A numerical simulation of a mixed-flow compressor under windmill conditions is conducted to investigate the cause of stagnation pressure loss captured in the previous experiment, and to clarify the qualitative flow structure under windmill conditions. As a result of the simulation, the compressor rotor causes a stronger load on the airflow even under windmill conditions, because the compressor is connected to the turbine. It turns out that the mass flow rate increases in the order of rated operating point: windmill conditions with turbine and windmill conditions without turbine. In addition, a negative angle of attack is confirmed for the first stator under windmill conditions, which leads to a large separation on the pressure-side of the blade. This tendency increases when the rotational speed decreases. By a simple analysis, it is clarified that the lower the pressure ratio and rotational speed, such as under windmill conditions, the further the rotor and stator angle of incidence become separated from the optimal degree.

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This paper proposes to apply a probability density ratio estimation technique to stochastic robust control design. The approach has the potential to reduce computational load during stochastic optimization. It is applied to a simple example problem of flight control and the result is promising.

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The first demonstration of target acceleration by a strong magnetic field is conducted. Two miniature targets, a gold ball and a neodymium permanent magnet, are accelerated by a magnetic field. A magnetic-field strength as high as 1 kT is produced using a capacitor-coil in which two copper disks are connected by a single-turn coil, and the capacitor was driven by two beams from the GEKKO-XII high-power laser. The targets are accelerated by the interaction force between two magnetic moments: the target and the capacitor-coil. The velocity of the accelerated gold ball was estimated as 10 m/s from shadowgraphy images. In the case of the magnet, although the image could not be observed clearly due to the plasma generated around the magnet, it was confirmed that the magnet interacts with the magnetic field of the capacitor-coil.

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This paper proposes a rapid trajectory planning algorithm using random search and a dynamics filter based on dynamic inversion. It can rapidly generate a collision-free trajectory for an unmanned aircraft in a highly constrained environment, including complex terrains with obstacles or waypoints. Conventional studies on trajectory generation mainly focus on global optimization; hence, the calculation cost grows exponentially with increased complexity. The proposed trajectory planner consists of two steps to effectively generate a collision-free flight trajectory. First, a sampling-based random search algorithm rapidly determines a collision-free pathway. However, the pathway generated by the random search is calculated geometrically, so the variations in the actual flight are difficult to follow. Therefore, the second step, named dynamics filtering, modifies the initial pathway to a dynamically flyable trajectory with a one-time-only integral calculation. The dynamic inversion technique is utilized to ensure flight-worthiness. In this paper, the implementation and computer simulation results of the proposed trajectory are described. The effectiveness of the proposed method is verified by a six-degrees-of-freedom flight simulation for a Mars exploration aircraft model developed by JAXA and associated research institutes.

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The relationship between impulse and crater formation on an Al ablator with repetitive irradiation of Nd:YAG laser pulses (wavelength of 1064 nm, pulse duration of 7 ns) is investigated. The mNs level impulse is measured in a vacuum by a torsion type impulse balance. Surface area changes caused by crater deepening are measured with a laser microscope, then used for calculating the effective fluence. The fluence is compared to a corresponding variation in the momentum-coupling coefficient with repetitive pulses. The impulse with repetitive pulses becomes undetectable because the effective fluence decreases to the ablation threshold. The momentum-coupling coefficient fits to a simple variation; that is, it sharply increases to a peak value as the effective fluence increases, then gradually decreases.

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Recently rapid maneuvering and precision pointing accuracy are two crucial characteristics for observation missions of microsatellites. Control moment gyroscopes (CMGs) are applied as ideal actuator for large torque output capability but are limited to the problem of inherent mechanical singularity. This paper proposes a simple yet effective robust attitude control methodology for microsatellites. It can guarantee convergence time and pointing accuracy in the presence of CMG practical restrictions, inertial uncertainties and various disturbances. Furthermore, pseudo-inverse steering logic based on mixed two-norm and least-squares minimization is chosen, as it can deal with both the internal singularity problem and momentum saturation singularities. It aims at precisely exporting commanded torque while avoiding singularity at the same time. Two key parameters of this steering logic and their characteristics for avoiding singularity are introduced. Hardware in the loop simulation result demonstrates the efficiency and feasibility of the proposed attitude control approach.

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This paper introduces an effort to precisely describe attitude motion under full orbit perturbations. To define the attitude of an Earth-orbiting spacecraft, this study introduces a reference frame being affected by orbit perturbations. Unlike the commonly adopted reference frame, the reference frame introduced here is fully perturbed, so that it rotates about not only the pitch axis, but also the yaw axis. To incorporate the mutual coupling effect between attitude motion and orbit motion, the method introduced considers the spacecraft as consisting of multiple facets and carefully models orbit perturbation-induced torque that varies the attitude. This paper focuses on the attitude dynamics of a small satellite with relatively low moments of inertia under full orbit perturbations, and provides some interesting results and the outcome from the method introduced.

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A ring-force balance system for a supersonic wind tunnel with a small test section was developed. This force balance system can measure an applied force independently by measuring the strain on the ring part. A theoretical analysis of this system was conducted under three conditions: an infinitesimally thin ring-force balance, a ring-force balance with finite thickness, and a ring-force balance with a support arm. From the analytical results, the azimuthal location, where the strain is zero for certain force components, varied based on the balance characteristics, such as the thickness or diameter of the ring part. A ring-force balance, which is based on this analysis, was designed and fabricated. The calibrated results showed that the designed balance was able to measure the force components with high accuracy and minimal interaction.

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