Chapter 3 Japanese Aerospace Vehicle Programs - Aerospace Plane Technology: Research and

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Aerospace Plane Technology:
Research and Development Efforts in Japan and Australia
GAO/NSIAD-92-5 October 1991

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Chapter 3
Japanese Aerospace Vehicle Programs

Japan is conducting research and development on three different but coordinated spaceplane concept or system studies that consist of fundamental research on enabling technologies. These three programs are designed to develop the enabling technologies in a step-by-step approach to achieve Japan's goal of building an air-breathing single-stage-to-orbit aerospace plane.

The National Space Development Agency of Japan is studying HOPE as an operational, unmanned, reusable, shuttle-like reentry winged vehicle. Launched vertically by the H-II rocket booster, currently under development, HOPE would service the Japanese Experimental Module of the planned U.S. space station. Although not an air-breathing aerospace plane, HOPE would serve as a technology demonstrator for a future Japanese air-breathing aerospace plane and provide Japan with an unmanned space launch capability. The Institute of Space and Astronautical Science is conducting research and development of HIMES as a reusable, single-stage ballistic flight test vehicle with rocket propulsion to serve as a test bed for hypersonic flight and air-breathing engine technology. HIMES also would be an intermediate step in developing a future air-breathing aerospace plane. The National Aerospace Laboratory is conducting research and development on aerospace plane enabling technologies, developing an experimental hypersonic flight vehicle, and studying concepts for single- and two-stage-to-orbit[1] air-breathing aerospace planes.

National Space Development Agency of Japan's HOPE Spaceplane and H-II Launch Vehicle

The National Space Development Agency of Japan's HOPE spaceplane is planned to be launched by the H-II rocket booster in 1999. HOPE would be unmanned, perform autonomous scientific and engineering experiments in orbit, obtain hypersonic aerodynamic flight experience, and establish a technology base for future aerospace plane development.

1. A single-stage-to-orbit vehicle would take off horizontally from a conventional runway, reach hyper sonic speeds, attain low earth orbit, and return to land on a conventional runway. A two-stage-to orbit vehicle would consist of an air-breathing first stage, which would take off and land from a conventional runway, and a rocket-propelled upper stage, which, at a certain altitude, would separate and continue into orbit. The second stage, a reentry winged vehicle, would glide back to earth and land on a conventional runway. A two-stage-to-orbit vehicle could also consist of a heavy-lift transport aircraft first stage and a rocket-propelled second stage.

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HOPE Spaceplane

The Space Development Agency's Tsukuba Space Center is studying HOPE as an operational vehicle. It would be launched vertically by the H-II rocket booster, currently under development, from the Tanegashima Space Center, and would return to earth and land horizontally on a runway.[2] Small reaction rockets would be used for maneuvering while in orbit. Figure 3.1 shows the HOPE spaceplane being launched from Tanegashima Space Center by the H-II rocket booster.

2. The Space Development Agency is exploring several potential HOPE spaceplane landing sites, since the facilities at Tanegashima Space Center are only designed for launching rocket boosters.

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Figure 3.1: National Space Development Agency of Japan's HOPE Spaceplane and H-II Launch Vehicle

One of HOPE'S primary missions is to provide space transportation for supplying the Japanese Experimental Module of the planned U.S. space station. The space shuttle would still transport astronauts, since the shuttle is a man-rated vehicle. Other potential missions include providing transportation to and from components of future Japanese space infrastructure, such as space platforms and space factories in low earth

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orbit, and demonstrate the basic technology required for future space transportation systems.

HOPE would be 11 meters long, have a wingspan of 6 meters, and weigh about 10 metric tons at launch. HOPE is being designed to transport a cargo payload of about 1 metric ton into low earth orbit. However, Space Development Agency engineers acknowledge that with a payload capacity of only 1 metric ton, HOPE would not be the most efficient way to transport cargo into orbit. Typical missions are expected to last about 4 days.

The Space Development Agency is studying HOPE in a phased approach. HOPE is still in the research stage and is not yet a Japanese government-authorized development program. Phase A (Japan fiscal years[3] 1990 to 1991) is to conduct conceptual studies, define mission requirements, and begin feasibility studies. The Space Development Agency plans to request Phase B funding from the Japanese government beginning in Japan fiscal year 1992. Phase B (Japan fiscal years 1992 to 1997) will concentrate on preliminary design studies and full-scale testing.

