Adaptive nonlinear guidance law considering control loop dynamics

A new adaptive nonlinear guidance law is proposed here. The fourth order state equation for integrated guidance and control loop is formulated taking into consideration the target uncertainties and control loop dynamics. The state equation is further changed into the normal form by nonlinear coordinate transformation. Using the normal form of state equation, an adaptive nonlinear guidance law is proposed to compensate for the uncertainties in both target acceleration and control loop dynamics. The proposed law adopts the sliding mode control approach with adaptation for unknown bound of uncertainties. The present approach can effectively solve the existing guidance problem against target maneuver and the limited performance of control loop. We have provided the stability analyses and performed simulations comparing favorably our approach to the state of the art.     

Step load response of a current-mode-controlled DC-to-DC converter

This paper analyzes the step load response of a current-mode-controlled pulsewidth modulation (PWM) converter and also presents design guidelines for obtaining a good step load response. Analytical expressions for the step load response are derived in terms of the power stage and feedback compensation parameters. Control design to minimize the overshoot and settling time of the output voltage is presented. Analysis results are verified by large-signal simulations.     

Adaptive control for feedback-linearized missiles withuncertainties

A robust adaptive control scheme is proposed that can be applied to a practical autopilot design for feedback-linearized skid-to-turn (STT) missiles with aerodynamic uncertainties. The approach is to add a robust adaptive controller to a feedback-linearizing controller in order to reduce the influence of the aerodynamic uncertainties. The proposed robust adaptive control scheme is based on a sliding mode control technique with an adaptive law for estimating the unknown upper bounds of uncertain parameters. A feature of the proposed scheme is that missile systems with aerodynamic uncertainties can be controlled effectively over a wide operating range of flight conditions. It is shown, using Lyapunov stability theory, that the proposed scheme can give sufficient tracking capability and stability for a feedback-linearized STT missile with aerodynamic uncertainties. The six-degree-of-freedom nonlinear simulation results also show that good performance for several uncertainty models and engagement scenarios can be achieved by the proposed scheme in practical night conditions     

Linear time-varying eigenstructure assignment with flight control application

This work is concerned with the assignment of a desired PD-eigenstructure for linear time-varying systems. Despite its well-known limitations, gain scheduling control appeared to be a focus of the research efforts. Scheduling of frozen-time, frozen-state controllers for fast time-varying dynamics is known to be mathematically fallacious, and practically hazardous. Therefore, recent research efforts are being directed towards applying time-varying controllers. In this paper we: 1) introduce a differential algebraic eigenvalue theory for linear time-varying systems; and 2) propose a PD-eigenstructure assignment scheme via a differential Sylvester equation and a command generator tracker (CGT) for linear time-varying systems. The PD-eigenstructure assignment is utilized as a regulator. A feedforward gain for tracking control is computed by using the command generator tracker. The whole design procedures of the proposed PD-eigenstructure assignment scheme are systematic in nature. The scheme could be used to determine the stability of linear time-varying systems easily as well as to provide a new horizon of designing controllers for the linear time-varying systems. A missile flight control application is presented to validate the proposed schemes.     

Aerodynamic design optimization of helicopter rotor blades including airfoil shape for hover performance

This study proposes a process to obtain an optimal helicopter rotor blade shape for aerodynamic performance in hover flight. A new geometry representation algorithm which uses the class function/shape function transformation (CST) is employed to generate airfoil coordinates. With this approach, airfoil shape is considered in terms of design variables. The optimization process is constructed by integrating several programs developed by author. The design variables include twist, taper ratio, point of taper initiation, blade root chord, and coefficients of the airfoil distribution function. Aerodynamic constraints consist of limits on power available in hover and forward flight. The trim condition must be attainable. This paper considers rotor blade configuration for the hover flight condition only, so that the required power in hover is chosen as the objective function of the optimization problem. Sensitivity analysis of each design variable shows that airfoil shape has an important role in rotor performance. The optimum rotor blade reduces the required hover power by 7.4% and increases the figure of merit by 6.5%, which is a good improvement for rotor blade design.     

