The Compatibility Evaluation Method of the 500N & 120N Japanese Bi
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Trans. JSASS Aerospace Tech. Japan Vol. 12, No. ists29, pp. Pg_7-Pg_15, 2014 Original Paper The Compatibility Evaluation Method of the 500N & 120N Japanese Bi-Propellant Thrusters with the HTV System & Operation Design 1) 1) 1) 1) By Shinichi TAKATA , Hiroshi SASAKI , Tsutomu FUKATSU and Katsuhiko SUGIMORI 1) Japan Aerospace Exploration Agency (JAXA), Sagamihara, Japan (Received June 12th, 2013) This paper describes the evaluation method of the new Japanese thrusters design, balancing and verification of interface compatibility with the HTV system and operation design. Thruster performance directly affects the performance of the space craft. Therefore, the thruster replacement from the imported thrusters to the new Japanese thrusters required the evaluation from the view point of high-order system level. It is important to select the appropriate elements, verify their relationships, and create a feedback mechanism which allows modification of each element. This method will facilitate the overall systems design for future inter-orbit transfer vehicles. Key Words: HTV3, Propulsion, Thrusters, Optimum Design Nomenclature In conventional spacecraft system design whose propulsion system is not large and/or thrusters firing pattern is not severe, Duty : duty = {X/(X+Y)}*100, % the compatibility between thrusters and high-level systems is On Time : X(ms), Off Time : Y(ms) usually evaluated in one direction, which means thruster's Impulse : impulse bit ratio = X/Y compatibility with high-order system. But HTV is the largest Bit Ratio X : Integrated impulse at one pulse (N*s) vehicle in Japan and it's required to operate in severe pulse Y : Normal thrust*on-time at one pulse (N*s) firing patterns for a long duration especially in rendezvous TWmax : maximum chamber wall temperature at throat with the ISS. And JAXA aimed the unlimited pulse firing TWD : chamber wall temperature at root area thrusters. Therefore the thruster replacement required the fully evaluation of compatibility between thrusters and high-level 1. Introduction systems not in one direction but bi-directionally. This proper feedback mechanism allows modification of the new thrusters The two new types of Japanese bipropellant thrusters in design, evaluation of attitude controllability, revision of the HTV3 (KOUNOTORI 3) demonstrated flawless performance, specification between thrusters and high-order system and and delivered 16 tons of HTV3 to the International Space helps to predict the real profile on orbit. As a results, the Station (ISS). The 500N main engine and the 120N reaction optimum design was achieved. control system (RCS) thrusters were named HBT-5 and This paper describes the new compatibility evaluation HBT-1 respectively (Fig.1). method in large spacecraft system design based on the HTV thrusters development and HTV3 mission results. Fwd. RCS Thruster (HBT-1) 2. HTV System Description The outline of the HTV system configuration diagram is shown in Fig. 2. The HTV operation team designs a plan by considering the status of ISS, launch vehicle, ground system, Aft. RCS Thruster (HBT-1) and HTV. The plan outlines operation timelines, external thermal environmental conditions, and thruster maneuver tactics. The GN&C system defines the flight control functions. The propulsion system which include the thrusters, generate thrust based on the control command from the GN&C system. The propulsion module configuration diagram is shown in Fig. 3 1). Main Engine (HBT-5) Fig. 1. HTV3 view from ISS (C) NASA. Copyright© 2014 by the Japan Society for Aeronautical and Space Sciences and ISTS. All rights reserved. Pg_7 Trans. JSASS Aerospace Tech. Japan Vol. 12, No. ists29 (2014) ISS HTV Operation System Other Systems HTV starts approaching to ISS step by step. During the final approach from 500m point to ISS, the HTV Flight Segment thrusters that locates on +Z axis and face the earth are mainly Pressurized Logistics Carrier ISS : International Space Station used and the severe pulse firing continues for over one hour. GN&C : Guidance, Navigation and Control Un-pressurized Logistics Carrier Exposed Pallet ISS Proximity Phase Avionics Module GN&C System ISS(International Space Station) Approach Initiation Point Other Systems 10m(Capture Point) 30m Propulsion Module Propulsion System Thrusters Final Approach to ISS 250m Other Systems Other Components 500m (R-bar Initiation Point) Fig. 2. HTV system configuration diagram. - Generate thrust for orbital change To Earth RId Maneuver Main Function - Generate thrust for attitude control - Store propellants System Regulated/Blowdown Bi-Propellant System Fig. 5. HTV’s final approach to the ISS Fuel : MMH Propellant Oxidizer : MON-3 (NTO) 3. Japanese Thrusters