahead of Japan in the development of three
enabling technologies considered critical for an aerospace plane:
air-breathing propulsion, advanced materials, and computational
fluid dynamics. However, Japan is studying a single-stage-to-
orbit aerospace plane using scramjet propulsion, which is the
most technologically challenging aerospace plane concept.
Nonetheless, the United States is the only country that has gone
beyond the initial design phases and tested major large-scale
components of an air-breathing aerospace vehicle. Japan is making
significant progress in the development of enabling technologies,
particularly in advanced air-breathing propulsion and advanced
materials.
According to the Chief Scientist of the NASP Program, who visited
Japan as part of the NASP Joint Program Office Fact Finding
Group, the Japanese perform the necessary engineering work to
understand the enabling technologies and are able to show the
results effectively through technical presentations. The Chief
Scientist said the Japanese are able to show not only the overall
detail, but also the finer detail. He was impressed with the
breadth of the work and said high quality and state-of-the-art
aerospace engineering is evident in Japan.
According to a U.S. expert in hypersonics, the broad-based nature
of Japanese spaceplane programs, with extensive ground and flight
testing, is a good measure of Japan's commitment to the
development of hypersonic technology. A U.S. expert in hypersonic
propulsion said that the NASP Program is the most technically
challenging program in the world today. However, NASP is almost
the exclusive focus of the U.S. effort in hypersonics. The expert
cautioned that the United States could fall seriously behind
Japan (even if NASP is successful) in high-speed commercial
transport aircraft or hypersonic applications due to Japan's
broad-based program in hypersonic research.
GAO/NSIAD-92-5 -- page 59
United States Is Advancing Hypersonic Technology the Furthest
The United States is advancing hypersonic technology further than Japan. The Deputy Administrator, National Aeronautics and Space Administration, testified[l] before a joint hearing on the NASP Program in March 1991 that the United States is "quite a bit ahead" of Europe and Japan in the development of hypersonic technologies due to U.S. levels of investment. In addition, the Director of Defense Research and Engineering, Department of Defense, testified at the same joint hearing that the United States is the "pacesetter" in all hypersonic technologies and is clearly ahead of its competition. The NASP Program is designing the X-30 as an accelerator vehicle with the primary goal of demonstrating single-stage-to-orbit space launch capability. Hypersonic cruise capability is an expected result of single stage-to-orbit capability. An experimental flight test vehicle is required, since ground test facilities cannot simulate flow conditions above Mach 8, especially for testing the propulsion system. The X-30 has progressed into the early stages of the vehicle's preliminary design, i.e., the X-30's basic configuration and technologies have been defined. Its final design is expected to be determined in late 1991 or early 1992. NASP technology development tasks have reached the stage of hardware demonstrations of many subscale and some large scale vehicle components and systems. The NASP Program plans to develop an air-breathing propulsion system for the X-30 that has a higher speed and similar altitude capability compared with Japanese aerospace plane concepts. The X-30's scramjet is expected to achieve speeds of up to Mach 25 and sustained hypersonic cruise in the atmosphere in the Mach 5 to 14 range and at altitudes of up to an estimated 150,000 feet. The NASP Program plans to use air breathing scramjet propulsion up to the highest speed at which it is optimal and then augment the air-breathing propulsion with rocket propulsion. Flight testing of the X-30 will determine the optimal speed for using rocket propulsion to continue the X-30's acceleration and final ascent maneuver to orbit. Future operational space launch vehicles developed with NASP technology will initiate use of rocket propulsion at a speed optimized for their particular design. In comparison, Japan's National Aerospace Laboratory single-stage-to-orbit aerospace plane's1. The testimony was part of a joint hearing on the NASP Program on March 12, 1991, before the Subcommittee on Technology and Competitiveness, House Committee on Science, Space, and Technology, and the Subcommittee on Research and Development, House Committee on Armed Services.
GAO/NSIAD-92-5 -- page 60 scramjet is expected to achieve speeds of up to Mach 20 and an altitude of about 160,000 feet. The X-30 is also expected to be able to withstand the highest temperatures-about 5,000 degrees Fahrenheit[2] - compared to Japan's National Aerospace Laboratory aerospace plane's 4,000 degrees Fahrenheit. According to National Aeronautics and Space Administration officials, temperatures for any aerospace plane will peak at speeds of about Mach 15. The officials said 5,000 degrees Fahrenheit corresponds to the maximum heating of an uncooled vehicle; 4,000 degrees Fahrenheit would still be too high a temperature for the same vehicle even with active structural cooling. NASP'S first flight is scheduled for 1997 and its first orbital flight is scheduled for 1999. HOPE'S first unmanned flight is scheduled for 1999. HIMES' first planned flight is expected in 1998. The Japanese aerospace plane's first planned flight is not anticipated until sometime after the year 2000. Like NASP, the National Aerospace Laboratory's single-stage- to-orbit aerospace plane concept includes use of an active cooling system, powered landing capability, and use of a scramjet-considered by U.S. and foreign government officials and industry representatives as the most advanced and technologically challenging air-breathing engine.
U.S. Leads Japan in Testing of Major Aerospace Vehicle Components
The United States is the only country that has gone beyond the initial design phases[3] and tested major subscale air-breathing aerospace plane components. For example, the NASP Program has tested major components of a subscale scramjet up to speeds of Mach 17 and simulated the airflow within a scramjet up to speeds of Mach 24. Large-scale ramjet and scramjet models have been tested up to Mach 5 and tests are planned up to Mach 8. Over 1,000 test runs have been completed with subscale (one-fourth to one-sixth scale) scramjet engines up to Mach 8 in2. According to a U.S. expert in hypersonics, 5,000 degrees Fahrenheit is too high a temperature for most airframe or engine materials to withstand without active cooling. According to the Deputy Program Director of the NASP Joint Program Office those areas of the X-30 exposed to extreme temperatures of 4,000 to 5,000 degrees Fahrenheit (such as the nose cone; the wing, tail and engine cowl leading edges; and the inside walls of the engine s combustion chamber) would be actively cooled even though they will be made of advanced heat-resistant materials. 3. The design process for an aerospace vehicle generally includes (l) a conceptual design that results in a calculated initial number for the vehicle s weight size and performance characteristics; (2) a preliminary design that incorporates specific hardware and utilizes test data while continually improving and changing the design; and (3) a detailed design that integrates specific hardware in a frozen design. Although the NASP Program is moving into the preliminary design phase the X-30 will require additional testing and concurrent technology development. Major tests are still being conducted for subscale and/or non-flight-weight hardware.
