The pintle injector is a promising candidate for injection systems of future rocket engines because of the throttling capability, the combustion stability, and the low manufacturing cost. Few studies focusing on fundamental aspects of a pintle injector have been conducted, and most of the design parameters of a pintle injector is determined mainly based on the empirical knowledge. Among the design parameters, total momentum ratio (TMR) is one of the most important parameters since spray structure is dominated by TMR. Therefore, combustion experiments using an ethanol/liquid oxygen rocket engine combustor with a planar pintle-type injector which is designed for optical measurements for a pintle injector are conducted at combustion pressure (P_c) = 0.37-0.42MPa, mixture ratio (O/F) = 1.31-1.49, TMR = 0.32-3.65 to investigate the effects of propellant momentum ratio on the combustion behavior. The spray structure under hot fire conditions is observed using high-speed imaging techniques with a backlit configuration. In the oxidizer-centered configuration, the characteristic exhaust velocity efficiency (η_C^*) decreases with the increase of the TMR. The atomized propellant impinge on the combustor wall before the vaporization and reaction at higher TMR. In the fuel-centered configuration, though the propellant spray is more inclined to the direction of the upper combustor wall at higher TMR, the η_C^* does not change with the TMR. In both oxidizer-centered and fuel-centered, higher η_C^* is provided in the condition of higher injection pressure drop.

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This paper is concerned with evaluation of GNC systems for D-SEND#2. D-SEND is a project to demonstrate a low sonic boom aerodynamic design concept. In the #2 part of this project, an unpowered test vehicle is lifted to an altitude of 30km by a balloon from which it then separates. After the separation, the vehicle's on-board flight control computer selects a target Boom Measurement System (BMS) according to the separation point. The vehicle then autonomously flies to the selected BMS and establishes prescribed sonic boom measurement flight conditions. Since it is required to achieve mission objectives at the very first flight in such a flight testing using a balloon, evaluation of mission success chance is mandatory adding to that of controller stability. It is also important to establish operational criteria for various anomaly cases. We propose an inclusive evaluation method effective for balloon launch flight testing, and the actual flight results are also presented.

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In order to improve the thrust force of the μ 10 microwave discharge ion thruster, its ion source which is biased at a screen voltage is separated into three parts; 1.waveguide, magnet, and a grid holder, 2.magnet spacers, and 3.a screen grid by ceramic rings. Connection of a high voltage power supply is selectable among each component independently, and maximum beam currents are measured in all six cases in addition to the nominal setup. Except for one case, the maximum thrust force is increased from the HAYABUSA's 8mN and HAYABUSA2's 10mN. The highest thrust force 11.2mN is recorded at Isp 3150sec when the magnet spacers are not connected to the power supply. At this time, the potential of the isolated magnet spacers is increased from 1500V to 1525V. The increase of the potential of the spacers regulates collisions of ions, resulting in increase of the ion currents. This study firstly demonstrates the effect of the segmentation of the discharge chamber of microwave ion thrusters and achieves the improvement of 4% of the total efficiency and of 40% of the thrust force since the HAYABUSA's flight model.

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In the present paper, an alternative numerical approach based on distinct element method (DEM) for the impact collapse analysis of thin-walled structures was proposed. Starting from the equilibrium equation for the thin plate bending, new element for bending and twisting has been introduced using single layer element in DEM. Furthermore, non-linear element taking into account the plastic deformation has been applied in the present method. The validity of the present numerical approach was considered and inspected through some numerical demonstrations for the impact collapse and plastic buckling problems of thin-walled structure.

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Fluid dynamic effects between adjacent streamline bodies have a conspicuous role in drag reduction. One typical example is a dolphin drafting. When two dolphins such as a mother and a calf swim side by side, the calf seldom flaps its tail fin, indicating the calf utilizes the fluid dynamic force between the two bodies as a thrust. This force is generated by the Venturi effect. In this study, wind tunnel tests were conducted with two streamline bodies of different sizes that mimicked the mother and the calf dolphins to clarify the fluid dynamic effects between two bodies at various relative positions. In consequence, the increase of friction drag by the acceleration of flow between two bodies and the thrust generation by the Venturi effect were confirmed as well as the optimum position to maximize the thrust, indicating the possibility of effective design of airplanes with external appendages.

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In order to evaluate the debond fracture toughness between face sheet and core in sandwich panel under mode-I type loading, sandwich double cantilever beam (DCB) test is often utilized. To analyze the DCB test specimen considering the elastic deformation of the core, a beam on Winkler foundation model was proposed. However, there has been an argument over the definition of the Winkler foundation property. In this study, the Vlasov foundation model, or more specifically the refined Vlasov method, is applied to analyze the sandwich DCB test specimen. The compliance and the energy release rate of sandwich DCB test specimens calculated using the present method show good agreement with those obtained from finite element analysis.

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