AIAA 2009-5139 45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit 2 - 5 August 2009, Denver, Colorado Design and Operational Concepts for Reusable Rocket Engine Makoto Yoshida*, Satoshi Takada†, Yoshihiro Naruo‡ Japan Aerospace Exploration Agency (JAXA), 1, Koganezawa, Kimigaya, Kakuda, Miyagi 981-1525, JAPAN and Kenichi Niu§ Mitsubishi Heavy Industries Co., Ltd., 1200, Higashi-tanaka, Komaki, Aichi 485-8561, JAPAN Abstract A 40kN rocket engine, Pilot Engine, is being developed in Japan. Pilot Engine development has been initiated relating to the reusable sounding rocket, which is also developed in Japan. This rocket vertically takes off, reaches to 120km altitude, lands vertically on the launch site and is launched again within several days. This rocket will provide observation mission chances with low cost and with quickness utilizing the advantages of reusability. This program has been authorized as a technology demonstration phase, and most of the technologies required for the vehicle are to be demonstrated in a few years. In order to realize this rocket concept, the engines installed on the rocket should have features of reusability, long life, deep throttling and health monitoring. Those have not yet been established in Japanese rocket engines. To solve the engineering subjects about those features, a new design methodology, advanced engine simulations and engineering testing are focused in the Pilot Engine development. Especially in engineering testing, limit condition data is acquired and new diagnostic techniques. Those can be applied utilizing mobility of small size hardware. In this paper, development status of Pilot Engine is mentioned, including fundamental design, engineering tests and operation and maintenance schedule. I. Introduction A rocket is an only way to carry payloads to an outer space such as scientific satellites, broadcasting satellites, communication satellites and meteorological satellites. In addition to an importance of their mission, these satellites are very expensive. Therefore, high reliability is required to the rocket system. Taking the case of H-2A rocket, Japanese main launcher, a success rate of H-2A is about 92 % up to now, which is almost equal to Europe or U.S.A. launchers. But this success rate means that there is a possibility that one failure may occur out of 20 launches, and this kind of transportation system is extremely adventurous compared to other transportation system. In the meanwhile, existing rockets are expendable except Space Shuttle. It is very wasteful to spend expensive rocket each time, so we carry out research and development to realize reusable launch system. In this paper, development status of reusable rocket engine which has been initiated relating to the * Section Leader, Tribology Technology Section, Space Transportation Mission Directorate, AIAA Member. Senior Researcher, Tribology Technology Section, Space Transportation Mission Directorate, . ‡ Research Associate, Department of Space Systems and Astronautics, ISAS, 3-1-1, Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan, AIAA Member. § Manager, Liquid Rocket Design Section, Engine & Control Equipment Engineering Department, AIAA Member. † 1 American Institute of Aeronautics and Astronautics Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. reusable sounding rocket and its design and operational concept. II. Reusable Sounding Rocket A reusable sounding-rocket program has been initiated in Japan following the reusable rocket vehicle test (RVT) program which has been conducted since 1999 at the Noshiro Testing Center of the Japan Aerospace Exploration Agency (JAXA) 1,2. Through flight tests reaching an altitude of 42 m, the RVT program has demonstrated the feasibility of a reusable launch system characterized by vertical takeoff and landing and utilizing a propellant combination of LOX and LH2. The new rocket will utilize the same system as that previously tested, will be scaled up to a diameter and length about twice those of the pilot engine and will reach an altitude of 120 km. Due to the advantages of reusability, successful development of this rocket will mean that observation missions can be undertaken more frequently and economically. In order to realize the rocket concept, the engines installed on the rocket should be characterized by reusability, long life, deep throttling and health monitoring, features which have not yet been established in Japanese rocket engines. Development of a 40-kN rocket engine, a pilot engine, with the target features of the reusable sounding rocket, has been under way since 2005. To solve the engineering challenges entailed by these features, a new design methodology, advanced engine simulations and engineering testing are being focused on in the pilot engine development program. Figure 1 shows a flight demonstrator of RVT and an image of the reusable sounding rockets, which utilize a propellant combination of LOX and LH2. Figure 1 Flight demonstration of RVT(left) and reusable sounding rockets(right) III. Engine Concept Two pairs of