Laser-sustained plasma (LSP) is a promising method for generating atmospheric pressure plasmas. Although diode lasers are a highly efficient, compact, and low-cost light source for this method, previous studies have only reported LSP generation under gas-filled conditions. In this study, LSP generation under argon gas flow conditions using a 4-kW-class diode laser was investigated, and its various characteristics were examined. The minimum laser power required for LSP generation remained constant at 2,900 W for flow velocities between 0 and 220 mm/s at 2.0 MPa. The LSP temperature increased from 12,000 K to 14,000 K as flow velocity increased. The length of the LSP did not change with flow velocity, but the LSP position decreased from 2.0 mm to 1.3 mm as the flow velocity increased.

Spillage drag varies with capture area ratio (CAR). However, it is not easy to investigate it experimentally since the shape inside a flow-through nacelle of a testing model needs to be changed. Numerical analyses using computational grids of annular plugs inside the flow-through nacelle were performed to clarify the change in the spillage drag for the flow-through nacelle of a business-jet-geometry testing model. As a result, differences in CAR and the axial component of the aerodynamic coefficient were observed by adding the plug. It was shown that a significant change in CAR is only apparent if the plug is squeezed significantly. However, a large squeeze can cause flow separation inside the nacelle and adversely affect the aerodynamic coefficient. Finally, we showed a range where the difference was little affected by parameters other than the CAR and the preliminary result of the correction of the spillage drag using the CFD data.

Autonomous navigation is an essential technique for distant small-body exploration to update the spacecraft state and control the spacecraft position relative to the asteroid. This paper describes a point cloud-based navigation method for self-localization estimation by matching asteroid point cloud data and asteroid images using Hough transformation. Point cloud data is a set of vertices of a shape model and is a sparse shape model. Although conventional image-based navigation is necessary for dense shape model or high-resolution images, in the Hayabusa2 mission, accurate navigation was achieved during descent and landing by manually matching between the asteroid image and about thousands of points. Therefore, this paper proposes a matching method for sparse point clouds and images that manually reproduces matching between points and images using Hough transform. For this study, simulations were performed on the number of points cloud varies from 1,000 to 10,000 points under various sunlight conditions. The proposed method achieves a matching accuracy below 1 [px] at 4,050 points. Moreover, below 2,000 points, the estimation accuracy is superior to the conventional method.

The burning rate of boron potassium nitrate (BKNO₃) pellets with a diameter of 3.2 mm under vacuum in the temperature range between −40 and 60°C for micro-thrusters and pyrotechnics for small spacecraft was measured. The effects of the boundaries of the pellets –such as joints and bases when stacking and bonding the pellets– on the burning rate were also investigated. The measurements showed that the burning rate of BKNO₃ pellets with a diameter of 3.2 mm increased with increasing initial pellet temperature, and the burning rate at 60°C was approximately twice that at −40°C. The increase in the burning rate was small in the temperature range of −40 to 0°C, ranging from 3.8 ± 0.3 mm/s to 3.9 ± 0.2 mm/s. The rate of increase rose significantly above 0°C, and the burning rate was 5.3 ± 0.5 mm/s at 40°C and 7.9 ± 0.6 mm/s at 60°C. In contrast, the burning rate of infinitely stacked BKNO₃ pellets with a diameter of 3.2 mm and a length of 2.0 mm decreased by approximately 20% due to the presence of joints. The decrease in the burning rate due to the presence of bases is relatively greater when the pellet length is shorter and the temperature is higher.

The structural characteristics of a lattice structure depend on the structure of its unit cells. This allows morphing wings to exhibit anisotropic structural characteristics in certain sections and allows them to be lightweight while maintaining the necessary stiffness. In this study, five types of lattice structure are subjected to bending, tensile, compressive, and torsional tests, and the equivalent stiffness of each type is calculated. Among these structures, the cube lattice has high bending stiffness and low torsional stiffness, making it suitable for twist-morphing wings. A twist-morphing wing composed of a cube lattice has relatively low torsional stiffness and can be twisted using an actuator while maintaining the bending stiffness in the wingspan direction. However, the low torsional stiffness can cause excessive torsional deformation when the aircraft is subjected to a large disturbance or load. When the twist angle exceeds a certain value, the torsional stiffness must thus be increased. We propose a shear stopper mechanism and evaluate its effectiveness. A prototype is manufactured and subjected to a torsion test. The results indicate that the proposed mechanism can increase stiffness when the torsional deformation is larger than a certain value. The developed shear stopper is thus effective for morphing wing systems.

The authors propose an enthalpy determination method for arcjet flows. The present method assumes the application combined with the spectroscopic emission measurement in a blunt probe shock-layer. The theoretical aspect of the proposed method is given in detail, emphasizing that thermal equilibrium is a necessary condition for the present method. Two types of arcjet wind tunnel experiments are performed to evaluate the accuracy and feasibility of the proposed method. Note that the spectroscopic emission from the arcjet flow fields is measured, which nearly satisfies the conditions necessary for the present method, and not from the shock-layer over the blunt body. For comparison, a computational fluid dynamics method is used to simulate the arcjet flows of interest. A comparison of the results indicates that the proposed method successfully predicts the centerline enthalpy.