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Dive into the research topics where Chang-Kyung Ryoo is active.

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Featured researches published by Chang-Kyung Ryoo.


Journal of Guidance Control and Dynamics | 2005

Optimal Guidance Laws with Terminal Impact Angle Constraint

Chang-Kyung Ryoo; Hangju Cho; Min-Jea Tahk

Optimal guidance laws providing the specified impact angle as well as zero terminal miss distance are generalized for arbitrary missile dynamics. The optimal guidance command is represented by a linear combination of the ramp and the step responses of the missile’s lateral acceleration. Optimal guidance laws in the form of the state feedback for the lag-free and the first-order lag system are derived, and their characteristics are investigated. Practical timeto-go calculation methods, which are important for the implementation of the optimal guidance laws, are proposed to consider the path curvature. Nonlinear and adjoint simulations are performed to investigate the performance of the proposed laws.


IEEE Transactions on Control Systems and Technology | 2006

Time-to-go weighted optimal guidance with impact angle constraints

Chang-Kyung Ryoo; Hangju Cho; Min-Jea Tahk

In this paper, the optimal guidance law with terminal constraints of miss distance and impact angle is presented for a constant speed missile against the stationary target. The proposed guidance law is obtained as the solution of a linear quadratic optimal control problem with the energy cost weighted by a power of the time-to-go. Systematic selection of guidance gains and trajectory shaping are possible by adjusting the exponent of the weighting function. A new time-to-go calculation method taking account of the trajectory curve is also proposed for implementation of the proposed law. Nonlinear and adjoint simulations are performed to investigate the performance of the proposed guidance law and time-to-go calculation method.


IEEE Transactions on Aerospace and Electronic Systems | 2002

Recursive time-to-go estimation for homing guidance missiles

Min-Jea Tahk; Chang-Kyung Ryoo; Hangju Cho

This paper addresses the problem of computing accurate time-to-go estimates, which is an important issue in implementing various optimal guidance laws developed for missiles of time-varying velocity. A recursive time-to-go computation method which updates the time-to-go in a noniterative way is presented. The recursive method includes an error compensation feature which explicitly computes the time-to-go error produced by nonzero initial heading errors. The proposed method is simple and straightforward to implement for any missile velocity profiles. Various numerical examples show that the proposed method works effectively for optimal guidance laws as well as proportional navigation and augmented proportional navigation.


Journal of Guidance Control and Dynamics | 2005

Line-of-Sight Guidance Laws for Formation Flight

Min-Jea Tahk; Chang-Su Park; Chang-Kyung Ryoo

Two-dimensional formation guidance laws for formation flight using only line-of-sight angle information are addressed. The main idea is to use the line-of-sight angles to two nearby vehicles to maintain the formation position of the current vehicle. Such a formation guidance law is useful because measurement of the line-of-sight angles does not require data communication between the vehicles. We propose two methods of using the line-of-sight angle information for formation guidance: the angle information is used to control the flight-path angle and the velocity of the formation vehicle. Approach guidance and formation guidance of the two leading vehicles are also proposed. Stability of the proposed formation guidance laws is analyzed by using the Jacobian at the equilibrium point. Multiple-vehicle formation flight is simulated to verify the guidance laws proposed. ORMATION flight of manned aerial vehicles is in general vi- sually coordinated by the pilots. The pilots maneuver their air- crafts to align other aircrafts on specific points inside their cockpit. However, continuing formation flight for an extended period of time is a tiresome job for the pilots. Autonomous formation flight relieves the pilots and is also applicable for a group of unmanned aerial vehicles (UAVs) performing complex missions. Recently, NASA used two F-18s to check the feasibility of autonomous formation flight and the aerodynamic energy benefits. 1 Also a study on tight- formation flight of Lockheed C-5 transport models has shown a reduction in power demand that is directly related to extension in range. 2 To achieve autonomous formation flight, communication is re- quired between the vehicles involved. Depending on the formation control method, some of the vehicles data are broadcast to the en- tire group or they are passed on to the adjacent vehicles only. The simplest case involves transmitting only the leaders position to the followers. 2−4 All the vehicles in formation have an independent navigation system to acquire their own position and velocity infor- mation. In Ref. 5, a wireless communication network approach to formation control is introduced. It uses mobile nodes that require position and velocity data of each vehicle. Data received from other vehicles are first used to update the receivers state of formation. Then the modified data are relayed to other vehicles. This reduces the total bandwidth of communications involved in the formation. For rapid formation maneuvers, the use of the leaders Euler data in addition to position and velocity is proposed for better performance. 6 In Ref. 7, a globally stable automatic formation flight control is de- rived on a formation that requires position, velocity, heading, and leaders input data by the aircrafts. Because most autonomous formation flight methods require an active communication link between the vehicles, damage to the re- ceiver or the transmitter is critical to mission success. Vehicles with defective sensors are commanded to leave the formation and a re- configuration of the formation is required. 8,9 Communication delay also affects the formation. 10 Thus, military missions generally pre- fer low-bandwidth communication and, if possible, radio silence for stealth purposes. Passive detection of another vehicle and main- taining the formation, if possible, would be much preferred to the methods that use two-way data links.