GAO/NSIAD-92-5 -- page 61 scramjet test facilities. Components, such as inlets, combustors, and nozzles, have been tested up to Mach 17 in shock tunnels or high-speed facilities with brief run times. However, not all major components of the final scramjet engine can be tested, since the final engine configuration has not yet been determined. However, according to a U.S. expert in hypersonics, the NASP Program has not tested any actual flight-weight scramjet component at any speed. Designing and testing actual flight-weight scramjet components would occur in Phase III of the NASP Program once the final engine design is established. In fact, the program has not yet designed a flightweight scramjet engine component. Rather, the program has conducted only aerodynamic performance-type tests of parts that are geometrically similar to scramjet engines made of heat-sink type materials.[4] As of July 1991, tests have not included the materials and systems (such as cooling, fuel, control, and thermal protection) that an actual engine component must have.[5] A number of components, including the scramjet module inlet and fuel injectors, have been tested with partial simulation at speeds of Mach 12 to 17. The flow within a scramjet has not been simulated at speeds above Mach 8, because no facility currently exists that can actually simulate the flow within a scramjet at speeds above Mach 8. Tests have been made that simulate some portion of the flow within a scramjet at higher speeds. According to the Deputy Program Director of the NASP Joint Program Office, the NASP Program has conducted tests of a subscale scramjet up to Mach 8.[6] It has also conducted tests of scramjet inlets, combustors, and nozzles individually but not together at speeds above Mach 8 and tests of scramjet combustion and airflow at significant levels (at speeds above Mach 24) in shock tunnels. Sets of combustor components with simulated inlet and nozzle effects
4. Hundreds of wind tunnel test points have provided NASP scramjet performance data in numerous wind tunnel facilities. The models were designed for wind tunnel testing and not night operations. The models were appropriately designed, sized, and instrumented for ease and efficiency of testing for on- and off-design conditions. 5. National Aeronautics and Space Administration officials explained that the new paths for the complete or partial engines (i.e., inlets, combustors, and nozzle segments) are correct, but the materials used in the tests are typically high-conductivity metal. Thus, the test process remains unencumbered with the need to accommodate operational hardware, such as systems for active cooling. Research and development wind tunnel models are made to be as simple, operationally flexible, and inexpensive as possible. The models meet the needs of current NASP testing requirements. The models are not intended to meet flight conditions with fully developed systems for a final engine design. 6. Test periods of minutes are available in several facilities at conditions for aerospace vehicle speeds up to approximately Mach 8. At speeds of Mach 12 or higher, test periods in shock tubes or other facilities are very short. since full-scale scramjet nows spend only milliseconds in the engine combustor, test times for very high speed facilities actually provide similar "residence" times. The chalonly achieving a steady-state now in milliseconds but also in measuring the results.
GAO/NSIAD-92-5 -- page 62 have been tested at Mach 12. According to NASP Program officials, many high-speed propulsion tests are better conducted during actual flight of an experimental vehicle. The United States has also completed aerodynamic wind tunnel testing on several NASP design configurations. Large sets of data are available from a series of wind tunnels representing a range of conditions from takeoff (with ground effects) to high hypersonic speed (with and without powered effects). Testing with power on and off has helped define techniques to guide integration of the engine and airframe. Advancements in computational fluid dynamics now allow the calculation of details of internal and external flow fields up to orbital velocity. Structural and material technology has been advanced through the fabrication and testing of small and large-scale components. For example, McDonnell Douglas Corporation has built a full-size (8 by 8 by 4 feet) X-30 fuselage section from silicon carbide-reinforced titanium and manufactured a 900-gallon cryogenic hydrogen fuel tank from a graphite-epoxy composite and installed it in a titanium aluminide composite structure representative of a segment of the X-30's fuselage. The tank-fuselage assembly was instrumented and is being tested at Wyle Laboratories in Norco, California. Other X-30 structures being tested include wing sections, fuselage panels, elevons, and actively cooled panels. Although General Dynamics Corporation has fabricated and tested large, oxidation-coated carbon-carbon composite structures, carboncarbon composites still lack the strength to be used as structural materials, according to U.S. aerospace industry representatives. Nonetheless, NASP Program officials said that manufacturing and coating techniques for advanced (very high-temperature) carbon-carbon are progressing well. The material is strong, lightweight, and heat resistant. Other NASP technology development and testing includes vehicle flight controls; the production, handling, and storage of slush hydrogen; and special hightemperature instrumentation. In October 1990 the NASP National Program Office selected a single composite design configuration for the X-30 from multiple competing concepts: a lifting body incorporating short wings, twin vertical stabilizers, a two-person dorsal crew compartment, and three to five scramjet engine modules incorporating a small rocket.
GAO/NSIAD-92-5 -- page 63 Japan, on the other hand, is still in the initial definition and design phase of its air-breathing aerospace vehicle program. For example, the National Aerospace Laboratory has developed several aerospace plane designs and has tested small models of these design configurations in wind tunnels up to Mach 11. A scramjet engine inlet model and cooled structural panels that could be used in a scramjet engine have been tested up to Mach 4 at the Laboratory's Kakuda Branch. According to National Aeronautics and Space Administration officials, Japan is taking a vigorous approach to hypersonic propulsion. Japan is hiring foreign companies to help it quickly gain international competence in both hypersonic technology and hypersonic test facilities.
High-Speed Air-Breathing Propulsion
The most critical enabling technology is the propulsion system. For a single-stage-to-orbit aerospace vehicle, a propulsion system must be developed with sufficient thrust and efficiency to power the aerospace vehicle over the full range of speed from takeoff to Mach 25, which is orbital velocity. Similarly, for a two-stage-to-orbit aerospace vehicle, such as the concept once considered by the National Aerospace Laboratory, a propulsion system must be developed to power the vehicle from takeoff to Mach 6 to 7--separation velocity of the rocket-powered second stage from the air-breathing first stage. Propulsion systems envisioned for future aerospace vehicles must operate over a range of speeds. Currently, the ramjet is the primary propulsion system for aircraft and for some missiles operating at speeds of about Mach 2 to 6.5. However, the ramjet is generally not applicable at speeds below Mach 2 and above Mach 6.5 due to the lack of sufficient net thrust. Propulsion technology, according to a U.S. expert in hypersonic propulsion, is the best indicator of where a country intends to go in future hypersonic vehicle applications. Unlike materials technology, for example, hypersonic propulsion has virtually no spinoff to other applications. Thus, hypersonic propulsion is a clear indicator of the future markets a country intends to capture. Moreover, hypersonic propulsion can only be developed by building and testing engine components and entire propulsion systems that are expensive and often require specialized facilities. Finally, the type of propulsion concepts being developed indicate the type of application being considered. For these reasons, the expert believes that the intentions of another country in hypersonicsGAO/NSIAD-92-5 -- page 64 can best be determined by looking at what it is doing in hypersonic propulsion. Hypersonic air-breathing (primarily scramjet) propulsion technology is a Department of Defense high-priority effort in air-breathing propulsion technology. It has the potential, through the NASP Program, to extend military missions to new flight regimes and to provide more cost-effective and on-demand assured access to space. A hypersonic cruise airplane with sustained cruise capability between speeds of Mach 5 and 14 could enhance military capability by carrying out potential military missions, such as interdiction, reconnaissance, surveillance, precision targeting and weapons guidance, strategic bombing, and strategic airlift. According to the Department of Defense, Japanese research and development in the following areas indicate a moderate technical capability with possible leadership in some niches of air-breathing technology and a potential capability for making important contributions to meeting U.S. challenges and goals in air-breathing propulsion:
- development and design integration of lightweight, high-temperature, high-strength materials and
- reduction of observables in high-temperature, air-breathing propulsion systems.