pilot engines will be installed on the bottom of the reusable sounding rocket, each pair consisting of two engines opposite each other to be controlled at the same thrust level. In case of one engine failure, the pair of engines including the failed one will be shut down, and the other pair of engines will provide the vehicle with the necessary thrust. Corresponding to this vehicle concept, the engines should be robust and have health monitoring capability and a wide range of throttling capability. The maximum thrust of the engine is set at 40-kN, and the minimum is 24 kN, namely, 60% of the maximum level. Figure 2 shows the nominal mission of the rocket. By taking off vertically, reaching an altitude of 120 km, and having the engine cut off, the vehicle will provide the payload with an observation environment or conditions. After the observation, a pair of the vehicle engines will be restarted and in the descent phase, and finally land vertically with a thrust level of 60% to 100%. Another pair of engines will be restarted as an idle mode just in case serious accident may happen to operating engines. The engine cycle is an expander bleed cycle, which is the same as that of the LE-5B engine, thought to be as one of the most robust systems, and will also be applied to future engines in Japan 3,4,5. 2 American Institute of Aeronautics and Astronautics The major components of the engine are the coaxial injector, regenerative copper combustion chamber, fuel turbopump (FTP), oxidizer turbopump (OTP) and electro- mechanically actuated valves. Figure 3 shows an image of the engine. A dual bell nozzle will be attached beneath the exit of the combustion chamber to compensate for the atmospheric pressure change and realize a higher specific impulse totally from sea level to high altitude in vacuum conditions than that possible with the conventional bell nozzle. The fundamental model will be constructed in FY2010 to demonstrate the key features of reusability, long life, operability, deep throttling and health monitoring capability with full scale major components. Turbopump bearings, the combustion chamber inner liner, turbopump shaft seals and valve seals are the major components related to engine life and health monitoring. Pump performance and stability, turbine efficiency, regenerative cooling characteristics, and injector combustion performance and stability are the major components related to the deep throttling feature. Figure 2 Flight type Nominal mission of reusable sounding rocket Demonstrator Figure 3 Reusable rocket engine IV. Design Status In order to realize a robust engine corresponding to that of an actual reusable sounding rocket, the following design activities have been applied. In selecting the engine system cycle, hundreds of engine balances have been studied not only at the design point, but also at the throttling point. Also, not only the engine system performance but also the operating conditions of the engine system and its major components have been evaluated. Besides this engine balance study, the judgment of specialists on quality function deployment (QFD) has also been elicited. As the result of both the engine balance study and QFD considerations, the expander bleed engine has been selected. Regarding the expander bleed cycle, hundreds of balances have been evaluated in the whole operating 3 American Institute of Aeronautics and Astronautics range with different combinations of key design parameters of both the system and its major components. The operating range was estimated by the following process. The mission requirements, variation of the component characteristics, interface conditions and control accuracy are integrally considered in the engine balance calculation. The operating ranges of major components and resulting possibility distributions are estimated. The margin of the acceptable limit of each parameter is calculated as a sigma value, which is the value of the difference between the minimum or maximum and the acceptable limit divided by the variation of the component characteristics. Figure 4 shows an example of the margin optimization. The parameter with minimum margin is identified, and another design parameter combination is selected to increase the minimum margin. Through these activities, the optimum engine has been selected from hundreds of engines. This approach is the first trial and has not previously been established in Japan. Through pilot engine development activity, this new approach will also be evaluated. Reflecting the results of the pilot engine system design evaluation, a modified or more advanced approach will be applied to future engines in Japan. In this approach, iteration between the design of the engine system and those of the components is necessary. So far, three cycles of iteration have been conducted. At this point, the nominal full power operating point is a combustion chamber pressure of 3.4 MPa, a combustion chamber mixture ratio of 6.8, an engine total mixture ratio of 4.8, an FTP speed of 55,000 rpm and an OTP speed of 20,000 rpm. As a