An introduction to the lunar and planetary science activities in Korea

Korea is planning a series of lunar space programs in 2020 starting with a lunar orbiter and a lander with a rover. Compared to other countries, Korea has a relatively brief history in space and planetary sciences. With the expected Korean missions on the near-term horizon and the relatively few Korean planetary scientists, Korea Institute of Geoscience and Mineral Resources (KIGAM) has established a new planetary research group focusing on development of prospective lunar instruments, analysis of the publicly available planetary data of the Moon, organizing nationwide planetary workshops, and initiating planetary educational programs with academic institutions. Korea has also initiated its own rocket development program, which could acquire a rocket-launch capability toward the Korean lunar mission. For the prospective Korea’s lunar science program, feasibility studies for some candidate science payloads have been started since 2010 for an orbiter and a lander. The concept design of each candidate instrument has been accomplished in 2012. It is expected that the development of science payloads may start by 2014 as Phase A. Not only developing hardware required for the lunar mission but also educational activities for young students are high priorities for Korea. The new plan of the Korean lunar mission can be successfully accomplished with international cooperative outreach programs in conjunction with internationally accessible planetary data system (PDS). This paper introduces the KIGAM’s international cooperative planetary research and educational programs and also summarizes other nationwide new developments for Korean lunar research projects at Kyung Hee University and Hanyang University.     

Generation of satellite tracking profile: Problems and validation algorithms

Recently, as a satellite mission becomes complicated, it has been required to generate the schedule of satellite antenna movements automatically without relying upon operator’s ad hoc knowledge. To generate the satellite antenna schedule autonomously, this paper first addresses geometrical problems associated with the antenna scheduling and mission planning problems that can be formulated from satellite navigation and antenna orientation information. Then, based on the solutions of the geometrical problems, a set of antenna azimuth and elevation angles that enables the antenna to point towards the desired ground station is obtained systematically. Using the computed azimuth and elevation angles, the satellite tracking profile (TP) is generated, and to validate it, TP validation algorithms are developed.     

Precise orbit determination using the batch filter based on particle filtering with genetic resampling approach

In this study, genetic resampling (GRS) approach is utilized for precise orbit determination (POD) using the batch filter based on particle filtering (PF). Two genetic operations, which are arithmetic crossover and residual mutation, are used for GRS of the batch filter based on PF (PF batch filter). For POD, Laser-ranging Precise Orbit Determination System (LPODS) and satellite laser ranging (SLR) observations of the CHAMP satellite are used. Monte Carlo trials for POD are performed by one hundred times. The characteristics of the POD results by PF batch filter with GRS are compared with those of a PF batch filter with minimum residual resampling (MRRS). The post-fit residual, 3D error by external orbit comparison, and POD repeatability are analyzed for orbit quality assessments. The POD results are externally checked by NASA JPL’s orbits using totally different software, measurements, and techniques. For post-fit residuals and 3D errors, both MRRS and GRS give accurate estimation results whose mean root mean square (RMS) values are at a level of 5 cm and 10–13 cm, respectively. The mean radial orbit errors of both methods are at a level of 5 cm. For POD repeatability represented as the standard deviations of post-fit residuals and 3D errors by repetitive PODs, however, GRS yields 25% and 13% more robust estimation results than MRRS for post-fit residual and 3D error, respectively. This study shows that PF batch filter with GRS approach using genetic operations is superior to PF batch filter with MRRS in terms of robustness in POD with SLR observations.     

A new approach to the telescope operation method for satellite tracking using a time synchronization technique

For the development of a telescope that is capable of precisely tracking satellites and high-speed operation such as satellite laser ranging, a special method of telescope operation is required. This study aims to propose a new telescope operation method and system configuration for the independent development of a mount and an operation system which includes the host computer. Considering that the tracking of a satellite is performed in real time, communication and synchronization between the two independent subsystems are important. Therefore, this study applied the concept of time synchronization, which is used in various fields of industry, to the communication between the command computer and the mount. In this case, communication delays do not need to be considered in general, and it is possible to cope with data loss. Above all, when the mount is replaced in the future, only the general communication interface needs to be modified, and thus, it is not limited by replacement in terms of the overall system management. The performance of the telescope operation method developed in this study was verified by applying the method to the first mobile SLR system in Korea. This study is significant in that it proposed a new operation method and system configuration, to which the concept of time synchronization was applied, for the observation system that requires an optical telescope.