- modeling and simulation (including computational fluid dynamics) of complex aerothermodynamic flow and empirically calibrated data bases and
- development of scramjet propulsion.
GAO/NSIAD-92-5 -- page 65 activity in the NASP Program. However, according to the Department of Defense, Japan has a strong interest in scramjet and combined-cycle engines. Japan is accelerating its technical effort. Japanese programs include development of a methane-fueled ramjet capable of stable flight up to Mach 5 and a small combined-cycle ramjet/turbojet engine. Japan also has initiated a major effort to enhance its aerospace materials and propulsion capabilities by establishing the Material Research Center and Institute to study ultra-heat-resistant materials for use up to 2,000 degrees Celsius. If successful, according to the Department of Defense, this research could result in major advances in the field of hypersonic air-breathing propulsion.
Status of Japanese Advanced Propulsion Systems
Japanese advanced propulsion systems are in various stages of maturation ranging from concept development to being operational. The gas generator cycle LE-5 cryogenic propulsion engine for the second stage of the H-I expendable launch vehicle is presently operational. Development of the LE-5A expander bleed-cycle engine and LE-7 pre-burner cycle cryogenic engine for the first stage of the H-II launcher is underway. The experimental high-pressure expander-cycle engine represents an additional new liquid-hydrogen engine development. The liquid air cycle engine, also in advanced development stage, is a generic propulsion system oriented toward advancing air-breathing propulsion systems, such as strap-on boosters for larger versions of the H-II or hypersonic propulsion applications. In terms of air-breathing engines, the air-turboramjet experimental engine, an expander-cycle air-turboramjet system that uses much of the technology from the high-pressure expander-cycle engine, is also in the advanced development stage. A Mach 0 to 5 turbojet/ramjet engine development program, announced in April 1989, is being supported by the Ministry of International Trade and Industry as a basic research and development project composed mainly of component research. The hybrid engine would integrate a turbojet and ramjet. Finally, scramjet concept development is underway at the National Aerospace Laboratory for future hypersonic aerospace vehicle applications.Japanese Adaptation of Engine Components From Existing Programs to New Efforts
Japanese space propulsion programs, as of August 1990, are characterized by the adaptation of components from existing rocket programs to new propulsion efforts. For example, the liquid air cycle demonstrator engine uses the liquid hydrogen pump and combustor from the LE-5 engine, along with new components for the air liquefier and the liquidGAO/NSIAD-92-5 -- page 66 air pump. According to U.S. government and university propulsion experts who were members of the Japanese Technology Evaluation Center[7] panel on Japanese aerospace propulsion, the Japanese do a very effective job of using previously demonstrated components in advanced projects. In addition to the liquid air cycle engine, the high-pressure expander-cycle and air-turboramjet experimental engines are similar to Japanese liquid rocket engines as well. For example, the air-turboramjet experimental engine relies upon Ishikawajima-Harima's existing turbojet-turbofan production and design experience, as well as the expander-cycle technology developed in the high-pressure expandercycle engine. This interchangeable component technology appears to provide cost-effective progress in Japan's new programs, while enhancing the reliability of its liquid rocket engines. Although a considerable amount of technology development is directed toward scramjet applications, Japanese scramjet work is only in the concept definition phase, and scramjet demonstration engine development is not imminent. According to Japanese Technology Evaluation Center panel members, the technology is now available for the liquid air cycle and air-turboramjet experimental engines, but technology for a scramjet engine is not yet accessible. Japanese scramjet technology programs include experimental studies of supersonic combustion, including ignition and diffusion flame studies, and shock tube studies of elementary reaction kinetics of hydrogen. In addition, high-speed inlet tests are currently underway on a scale model. This work is being conducted at the National Aerospace Laboratory and at several universities. Two new Japanese university efforts are underway involving 20 faculty members at several universities oriented toward hypersonic reacting flows and component technology for advanced propulsion systems. To complement these experimental studies, computational fluid dynamics studies of scramjet configurations are being conducted by the
7. The Japanese Technology Evaluation Center is operated for the U.S. government by Loyola College in Baltimore Maryland to provide assessments of Japanese research and development in selected technologies. The National science Foundation is the primary support agency. other sponsors include the Defense Advanced Research Projeets Agency, the Nabonal Aeronautics and space Administration and the U.S. Department of Energy. The Japanese excel at acquisition and perfection of foreign technologies. As Japan becomes a leader in research in targeted technologies, the Center helps the United States get access to the results. The Center's assessments contribute to more balanced technology transfer between Japan and the United states by alerting U.S. researchers to Japanese accomplishments. The assessments are conducted by a panel of technical experts selected from government, industry, and academia. Panel members are leading authorities in their fields technically active and knowledgeable of Japanese and U.S. research programs.
GAO/NSIAD-92-5 -- page 67 National Aerospace Laboratory's Chofu facility, where researchers are using this experimental data to validate computational fluid dynamics codes. Scramjet test facilities in Japan are located at the Laboratory's Chofu Headquarters, Kakuda Branch, and the University of Tokyo, all of which have capabilities to test some aspect of internal flow of a scramjet up to speeds of Mach 2. A new scramjet engine test facility is being built at the Laboratory's Kakuda Branch and is expected to be in operation in 1993.
Fuels Development
Japan is also pursuing advanced fuels development and plant construction for stepping up its hydrogen production capabilities to serve the H-II rocket booster. Japan has the resources to develop advanced fuels for rockets as well as the capability to manufacture, store, and transport hydrogen.Applications of Computational Fluid Dynamics to Advanced Propulsion
According to the Japanese Technology Evaluation Center propulsion panel, Japan will soon be moving into hydrogen production for the new series of hydrogen-fueled rockets and spaceplane research. According to Japanese Technology Evaluation Center panel members, computational fluid dynamics represents an area of strength in Japan. Japanese supercomputers are among the world's best, and major supercomputing facilities are located at the National Aerospace Laboratory and at the privately owned Institute for Computational Fluid Dynamics.[8] Japanese national universities also have excellent supercomputing capabilities. The availability of and access to supercomputers in Japan has resulted in rapid progress in computational fluid dynamics. The Japanese routinely include real gas effects and complex reaction kinetics in flow field analyses, and their computational fluid dynamics codes are based on the latest algorithms. According to Japanese Technology Evaluation Center scientists, Japanese visualization and postprocessing capabilities are also on the leading edge.[9] The Japanese have demonstrated appropriate computational fluid dynamics capabilities that could allow them to move rapidly in this aspect of pro pulsion development.8. The Institute is operated by an Institute of Space and Astronautical Science professor out of his home. 9. A Science and Technology Agency official said, in Japan, these advanced techniques would not generally be used.
