Sang-Ryool Lee

Overview of KOMPSAT-5 program, mission, and system

Korea Aerospace Research Institute (KARI) are developing the KOMPSAT-5 system of which primary payload is X band Synthetic Aperture Radar (SAR). The program overview, mission and system characteristics of KOMPSAT-5 are described in this paper.

Sensor Alignment Calibration for Precision Attitude Determination of Spacecrafts

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.

Very Small Satellite Program for Expending the Space Technology Base: CanSat Competition

This paper presented the CanSat competition as one of very small satellite programs for expending the space technology base. The CanSat was compared and characterized with a real satellite and the foreign CanSat competition cases and domestic CanSat development trends were summarized. On the basis of the above information, the organizational structure and function were suggested for domestic CanSat competition and the required technologies, such as satellite, launcher and ground station were described. And also, the prior plan for competition, including mission, education and schedule were suggested.

Conceptual Design of Korea Aerospace Research Institute Lunar Explorer Dynamic Simulator

In lunar explorer development program, computer simulator is necessary to provide virtual environments that vehicle confronts in lunar transfer, orbit, and landing missions, and to analyze dynamic behavior of the spacecraft under these environments. Objective of simulation differs depending on its application in spacecraft development cycle. Scope of use cases considered in this paper includes simulation of software based, processor and/or hardware in the loop, and support of ground-based flight test of developed vehicle. These use cases represent early phase in development cycle but reusability of modeling results in the next design phase is considered in defining requirements. A simulator architec - ture in which simulator platform is located in the middle and modules for modeling, analyzing, and three dimensional visualizing are connected to that platform is suggested. Baseline concepts and requirements for simulator development are described. Result of trade study for selecting simulation platform and approaches of defining other simulator com - ponents are summarized. Finally, characters of lunar elevation map data which is necessary for lunar terrain generation is described.

The Failure Analysis of Paralleled Solar Array Regulator for Satellite Power System in Low Earth Orbit

Therefore, it is necessary to develop an accurate model for the main components of a power system and, based on that, to develop an accurate model for the entire power system. Through the power system modeling, the overall effect of failure on the main components of the power system can be considered and the protective design can be devised against the failure. In this study, to analyze the failure mode of the power system and the effects of the failure on the power system, we carried out modeling of the main power system components including the solar array regulator, and constituted the entire power system based on the modeling. Additionally, we investigated the effects of representative failures in the solar array regulator on the power system using the power system model.

Energy Balance and Power Performance Analysis for Satellite in Low Earth Orbit

E-mail: ssjang@kari.re.krTel: +82-42-860-2389 Fax: +82-42-860-2007This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://cre-ativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Adaptive backstepping radial basis function neural network controller design for a Mars lander during the powered descent phase

When a Mars lander is guided to follow a predetermined reference trajectory during the powered descent phase, large tracking errors occur due to strong perturbations caused by enormous external disturbances, such as the Martian atmosphere and wind and dust storms, as well as considerable uncertainties. The tracking performance is determined directly by the accuracy of the system model, especially with regard to nonlinear terms. In this paper, an adaptive backstepping radial basis function neural network controller is developed for a Mars lander to achieve precise tracking to a reference trajectory during the powered descent phase. The main part of the controller is designed with backstepping, and a radial basis function neural network with an online adaptive law for the weight vector is used as an auxiliary part to approximate unknown nonlinear functions, including the gravitational force, Coriolis force, centrifugal force, atmospheric drag force, atmospheric lift force, wind force, and unknown uncertainties. The proposed adaptive backstepping radial basis function neural network controller guarantees that tracking errors and radial basis sunction neural network weight estimation errors eventually converge to the uniformly ultimately bounded values according to the Lyapunov stability theory. Additionally, this study presents an online adaptive law for the weight vector. The simulation results show that the adaptive backstepping radial basis function neural network controller has an excellent tracking performance in the severe environmental conditions of Mars with strong external disturbances and large variations in uncertainties. Furthermore, this study reveals that the radial basis function neural network has an outstanding capability to approximate unknown nonlinear functions.

Low-speed friction compensation of reaction wheels using command shaping

The friction discontinuity at low-speed of reaction wheel causes an undesirable impulsive jerk disturbance in spacecraft control system. In order to compensate the disturbance of static friction discontinuity, this paper proposes a simple and effective friction compensation method applying a command shaping technique to the wheel command torque. A simulation of the three-axis spacecraft attitude control system with reaction wheel is performed and the usefulness of the proposed command shaping to deal with the nonlinearity of the reaction wheel is demonstrated. The friction compensation method suppresses an undesirable impulsive jerk disturbance from the static friction discontinuity in reaction wheel and minimizes control error in attitude control system of spacecraft.

Analysis of Delta-V of Earth-Moon Transfer Trajectories for Minimization of Fuel Consumption

After lunar explorations were restarted in 1990s, the world space advanced countries have been competing actively to preoccupy the Moon from the 2000s. Korea has been also conducting precedent study on lunar exploration to carry out that by ourselves in 2020. This study analyzed delta-V of various Earth-Moon transfer trajectories for minimization of fuel consumption. Through the simulation, the best Earth-Moon transfer trajectory for Korean lunar mission is suggested and it will be used as useful materials of Korean lunar mission.