Jinyoung Suk

Collision Avoidance Maneuver Planning Using GA for LEO and GEO Satellite Maintained in Keeping Area

In this paper, a collision avoidance maneuver was sought for low Earth orbit (LEO) and geostationary Earth orbit (GEO) satellites maintained in a keeping area. A genetic algorithm was used to obtain both the maneuver start time and the delta-V to reduce the probability of collision with uncontrolled space objects or debris. Numerical simulations demonstrated the feasibility of the proposed algorithm for both LEO satellites and GEO satellites.

A Modified Nonlinear Guidance Logic for a Leader-Follower Formation Flight of Two UAVs

This paper presents a guidance algorithm for formation flight of two UAVs. Since the nonlinear guidance algorithm have good properties to follow nonlinear flight trajectory based on geometric and kinematic, the nonlinear guidance algorithm is modified as a leader-follower station keeping formation control law for two UAVs using the relation of the nonlinear guidance algorithm to the proportional navigation. The proposed guidance algorithm provides a good performance and relatively simple control logic. The performance of the proposed guidance algorithm is tested via semi-flight test environment that is composed of near-real-time simulation for the leader and real flight for the follower.

A Glidepath Tracking Algorithm for Autolanding of a UAV

In this paper, a glidepath tracking algorithm of a UAV was proposed and the performance was analyzed. The glidepath tracking strategy was implemented using precision longitudinal flight control law. A performance output- based design method was proposed for smooth transition to the new state minimizing saturation of the control effectors. By comparison with several LQ servo design methods such as Brysons general rule and frequency domain matching method, the suggested design shows fast and smooth responses through numerical simulation. Furthermore, the performance of the strategy was investigated through the touch down point(TDP) error analysis with regard to atmospheric disturbance. It was verified that the proposed glidepath tracking strategy can be successfully applied to the practical autolanding of UAV systems.

System identification and stability evaluation of an unmanned aerial vehicle from automated flight tests

This paper presents a consequence of the systematic approach to identify the aerodynamic parameters of an unmanned aerial vehicle (UAV) equipped with the automatic flight control system. A 3-2-1-1 excitation is applied for the longitudinal mode while a multi-step input is applied for lateral/directional excitation. Optimal time step for excitation is sought to provide the broad input bandwidth. A fully automated programmed flight test method provides highquality flight data for system identification using the flight control computer with longitudinal and lateral/directional autopilots, which enable the separation of each motion during the flight test. The accuracy of the longitudinal system identification is improved by an additional use of the closed-loop flight test data. A constrained optimization scheme is applied to estimate the aerodynamic coefficients that best describe the time response of the vehicle. An appropriate weighting function is introduced to balance the flight modes. As a result, concurrent system models are obtained for a wide envelope of both longitudinal and lateral/directional flight maneuvers while maintaining the physical meanings of each parameter.

Development of near-real-time simulation environment for multiple UAVs

This paper describes development of a simulation environment for multiple UAVs. The simulation environment consists of several PCs, each of them represents simulated motion of individual UAV and a host PC that controls and monitors the whole UAVs. UAVs can fly individually or sometimes they can cooperate to fly in formation following the leader. Each UAV has inherent stabilization capability and autopilot, while the leader UAV can monitor the motion of other UAVs and perform group coordination. Flight information of one UAV can be transferred to the other UAVs via UDP communication. Several simulation flight sorties were performed from individual flight to formation flight in order to demonstrate the multi-vehicle simulation environment.

GPS Output Signal Processing considering both Correlated/White Measurement Noise for Optimal Navigation Filtering

In this paper, a dynamic modeling for the velocity and position information of a single frequency stand-alone GPS(Global Positioning System) receiver is described. In static condition, the position error dynamic model is identified as a first/second order transfer function, and the velocity error model is identified as a band-limited Gaussian white noise via non-parametric method of a PSD(Power Spectrum Density) estimation in continuous time domain. A Kalman filter is proposed considering both correlated/white measurements noise based on identified GPS error model. The performance of the proposed Kalman filtering method is verified via numerical simulation.

Guidance and Control System Design for Automatic Carrier Landing of a UAV

This paper presents the guidance and control design for automatic carrier landing of a UAV (Unmanned Aerial Vehicle). Differently from automatic landing on a runway on the ground, the motion of a carrier deck is not fixed and affected by external factors such as ship movement and sea state. For this reason, robust guidance/control law is required for safe shipboard landing by taking the relative geometry between the UAV and the carrier deck into account. In this work, linear quadratic optimal controller and longitudinal/lateral trajectory tracking guidance algorithm are developed based on a linear UAV model. The feasibility of the proposed control scheme and guidance law for the carrier landing are verified via numerical simulations using X-Plane and Matlab/simulink.

Flight test of a Flying-Wing Type UAV with Partial Wing Loss Using Neural Network Controller

This paper presents flight test result of flying-wing type UAV with partial wing loss using neural network controller. 22% and 33% loss of wing area moment were considered for the damage configuration. A new trim state was obtained for each damaged model with the variation of mass, center of gravity and moment of inertia. A numerical simulation was performed to investigate the changed flight dynamics. It is verified that the damaged UAV shows sluggish roll behavior with unstable longitudinal response. A neural network based adaptive controller combined with feedback linearization was designed in order to compensate for the partial damage. It is verified that the instability caused by partial wing damage can be effectively controlled, and the overall system can be stabilized via neural network controller.

A Design of Dual Frequency Bands Time Synchronization System for Synchronized-Pseudolite Navigation System

Time synchronization system using dual frequency bands is designed and the error sources are analyzed for alternative synchronized-pseudolite navigation system (S-PNS) which aims at military application. To resolve near/far problem, dual frequency band operation is proposed instead of pulsing transmission which degrades level of reception. In dual frequency operation H/W delay should be considered to eliminate errors caused by inter-frequency bias (IFB) difference between the receivers of the pseudolites and users. When time synchronization is performed across the sea, multipath error is occurred severely since the elevation angle between pseudolites is low so total reflection can be happened. To investigate the difference of multipath effects according to location, pseudolites are set up coastal area and land area and performances are compared. The error source related with tropospheric delay is becoming dominant source as the coverage of the PNS is broadening. The tropospheric delay is measured by master pseudolite receiver directly using own pseudorange and slave pseudorange. Flight test is performed near coastal area using S-PNS equipped with developed time synchronization system and test results are also presented.

Control System Design for a Ducted-Fan Unmanned Aerial Vehicle Using Linear Quadratic Tracker

Tracking control system based on linear quadratic (LQ) tracker is designed for a ducted-fan unmanned aerial vehicle (UAV) under full flight envelope including hover, transition, and cruise modes. To design the LQ tracker, a system matrix is augmented with a tracking error term. Then the control input can be calculated to solve a single Riccati equation, but the steady-state errors might still remain in this control system. In order to reduce the steady-state errors, a linear quadratic tracker with integrator (LQTI) is designed to add an integral term of tracking state in the state vector. Then the performance of the proposed controller is verified through waypoint navigation simulation under wind disturbance.