GAO/NSIAD-92-5 -- page 68
Engine Contractor Selection in Japan
According to the Japanese Technology Evaluation Center panel, selection of an engine contractor in Japan differs considerably from that in the United States. Although competition exists, particularly at the concept development level, the award of new propulsion contracts is generally based on the technical capabilities that the contractors have demonstrated in previous projects. For example, Mitsubishi is generally the overall engine developer for liquid rocket engines, while Ishikawajima-Harima is expected to emerge as the turbomachinery contractor, according to the Japanese Technology Evaluation Center panel. In Japan, a company's share of a project's contract generally appears to be set by historical factors, rather than by competitive procedures. Moreover, the role of Japanese industry is coordinated and strengthened through the Keidanren and the Society of Japanese Aerospace Companies. However, according to the Executive Director of the National Space Development Agency of Japan, the Space Development Agency does not award contracts for its projects based on the results of coordination by either the Keidanren or the Society of Japanese Aerospace Companies. The High Commissioner of the Space Activities Commission and the Director for Space Transportation Research in the Science and Technology Agency disagree with the panel's view on engine contractor selection and believe the way to select an engine contractor in Japan would be similar to that in the United States. The High Commissioner and Director suggested selection of an engine contractor in Japan is primarily based on the technological capabilities demonstrated in previous projects through competition, since an aerospace vehicle engine would require strict reliability.Japanese Engine Development Work
The Japanese are conducting several analytical investigations and experimental programs involving component testing and demonstration engines on several aerospace plane advanced propulsion systems, including a turbojet, ramjet, turboramjet, air-turboramjet, liquid air cycle engine, and scramjet. The propulsion systems of primary Japanese interest are (1) those in the Mach 3 to 6 range for hypersonic cruise airplanes and single-stage-to-orbit space launch vehicles, (2) strap-on booster augmentation engines for vertical launch systems, and (3) air breathing engines for a high-speed commercial transport aircraft. Japanese technology development efforts in higher Mach number propulsion systems are aimed more at accumulating a data base. Two classes of engines are currently in the prototype phase of development in Japan: Ishikawajima-Harima's air-turboramjet experimentalGAO/NSIAD-92-5 -- page 69 engine and Mitsubishi's liquid air cycle engine. Kawasaki is developing a turboramjet. Even though this is probably the least complex and risky engine cycle of the advanced propulsion systems, Japanese Technology Evaluation Center propulsion engineers indicated it does not appear that the engine components are currently available for this engine. Although demonstration engines have been built for the liquid air cycle and air- turboramjet experimental engines, the development programs had been temporarily put on hold beginning in 1989 because liquid hydrogen facilities in Japan were dedicated to LE-7 engine development.
Ishikawajima-Harima's Air-Turboramjet Experimental Engine
Ishikawajima-Harima's detailed design and construction of the air turboramjet is part of a collaborative program with the Institute of Space and Astronautical Science. The air-turboramjet experimental engine cycle is based on the heat capacity of liquid hydrogen (expander cycle). Ishikawajima-Harima is the lead contractor. Like the liquid air cycle engine concept, an earlier version of this engine was developed in the United States by Aerojet in the late 1950s. However, the Aerojet engine was based on the gas generator principle and not the expander cycle. Ishikawajima-Harima's analysis indicates that the air-turboramjet system would be competitive with the liquid air cycle engine or turboramjet up to Mach 5 and would be effective up to Mach 7 or 8. According to Japanese Technology Evaluation Center engineers, hardware has been developed so that tests of a complete engine could be conducted when liquid hydrogen test facilities become available in Japan. According to Ishikawajima-Harima, development of the engine may take 8 to 10 years.Kawasaki's Turboramjet
The Japanese have analyzed turboramjet engine cycles for conditions appropriate for an aerospace plane up to Mach 6. This cycle is the least complex and least risky cycle to be developed for this flight regime. According to Kawasaki, the engine cycle analysis, conceptual design, and hydrogen ram combustion test/analysis have been studied.Mitsubishi's Liquid Air Cycle Engine
The liquid air cycle engine is essentially a hydrogen/oxygen propellant rocket engine that uses atmospheric oxygen liquified during flight as an oxidizer. Mitsubishi is the lead contractor for the liquid air cycle engine. According to the company, its studies indicate that the liquid air cycleGAO/NSIAD-92-5 -- page 70 engine would perform well up to Mach 6 and may be effective up to Mach 8. The liquid air cycle engine would power both a single-stage-to-orbit aerospace plane or vertically launched conventional rocket boosters. Air enters the engine through an internal contraction inlet, which reduces the airflow to subsonic speeds. The air is then condensed in a liquefier, pumped as a liquid to high pressure, and injected into a rocket motor type combustion chamber, where it is burned with gaseous hydrogen fuel. Liquid hydrogen is pumped to high pressure in a turbopump and is then used to liquify the air in the heat exchanger. Gaseous hydrogen is then injected into the combustion chamber. The turbopump is driven by hot gas produced in a gas generator instead of by the hydrogen fuel itself. The LE-5 rocket engine's hydrogen pump and the combustion chamber nozzle are used in the liquid air cycle engine. According to Japanese Technology Evaluation Center propulsion engineers, this component interchange demonstrates compatibility among programs and appears to be a distinctive feature of Japanese propulsion system development programs. The objective of the liquid air cycle engine is to increase launch specific impulse by eliminating a large portion of the liquid oxygen tankage that a conventional rocket booster must carry to reach orbit. However, a potential problem with the liquid air cycle engine concept is that savings in tankage weight could be offset by the potential weight of the engines. Mitsubishi officials said liquid air cycle engine development is a relatively low-risk effort since much of its machinery is based on existing cryogenic technology. Mitsubishi program managers at the company's headquarters in Tokyo commented that although its ultimate goal is to develop the liquid air cycle engine for use in a single-stage-to-orbit aerospace plane, company engineers believe the liquid air cycle engine could also be integrated into a later version of the H-II launch vehicle as a strap-on booster. In a technological advancement, the Japanese may have solved the fundamental problem of icing in development of a liquid air cycle engine. The concept of the liquid air cycle engine was originally developed in the United States and patented by The Marquardt Company in 1958. The Marquardt Company continued to conduct tests on the engine through 1964. However, the company encountered frost buildup on the heat
