In this study, direct numerical simulations are performed to reveal the effect of the riblet on the transition location and the viscous drag in the transitional flow region. It is found that due to the tendency of the riblet to be more affected by the partial derivatives of instantaneous pressure in the spanwise direction, the turbulent intensity in the spanwise direction increases more upstream than on the smooth surface, resulting in promoting turbulent transition via TS instability a little. It is also found that the riblet increases the viscous drag in the transitional flow region because the coherent structure of vortices is more likely to be formed by TS waves on the riblet surface compared to the smooth surface in that region.

For future Mars entry missions, accurate prediction of infrared radiative heating from CO₂ in the aftbody aeroshell of the capsule is required in order to optimize the thermal protection system. CO₂ in the aftbody region is mainly produced by recombination of CO--O system. In general, recombination rate coefficients are calculated by the principle of detailed balancing using dissociation rate coefficients and the equilibrium constant. However, in the flow of the aftbody region, where strong chemical nonequilibrium conditions are expected, the recombination rate coefficient calculated by the principle of detailed balancing is questionable. Therefore, in this study, infrared radiation from CO₂ in nonequilibrium flow was measured using a shock tube with divergent nozzle in JAXA Chofu Aerospace Center. It was shown that the recombination rate coefficient of CO--O system is dominant by sensitivity analysis. Tests at different conditions for shock wave velocity suggested that the apparent recombination coefficient was larger at lower temperatures. By comparing the measured radiation intensity time histories with JONATHAN and SPRADIAN calculation, it was shown that recombination rate coefficient of CO--O system under nonequilibrium flow field is larger than that calculated by the principle of detailed balancing.

In this study, we analyzed the relationship between aircraft routes and precipitation data focusing on the segment where aircraft are in the process of severe weather avoidance. Currently, pilots mainly avoid severe weather using weather information from the onboard weather radar on the basis of their knowledge and experience. Consequently, avoidance routes vary, which leads to the uncertainty of flight time while improvements of trajectory prediction are required. Also, the procedures of pilots and air traffic controllers to deal with the avoidance could be one of the factors that increases their workloads. For safer and more efficient future operation, strategic planning considering weather phenomena is of importance. For this purpose, we discussed the establishment of quantitative criteria that corresponds to pilot decision-making. As a result, it was demonstrated that the avoidance distance tends to increase as the precipitation intensity increases. Also, it was indicated that aircraft even avoids the area where the echo intensity is weak in cruise phase while passing through the area in climb and descent phases. Additionally, it was clarified that there were cases where the aircraft avoided the areas where no precipitation was observed, which could be due to phenomena such as clear air turbulence. The results suggested that precipitation intensity could be one of the criteria for severe weather avoidance.

This study examines methods for executing high-speed three-axis attitude maneuvers for spacecraft with flexible structures. To apply the design methodology of feedforward control input for single-axis attitude maneuvers to three-axis maneuvers, we realized three-dimensional rotation as a single-axis rotation around the Euler axis. First, we expressed the equations of motion of the spacecraft in a coordinate system with the Euler axis as the single axis. Next, we derived the equations of motion for the global modes. Using these equations, we demonstrated that the control input is applied to the single axis around the Euler axis, achieving three-axis attitude maneuvers. Numerical simulations were conducted using two types of feedforward control inputs: step-type and continuous-type. The results indicate that the continuous-type control input excites almost no oscillatory modes and achieves minimal attitude error. On the other hand, the step-type control input requires less control torque compared to the continuous-type for the same maneuver duration. By adopting a two-degree-of-freedom system that simultaneously uses feedforward and feedback control, we demonstrated robustness even in the presence of variations in vibration frequencies and damping.

Returning samples from Mars is expected to provide significant scientific knowledge about the formation of planets and the origin of life. The LifeSpringsMars Mission, a novel mission concept designed by a multinational consortium from Australia, Japan, the United States, and New Zealand, aims to return samples from the Columbia Hills on Mars at a low cost. To achieve cost reduction, LifeSpringsMars mission plans to transfer samples in deep space instead of using the conventional method of transferring samples in Mars' low orbit. However, relaying samples in deep space has a high risk of losing samples in deep space, so trajectory design that accounts for uncertainties of Mars Ascent Vehicle is required. This paper presents a method to optimize the rendezvous trajectories between multiple spacecraft by extending stochastic trajectory optimization that takes account of disturbances. Introducing the Unscented Transform, the method lets us compute and optimize the stochastic trajectories. Finally, numerical examples demonstrate the feasibility of the proposed mission architecture.