Program costs, based on a 1988 estimate, are expected to total about $2.73 billion. This figure includes research, development, and testing through HOPE'S first scheduled unmanned flight in 1999. The Director for Space Transportation Research in the Science and Technology Agency added that cost estimates for the HOPE program have not been officially approved.

Space Development Agency officials are also studying a plan to double the size of HOPE to a 20-metric ton vehicle. According to an Agency engineer, a 10-metric ton class orbiter may not be feasible, since its payload capacity may be too small. If the Agency determines that a larger spaceplane is required, then a rocket booster larger than the H-II would also be necessary. Such a rocket booster (the H-IID) would be one of the largest launchers in the world after the Soviet Energia booster and U.S. Titan IV launch vehicle. The Space Development Agency cautioned this project is still under study and configuration details have not yet been determined.

Large portions of HOPE'S primary structure would be made of composite materials to reduce weight. HOPE'S tip fin and wing leading edges would be constructed of a carbon-carbon composite materials or the superalloy

3.Japan's fiscal year is from April 1 to March 31.

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Rene 41. Ceramic tiles containing silica and alumina fibers would cover the fuselage. Advanced materials for HOPE'S thermal protection system being studied include titanium alloy, nickel alloy, and advanced carbon-carbon, according to Space Development Agency thermal and structural engineers. Research is being conducted on new structural materials, such as graphite-polyimide composites, to support the load with the goal of finding a lightweight composite material that can replace conventional aluminum alloy.

The aerodynamic shape of HOPE'S wing would be that of a double delta platform to achieve good lift characteristics during hypersonic and low-speed flight conditions. Early in the HOPE program, canards were considered for increasing lift and stabilization characteristics, but thermal and aerodynamic concerns ruled out their use. According to Space Development Agency officials, the HOPE concept is still evolving and all the dimensions, weights, and vehicle configurations could change as the design matures. During 1988 and 1989, for example, the Agency conducted about 1,600 wind tunnel tests on various HOPE configurations.

HOPE'S guidance, navigation, and control system will be critical during the vehicle's orbit, rendezvous, docking, deorbit, reentry, and landing phases. The Space Development Agency and National Aerospace Laboratory are conducting research of design concepts for HOPE in aerodynamics, guidance, and structures. In 1990 the Laboratory began functional tests of a navigation and guidance subsystem at Sendai Airport. HOPE is expected to be equipped with a U.S. Navstar Global Positioning System receiver. In 1994 the two agencies plan to launch an experimental model on a suborbital trajectory to demonstrate reentry aerodynamics and guidance beginning at Mach 10.

According to the Director of Aerodynamics at the National Aerospace Laboratory's Chofu facility, the only place where HOPE hypersonic testing is being conducted is in the Laboratory's hypersonic wind tunnel, which can test models up to Mach 11. Currently, the Laboratory is using its computational fluid dynamics capability to simulate HOPE'S aerodynamics.

Plans to build a spaceport for the takeoff and landing of future spaceplanes, including HOPE, are beginning to be explored in Japan, since the facilities at Tanegashima Space Center can only accommodate vertically launched rocket boosters. Potential future Japanese spaceports may include Kagoshima on Kyushu Island in southern Japan near Tanegashima, the Iwate Prefecture Spaceport on Honshu Island, and the

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Hokkaido Space Center on Hokkaido Island in northern Japan. Figure 3.2 shows the future Iwate Prefecture Spaceport design concept as presented by the local government.

Figure 3.2: Iwate Prefecture Spaceport Design Concept

Figure 3.3 shows the future Hokkaido Space Center design concept as presented by the local government.

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Figure 3.3: Hokkaido Space Center Design Concept

Other potential future Pacific spaceports may include the proposed Cape York International Spaceport in Australia; Kiribati in the central Pacific ocean; Kiritimati Island in the northern Pacific ocean; Hawaii; Vandenberg Air Force Base, California; and the proposed National Space Port 2000 at Edwards Air Force Base, California. Florida is also being considered as a site for a future commercial spaceport by a consortium that includes the state of Florida. The National Space Development Agency of Japan is also considering a water landing with ocean recovery for its HOPE spaceplane.