GAO/NSIAD-92-5 -- page 71 exchanger surface, which drastically changed heat exchanger performance. The Marquardt Company abandoned the liquid air cycle engine in 1968 with cancellation of an aerospace plane program, because the technology was insufficient and no application was seen for a liquid air cycle engine. Mitsubishi began development of its own heat exchanger in 1986 and began testing critical liquid air cycle engine components in 1988. According to Mitsubishi officials in Nagoya, hardware for an air liquefier has been tested twice. We viewed video tapes of these tests at Mitsubishi's Nagoya plant and again in Washington, D.C., with U.S. propulsion experts. The tests demonstrated that Mitsubishi had solved the icing problem. The liquefier is a critical component because of the possibility that the heat transfer surfaces can become clogged with water and carbon dioxide, which solidify at the temperature required to liquify air. Failure to solve this problem was the primary reason the United States stopped working on a liquid air cycle engine in the 1960s. Mitsubishi engineers said that by modifying the tube arrangement, providing spacing between the tubes, and changing the sequence from ambient temperature to cryogenic temperature, they were able to demonstrate that frost buildup can be avoided. The key manufacturing technique, according to Mitsubishi engineers, is to densely arrange the tubes. Tubes may be built of columbium or ceramics, although ceramics are difficult to shape. National Aerospace Laboratory engineers at the Laboratory's Kakuda Branch suggested that vibration of the heat exchanger tubes may have prevented icing in the Mitsubishi tests. U.S. engineers told us that, if this is the solution, then metal fatigue may be a problem. Mitsubishi is developing a heat exchanger for a 10-ton engine. Testing occurred between 1985 and 1988. In 1989 the heat exchanger was scheduled to be tested with the 10-ton engine and turbopumps. Since 1989, tests have been stopped due to use of liquid hydrogen facilities for LE-7 development work. An LE-7 engine modified to the liquid air cycle engine configuration would perform as a liquid air cycle engine at speeds up to about Mach 5 and altitudes up to 40 kilometers. Above Mach 5, the engine would function as a rocket. A liquid air cycle engine developed for a single-stage-to-orbit aerospace plane would differ from those used in a vertically launched rocket
GAO/NSIAD-92-5 -- page 72 booster. Mitsubishi officials commented that aerospace plane liquid air cycle engines would probably use higher density, lower volume slush hydrogen and slush oxygen. To improve specific impulse at takeoff, only slush hydrogen would be burned by the engine during the air-breathing portion of flight, which would end at a speed of Mach 10 at an altitude of 40 kilometers. Although much of the liquid air cycle engine concept is based on existing technology, development of a lightweight liquefaction system, advanced materials development, and heat exchanger design difficulties must be overcome before a fully functioning liquid air cycle engine can be developed, according to the manager of engine engineering at Mitsubishi. A working first stage heat exchanger for a 10-ton thrust liquid air cycle engine was fabricated in 1988 and tested at Mitsubishi's Tashrio Field Laboratory in northern Japan. The heat exchanger houses more than 10,000 cooling tubes, each of which is less than 3 millimeters in diameter and has used liquid hydrogen to achieve an air liquefaction ratio of 3 to 1. Mitsubishi officials said the company expects to adopt the liquid air cycle engine concept but has not determined a firm schedule. They want to demonstrate the liquid air cycle engine to the National Aerospace Laboratory and evaluate the feasibility of the engine for use in an aerospace plane by 1991 or 1992. Mitsubishi expects to receive Japanese government contracts in the future for work on the engine.
Scramjet Technology
Several Japanese government and industry officials indicated work on scramjets would be delayed, since the technology is not available. Mitsubishi officials said whereas the liquid air cycle or air turborocket cycle engine systems are currently technologically accessible, the scramjet cycle is not. However, the Japanese are carrying out basic scramjet technology experiments at several locations in Japan. This work includes experimental and computational fluid dynamics efforts in inlet configurations and in mixing and combustion technology. The Science and Technology Agency is planning to spend the next 3 years building a subscale model of a scramjet, which Agency officials believe is the most likely candidate for Japan's single-stage-to-orbit aerospace plane. The scramjet model is expected to be about one-fifth the size of a full-scale engine. The model would be less than one meter in diameter and about two meters long. The Agency is expected to conductGAO/NSIAD-92-5 -- page 73 the studies and test components, such as the air-intake duct and combustion chamber, before assembling the complete scramjet model. Mitsubishi is expected to build the subscale engine under contract from the Japanese government. The National Aerospace Laboratory is conducting scramjet inlet testing at its Kakuda Branch using a small Mach 4 supersonic wind tunnel. Figure 4.1 shows a scramjet test in the Laboratory's Ram/Scramjet Combustor Test Facility at its Kakuda Branch.
GAO/NSIAD-92-5 -- page 74 U.S. government and industry propulsion experts told us the test program at the National Aerospace Laboratory's Kakuda Branch appears to be well coordinated with its Numerical Computations Center in Chofu. National Aerospace Laboratory managers stated that, a scramjet inlet testing progresses, different scramjet configurations will evolve with emphasis on both high-speed and low-speed configurations. Scramjet tests at various Mach numbers are planned in the National Aerospace Laboratory's 50 centimeter Hypersonic Wind Tunnel at Chofu.
GAO/NSIAD-92-5 -- page 75 Ishikawajima-Harima began studying scramjets in 1986 and is involved in computational fluid dynamics and scramjet combustion testing at the Laboratory's Kakuda Branch. In addition to computational fluid dynamics analysis of scramjets, a number of cycle codes are being developed at the National Aerospace Laboratory to predict the performance of the scramjet as a function of geometry, area ratio, and mixing schedule. U.S. propulsion experts stated that the mixing schedule from the Langley Hypersonic Propulsion Branch at the National Aeronautics and Space Administration's Langley Research Center in Hampton, Virginia, is being used as the technique to model fuel mixing in the combustor. They also noted that a scramjet optimization code being developed in Japan is unique.
Advanced Propulsion Activities at Japanese Universities
Supersonic mixing and combustion studies are being conducted at Japanese National Aerospace Laboratory facilities at Chofu and Kakuda and at the University of Tokyo. Four Japanese universities are also conducting research with the national laboratories and industry on propulsion and combustion. They are the University of Kyushu (aeroengine), University of Kyoto (propulsion), University of Nagoya (aeroengine and propulsion), and University of Tokyo (space propulsion, rockets, jet propulsion, and aeroengine). Supersonic combustion research has been conducted at the University of Tokyo since 1974 when the Mach 2 pebble bed heater facility was built at the Research Center for Advanced Sciences and Technology. The University of Tokyo is conducting Mach 2 direct connect tests to study both perpendicular and parallel mixing and combustion to validate computational fluid dynamics codes. About 20 professors at the University of Nagoya are coordinating a study of hypersonic reactive flows in scramjet engines. In 1989 a joint institute of the University of Tokyo and National Aerospace Laboratory was formed to conduct joint research on high-speed, air-breathing engine technology. This group will concentrate its research on the (1) performance of air-breathing engines, (2) fundamental component technology for turbo-engines, (3) fundamental component technology for ram/scramjet engines, and (4) measurement technology for internal flow of engines. Scramjet combustion research is also being conducted by the National Aerospace Laboratory's Kakuda Branch with Ishikawajima-Harima andGAO/NSIAD-92-5 -- page 76 the University of Tokai. The University of Nagoya has an active highspeed combustion research program.
