The attitude motion estimation of objects in orbit is a fundamental problem in space missions, such as automated satellite capture and servicing, debris capture and mitigation, and large space structure assembly and maintenance. This paper proposes a new method for attitude estimation using only qualitative information about “What surface of the object is visible.” To acquire such qualitative information, this paper assumes to use RFID. Simulation results demonstrated that this method enables the accurate estimation of attitude state and is robust against observation errors despite using only coarse information.
In this paper, to deal with the complex damage propagations in various composite structures under quasi-static transverse loads, a numerical simulation methodology based on the three-dimensional (3D) finite element method is proposed. In this numerical model, two categories of damage patterns existing in composite structures under transverse loads are tackled independently. First, a stress-based criterion is adopted to deal with the first category, i.e. various in-plane damages, such as fiber breakage, transverse matrix cracking etc. Second, a bi-linear cohesive interface model is employed to deal with the second category, i.e., interface damages, such as delaminations. Also, to remove the numerical instability when using the cohesive model, we propose a simple and useful technique, where the move-limit in the cohesive zone is built up to restrict the displacement increments of nodes in the cohesive zone after the occurring of delaminations. This numerical model is further applied to various composite structures, such as 2D laminated plates and 3D laminated shells under the transverse loads. A lot of information is provided for understanding the propagation mechanisms of various damages in composite structures.
A two-stage magnetic field with cusp and divergent shapes was applied in a magneto-plasma-dynamic (MPD) thruster discharge chamber. The thrust efficiency intensively increased with enhanced thrust and unchanged discharge voltage because of more effective ionization/heating and swirl acceleration due to the applied magnetic field. When the magnetic field became much stronger and the arc current became much higher, the thrust approached the self-magnetic thrust. As a result, an optimum magnetic field strength existed. The plasma flow was observed by a high-speed camera, and plasma density, temperature and velocity were measured with electrostatic probes. Through the magnetic nozzle the exhausted plasma rotated and spreaded radially-outward, and the plasma density decreased near the central axis. Accordingly, the plasma characteristics agreed with the measured thrust performance, considering intensive plasma heating due to Hall current and swirl acceleration, i.e. conversion from azimuthal kinetic energy to axial kinetic energy.
Aluminum alloys have been widely used in constructing various space structures including the ISS (International Space Station) and launch vehicles. In order to apply the welding technology in space, welding experiments on aluminum alloy were performed using by the GHTA (Gas Hollow Tungsten Arc) welding processes using an inverter controlled DC/AC GTA welding machine in vacuum. We observed the removal mechanism of aluminum-oxide films on molten metal in detail during the welding using a high-speed video camera. As a result, it is clarified that the impact arc pressure produced by pulsed current mechanically crushes and removes aluminum-oxide films on the molten pool. This removal mechanism of aluminum-oxide films is completely different from a removal mechanism by cleaning action.
The Integrated Design Methodology is strongly required at the conceptual design phase to achieve the highly reliable space transportation systems, especially the propulsion systems, not only in Japan but also all over the world in these days. Because in the past some catastrophic failures caused some losses of mission and vehicle (LOM/LOV) at the operational phase, moreover did affect severely the schedule delays and cost overrun at the later development phase. Design methodology for highly reliable liquid rocket engine is being preliminarily established and investigated in this study. The sensitivity analysis is systematically performed to demonstrate the effectiveness of this methodology, and to clarify and especially to focus on the correlation between the combustion chamber, turbopump and main valve as main components. This study describes the essential issues to understand the stated correlations, the need to apply this methodology to the remaining critical failure modes in the whole engine system, and the perspective on the engine development in the future.
To investigate a role of a hollow anode for discharge stabilization in anode-layer hall thrusters, plasma dynamics inside a thruster was computed using the fully kinetic 2D3V Particle-in-Cell (PIC) and Direct Simulation Monte Carlo (DSMC) methods. The developed code successfully reproduced the measured discharge current waveform and threshold magnetic flux density for the oscillation onset. At the low magnetic flux density corresponding to the stable discharge case, ionization in the hollow anode was found vigorous and an ion sheath was created on the anode surface. This sheath contributed to the discharge stabilization. However, the amount of ionization in the anode decreased with the magnetic flux density, and the sheath structure changed to an electron sheath at the threshold magnetic flux density.
A multi-objective design exploration for a three-element airfoil consisted of a slat, a main wing, and a flap is carried out. The lift curve improvement is important to design high-lift system, thus design has to be performed under various angle of attacks. The objective functions considered here are to maximize the lift coefficient at landing and near stall conditions simultaneously. Genetic Algorithm (GA) is used as an optimizer. Although it has advantage of global exploration, its computational cost is expensive. To reduce the computational cost, the Kriging surrogate model which is constructed based on several sample designs is introduced. The solution space is explored based on the maximization of Expected Improvement (EI) value corresponding to objective functions on the Kriging models. The improvement of the model and the exploration of the optimum can be advanced at the same time by maximizing EI value. In this study, a total of 90 sample points are evaluated using the Reynolds averaged Navier-Stokes simulation (RANS) for the construction of the Kriging model. Through the present exploration process, several designs were obtained with better performance than the baseline setting in each objective function. To obtain the information of the design space, functional Analysis of Variance (ANOVA) which is one of the data mining techniques showing the effect of each design variable on the objectives is applied. Main-effects of the design variables are calculated to recognize the effect of design variables on the objective functions. This result suggests that the gap and the deflection of the flap have a remarkable effect on each objective function and the gap of the slat has an effect on near stall condition.