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The High Commissioner of the Space Activities Commission and the Director for Space Transportation Research in the Science and Technology Agency cautioned that Japan has not yet begun a concept study of a future spaceport. The High Commissioner and Director noted that Japan has only programs to study the concept of future aerospace vehicles. They said a concept study of a future spaceport, including potential sites, is premature and should not be started until the concept study of an aerospace vehicle is completed.

Orbiting Reentry Experimental Vehicle

In 1990 the Space Development Agency began a program to establish a data base for hypersonic aerodynamic heating. The Agency plans to develop the Orbiting Reentry Experimental Vehicle to test thermodynamic heating estimations and thermal protection system designs used in the development of HOPE. The experimental vehicle would be launched from the Tanegashima Space Center on H-II's first mission in 1993. The surface of the test vehicle's thermal protection structure would be covered with advanced materials that would be evaluated for use in HOPE'S thermal protection system.

Once placed into orbit by the H-II booster, the advanced materials would be evaluated as the vehicle reenters the atmosphere. The test vehicle would fire its braking rocket to reenter the atmosphere at the same angle of attack and velocity as the HOPE spaceplane. Telemetry data collected during reentry would be received before splashdown in the northern Pacific Ocean near Kiritimati Island. The vehicle would not be recovered. A Science and Technology Agency official said funding for the Orbiting Reentry Experimental Vehicle is contained in the HOPE program. According to the Space Development Agency, the total cost of this project has not been officially authorized.

H-II Launch Vehicle

The H-II launcher is being developed as a conventional two-stage expendable rocket booster to replace Japan's H-I launchers. The H-II's primary mission would be to launch satellite payloads into geostationary orbit and launch the HOPE spaceplane. The H-II is being designed as Japan's primary heavy lift launch vehicle for the late 1990s and is similar to the European Space Agency's Ariane 4 and Martin Marietta's Titan 34D launchers. According to the Space Development Agency, the H-II rocket would be capable of placing 2 metric tons of payload into geostationary orbit and 10 metric tons of payload into low earth orbit. Whereas earlier launchers rely on U.S. technology, the H-II would rely entirely on Japanese technology.

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Mitsubishi is the integrator for H-II and is responsible for the second stage LE-5 engine. Ishikawajima-Harima is responsible for the main components (turbopumps) of the first stage LE-7 cryogenic engine. Kawasaki is developing the rocket's fairing, and Nissan Motor Company is developing the launcher's two solid rocket boosters. Three Japanese companies are studying the design for the H-IID, an enlarged version of H-II, that could launch a 20-metric ton HOPE spaceplane into a low earth orbit. Mitsubishi is conducting overall integration studies for HOPE and the H-IID launcher. Ishikawajima-Harima and Kawasaki are also involved in H-IID research. Although Fuji is not yet involved in H-IID research, Fuji is studying launching the larger version of HOPE using the H-IID launch vehicle.

According to Space Development Agency officials, cracks in the turbine blades of the LE-7 main rocket engine and problems with its starting sequence have plagued the engine's development. Two LE-7 engine tests at Tanegashima Space Center in 1989 ended in failure. Also, the LE-7 engine caught fire four times during engine tests.[4] These setbacks forced the Agency to delay the first H-II mission from 1992 to 1993.

According to the Space Development Agency, the LE-7 continues to experience test failures. Hydrogen gas exploded during an LE-7 fueling test in May 1991 at the Agency's Kakuda Propulsion Center in Kakuda. A manifold in the LE-7 engine's main fuel injector burst during a Mitsubishi test at its Guided Propulsion Plant in Komaki City in August 1991, causing a pressure explosion. A launch pad for the H-II was built in 1990 at the Tanegashima Space Center.

Rocket Plane

The Space Development Agency is also considering a rocket plane that would use rocket engines instead of air-breathing propulsion. The rocket plane is only being considered by the Space Development Agency and is not a program being conducted by the Japanese government. The reusable rocket plane would be vertically launched and land horizontally on a conventional runway. The rocket plane would consist of an orbiter joined to a strap-on fly-back booster. The rocket plane would weigh approximately 630 tons at takeoff and carry a 15- to 20-ton payload.

