An explicit guidance law is developed for a reentry vehicle. Motion is constrained to a three-dimensional Bezier curve. Acceleration commands are derived by solving an inverse problem related to Bezier parameters. A comparison with pure proportional navigation shows the same accuracy, but a higher capability for optimal trajectory to some degree. Other advantages such as trajectory representation with minimum parameters, applicability to any reentry vehicle configuration and any control scheme, and Time-to-Go independency make this guidance approach more favorable.

View full abstract

For more accurate and reliable aviation navigation systems which can be used for civil and military aircraft or missiles, researchers have employed various filtering methods to reduce the measurement noise level, or to integrate sensors such as global navigation satellite system/inertial navigation system (GNSS/INS) integration. Most GNSS applications including Differential GNSS assume that the GNSS measurement error follows a Gaussian distribution, but this is not true. Therefore, we propose an integrity monitoring method using particle filters assuming non-Gaussian measurement error. The performance of our method was contrasted with that of conventional Kalman filter methods with an assumed Gaussian error. Since the Kalman filters presume that measurement error follows a Gaussian distribution, they use an overbounded standard deviation to represent the measurement error distribution, and since the overbound standard deviations are too conservative compared to actual deviations, this degrades the integrity monitoring performance of the filters. A simulation was performed to show the improvement in performance provided by our proposed particle filter method, which does not use sigma overbounding. The results show that our method can detect about 20% smaller measurement biases and reduce the protection level by 30% versus the Kalman filter method based on an overbound sigma, which motivates us to use an actual error model instead of overbounding, or to improve the overbounding methods.

View full abstract

In this paper, a low-thrust, multi-revolution orbit transfer under the constraint of a complex switch function is investigated. First, the effect of the switch function, especially that of a switch function with no prior information, is analyzed. Then, by utilizing the concept of the Lyapunov feedback control law, the semi-analytical expressions of suboptimal thrust angles are derived, and a near-optimal solution could approach the optimal solution by adjusting the five weights in the Lyapunov function using sequential quadratic programming (SQP). In the novel method, except for optimization of the weight factors in the Lyapunov function, no iteration is contained in the process of design and optimization, so the method is rapid and has good convergence. This method also overcomes the drawbacks about convergence of traditional calculus of variation (COV). It is an effective method for the design of low-thrust, multi-revolution orbit transfer with no prior information switch functions.

View full abstract

How can a prolate satellite spinning about its axis of minimum moment of inertia be attitude-stabilized using dual spin? To this question, we find a simple, clear answer. We replace the satellite with an equivalent frame model and describe its attitude motion as small deviations from its nominal attitude. We show that a friction-like torque applied to the spin axis reduces its nutation motion, and that a similar torque is generated by a nutation damper on a de-spun platform. Thus, we derive a simple attitude-stability theory using minimal mathematical analysis. This theory is applicable to the spin stabilization of geosynchronous communication satellite.

View full abstract

A practical, high-precision method for measuring the mass of an astronaut under microgravity conditions is proposed. Using an instrument called the “Space Scale”, the velocities of a target object and a reference mass are measured with high accuracy by optical interferometry. The two are connected by a linear ball bearing and have separate linear-motion states, with some acceleration due to friction in the linear ball bearing. For this paper, a ground instrument was developed in which linear motion of the whole mechanical system is achieved with negligible external force by means of a pneumatic linear bearing. The effect of linear ball bearing friction that involves the target object and the reference mass is theoretically negligible, as we proved experimentally in this study. We conclude that an operational model for in-orbit use, which takes advantage of an optical interferometer, would be extremely compact and accurate.

View full abstract

The motion of an aircraft controlled by a pilot is decided depending on the characteristics of a man-machine system. Although analysis and investigation are usually performed using a mathematical model of the aircraft including the control system, a method for making a mathematical model of the pilot, which is necessary for the analysis and study of man-machine systems, has not been established. Although a method for constructing a mathematical model of a pilot using a transfer function ¹⁾ has been reported, it is thought that a more accurate and more flexible pilot model may be obtained by applying a neural network (NN). Therefore, various studies have examined a pilot model to which a NN has been applied. As a result, it has been clarified that the application of a NN to a pilot model provides better performance compared to the case of applying a transfer function. Moreover, it has also been clarified that a single versatile pilot model, which can deal with various conditions, can be obtained by applying a NN and studying the control results under various conditions.

View full abstract

This study proposes a design method for cable network structures considering the flexibility of supporting structures. Tensions in cables are designed by the force density method. Subsequently, the designed tensions of the cables are modified to achieve the objective shapes for the cable-network structures using the proposed method, while the supporting structure is deformed. The conventional design method using an iteration technique is also considered. A number of numerical simulations are carried out. The cable network structures are designed using the proposed method, conventional method, and force density method without the modification of the cable tensions, and compared using these numerical simulations. From the comparison, it is observed that the accuracy of the shapes of cable network structures is improved and the standard deviation of the cable tensions is decreased using the proposed and the conventional methods. The results show that the cable network structures can be satisfactorily designed using the proposed method without the need for iterations. Therefore, it can be concluded that the proposed method is efficient.

View full abstract

The effectiveness of a fuzzy-logic control law for automatically landing an aircraft that handles both the control to lead an aircraft from horizontal flight at an altitude of 500 meters to flight along the glide-path course near the runway, as well as the control to direct the aircraft to land smoothly on a runway, was investigated. The control law for the automatic landing was designed to match the design goals of directing an aircraft from horizontal flight to flight along a glide-path course quickly and smoothly, and for landing smoothly on a runway. The design of the control law and evaluation of the control performance were performed considering the ground effect at landing. As a result, it was confirmed that the design goals were achieved. Even if the characteristics of the aircraft change greatly, the proposed control law is able to maintain the control performance. Moreover, it was confirmed to be able to land an aircraft safely during air turbulence. The present paper indicates that fuzzy-logic control is an effective and flexible method when applied to the control law for automatic landing, and the design method of the control law using fuzzy-logic control was obtained.

View full abstract

In this paper, we propose a new configuration for a strap-down, integrated INS/GPS (Inertial Navigation System/Global Positioning System) navigation system. It is aimed at general-purpose use, and utilizes MEMS (microelectromechanical system) sensors and a quaternion-based model that enable the development of a precise system with a degree of portability that traditional INS/GPS devices cannot achieve. In order to examine the effectiveness of our system, we built a prototype instrument and performed an experiment comparing its performance with GAIA, an ultra high-precision INS/GPS device developed by the Japan Aerospace Exploration Agency (JAXA). The results show that our small, light and low-cost system is applicable to general-purpose use, having a position error of only a few meters and under 2 degrees of roll and pitch error, which is sufficiently precise for the general control of moving objects.

View full abstract