Development Process Pressurization Gas : Helium Main Engine : 500N×4 Thruster RCS(Reaction Control System) : 120N×28 3.1. The goal of HTV thruster development Dry Weight 1380kg The goal of Japanese thruster development was to acquire Maximum MON 1514kg凡MMH 918kg Propellant key technology for inter-orbit transfer system, find injector Size Length : 1273mm× Diameter : 4216mm parameter design know-how to improve the combustion High Pressure Area : 23.1MPa Pressure chamber’s temperature stability during severe pulse firing, Low Pressure Area : 2.75MPa cost reduction, and easy procurement control. Fig. 3. HTV propulsion module configuration. In HTV1 and 2, the imported thrusters that were flight-proven in Apollo and Shuttle missions were used in Almost all components of propulsion system are installed in order to mitigate the component development risks. However, the Aft. propulsion module. Fwd. RCS modules are installed constraints were observed during certain pulse firing in pressurized logistic carrier, so it has the long external tubes conditions. Therefore, key components of the inter-orbit space which feed propellant from tank to Fwd. RCS thrusters (Fig.4). transportation system were domestically developed after And the Fwd. RCS propellant manifold volume is designed to validation of the spaceship’s design technology. be minimized because of mitigating the Extravehicular In the beginning of the Japanese thrusters development, it Activity(EVA) hazard on the propellant leakage failure. As a was planned that the imported thrusters would be simply result, the external tubes and Fwd. RCS manifold tubes are replaced with the Japanese new thrusters. But as shown below, required to be long, but thin. the performance of the Japanese RCS thrusters during pulse operation became different from that of the imported ones. This is because the chamber temperature stability during pulse External Tubes operation with large inlet pressure oscillations was made a top Fwd. RCS thrusters priority in all of the requirements to thrusters including the thrust performance. But the performance in HTV system level like a rendezvous capability or an attitude controllability could not be changed, then the compatibility of high order system with thruster performance was finally achieved by changing the interface specification between them and making some Propellant Tank Propulsion Module substantial improvements in the thruster injector designs as much as possible. 3.2. Surge pressure evaluation and control Fwd. RCS manifold tubes In general, a large surge pressure occurs in the propellant feed line during initial priming after separation from launch vehicle by opening of either latch valves or pyrotechnic valves. Its level and behavior must be accurately evaluated by Fig. 4. HTV propulsion system configuration. conducting system level firing test or analysis on the ground in order to prevent a component failure, system rupture or The operation method in ISS proximity phase is shown in leakage. Usually this is the only problem in the initial Fig. 5. After departure of the approach initiation point, HTV activation phase of a spacecraft propulsion subsystem. The conducts a few small maneuvers by RCS thrusters to shift the methodology for analytical prediction of priming water final approach mode (beneath of 500 m from the ISS). Then Pg_8 S. TAKATA et al.: The Compatibility Evaluation Method of the New Japanese Thrusters with the HTV System Design hammer pressures has been developed and applied to the design and development of a number of spacecraft Operation Plan/GN&C System Design applications. 2) • Generate Mission Duty Cycle using When severe pulse firing operation is required, the pressure the model of limited thrusters fluctuations at inlet of thrusters during pulse operations should performance be fully evaluated. In general, surge pressure is calculated via the following Nikolai E. Zhukovskii’s Eq.(1). It means that Propulsion System Design • Evaluate Surge Pressure Level during operation surge pressure becomes larger as the propellant tube becomes plan pulse firing thinner and the 'v becomes larger. The surge pressure modification reaches maximum in the long propellant tube. 'h 'p/Ug (c/g)'v (1) Check Thrusters Characteristics Where : h = head of surge pressure • Additional Verification if necessary p = surge pressure U = fluid density No Constrain to Operation g = acceleration of gravity c = net fluid speed of sound Fig. 6. General Development Flow of propulsion sub-system. and v = fluid velocity in tube In the development of the MARS Polar Lander descent the thrusters impulse performance during short on-time pulse propulsion system and the Phoenix landing propulsion system, operation must be evaluated accurately in order to conduct the water hammer level was also tested and evaluated because