4. According to Mitsubishi, the full-duration firing test of the LE-7 engine was successfully conducted in February 1991. According to a National Aeronautics and space Administration official, a second full-duration firing test of the LE-7 engine was successfully conducted in May 1991.

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The orbiter would weigh about 130 tons at takeoff, be about 50 meters long, and have a wingspan of about 20 meters. The orbiter would contain liquid oxygen and liquid hydrogen fuel tanks and be powered by the LE-7 cryogenic engine. The fly-back booster would weigh approximately 500 tons at takeoff, be about 55 meters long, and have a wingspan of about 24 meters. The fly-back booster would contain methane and liquid oxygen fuel tanks and be powered by an improved LE-7 cryogenic engine and a turbojet for its fly-back phase. A Space Development Agency official commented the rocket plane would be an interim step between HOPE and an air-breathing aerospace plane.

Alternative Japanese Spaceplane Launch Concepts

Taisei Corporation, a major Japanese construction company, is studying the feasibility of a Linear Motor Catapult (launch) System for a Space Vehicle. The concept would consist of a track on a conical framework constructed of high-tensile steel alloy. The curved launch ramp would measure 2,000 meters high and 3,650 meters long. Tracks from five spaceplane orbiter hangars would feed into the launch track. The spaceplane orbiter would be launched vertically by a linear motor cart system powered by superconducting magnets. Figure 3.4 shows an artist's concept of a linear motor catapult launch system.

Figure 3.4: Taisei Corporation's Linear Motor Catapult Spaceplane Launch System

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A magnetically levitated cart would carry the spaceplane orbiter along a horizontal stretch of track and then accelerate at high velocity along track inclined at 72 degrees. When the cart reached the top of the ramp, the spaceplane orbiter would ignite its engines and separate from the cart, which would be diverted onto a side track. At an altitude of about 146,000 feet and a speed of Mach 4.2, the spaceplane orbiter would jettison its external engine and continue into space. According to Taisei Corporation, the advantage of a linear motor launch system is the tremendous fuel savings compared with conventional shuttle launches using rockets.

Hazama-Gumi, a large Japanese engineering company, has studied the feasibility of an underground rocket launcher concept known as the Compressed Air Launching System. Compressed air would be used to blow a Japanese manned spaceplane and its booster out of a mile deep silo at a speed of Mach 1. Hazama-Gumi officials believe this concept would save rocket propellant. The launch silo would be 2,000 meters deep and 20 meters wide. An expendable rocket booster and spaceplane, configured like HOPE and the H-II booster, would be stacked above ground then lowered into the silo. Magnetic energy from superconducting magnets would suspend the launch platform between the silo's circular wall. Massive compressed air tanks would then be opened, forcing high-pressure air into the silo under the launch platform. The air would accelerate the vehicle to Mach 1 by the time it reaches the surface. The booster's engines would then be ignited as it cleared the silo. According to Hazama-Gumi, this would enable a launch vehicle to place several hundred more pounds into space than the same launch vehicle launched from a stationary pad. These efforts are indicative of Japan's nonaerospace companies' interest in building a space infrastructure for activities in the 21st century.

Institute of Space and Astronautical Science's Highly Maneuverable Experimental Space Vehicle

The Institute of Space and Astronautical Science's HIMES vehicle would be a fully reusable, unmanned, single-stage ballistic flight test vehicle. Astronautical HIMES is being designed as a boost-glide vehicle to be launched vertically using rocket propulsion or a rocket-powered wheeled-trolley or sled. It would land horizontally. The spaceplane would serve as a test bed for hypersonic flight and air-breathing engines. It would also demonstrate atmospheric reentry flight and expand the capabilities of sounding rockets in the upper atmosphere. Based on current Japanese technology, HIMES Is designed to be an interim vehicle in the development of a future Japanese air-breathing aerospace plane. Figure 3.5 shows an artist's concept of a vertically launched HIMES vehicle.

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Figure 3.5 Institute of Space and Astronautical Science's HIMES Vehicle

The Institute has been conducting research and development on winged space vehicles since 1982 and announced its plans for the HIMES project in 1985. In 1982 the Institute established a Working Group for a Winged Space Vehicle to conduct basic studies and flight testing of various spaceplane concepts. This group recommended that the Institute develop HIMES as a technology demonstrator for (1) a fully reusable

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rocket, (2) an atmospheric reentry test vehicle, (3) a flying test bed for advanced technology for thermal protection, (4) air-breathing propulsion, and (5) unmanned landing technology.