Journal of Guidance Control and Dynamics | 2014

Optimal Impact Angle Control Guidance Law Based on Linearization About Collision Triangle

Hangju Cho; Chang-Kyung Ryoo; Antonios Tsourdos; Brian White

C ONTROL of missile-target-relative geometry is one of the desired features of guidance in many modern applications. A typical example is to impact a ground target in a direction perpendicular to the tangent plane of the terrain with very high precision both in miss distance and impact angle [1]. Various needs for the maximum warhead effectiveness, and sometimes enhancement of survivability of the missile launch vehicle, in naval applications call for guidance laws that can achieve a specified final direction of approach to the target as well [2]. Also, ensuring a small angle of the missile body relative to the target during the whole engagement process is critical in the case of missiles with strapdown seekers [3]. This necessity of control of terminal engagement geometry has been amajor thrust for much of the researchwork in the area of guidance law design with impact angle constraints. In this Note, a novel method of optimal impact angle control guidance law development based on linear quadratic optimal framework [4] against an arbitrary maneuvering target is presented. Throughout the Note, the missile velocity profile is assumed to be arbitrary. The equation of motion of a missile is often written in terms of the angular variables associated with velocity vectors; in this case, the missile acceleration is computed as the angular rate of its velocity vector multiplied by the magnitude of the velocity, which is directly realizable for aerodynamically controlled missiles. The main problem here is the fact that the kinematics is now nonlinear, defying closed-form solutions of many optimal guidance problems of interest. Thus, it has been common practice to linearize the kinematics (e.g., [5]) or approximate by linear equations [6] to come up with a nice linear quadratic optimal guidance problem. A natural question to follow is then how we linearize the kinematics in a right manner. This question, however, has not been addressed adequately in the literature and linearization has been performed in many cases with the usual assumption of small values of angular variables involved. As a result, the guidance laws often yield poor performance when the associated angular variables get larger. Usually, the collision triangle is defined to be the triangle formed by the initial positions of target and missile, and the intercept point at which the missile hits the target when flown by a straight (with zero effort) line. When no specific requirement on final engagement geometry is posed, the linearization about the usual collision triangle works reasonably well (e.g., [7]; also see [8]). If a specific impact angle between the missile and target velocity vectors is required, however, the usual collision triangle no longer serves as zero-effort collision geometry because the missile trajectory may largely deviate from the collision triangle to satisfy the specific impact angle requirement. This is why some papers just assume before linearization that the end game is initiated with a collision triangle satisfying closely the impact angle requirement [9]. No attempt, however, has been made yet to address specific questions such as what collision trianglewe should be looking for and howwe compute and use it for the linear optimal guidance problem formulation. In this Note, we introduce and use, as the basis of linearization, the perfect (or zero effort) collision triangle for the impact angle control problem, which varies depending on the value of the prescribed impact angle, and solve a linear optimal guidance problem.