result of these processes, it has been revealed that the following parameters should be modified or cannot be utilized in Japan. a) Fuel Turbopump Flow Ratio (Q/Qd) Range b) Injector Velocity Ratio c) System Pressure Drop Adjustablity In order to evaluate these items, another cycle of iteration is in progress involving engine system design, component design and engineering tests. Regarding system design and component design, it is confirmed if it is possible to increase the minimum margin. As for engineering testing, additional data necessary to refine the acceptable limits and to extend knowledge need to be acquired. Figure 4 Margin optimization example V. Target of The Technical Demonstration In the reusable sounding rocket project, ground demonstrator engine will be developed before the development of flight type engine to solve the key technologies. One of the key technologies is reusability for a hundred times which has not been realized in the rocket engines, another technology is advanced functions such as throttling by the request of the rocket system. 4 American Institute of Aeronautics and Astronautics A. Hundred Times Reusability. The most important point to reuse rocket engine is a lifetime of the engine and its components. In the case of an expendable rocket, there is a standard of accomplishment, 4-MDC (MDC: Mission Duty Cycle). For example, the first stage engine whose operational time is about six minutes, twenty four minute operation without malfunctioning is enough to be approved as accomplishment. In the development of reusable engine for the reusable sounding rocket, three elements are picked up as important lifespan elements. Combustion chamber was picked up as first lifespan element because its thermal environment is very severe and suffers hard thermal shock during the start up and cutoff sequence. Bearings and shaft seals of the trbopumps are also picked up because they are mechanical elements which support high speed rotors of the turbopumps. We have been examined these three elements to improve an lifetime estimation method, to extend the lifetime and to improve the operational technique. B. Advanced Functions Figure 2 shows an nominal mission profile of the reusable sounding rocket. By taking off vertically, reaching an altitude of 120 km, and having the engine cut off, the vehicle will provide the payload with an observation environment or conditions. After the observation, a pair of the vehicle engines will be restarted and in the descent phase, and finally land vertically with a thrust level of 60% to 100%. The following two functions are required to accomplish this operation. 9 Smooth and continuous throttling (60 to 100%) and enough speed of response. 9 Re-ignition capability after coasting. C. Approach to Technical Subjects The following tests have been planned to obtain data to be utilized in system design and component design 6,7. Especially, the acquired limit characteristics of components can be utilized to gain more experience and deepen understanding of the phenomena related to the limit of engine life or operating conditions. These data will also be helpful in building up the health monitoring system. Due to the mobility of the small-sized pilot engine, these data can be more easily acquired than is possible with larger-sized hardware. a) Critical performance test of bearings b) Shaft seal test for LOX turbopump c) Injector element test d) Subscale combustion test e) Turbine rig test f) Pump flow test VI. Operation and Maintenance Concept The concept of operation and maintenance has been examined based on the system level requirements of the reusable sounding rocket, which are as follows: 1) The nominal flight frequency is ten times per year and can be increased if needed. 2) Each experimental series consists of five flights in less than one month, with two series per year. 3) The nominal flight interval is 5 days (normal operation phase). 4) The minimum flight schedule is two flights per two days. 5) The system configuration has to minimize inspection per flight and maintenance per series 6) The total system should be capable of being reused 100 times, and exchange of parts should be limited to less than one hundred times. 7) The sub-system level of engine life time has to be guaranteed with an appropriate maintenance schedule meeting the requirement 6). 8) Uchinoura Space Center is assumed to be the homeport, but deployment to other sites should be considered. Figure 5 shows the experiment and vehicle maintenance schedule for one year, and Figure 6 shows the concept of the operation, inspection and maintenance schedule of the reusable sounding rocket 8. In inspections between flights, visual inspection, automatic self-diagnosis, and data evaluation will be done 5 American Institute of Aeronautics and Astronautics without disassembling the airframe and engines. In A-type maintenance, items judged to have a middle malfunction risk rate will be included and the maintenance will be done at the launch site or in a hanger. In B-type maintenance, an overhaul will be carried out in a hanger or a factory. 