The Japanese Ministry of Education, Science, and Culture provided about $2 million for basic studies of winged vehicles. Institute and industry officials estimate that development costs for HIMES, including new engine technology, will total about $137.5 million. The Institute estimates that the completion date for a HIMES prototype vehicle would be 1998--if it receives approval from the Japanese government to pursue this project. As of November 1988, 10 to 15 researchers at the Institute's Sagamihara facility were working part-time on HIMES and advanced propulsion. They were supported by about 100 engineers, also working on HIMES and advanced propulsion part-time.

As a flight demonstrator, HIMES would not achieve orbital velocity (Mach 25); however, its flight envelope in the atmosphere would cover regions that offer operational conditions for an air-breathing engine. HIMES would experience relatively high heating flight conditions that future aerospace planes would also encounter during ascent.

Institute engineers stated that although various configurations were under consideration, they expect HIMES to have a delta wing with a span of 9.33 meters, a total length of 13.6 meters, and a takeoff weight of 14 metric tons. HIMES would use conventional materials, such as titanium alloys, for its skin and carbon-carbon composites for its nosecap and leading edges. According to researchers in the Institute, advanced materials currently available are being considered for use in the vehicle to shorten development time.

The multipurpose reusable sounding rocket's propulsion system would use liquid hydrogen and liquid oxygen. The fuselage is expected to be made of conventional aluminum and contain propellant tanks and a small payload bay. Two small rocket engines would provide the vehicle with maneuverability in the upper atmosphere and allow deceleration to avoid a steep reentry.

Institute engineers are also conducting studies on launching HIMES horizontally using a magnetically levitated transportation system. The Institute conducted a feasibility study of an experimental linear-motor-assisted takeoff system consisting of HIMES and a magnetically levitated and propelled sled developed by Japan Railway Tokai in Nagoya, Japan, as shown in figure 3.6.

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Figure 3.6: Artist's Concept of Linear-Motor-Assisted Horizontal Takeoff of HIMES

Using the linear-motor-assisted takeoff system, the sled would accelerate the HIMES vehicle to a speed of 300 kilometers per hour when HIMES' rocket engines would ignite. The rocket engines would accelerate HIMES to a speed of 450 kilometers per hour-enough to aerodynamically lift the vehicle by its wings at a distance of 2 kilometers from the starting point. A fastening mechanism would then be unlocked, separating HIMES from the sled. After takeoff of the HIMES vehicle, the sled would be magnetically decelerated to a stop.

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Researchers in the Institute concluded the fundamental technology for a linear-motor-assisted takeoff system is available for a small aerospace plane like HIMES. They also concluded it could be used as an experimental system for launching larger air-breathing aerospace vehicles horizontally.

The Institute is also working on several engine concepts for HIMES. It has formed a liquid propulsion group that is developing a high-pressure expander-cycle cryogenic engine. A heat exchanger is installed in the combustion chamber to extract a larger amount of thermal energy from the fuel's combustion. The engine will use hydrogen from the heat exchanger to drive the turbopumps for HIMES's rocket engines. Figure 3.7 shows a schematic drawing of the high-pressure expander-cycle engine.

Figure 3.7: Institute of Space and Astronautical Science's High-Pressure Expander-Cycle Engine

Institute engineers are also studying an air-turborocket for possible use by HIMES to demonstrate air-breathing engine technology. The Institute is evaluating combined turbine/rocket engine systems for use by future aerospace planes. Engineers from the Institute and Ishikawajima-Harima plan to expand and test a high-pressure expander-cycle engine

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by adding an air-turboramjet[6] with a precooler. Nissan Motor Company is developing carbon-carbon material for the engine's heat exchanger. Three types of turbo engines using liquid hydrogen as a fuel are also being evaluated: air-turboramjets, expander air-turboramJets, and gas generator air-turboramjets. Research on a precooler to protect the turbomachinery for hypersonic flight conditions is also being conducted.

