A numerical simulation was carried out corresponding to recent experiments using delta wings with sharp and blunt leading-edges, which indicates the second primary vortex, at NASA Langley Research Center. However, the experimental data did not reveal the detailed physical phenomena regarding the second primary vortex, because the experiment used only on-the-body-surface data. In the present study, the physical phenomena were revealed using Reynolds-averaged Navier-Stokes computations with three one-equation turbulence models on an unstructured hybrid mesh. The adaptive mesh refinement method in the vicinity of the vortex center was also applied to have more mesh resolution. Consequently, the result quantitatively revealed that appropriate modeling regarding turbulent kinematic viscosity was significant. Moreover, the three-dimensional visualization of the computational fluid dynamics results suggested that the second primary vortex was a developing shear layer merging into an open-type separation generated late by the primary vortex.

View full abstract

A command to line-of-sight (CLOS) guidance law is developed against head-on high-speed maneuvering targets. Preliminary studies have shown that the aspect angle of the interceptor at lock-on near 180 deg is a fundamental requirement for achieving small miss distance against a very high-speed incoming target. The solutions of missile trajectory obtained before under this guidance scheme seemed tedious and incomplete. Now, in this study, exact and complete solutions which are more general and comprehensive than those obtained before are derived for head-on high-speed maneuvering targets. Some related important characteristics such as lateral acceleration demand and normalized missile acceleration are investigated and discussed. Additionally, illustrated examples of target maneuvering are introduced to easily describe the trajectory of the target. The results obtained in this study are very significant and practical, and will be useful in actual application.

View full abstract

Capture of tumbling objects in space will be one of the important on-orbit service technologies in the future. It requires a series of technologies such as camera-image tracking of the target, target attitude motion estimation, and attitude control of the chaser to approach and grasp the target. Based on theoretical and simulation-based research, the University of Tokyo successfully performed an on-orbit experiment of some of these technologies on a Japan Aerospace Exploration Agency’s (JAXA, formerly NASDA) microsatellite named “μ-LABSAT.” In this paper, the objectives and procedures of these experiments, the control and estimation algorithms, and the results are described.

View full abstract

The Quasi-zenith Satellite System is a satellite navigation system in Japan which is designed to complement and augment global-positioning satellites (GPS). This paper investigated the impact of the integration of GPS and development of the QZSS system in the East Asian Region. QZSS satellite constellation and signal structure are briefly introduced, four QZSS satellite orbit options (8-shaped, Egg-shaped 1, Asymmetric 8-shaped, Egg-shaped 2) are introduced in this research. Performance analyses in the East Asian region when GPS with and without QZSS augmentation were obtained by triple-frequency simulator. The availability and accuracy of satellite positioning was assessed using a measurement of the number of visible satellites, position dilution of precision, respectively. The efficiency and reliability of GPS was evaluated using the GPS L1 carrier phase ambiguity resolution success rate. The simulator results showed that, with extra satellites and extra signals, QZSS not only improves the availability and accuracy, but also offers more efficient and reliable GPS in Japan and most East Asian regions.

View full abstract

A hybrid heuristic optimization technique based on genetic algorithms and particle swarm optimization has been developed and tested for trajectory optimization problems with multi-constraints and a multi-objective cost function. The technique is used to calculate control settings for two types for ascending trajectories (constant dynamic pressure and minimum-fuel-minimum-heat) for a two-dimensional model of an aerospace plane. A thorough statistical analysis is done on the hybrid technique to make comparisons with both basic genetic algorithms and particle swarm optimization techniques with respect to convergence and execution time. Genetic algorithm optimization showed better execution time performance while particle swarm optimization showed better convergence performance. The hybrid optimization technique, benefiting from both techniques, showed superior robust performance compromising convergence trends and execution time.

View full abstract

This study presents a means of explicit guidance for ballistic entry using an improved method of matched asymptotic expansions. The trajectory of ballistic entry into a planetary atmosphere is still an important and often critical phase of a mission. In the paper, feedback control via drag modulation is used to guide the vehicle during the atmospheric entry, whereas a matched asymptotic solution for the entry trajectory is available to aim the target. The feedback control ensures the stability of a trajectory around the nominal trajectory by compensating for the non-linear terms in the motion of the vehicle. Using the improved method of matched asymptotic expansions, the control algorithms for the guidance law are derived explicitly and tested against the 1976 U.S. Standard Atmosphere. Simulation results indicate that the control algorithms can effectively control the trajectories in the lower atmosphere under the targeting dispersions of atmospheric variations.

View full abstract

The concept of a smart vortex generator (SVG) is proposed. The SVG has an upright position when acting as a vortex generator during takeoff and landing, and a stowed position when cruising. This SVG consists of a shape memory alloy (SMA) plate that memorizes the upright position near the ground at high temperatures and a blade spring hooked to the SMA plate that moves the plate into the stowed position when exposed to low temperatures associated with high-altitude cruising. To study the deformability of the SVG, numerical simulations were performed using a simple mathematical model. The results revealed that the temperature of the SVG can smoothly follow the changes in ambient temperature both in ascending and descending phases, and that the SVG can vary its shape from the upright position to the stowed position and vice versa according to the ambient temperature without requiring additional energy. Moreover, it was found that the temperature range for deformation depends on the stiffness of the spring, and that the degree of deformation depends not only on the stiffness of the spring, but also on the martensite variants which appear when cooled.

View full abstract

The aerodynamics of formation flight are studied by modeling wings using a horseshoe vortex. During flight in formation, wings receive upwash created by other wings, and the required power consequently decreases. The leading wing in a V formation receives less benefit, while in a U formation, the power reduction rate remains identical over all wings. In long-distance flights, the U formation is optimal. However, when the process of shifting the leader position in a V formation is considered, as is often observed in actual bird flocks in long-distance flights, the power reduction rates of all wings converge into the same value after several shifts. This value is identical to that of the U formation.

View full abstract

The Japan Aerospace Exploration Agency, JAXA, announced a long-term vision recently. In the vision, JAXA aims to develop hypersonic aircrafts. A pre-cooled turbojet engine has great potential as one of newly developed hypersonic airbreathing engines. We also expect the engine to be installed in space transportation vehicles in the future. For combustion test in the real flight conditions of the engines, JAXA has an experimental plan where a small test vehicle is released from a high-altitude balloon. This paper applies numerical analysis and optimization techniques to conceptual designs of the test vehicle in order to obtain the best configuration and trajectory for the flight test. The results show helpful knowledge for designing prototype vehicles.

View full abstract