Byung-Chan Sun

Coevolutionary augmented Lagrangian methods for constrained optimization

This paper introduces a coevolutionary method developed for solving constrained optimization problems. This algorithm is based on the evolution of two populations with opposite objectives to solve saddle-point problems. The augmented Lagrangian approach is taken to transform a constrained optimization problem to a zero-sum game with the saddle point solution. The populations of the parameter vector and the multiplier vector approximate the zero-sum game by a static matrix game, in which the fitness of individuals is determined according to the security strategy of each population group. Selection, recombination, and mutation are done by using the evolutionary mechanism of conventional evolutionary algorithms such as evolution strategies, evolutionary programming, and genetic algorithms. Four benchmark problems are solved to demonstrate that the proposed coevolutionary method provides consistent solutions with better numerical accuracy than other evolutionary methods.

Missile guidance using neural networks

Abstract This paper introduces a new guidance algorithm using neural networks for bank-to-turn (BTT) missiles. The proposed guidance algorithm compensates for the missile dynamics by using the inverse dynamics learned by neural networks. The new guidance law is applied to a full-order nonlinear BTT missile model, and the performance is compared with that of the proportional navigation guidance law.

Practical Dual-Control Guidance Using Adaptive Intermittent Maneuver Strategy

A new adaptive intermittent maneuver strategy is proposed, which has switching threshold levels dependent on the estimated time-to-go for dual-control guidance of passive homing missiles. Guidance performance in terms of control effort and target observability fortheadaptiveintermittentmaneuver strategy arealso analyzed, as well as proportional navigation guidance. With intermittentmaneuvers the guidance command is occasionally disabled to intentionally increase guidance errors. When provided with suitable switching threshold levels, this intermittent maneuver strategy improvestarget observability and, consequently, intercept performance. Statistical simulations for an atmospheric engagement demonstrate the effectiveness of the proposed intermittent maneuver strategy.

Sloshing analysis using ground experimental apparatus

The natural frequencies and damping ratio of the liquid in cylindrical tank and cylindrical tank with spherical bottom are studied. The experimental frequencies and damping ratio are in good agreement with the results of the theoretical calculations for various liquid depths. Furthermore, this result will be applied to predict the sloshing parameters for a liquid propellant stage of KSLV-II using ground experimental apparatus.

Payload fairing separation analysis using constraint force equation

The dynamics associated with the jettisoning of the payload fairings from the parent launch vehicle is investigated. The separation dynamics of the fairings is derived using the constraint force equation (CFE) methodology. The analysis considers a spring and a hinge type separation system employed to jettison the fairings from the accelerating on-going stage. This study presents the results of determining the minimum permissible relative velocity of separation of the fairing and the spring force magnitude required for the separation velocity. The simulation results of the payload fairing separation dynamics are in good agreement with the results of the industry standard benchmark code. Furthermore, this result will be applied to design the parameter of the payload fairing separation system of Korea space launch vehicle (KSLV)-II.

Robust control design for spinning rocket

This paper deals with an attitude control sys tem design technique of a spinning sounding rocket. A gain-scheduled PID type controller is developed for a dynamic model simplified by complex summa tion method which identifies the cross coupling with imaginary coefficients in the derived model. The op timal PID gains at each design points are automat ically obtained by using the evolutionary program ming(EP) technique which easily formulates several performance specifications and constraints required for the rocket. The performance index optimized in this paper includes specifications for gain margin, phase margin, and time delay margin which compen sates for time delay occurring in signal processing. The performance of the control system is verified by using 6 degrees-of-freedom simulation. It is shown that the resulting control system is robust against plant uncertainties and disturbances.

A Study of Attitude Control and Stability Analysis Using D-Decomposition Stability Area Technique for Launch Vehicle

This paper concerns analysis technique on determining of attitude control gain in the low frequency region using stability area. The stability area is defined by the D-Decomposition method, which was designed by Neimark. In this paper, it is introduced D-Decomposition method from reference paper and design attitude control gain of generic launch vehicle during first stage flight phase. For selecting PD control gain, it is considered the system parameter uncertainty about whole first-stage flight phase, represented the stability area boundary on each case. After deciding the PD control gain using stability area method, it is applied to launch vehicle linear model, and checking the stability margin requirement, frequency response characteristics.

Hardware in the loop tests for upper stage control systems of Korean space launch vehicle

This paper concerns the development tests for the upper stage control systems of Korean Space Launch Vehicle. Hardware in the loop tests are accomplished for an engineering model of KSLV-I. The upper stage control system of KSLV-I consists of a navigation and guidance unit in which several inertial sensors and a guidance computer are included, a thrust vector control system which is used for pitch and yaw attitude control during thrusting phase, and a reaction control system which is used for three axis attitude control during coasting phase. The HIL tests of KSLV-I are basically accomplished for a nominal flight condition. Based upon the nominal flight condition, perturbed flight conditions are defined to evaluate the variations in stability and performance of the system. The HIL test equipments including a three axis flight motion simulator and a real time system are setup, and the coordinate systems which are required during the HIL tests are also defined. The typical angular motions of KSLV-I are given through several HIL test results.

Attitude Control Design and Analysis for Thrust Vector Control System of 3-Staged Launch Vehicle

This paper concerns attitude controller design for a 3-staged launch vehicle which has movable nozzle TVC systems for all stages as its control systems. The PD-type control gains are determined by shaping the corresponding closed-loop natural frequencies for the purpose of guaranteeing the required stability margin. Bending filters are also designed to stabilize the bending modes by using parametric optimization method. The designed controllers are verified using six degree of freedom flight simulations in MATLAB.

Development Directions of Succeeding Launch Vehicles of KSLV-II and Outlooks for Technology Advancement

In this paper the development directions of the next generation launch vehicle program following KSLV-II has been discussed, which are to be executed after year 2020 according to the Medium and Long Term Plan for National Space Development. Also, several areas of technology advancement have been identified for the successful development of the LVs. The next generation LV must aim for not only the high performance but also for low cost as well as high reliability in order to compete against global commercial launch service providers. To this end, the next generation LVs program shall capitalize on many anticipated accomplishments of the KSLV-II program such as the 75 ton class LOX/kerosene rocket engine.