The Institute has been conducting research and development on the air-turboramjet engine since 1988, which is a successor program of the Institute's liquid propulsion rocket system. This effort is a collaborative program between the Institute and Ishikawajima-Harima. The Institute is responsible for the engine concept and testing. Ishikawajima-Harima is responsible for the engine's detailed design and construction. Institute engineers expect that the air-turboramjet engine will be employed by the fly-back booster of the two-stage-to-orbit aerospace vehicle.

In 1990 the first proto-model (a pre-prototype, small-scale research device) of the expander-cycle air-turboramjet was tested at the Institute's Noshiro Testing Center at sea-level static test conditions (see fig. 3.8). Air-turboramjet engine development costs are expected to total about $1.5 million, including investment by Ishikawajima-Harima.

6. According to a National Aeronautics and Space Administration expert in hypersonic propulsion, the term air-turboramjet is a misnomer resulting from the apparent inadvertent contraction of air-turborocket/ramjet. This combined-cycle engine utilizes an air-turborocket initial mode followed by a conversion to subsonic combustion ramjet mode for high-speed acceleration and cruise.

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Figure 3.8: Expander-Cycle Air Turboramjet Proto-Model Test at the Institute of Space an Astronautical Science's Noshiro Testing Center

HIMES Subscale Flight Tests

The Institute was, as of September 1990, the only organization in the world outside of the United States and Soviet Union[6] that had conducted actual flight tests of a subscale spaceplane. In 1986 the Institute conducted the first in a series of low-speed gliding flight tests using sub scale models of HIMES that were released from a helicopter over the Sea of Japan near Tokyo. The three gliding flight test vehicles that had been recovered were each about 2 meters long, had a delta wingspan of about 1.52 meters, and twin canard tail fins. We observed that the models were made of aluminum and fiber-reinforced plastics and contained an on-board computer for attitude control and radio guidance. Of the four gliding flight test vehicles built, three were constructed by the Institute and one by Kawasaki.

In June 1986 the Institute conducted the first in a series of drop-flight tests to establish a technique for future approach and landing testing. Two test models controlled by on-board computers were suspended from a helicopter flying at an altitude of about 3,000 feet. The first test

6. Beginning in 1982, the Soviet Union conducted a series of atmospheric reentry flight tests of the BOR-4, a subscale reentry winged vehicle launched into orbit by the IL-16 rocket booster. According to the Chief Design Engineer of the Soviet space shuttle Buran, the BOR-4 was used to test the thermal protection system for the Buran shuttle and as a second stage for a two-stage-to-orbit spaceplane. At least 12 suborbital and orbital flights were made.

GAO/NSIAD-92-5 -- page 48 vehicle stalled immediately upon release from its cradle and was destroyed after hitting the water surface. The second model glided for about 50 seconds before making a water landing. It was recovered intact.

Figure 3.9 shows the subscale HIMES vehicle being dropped from the helicopter.

Figure 3.9: Flight Test of a Subscale Model of HIMES

As a result of these tests, the Institute conducted atmospheric flight tests at its Kagoshima Space Center in 1987 to validate HIMES' flight capability at a high angle of attack during high-speed reentry flight conditions. Subscale winged models of HIMES were carried aloft and launched from a balloon by a solid rocket booster using the Rockoon technique.

In 1987 the first test to verify the helium balloon and vehicle release from a gondola hanging from the balloon was conducted successfully. However, a second test in 1988 ended in failure when the balloon tore at an altitude of 18 kilometers and dropped the $2.2 million test vehicle into the Pacific Ocean. The 500 kilogram model was to have been boosted to an altitude of 80 kilometers and reenter the atmosphere at

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speeds up to Mach 4. Institute officials are preparing for another test in early 1992.

Figure 3.10 shows a vertical assembly of the subscale HIMES vehicle with booster that was used in the 1988 atmospheric reentry test.

Figure 3.10: Vertical Assembly of Subscale Model of HIMES and Booster Used in Atmospheric Reentry Test

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National Aerospace Laboratory's Single-Stage-to-Orbit Aerospace Plane Concept

The National Aerospace Laboratory's current activities for an aerospace plane include (1) a system study of an aerospace plane for a manned space transportation system, (2) a conceptual study of hypersonic experimental aircraft and propulsion, (3) development of enabling technologies, and (4) construction of test facilities. The objectives of the conceptual study for a hypersonic experimental aircraft are to identify the state of the art of Japanese technology bases, establish a flying test bed for air-breathing engines and advanced materials, and use manned hypersonic flight to stimulate the development of an aerospace plane.