Assessment of Advanced Propulsion Work in Japan
According to the NASP Program's Chief Scientist, advanced propulsion work in Japan is appropriate for the stage of aerospace plane development in Japan. The Japanese are conducting research on a wide variety of advanced propulsion concepts and their approach is state of the art, according to the Chief Scientist. He said the results look plausible and realistic. The Chief Scientist said Japan has done the necessary preliminary work (computations and some experimental tests) on advanced propulsion systems for an aerospace plane. For example, in 1988 Japan conducted heat transfer computations inside a scramjet, including computations for fuel flow. These computations included the intake, strut, combustor, and nozzle. The Japanese then conducted a systems study comparing engines. They concluded the system with the least weight in hardware and propellant is the best engine. The two best combined engine concepts the Japanese came up with, according to the Chief Scientist, were the air-turboramjet/scramjet/rocket and the liquid air cycle engine/ scramjet. These are the same two combined types of engines the United States determined were the best more than 30 years ago. Importantly, Japan now has an engineering basis for selecting these two engines for further development. Some National Aeronautics and Space Administration and U.S. aero space industry propulsion experts expressed concern to us that Japan is developing several important aerospace plane propulsion systems that the United States has either abandoned or is not working on at the present time. These systems include the liquid air cycle engine, air turboramjet experimental engine, and high-pressure expander-cycle engine. They are concerned the United States is placing all of its emphasis on a scramjet propulsion system for the X-30. In 1988 Japanese engineers at the National Aerospace Laboratory's Kakuda Branch took a National Aeronautics and Space Administration Langley Research Center engine design from the 1970s and repeated U.S. tests on the engine to gain experience. They were able to duplicate the National Aeronautics and Space Administration's test results. These tests provide Japan with experience in hypersonics, something the Japanese repeatedly told us they lack.GAO/NSIAD-92-5 -- page 77 The Japanese have a broadly based advanced propulsion program. According to Japanese Technology Evaluation Center propulsion engineers, the Japanese schedule is ambitious, but achievable. Currently, the Japanese advanced propulsion program is behind that of the United States, but they are making rapid progress in selected systems. The Japanese are one of the world's leaders in such key technologies as advanced materials, and they enjoy a high level of project consistency and continuous funding. Japan's aerospace plane development has been evolutionary in nature, while the U.S. program has placed greater emphasis on revolutionary advances through technological breakthroughs. Japanese projects tend to be smaller than those in the United States, focusing on incremental advances in technology, with a good record of applying proven technology to new projects as seen in their high-pressure expander-cycle engine, liquid air cycle engine, and air-turboramjet experimental engine programs. This evolutionary approach, coupled with an ability to obtain technology off the shelf from other countries, has resulted in relatively low development costs, steady progress, and enhanced reliability. According to the Japanese Technology Evaluation Center propulsion panel, Japan is clearly positioned to be a world leader in advanced propulsion technology for aerospace planes by the year 2000. Japanese government officials said Japan does not have any intention of gaining such a position and Japan is only studying aerospace plane concepts to make an appropriate contribution in this field. According to a U.S. expert in hypersonic propulsion, Japan is pursuing a very deep and broad-based research and development program in hypersonic propulsion. The expert said that although the United States is ahead of Japan in NASP propulsion technology, Japan may be ahead of the United States in air-breathing hypersonic propulsion technology for several other important applications, including two-stage-to-orbit space launch vehicles and high-speed commercial transport aircraft. The Japanese are building and testing components and complete engines using a variety of propulsion cycles that are suitable for a variety of applications. The expert said no other country is pursuing such a comprehensive program in hypersonic propulsion. According to the expert, the United States has placed essentially all of its hypersonic technology in the NASP Program. The expert added that although the NASP propulsion system may be a good choice for a single-stage-to-orbit acceleratortype vehicle, the NASP propulsion concept is very inefficient for a future operational high-speed commercial transport aircraft in the Mach 3 to 6 speed range. Japan's air-turboramjet experimental engine (a composite
GAO/NSIAD-92-5 -- page 78 cycle engine concept using a hydrogen-cooled inlet with an expandercycle air-turboramjet) would have three to four times the specific impulse from Mach 0 to 6 as would the NASP propulsion system. In addition, according to the expert, the Japanese engine is being developed on the ground using existing facilities. The Japanese are not only developing this engine but are building and testing a variety of other hypersonic propulsion concepts, including liquid air rockets, liquid air turboramjets, and scramjets. One U.S. expert in hypersonic propulsion believes that Japan intends to be in a position early in the 21st century to become the world leader in high-speed commercial transport aircraft capable of achieving speeds above Mach 3. The expert indicated the Japanese believe they cannot compete with U.S. and European aircraft manufacturers in the nearterm for high-speed (supersonic) commercial transport aircraft. However, the Japanese intend to be ready to compete in the Mach 3 and above (hypersonic) transpacific transport aircraft market, which the Japanese believe will become viable in the next century. The expert said the Japanese are doing everything a prudent nation would do if that were its goal. Japan may be in a position to leapfrog over the U.S. aerospace industry in the next 5 to 10 years, according to the expert.
Advanced Materials
The second most critical enabling technology is advanced materials. The weight of an aerospace vehicle must be reduced as much as possible to minimize the fuel and thrust required by the engine. Also, hypersonic flight causes extremely high temperatures due to air resistance on the vehicle's surfaces and within the engine. For example, the X-30's nose cone could reach more than 5,000 degrees Fahrenheit, and the leading edges of the wing and tail could reach almost 3,500 degrees Fahrenheit. Therefore, materials must be developed that are able to withstand extremely high temperatures and are high-strength, lightweight, and reusable. Advanced materials include carbon-carbon, titanium-based alloys, beryllium-based alloys, fiber composites, and titanium aluminide produced either conventionally or by rapid solidification technology. According to the Department of Defense, ongoing research and development in Japan in the following areas indicate a moderate technical capability with possible leadership in some niches of advanced materials technology and a potential capability for making important contributions to meeting U.S. challenges and goals in advanced materials:GAO/NSIAD-92-5 -- page 79
- development of composite materials capable of retaining structural properties at high temperatures;
- development of improved nondestructive evaluation techniques for advanced composites; and
- improvements in modeling and prediction of life-cycle failure.
- application of structural composites to reduce observables and
- improvements in characterization of composite material response to weapon effects.