Journal of The Korean Society for Aeronautical & Space Sciences | 2011

Integrated Guidance and Control Law with Impact Angle Constraint

Joongsup Yun; Woosung Park; Chang-Kyung Ryoo

The concept of the IGC(Integrated Guidance and Control) has been introduced to overcome the performance limit of the SGC(Separated Guidance and Control) loop. A new type of IGC with impact angle constraint has been proposed in this paper. Angle of attack, pitch angle rate, pitch angle and line of sight angle are considered as state variables. A controllability analysis and equilibrium point analysis has been carried out to investigate the control characteristic of proposed IGC. The LQR(Linear Quadratic Regulator) has been adopted for the control law and detailed explanations about the adoption has been provided. The performance comparison between the IGC and the SGC has been carried out. The result of numerical simulations show that the IGC guarantees better guidance performance than the SGC when the agile maneuver is needed for specific guidance geometry.


IEEE Transactions on Aerospace and Electronic Systems | 2010

Energy Optimal Waypoint Guidance Synthesis for Antiship Missiles

Chang-Kyung Ryoo; Hyo-Sang Shin; Min-Jea Tahk

Planar waypoint guidance synthesis methods for antiship missiles (ASMs) using optimal guidance laws are proposed. The energy optimal trajectory optimization problem with waypoint constraints is converted to an unconstrained optimization problem of finding the optimal boundary conditions at waypoints for the guidance laws. An optimal guidance law (OGL) for a 1st-order lag ASM with terminal constraints on the impact angle and lateral acceleration is newly proposed for this purpose. The proposed method produces the energy optimal trajectory with high numerical efficiency. If the ASM is approximated by a lag-free system, optimal boundary conditions become waypoint passing angles which can be simply determined from a set of linear algebraic equations. Since there are no time-consuming numerical optimizations in this approach, the energy optimal trajectory passing through all the waypoints can be generated in real time.


society of instrument and control engineers of japan | 2008

Guidance algorithms for tactical missiles with strapdown seeker

Se-Ah Jang; Chang-Kyung Ryoo; Keeyoung Choi; Min-Jea Tahk

Strapdown seekers have been recently adopted for short-range guided missiles to satisfy the demand for reducing the size and cost of guidance and control units. Since a strapdown seeker measures the look-angle only, rate gyros are additionally required for guidance command calculations. It is, however, well known that this kind of sensor combination inevitably includes a parasite loop which severely degrades the guidance performance. In this paper, we address how to design guidance algorithms to overcome problems due to the parasite loop. The performance of the proposed algorithms is investigated via numerical simulations for short-range tactical missiles.


Journal of Guidance Control and Dynamics | 2014

Missile Guidance Law Estimation Using Modified Interactive Multiple Model Filter

Joongsup Yun; Chang-Kyung Ryoo

This paper presents an interactive multiple-model-based guidance law estimation filter. An antiship missile’s threat index, such as the remaining time of flight and impact angle, can be estimated by using the guidance law estimation filter. The filter bank of the filter was composed of models based on proportional navigation and impact angle control guidance laws. In the guidance law estimation filter, state variables, rather than fixed values of navigation constant or impact angle, are used for estimation. To that end, the modified interactive multiple model, which is a modified version of the conventional interactive multiple model method is presented in this paper. The modified interactive multiple model method minimizes the degradation of estimation performance by systematic approach for different state vectors. The effectiveness of the modified interactive multiple model method and the performance of the guidance law estimation filter are examined through the numerical simulation of various engagemen...


International Journal of Aeronautical and Space Sciences | 2004

Sensor Alignment Calibration for Precision Attitude Determination of Spacecrafts

Il-Hyoung Lee; Chang-Kyung Ryoo; Hyochoong Bang; Min-Jea Tahk; Sang-Ryool Lee

A new alignment calibration method of attitude sensors for the precision attitude determination of a spacecraft based on the extended Kalman filter is proposed. The proposed method is divided into two steps connected in series: the gyro and the star tracker calibration. For gyro calibration, alignment errors and scale factor errors are estimated during the calibration maneuver under the assumption of a perfect star tracker. Estimation of the alignment errors of the star trackers and compensation of the gyro calibration errors are then performed using the measurements including payload information. Performance of the proposed method are demonstrated by numerical simulations.

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Sanghyuk Park

Korea Aerospace University

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Hangju Cho

Agency for Defense Development

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