The system study envisions an aerospace plane that would transport eight crew members plus two pilots into a 500-kilometer orbit. The space launch vehicle would have a takeoff weight of about 350 metric tons. Its propulsion system would consist of air-breathing and rocket engines. Design configurations to be studied include single- and two-stage-to-orbit aerospace planes.

To achieve the conceptual study's objectives, the Laboratory, at the time of our review, planned to develop a 10-metric ton unmanned hypersonic experimental aircraft that would achieve a maximum speed of Mach 7 and an altitude of 150 kilometers. Its propulsion system would consist of both jet and rocket engines, technology for which is currently available in Japan. The vehicle would also provide a test bed for subscale air breathing engines. The manned vehicle would have two crew members.

In 1988 the Liaison Group for Spaceplane Research and Development between the National Space Development Agency of Japan, Institute of Space and Astronautical Science, National Aerospace Laboratory, industry, and universities requested that Japanese industry develop a manned hypersonic experimental aircraft concept. Using a National Aerospace Laboratory baseline configuration, Fuji, Kawasaki, and Mitsubishi each designed a subscale experimental aircraft concept for a vehicle with two crew members, two jet engines, and two rocket engines. National Aerospace Laboratory officials told us development of these concepts was voluntary by Japanese industry and did not involve any contracts. Figure 3.11 illustrates proposed Japanese industry manned hypersonic experimental aircraft configurations.

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Figure 3.11: Japanese Industry Hypersonic Experimental Aircraft Configurations

Fuji's proposed configuration is a 50-metric ton, 35.25-meter long, twin-engine, dual-stabilizer concept with a 14-meter wingspan. Kawasaki's

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proposed configuration is a 40-metric ton, 26.39-meter long, three-engine, single-stabilizer concept with a 11.5-meter wingspan. Mitsubishi's proposed configuration is a 32-metric ton, 22.8-meter long, twin-engine, dual-stabilizer concept with a 10.26-meter wingspan. National Aerospace Laboratory officials noted these preliminary design concepts are being used by the companies in their research on aerospace plane technology but are not expected to be the baseline for an actual vehicle. Laboratory officials stressed that these are not yet competing concepts. Figure 3.12 shows an artist's concept of Kawasaki's single- stage-to-orbit aerospace plane concept.

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Figure 3.12: Kawasaki Heavy Industries' Single-Stage-to-Orbit Aerospace Plane Concept

According to the Director for Space Transportation Research in the Science and Technology Agency and the National Aerospace Laboratory, the status of aerospace plane activity at the Laboratory as of March 1991 is somewhat different than it was several years ago. Only a single-stage-to-orbit aerospace plane is being studied now and its configuration has not yet been determined. The two-stage-to-orbit aerospace plane concept has apparently been dropped. National Aeronautics and Space Administration officials said that although the Laboratory may have

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discontinued its study of a two-stage-to-orbit aerospace plane concept, Japan has not ruled out a two-stage-to-orbit vehicle.

In terms of the hypersonic experimental aircraft, Laboratory officials are concerned about the contour of the vehicle; integration of the engine and airframe; advanced materials that are lightweight for the fuselage, wing, and cryogenic fuel tank; a thermal protection system; and test facilities. Laboratory officials are also concerned about appropriate sites for takeoff and landing as well as a flight test range over a densely populated Japan.

The objectives of the conceptual study of hypersonic propulsion are to devise a propulsion system for an aerpspace plane; achieve a conceptual design of hypersonic air-breathing engines for technology verification; and plan for the engines' development, testing, and operation.

The National Aerospace Laboratory is exploring three hypersonic air-breathing engine systems for future aerospace planes: turbo engines (including a turbojet, supersonic fan, turboramjet, and air-turboramjet), a liquid air cycle engine, and a scramjet. The Laboratory is working with Kawasaki in developing the turboramjet system, Ishikawajima-Harima in developing the air-turboramjet engine concept, and Mitsubishi in developing the liquid air cycle engine concept. Ramjet combustor tests of an air-turboramjet engine have been conducted.