GAO/NSIAD-92-5 -- page 80 Japan is also embarking on a major initiative in materials to support development of next-generation air transports. In 1987 the Japanese Ministry of International Trade and Industry began research on metal composite, ceramic composite, advanced carbon-carbon, and carbonfiber materials. The Ministry concluded that development of advanced materials able to withstand high temperatures is a priority. In 1989 the Ministry initiated an 8-year program to develop new heat-resistent materials for a spaceplane and other purposes. The Ministry expects that advanced materials for use at temperatures up to 2,200 degrees Celsius will be available by the year 2000. According to the Department of Defense's Critical Technologies Plan,[10] the United States is judged to be the world's leader in composite materials. However, the U.S. lead in composite materials is being rapidly eroded by a combination of industrial technology transfer, such as aircraft composite technology, and strong research and development efforts by foreign countries, including Japan. For example, according to the Office of Technology Assessment, Japanese fiber producers could abrogate existing agreements and sell directly in the U.S. market. Also, the Japanese could use technology gained from joint ventures with a U.S. aircraft manufacturing firm to launch its own commercial aircraft industry. Although Japan is the world's largest producer of carbon fiber (a key ingredient in advanced composites), it has only been a minor participant to date in the worldwide application of advanced composites. One reason is that Japan has not developed a domestic aircraft industry- the industrial sector that currently uses the largest quantities of advanced composites. Another reason is that Japanese companies have been limited by licensing agreements from participating directly in the U.S. market. The National Space Development Agency of Japan is conducting research and development of titanium alloys and advanced carbon fiber polyimides, reinforced carbon-carbon composites, and thermal protection systems for HOPE. Agency contractors are conducting extensive tests on carbon-polyimide materials for use in HOPE'S structure. The Agency is also studying carbon-carbon coated with silicon
10. The third Annual Defense Critical Technologies Plan is a plan for developing the 21 critical technologies considered by the Secretary of Defense and the Secretary of Energy to be the technologies most critical to ensuring the long-term qualitative superiority of U.S. weapon systems and to outline an investment strategy to manage and promote the development of these technologies. See Critical Technologies Plan. Washington, D.C.: Department of Defense, 1991.
GAO/NSIAD-92-5 -- page 81 carbide and titanium and ceramic tiles for HOPE'S thermal protection system. Samples of these materials will be mounted and tested on the Orbiting Reentry Experimental Vehicle scheduled to be launched in 1993. Mitsubishi managers at the company's Nagoya plant told us they have mastered the autoclave bonding processes for forming HOPE structural components from all the candidate materials. The Agency is also conducting research and development of a thermal protection system using ceramic tiles. The Agency's test results have demonstrated that its tiles have the same thermal protection as tiles used on the U.S. space shuttle. The National Aerospace Laboratory is investigating fiber-reinforced metals and plastics and an advanced carbon-carbon thermal protection system. Fuji has a wide range of advanced materials capabilities, including carbon-carbon composites and reinforced carbon-carbon composites. Fuji is conducting research on superplastic forming, diffusion bonding, and electron beam-welding processes. Fuji is also studying molding processes of thermoplastic composites and carbon-polyimide, evaluating composite material characteristics under a space environment (e.g., electron beam radiation and thermal cycles), and developing various thermal protection systems. However, Fuji is not conducting research on titanium aluminides and does not have rapid solidification technology production capability. Mitsubishi has developed superplastic forming, diffusion bonding, and electron beam-welding processes. Its composite laboratory in Nagoya is conducting research on autoclave molding of titanium foil, studying advanced fabrication of carbon-carbon, studying molding processing for thermoplastic composites, and evaluating the thermal properties of composites. Thermal protection systems being studied include carbon-carbon composites, ceramic tiles, and metallic thermal protection systems. Kawasaki has tested carbon-carbon composite material to 1,700 degrees Celsius for 10 6-minute cycles. According to NASP Joint Program Office Fact Finding Group officials, Kawasaki officials stated their carboncarbon material is one of the best in the world. NASP Program officials and U.S. industry representatives were impressed with Kawasaki's carbon-carbon composite material and had no reason to doubt Kawasaki's claim. However, they questioned whether Kawasaki could
GAO/NSIAD-92-5 -- page 82 produce carbon-carbon composite materials in sufficient quantities to build an aerospace plane. Advanced structural materials industries have become increasingly international in character through acquisitions, joint ventures, and licensing agreements. According to the Department of Defense, this trend has important consequences for the United States: one can no longer assume that the United States will dominate the advanced structural materials technologies and their applications. According to the National Research Council, the United States is already lagging behind other nations in applying advanced materials to manufacturing processes. Also, the rate of technology flow among companies and between countries is likely to grow due to the increasingly multinational character of the materials industries. Some of the key technologies for a future Japanese spaceplane are being developed in nonaerospace industries. For example, titanium-aluminide used in the manufacturing of turbocharger rotors for motorcycle engines by Kawasaki could have spaceplane applications. Members of the Fact Finding Group cautioned that relatively small levels of investment in the development of enabling technologies in Japan (compared with investment levels in the United States) does not mean that significant research and development is not being conducted. Technology developed by nonaerospace industry in Japan is applicable to developing and building a spaceplane.
Assessment of Advanced Materials Work in Japan
According to U.S. government and university materials experts who were members of the Japanese Technology Evaluation Center panel on advanced composites, the Japanese believe that technological superiority in space structures and launch systems, and particularly in hyper sonic vehicles, will allow Japan to become a dominant force in the aerospace market. An enabling technology is advanced materials, one of three areas selected by the Ministry of International Trade and Industry for major national development investment. Many Japanese government and industry programs are long-term efforts geared to the future at the expense of short-term gains. For example, the Ministry's program to develop new heat-resistent materials for a spaceplane and other purposes is scheduled to last for 8 years-a longer time than would be possible in the United States. Parallel approaches to advanced materials research and technology are encouraged and supported by the Japanese. These approaches oftenGAO/NSIAD-92-5 -- page 83 involve overlapping activities between several groups with a sharing of information at the precompetitive stage, according to panel members. In contrast, the United States often tries to select one best approach initially and then frequently finds that other options are needed. According to panel members, requirements for Japanese government programs are usually set at a modest, realistic, and attainable level. In this way, Japanese government and public support can be maintained. Unlike the United States, the goals are not driven by requirements for a specific system. Also, in comparison to the United States, direct Japanese government funding for new materials is quite small, since it usually does not include personnel costs. Japanese government funding focuses on areas of national interest. According to panel members, a strong national unity drives Japanese industry to make much larger contributions to the support of new materials research and technology. According to the Japanese Technology Evaluation Center panel, some Ministry of International Trade and Industry materials programs have led to new consumer markets and ultimately to substantial returns on the Japanese government's investment. The Japanese have learned manufacturing skills and have formed technical teams within and across industries, which remain intact for the long periods of time required to develop and exploit the market. However, the new high temperature materials program is quite different. Although these materials may be an enabling technology for an aerospace plane and hypersonic transport aircraft, they may only be produced in small quantities. Japanese companies that only produce materials may have to reexamine the question of national commitment versus profit. A large, well-funded, and vertically integrated Japanese company may be able to produce the materials and aircraft structures internally. Panel members noted that a strong fiber and carbon industry makes Japan the leader in carbon fiber technology and that this technical base should allow Japan to not only match U.S. carbon fiber technology but also introduce lower cost manufacturing methods. However, panel members did not see any research in Japan on innovative approaches to oxidation protection. Although ceramic and intermetallic matrix composites are not being actively pursued in Japan at this time, they may be in the near future. Monolithic ceramic research and development activity is still at a high level. High-temperature monolithic intermetallic research is just beginning, although some products consisting of titanium aluminides have been manufactured. Panel members noted a novel Japanese approach in matrixless ceramic composites. Finally, technologies for
GAO/NSIAD-92-5 -- page 84 high-temperature composites fabrication exists in Japan but large numbers of panels or parts have not yet been produced. A decrease in the interest of Japanese companies in aluminum matrix composites that have lower temperature capabilities is due to the lack of a commercial market and not the availability of technology.
