The Quasi-Zenith Satellite System (QZSS) is a Japanese navigation satellite system that provides position, navigation and timing service, as well as augmentation services, to users in the Asia-Pacific region. Since the QZSS consists of satellites in inclined geosynchronous orbit and geostationary orbit, the changes in the observation geometry are smaller than those of other global navigation satellite systems (GNSSs) in medium Earth orbit such as global positioning satellites (GPSs). This feature is suitable for providing navigation signals to users in a specific region with a limited number of satellites. However, it is known that the QZSS orbit accuracy, especially in the along-track and cross-track directions, tends to have a large uncertainty with a limited number of ground-based observations alone as compared to other GNSSs. Therefore, the use of observation data with different sensitivity from ground-based L-band observations for QZSS precise orbit determination (POD) is beneficial to improve the accuracy of the QZSS orbit and clock estimates. This paper proposes an extended QZS system with low-Earth-orbit (LEO) satellites for observing QZSS L-band signals for future precise positioning services and reports the contribution of various types of LEO constellations to QZSS orbit and clock accuracy.

Dual-mode scramjet combustors have strong unsteady flow features due to interaction between the turbulent boundary layer and shock waves, especially in the ramjet-mode. Therefore, hybrid Reynolds-averaged Navier-Stokes/large eddy (RANS/LES) simulation was performed to predict the flow field within a dual-mode combustor with a cavity flame holder under the ramjet-mode operation. The time-averaged results were compared with experimental gas sampling and wall pressure measurement results. Consequently, the combustor exit fuel contour predicted using RANS/LES hybrid simulation was more accurate than that of RANS simulation. Additionally, the pressure distribution was in good agreement because the heat release was also accurately predicted using RANS/LES hybrid simulation compared to that of RANS simulation. The RANS/LES hybrid simulation revealed the effects of the disturbance caused by the pseudo-shock wave and the unsteady longitudinal vortices generated the cavity on the fuel/air mixing. The fast Fourier transform revealed that the fuel jet caused unsteady motion at a different frequency to that of the pseudo-shock wave motion, and the former motion caused pressure fluctuations within the pseudo-shock wave region slightly upstream of the fuel injector.

To investigate the aerodynamic characteristics of the reusable experimental vehicle “Reusable Vehicle-eXperiment (RV-X)” during a return phase (i.e., at 150–180° angles of attack), numerical calculations were performed on both actual-flight and wind-tunnel-test scales. The authors also validated the simulation results through comparing them with the data of corresponding wind tunnel tests. Especially, at an angle of attack of 180°, the results showed that the absolute axial force value |C_A| (i.e., drag working as an aerodynamic brake) under the flight conditions (Re = 9.0 × 10⁶) was approximately 87% smaller than that observed for the wind tunnel conditions (Re = 6.6 × 10⁵). It was discovered that this decrement is caused by a difference between the Reynolds numbers of the wind-tunnel-test and actual-flight scales. A comparison of the visualized flow fields clarified that the flow in the actual-flight scale with the larger Reynolds number does not tend to separate from the vehicle surface. Because of this, the accelerated and expanded flow at the base fillet area of the vehicle formed a significant low-pressure region, which pulled the vehicle in the direction of reducing |C_A| (i.e., decreasing aerodynamic braking).

The inherent stability of two-dimensional motion when hovering using beating wings that have a passive feathering motion is compared with that of rotary wings that have a passive flapping motion. The passive flapping motion of the rotary wings is determined by the bending elasticity, which is expressed by a spring at the wing root. The feathering motion of the beating wings is determined by the torsional elasticity, which is expressed by a damper and a spring at the wing root. The values of the damper and spring were determined by minimizing the necessary power in the present analysis. Unlike rotary wings with passive flapping motion, beating wings with passive feathering motion do not have pitch/roll damping. A flying robot with beating wings requires quicker flight control than one with rotary wings. The results indicate that a flying robot mimicking a living creature is more difficult to control than one with rotary wings.

Argon laser-sustained plasma (LSP) was generated using a 4-kW-class diode laser at pressures of 1.55–2.00 MPa. It was found that there is a tendency of the minimum laser power for LSP generation to decrease from 4,200 W to 2,850 W as the pressure increases. The temperature estimated based on emission spectroscopy was approximately 12,000 K for the variation of pressure and the laser power of 4,350 W. Because the estimated absorption coefficient increases with pressure assuming the inverse bremsstrahlung process, the decrease in minimum laser power as pressure increases pressure is consistent with the increase in the absorption coefficient. There was no significant tendency in temperature change as pressure increased. Furthermore, the inverse bremsstrahlung coefficient tended to increase slightly as pressure increased. This is because the electron number density increases as pressure increases at the same temperature. Therefore, the laser power for LSP generation decreases as pressure increases.