Laboratory engineers are studying component and material applications of scramjet engines. Laboratory officials said scramjet research focuses on the scramJet's torch igniter module and cooling system. Laboratory scientists are conducting research on heat resistance of carbon-carbon composite materials for scramjet engines in a joint program with Ube Industries and Shikishima Canvas Company.

The Laboratory is studying the feasibility of a liquid air cycle engine. Research on the liquid air cycle engine concept was originally conducted in the United States in the 1950s and 1960s at The Marquardt Company. According to the National Aerospace Laboratory's Director of the Engine Aerodynamics Laboratory, liquid air instead of liquid oxygen is used in the combustion chamber of the liquid air cycle engine for higher thrust and lighter weight. According to a Laboratory engineer, the liquid air cycle engine has the potential to (1) operate in the atmosphere up to about Mach 8 as an air-breathing engine and in the vacuum of space as a rocket engine and (2) provide a large amount of thrust while remaining lightweight, since the liquid air cycle engine is essentially a derivative of

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a rocket engine. The present concept of the liquid air cycle engine does not include the potential to perform the total mission from earth to orbit with one propulsion system, as had been previously suggested by Laboratory engineers. According to the engine program's chief engineer, the engine has a low development risk, since it makes full use of proven liquid oxygen and liquid hydrogen cryogenic technology.

Problems facing Laboratory scientists and engineers in hypersonic propulsion are integrating the engine and airframe, developing engine component technology, and developing advanced materials and structures, numerical aerodynamic simulation, and adequate test facilities.

Related research activities include aerodynamic wind tunnel testing of various hypersonic experimental aircraft configurations, developing composite materials, developing flight control systems, conducting scramjet combustor tests, computational fluid dynamics analyses, and developing life support technology.

Single-stage-to-orbit aerospace plane configurations, including engine components, are being tested at the National Aerospace Laboratory. A 3.2-meter model with automatically controlled surfaces is being tested in a low-speed wind tunnel at Chofu. A scramjet inlet model has been tested in a supersonic wind tunnel at Chofu. Also, an air-turboramjet built with advanced materials has been tested. Construction of test facilities is discussed in chapter 6.

Laboratory officials view research and development of the approximately 10-metric ton unmanned hypersonic experimental aircraft as the first step in a progressively more difficult and ambitious program to develop and build an aerospace plane. The hypersonic experimental aircraft would be conducted as a National Aerospace Laboratory project. Although Japan does not have a plan to actually build an aerospace plane, Laboratory officials suggested the next step would be to develop a 50-metric ton manned hypersonic experimental aircraft using an airbreathing propulsion system as a Japanese national program. Laboratory officials suggested the third step would be to develop a 350-metric ton single-stage-to-orbit aerospace plane prototype using a turboramjet or scramjet and rocket propulsion, also as a Japanese national program. Figure 3.13 shows an artist's concept of the Laboratory's single-stage-to-orbit aerospace plane. Again, the aerospace plane's configuration has not yet been determined.

GAO/NSIAD-92-5 -- page 56

Figure 3.13: National Aerospace Laboratory's Single-Stage-to-Orbit Aerospace Plane Concept

At the time of our visit, Laboratory officials indicated a two-stage-to-orbit prototype would also be developed as a backup. Development of an operational horizontal takeoff and landing single- or two-stage-to-orbit aerospace plane in Japan would require an international effort. Figure 3.14 shows an artist's concept of the Laboratory's two-stage-to-orbit aerospace plane. As of March 1991, the Laboratory was conducting research only on a single-stage-to-orbit aerospace plane concept.

GAO/NSIAD-92-5 -- page 57

Figure 3.14: National Aerospace Laboratory's Two-Stage-to-Orbit Aerospace Plane Concept

Laboratory officials said the aerospace plane does not even have a name; the vehicle is simply referred to as a single-stage-to-orbit aerospace plane. The Laboratory's aerospace plane is not a formally approved project. The Japanese Ministry of Finance told Laboratory officials the aerospace plane is too expensive as proposed. Any spaceplane program in Japan must be approved by the Science and Technology Agency, Ministry of Finance, and Ministry of International Trade and Industry.

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