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Optimal Control for Proximity Operations and Docking
Daero Lee,Henry Pernicka 한국항공우주학회 2010 International Journal of Aeronautical and Space Sc Vol.11 No.3
This paper proposes optimal control techniques for determining translational and rotational maneuvers that facilitate proximity operations and docking. Two candidate controllers that provide translational motion are compared. A state-dependent Riccati equation controller is formulated from nonlinear relative motion dynamics, and a linear quadratic tracking controller is formulated from linearized relative motion. A linear quadratic Gaussian controller using star trackers to provide quaternion measurements is designed for precision attitude maneuvering. The attitude maneuvers are evaluated for different final axis alignment geometries that depend on the approach distance. A six degrees-of-freedom simulation demonstrates that the controllers successfully perform proximity operations that meet the conditions for docking.
Daero Lee,George Vukovich 제어·로봇·시스템학회 2017 International Journal of Control, Automation, and Vol.15 No.3
This paper presents finite-time stabilization of spacecraft formation flying with a decentralized collisionavoidance in the framework of geometric mechanics. A finite-time control scheme is developed such that eachspacecraft achieves desired relative configuration and velocities with respect to the virtual leader autonomously. The finite-time control scheme is combined with a decentralized collision avoidance scheme. A Lyapunov analysisguarantees that the spacecraft motions converge to the desired state trajectories with the combined control schemein finite time. Numerical simulation results verify the successful application of the proposed combined controlscheme for spacecraft formation flying in the presence of unknown external disturbances while avoiding collisionsvia the decentralized collision avoidance.
Integrated System for Autonomous Proximity Operations and Docking
Daero Lee,Henry Pernicka 한국항공우주학회 2011 International Journal of Aeronautical and Space Sc Vol.12 No.1
An integrated system composed of guidance, navigation and control (GNC) system for autonomous proximity operations and the docking of two spacecraft was developed. The position maneuvers were determined through the integration of the statedependent Riccati equation formulated from nonlinear relative motion dynamics and relative navigation using rendezvous laser vision (Lidar) and a vision sensor system. In the vision sensor system, a switch between sensors was made along the approach phase in order to provide continuously effective navigation. As an extension of the rendezvous laser vision system, an automated terminal guidance scheme based on the Clohessy-Wiltshire state transition matrix was used to formulate a “V-bar hopping approach” reference trajectory. A proximity operations strategy was then adapted from the approach strategy used with the automated transfer vehicle. The attitude maneuvers, determined from a linear quadratic Gaussian-type control including quaternion based attitude estimation using star trackers or a vision sensor system, provided precise attitude control and robustness under uncertainties in the moments of inertia and external disturbances. These functions were then integrated into an autonomous GNC system that can perform proximity operations and meet all conditions for successful docking. A sixdegree of freedom simulation was used to demonstrate the effectiveness of the integrated system.
Robust Unscented Kalman Filter for Nanosat Attitude Estimation
Daero Lee,George Vukovich,Regina Lee 제어·로봇·시스템학회 2017 International Journal of Control, Automation, and Vol.15 No.5
A robust unscented Kalman filter based on a multiplicative quaternion-error approach is proposed fornanosat estimation in the presence of measurement faults. The global attitude parameterization is given by a quaternion,while the local attitude error is defined using a generalized three-dimensional attitude representation. Theproposed algorithm uses a statistical function including measurement residuals to detect measurement faults andthen uses an adaptation scheme based on multiple measurement scale factor for filter robustness against faultymeasurements. The proposed algorithm is demonstrated for the attitude estimation of a nanosat with an on-boardthree-axis magnetometer and rate-integrating gyros in the presence of measurement faults as well as satellite orbiterrors. To compare the estimation performance of the proposed algorithm, the robust unscented Kalman filter withsingle measurement noise scale factor, the standard extended Kalman filter and the unscented Kalman filter are alsoimplemented under the same simulation conditions.
Vision-Based Relative State Estimation Using the Unscented Kalman Filter
Daero Lee,Henry Pernicka 한국항공우주학회 2011 International Journal of Aeronautical and Space Sc Vol.12 No.1
A new approach for spacecraft absolute attitude estimation based on the unscented Kalman filter (UKF) is extended to relative attitude estimation and navigation. This approach for nonlinear systems has faster convergence than the approach based on the standard extended Kalman filter (EKF) even with inaccurate initial conditions in attitude estimation and navigation problems. The filter formulation employs measurements obtained from a vision sensor to provide multiple line(-) of(-) sight vectors from the spacecraft to another spacecraft. The line-of-sight measurements are coupled with gyro measurements and dynamic models in an UKF to determine relative attitude, position and gyro biases. A vector of generalized Rodrigues parameters is used to represent the local error-quaternion between two spacecraft. A multiplicative quaternion-error approach is derived from the local error-quaternion, which guarantees the maintenance of quaternion unit constraint in the filter. The scenario for bounded relative motion is selected to verify this extended application of the UKF. Simulation results show that the UKF is more robust than the EKF under realistic initial attitude and navigation error conditions.
정대로(Daero Jung),허강열(Kang Y. Huh) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Present Study is concerned with simulation of three dimensional, turbulent swirling flow characteristics of a small gas turbine combustor operating on methane/air under non-reacting and reacting conditions. The combustor geometry of a 60 degree sector is modeled with all important details such as air swirler, vane passages and liner holes. The realizable k-e model is employed to reproduce mean reacting and non-reacting turbulent field of the swirl flow. Reacting scalar fields are calculated by fast chemistry assumption with the EBU(Eddy Break-Up) model and PPDF(Presumed Probability Density Function) model for turbulence and chemistry interaction.
Angle-of-Attack Command Longitudinal Control for Supersonic Advanced Trainer Aircraft
Lee Daero,심지수,한광호,김종섭,고기옥 한국항공우주학회 2021 International Journal of Aeronautical and Space Sc Vol.22 No.1
This paper details the design procedure of developing an angle-of attack command longitudinal control system for the relaxed static stability aircraft in power approach mode. An advanced method of relaxed static stability is utilized for improving aerodynamic performance of a supersonic advanced trainer aircraft. The trainer aircraft adopts the relaxed static stability concept to improve the aerodynamic performance and to guarantee the aircraft stability. The longitudinal control law of the aircraft uses the dynamic inversion and proportional-plus-integral control methods. This paper addresses the analysis of the aircraft characteristics such as damping ratio, natural frequency, and gain and phase margins about the state variables for the longitudinal inner loop feedback design. In numerical simulations, the flight control performance of the developed angle-of-attack command longitudinal control system is compared with that of the existing pitch rate command longitudinal control system.