1 2 3 4 5 6 7 Experiment schedule Evaluiation/ ・Preparation Analysis Vehicle maintenance schedule Vehicle maintenance (A-type) Flight /Experiment schedule 8 9 10 Vehicle maintenance (A-type) (B-type per several years) Flight /Experiment schedule ：RESERVE Experiment and vehicle maintenance schedule for 5 Flights /month Payload： Space Science & Engineering Missions 12 Evaluiation/ ・Preparation Analysis ：Flight Experiment Figure 5 11 10 Flights /year 100 Flights /vehicle < 5 Flights 5 Flights (1 Campaign) Landing Landing Landing Landing Transfer Transfer & Engine Remove Transfer & Overhaul 20‐30 Flights <50 Flights Takeoff On site inspection 5days Continued number of flight Month Inspection in every flight ・ data transfer ・ visual inspection ・ leak check ・ fill up propellant Partially disassemble （launch site・hunger） 2‐3months A‐type maintenance（every 5 flight） ・valve check ・torque check ・spark check ・exchange parts Overhaul maintenance , changing parts （ hunger, factory） X months B‐type maintenance（every 5 – 20 flight） Exchanging parts with relatively short life time ・ turbopump （ bearing, seal） ・ valve ・inspection with （ seal, ） disassembly ・ chamber/injector ・sensor calibration ・engine re‐assemble ・check controll system ・airferame re‐assemble ・engine re‐assemble Figure 6 The concept of the operation, inspection and maintenance schedule of the reusable sounding rocket. Figure 7 shows an example of maintenance schedule. In the case of a rocket engine, estimation of the lifetime of the mechanical elements such as bearings and turbopump seal is now possible using the data obtained from the critical performance tests 9. However, as their lifetime is less than reuse a hundred times, 6 American Institute of Aeronautics and Astronautics they need to be regularly changed. In the case of the chamber, lifetime estimation by calculation showed that reuse more than one hundred times is possible. However, as the calculation estimation is not sufficiently accurate, further research to develop a more accurate lifetime estimation method and nondestructive testing method which can be done at the launch site is being conducted. Figure 8 shows the maintenance concept of the technology demonstrator engine. This engine is being designed to enable inspection and parts exchange by Type-B maintenance. イベント 制御系、計測系確認 データダウンロード 健全性評価 寿命・作動条件の管理 点火器目視点検 燃焼室内面目視点検 噴射面目視点検 上下流加圧 GHe供給 スロートプラグ装着 スロートプラグ取り外し 点検項目 ECB自己診断、各データ評価 フライトデータにより各データ評価 フライトデータにより各データ評価 フライトデータによる評価 ノズル出口より見える範囲で ノズル出口より見える範囲で ノズル出口より見える範囲で ベント漏れ、下流の外部漏れ 各データ健全性確認 目視点検 目視点検 シーケンスチェック 上流加圧 エンジントルクチェック 軸トルクチェック スパークチェック エキサイター取り外し バルブ実作動シーケンス確認 上流∼上下流漏れ、予冷戻り 各継手締付トルク（抜取） ロータートルク スパークレート、放電数 開口部目視点検 ターボポンプ取り外し ターボポンプ一部分解 噴射器取り外し センサー校正 コントローラ内部点検 ジンバル摺動面確認 エンジン再組 制御系、計測系確認 システム 100回中 のべ点検回数 Ｆｌｉｇｈｔ ﾌﾗｲﾄ回数 回 （基×回） 1 2 3 100 400 4 4 4 100 400 4 4 4 100 400 4 4 4 100 400 4 4 4 100 400 4 4 4 100 396 4 4 4 100 400 4 4 4 100 400 4 4 4 100 400 4 4 4 100 400 4 4 4 100 400 4 4 4 カテゴリー ﾌﾗｲﾄ毎点検 ﾌﾗｲﾄ毎点検 ﾌﾗｲﾄ毎点検 ﾌﾗｲﾄ毎点検 ﾌﾗｲﾄ毎点検 ﾌﾗｲﾄ毎点検 ﾌﾗｲﾄ毎点検 ﾌﾗｲﾄ毎点検 ﾌﾗｲﾄ毎点検 ﾌﾗｲﾄ毎点検 ﾌﾗｲﾄ毎点検 ｎｕｍｂｅｒ Daily Maintenance 5 4 4 4 4 4 4 4 4 4 4 4 6 4 4 4 4 4 4 4 4 4 4 4 7 4 4 4 4 4 4 4 4 4 4 4 8 4 4 4 4 4 4 4 4 4 4 4 9 4 4 4 4 4 4 4 4 4 4 4 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 A点検／5回毎 A点検／5回毎 A点検／5回毎 A点検／5回毎 A点検／5回毎 A点検／5回毎 20 20 20 20 20 20 80 80 80 80 80 80 4 4 4 4 4 4 4 4 4 4 4 4 開口部目視点検 軸受・シール点検、羽根部ザイグロ 開口部目視点検 単品でチェック スロット等接続部の目視点検 分解して摺動面目視点検 各継手締付トルク ECB自己診断、各データ評価 B点検／5-20回毎 B点検／5-20回毎 B点検／5-20回毎 B点検／5-20回毎 B点検／5-20回毎 B点検／5-20回毎 B点検／5-20回毎 B点検／5-20回毎 9 9 9 9 9 9 9 9 36 36 36 36 36 36 36 36 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 フライトセンサー ジンバル 軸受（FTP、OTP） シール（FTP、OTP） シール（電動弁、電磁弁、空圧弁） 摺動部品（電動弁、電磁弁、空圧弁） 3年（TBD） 50回(TBD) 30回(TBD) 30回(TBD) 30回(TBD) 30回(TBD) 1 1 3 3 1 1 4 4 12 12 4 4 TBD 0 0 A-Type B-Type ターボポンプ 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 Exchange elements バルブ バルブ常温機能点検 単体での常温漏れ作動確認 Figure 7 Example of maintenance schedule Structures should be easy to inspect and exchange parts. Ａ-type maintenance wiil be done at the launch site with open port inspection B-type maintenance turbopump ・Inspection of bearings and seals ・Inspection of turbine blades combustion chamber Re-maintenance ・visual inspection of inner wall ・measurement of throat diameter 4 4 4 4 4 4 valve (if needed) ・visual check inside the igniter ・visual observation of face plate ・Function check （operation・leak） Figure 8 Maintenance concept of the BBM engine 7 American Institute of Aeronautics and Astronautics VII. Summary A reusable engine program has been initiated for development of a reusable sounding rocket in Japan. Fundamental design and basic tests are being conducted. The operation and maintenance concepts were examined and a schedule for operation 100 times has been set. The prototype engine will be constructed as a technology demonstrator to demonstrate the following factors: reusability, long life, deep throttling, health monitoring, and operability (schedule and cost acceptability).. 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