Several methods have been proposed for three-axis attitude control using two control moment gyroscopes (CMGs) under the condition that the total angular momentum of the system is zero. Star sensors that recognize small stars are commonly used to precisely determine spacecraft attitudes. Because star sensors are highly sensitive, their boresight must not align with the Sun. However, previously reported underactuated steering laws are feedforward type controllers and cannot satisfy the attitude-path constraint for star sensors in real time. This paper proposes a novel underactuated steering algorithm for two skewed single-gimbal CMGs (SGCMGs) that addresses the limitations of previous steering laws by incorporating a barrier function to prevent the star sensor’s boresight from entering prohibited directions. The innovation of the proposed steering algorithm is that it can stabilize not only the spacecraft attitude towards the target attitude but also prevent the star sensor boresight from entering the prohibited area during maneuvers using only two skewed SGCMGs. The validity of the proposed algorithm is demonstrated through numerical simulations.

Numerical simulations of a T-tail flutter in subsonic and transonic flow regimes were conducted using a 3D Navier-Stokes code which considers the in-plane motion of the horizontal tail plane (HTP). In our subsonic flutter simulations, we confirmed that the flutter velocity of the T-tail is dependent upon the mean angle of attack of the HTP, and also confirmed that the results show a satisfactory agreement with those predicted using a lifting-surface theory. Thereby we were able to verify the reliability and accuracy of the 3D Navier-Stokes code. In transonic simulations, the sharp transonic-dip phenomena of the dynamic pressure of flutter and limit cycle oscillation (LCO) were predicted. It can be shown that the characteristics of LCO and flutter are considerably different depending on Mach number and the angle of attack of the HTP. As a possible cause of these phenomena, we examined the behavior of the shock wave generated on the upper or lower surface of the HTP, which varies strongly depending on the Mach number and the angle of attack of the HTP.

A 6U CubeSat EQUULEUS (EQUilibriUm Lunar-Earth point 6U Spacecraft) successfully executed an orbit transfer using a water-propelled propulsion system in deep space for the first time using AQUARIUS (AQUA ResIstojet propUlsion System), a water resistojet propulsion system. We report on-orbit performance analysis of AQUARIUS in its initial flight operation. AQUARIUS employed a distinct water droplet vaporization structure for efficient gas-liquid separation and a power-saving strategy for the large latent heat of water. The time-averaged thrust observed in two on-orbit operations using two thruster heads was approximately 6.0 mN, with a specific impulse of 91.0 s and a power consumption of less than 14 W. The thrust-to-power ratio increased with the temperature difference between the vaporization chamber and the adjacent communication device. This indicates that the necessary power for the vaporization of the water was effectively compensated for by the heat from the surroundings owing to the appropriate thermal design of EQUULEUS. The thrust coefficient efficiency was found to be approximately 0.86, which was higher than in the ground test (∼0.66). This is possibly due to the extremely low back pressure on orbit that mitigates the nozzle efficiency reduction due to low Reynolds number flows.

The purpose of the present research is to develop and to demonstrate the design architecture of the AFTS (Automatic Flight and Transition System) for “Lift/Cruise Thrust” type VTOL (Vertical Takeoff and Landing) aircraft such as tilt-wing, tilt-propeller, tilt-duct aircraft, etc. VTOL aircraft of this type, characterized by propulsor installations that reorient the thrust relative to the aircraft, offer advantages of a wide flight envelope. However, flight and stability characteristics significantly change depending on airspeed and configurations such as wing tilt angles or propulsor orientations. These make it difficult to operate VTOL aircraft safely and the AFTS, which comprises both autopilot and auto-transition algorithm, should be developed to provide the safe and effective means to control the aircraft over its entire flight envelope. In this research, the autopilot was designed to provide control commands that change control strategies and gains according to the configurations. Additionally, the auto-transition algorithm, which should be coordinated with the autopilot, was designed to select and change configurations for accelerated and decelerated flight. The proposed AFTS was installed to a “Lift/Cruise Thrust” type, QTW (Quad Tilt Wing) VTOL UAS (Unmanned Aircraft System), and fully automated operation capability was demonstrated through flight test both in calm and windy conditions.

Measurement methods based on photogrammetry are highly accurate and effective for large space structures. However, photogrammetry is difficult to use in a thermal vacuum chamber because a remote drive system is required for operating a camera, whose position and attitude must be constrained. The objective of this study is to evaluate the measurement accuracy of a photogrammetry system under camera constraints. We constructed a simplified rail-based measurement system that simulates the circular motion of a camera drive system in a chamber. The camera was constrained to moving on a circular rail that surrounded the specimen, taking photographs at regular intervals along the circumference. We conducted experiments at various camera heights and angles and determined the measurement error. A high measurement accuracy of about 0.02 mm root-mean-square was achieved under appropriate camera conditions. Placing the camera nearly perpendicular to the target was found to improve the measurement accuracy. It was also found that markers were more easily detected on the curved surface of a parabolic antenna than on the flat surface of an aluminum honeycomb plate. The results indicate that accurate photogrammetric measurements in a thermal vacuum chamber are possible, even with constraints on the camera position and attitude.