Computational Fluid Dynamics and Supercomputers
Computational fluid dynamics-the use of advanced computer programs to solve a set of mathematical equations with a high-speed digital computer-is extensively used in aerospace vehicle programs to simulate air flows, high temperatures, and pressure contours around various design configurations of an aerospace plane and within advanced propulsion systems at high Mach speeds. These calculations are used in the design of the vehicles' airframe and engine. Computational fluid dynamics is also used to simulate aerospace vehicle performance between speeds of Mach 8 and 25, where ground test facilities or capabilities are not adequate in terms of velocity duplication and actual test data are limited. Computational fluid dynamics computer programs must also be validated by actual test data at lower speeds, which are then compared to the theoretical calculations. Modifications to the computer programs are then made where appropriate. Advances in supercomputers over the past several years have allowed extensive used of computational fluid dynamics in Japanese aerospace vehicle research and development programs. Use of supercomputers has resulted in more accurate and faster air flow calculations. Three of the five supercomputer manufacturers in the world are Japanese: Fujitsu, Hitachi, and Nippon Electric Corporation. The other two, both U.S. companies, are Cray Research and Cray Computer Corporation. According to U.S. officials, growth in computational capability in Japan has been impressive, and Japan's national laboratories have the computing power to perform state-of-the-art computations on aircraft and propulsion systems. Further improvements in storage and performance are currently underway. The United States currently has a commanding lead in computational fluid dynamics, according to the Department of Defense. However, strenuous efforts are being made in Japan to develop a competitive capability, since computational fluid dynamics is recognized worldwide as a critical technology. Computational fluid dynamics is a powerful toolGAO/NSIAD-92-5 -- page 85 for modifying designs and solving problems, and its use by the U.S. aerospace industry for the design of the next-generation commercial aircraft is expected to help maintain the current U.S. dominance. According to the Department of Defense's Critical Technologies Plan, ongoing research and development in Japan in the following areas indicate a general lagging behind the United States but a potential capability of making contributions in selected areas in meeting U.S. computational fluid dynamics challenges and goals:
- to improve the application of computational fluid dynamics to complex three-dimensional aerothermodynamic analyses (including characterization of chemical reactions);
- to empirically validate codes for three-dimensional analysis of material response to high-strain/high-deformation rates; and
- to develop algorithms and programming tools to exploit massively parallel computing architectures.
GAO/NSIAD-92-5 -- page 86 achieved excellent computational fluid dynamics results. For example, figure 4.2 shows the shock wave and surface pressure distribution of an aerospace plane configuration computed by the Laboratory using advanced computational fluid dynamics techniques.
GAO/NSIAD-92-5 -- page 87 The Numerical Simulator System at the Laboratory has been used since 1987 to investigate the flow field around an aerospace plane through its propulsion system. Simulation of hypersonic flow around an aerospace plane, surface pressure contours, and shock waves using various Navier-Stokes computational fluid dynamics codes illustrate the advanced state of computational technology in Japan. U.S. engineers stated detailed resolution of flow fields produced at the Laboratory indicate Japanese capability to compute real gas effects and hydrogen engine injection processes. The Laboratory is currently conducting computational fluid dynamics temperature and pressure assessments for HOPE. Another major computational fluid dynamics effort is to solve flow field calculations for the Orbiting Reentry Experimental vehicle. The University of Osaka is working with the Laboratory to develop computational fluid dynamics techniques for scramjet applications. In addition, attention at the University of Nagoya is focused on shock wave capturing using Euler, thin layer Navier-Stokes, and parabolized NavierStokes computational fluid dynamics codes. According to the NASP Program's Chief Scientist, the Japanese demonstrated they can compute aerodynamics for an aerospace plane using Euler and Navier-Stokes computational fluid dynamics codes. National Aerospace Laboratory engineers were able to show in detail both the computed and measured correlation of an airflow around an aerospace plane. The computed flow was conducted using Navier-Stokes computational fluid dynamics codes and a supercomputer, and the measured airflow was conducted in the Laboratory's hypersonic wind tunnel. The Japanese have captured chemical or real gas effects in their computational fluid dynamics external flow codes for three-dimensional complex configurations. The Chief Scientist said the Japanese have been able to quickly grasp important technical issues in computational fluid dynamics and are achieving impressive results. He believes the United States has a 1- to 2-year lead in computational fluid dynamics due to the NASP Program. In terms of computer hardware, he believes Japan is already at parity with the United States. According to Japanese Technology Evaluation Center propulsion engineers, the Japanese routinely include real gas effects and complex reaction kinetics in their flow field analyses, and their codes are based on the latest algorithms. Japan's visualization and postprocessing capabilities are also at the leading edge. The propulsion engineers concluded that Japan clearly has the appropriate computational fluid dynamics
GAO/NSIAD-92-5 -- page 88 capabilities to enable it to move rapidly in this aspect of advanced propulsion development. According to the Director for Space Transportation Research in the Science and Technology Agency, in Japan, real gas effects and complex reaction kinetics are generally not included in flow field analyses. However, National Aeronautics and Space Administration of ficials are seeing more and more analyses in Japan involving real gas effects.
Technological Challenges
Japanese industry and government officials identified several areas as of November 1988 in which more research or technology maturation is required to develop various aerospace vehicles. The basic problem facing Japan is simply a lack of experience in hypersonics. Also, test facilities in Japan are inadequate for full-scale development of an aerospace plane. Japanese aerospace test facilities and their capabilities are discussed in chapter 6. National Space Development Agency of Japan officials told us the key technological challenges facing HOPE are hypersonic aerodynamics, aero dynamic heating (real gas effects), thermal protection system characteristics and validation, kinetic effects (chemical reaction with materials), a space station docking system, flight control, and anti-oxidation carbon. Also, the availability of the U.S. Navstar Global Positioning System for HOPE'S guidance, navigation, and control is a key issue. National Aerospace Laboratory engineers said the most challenging technologies for future Japanese aerospace plane development are air breathing propulsion and advance materials. They identified other critical technological challenges as problems associated with supersonic mixing in a combustion chamber, aerodynamic configuration, slush hydrogen, and fuel tank structure. Institute of Space and Astronautical Science officials mentioned hypersonic aerodynamics and integration of the engine and airframe as technological challenges.|
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