Woong-Rae Roh

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.

Design of an Initial Fine Alignment Algorithm for Satellite Launch Vehicles

In this paper, an initial fine alignment algorithm, which is developed for the strap-down inertial navigation systems of satellite launch vehicles, is considered. For fast and accurate alignment, a simple closed-loop estimation algorithm using a proportionalintegral controller is introduced. Through computer simulation for the sway condition in the launch pad, it is shown that a simple filter structure can guarantee fast computational speed that is adequate for real-time implementation as well as the required alignment accuracy and robustness. In addition, its implementation results are presented for the Naro-1 flight test.

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.

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.

Error analysis of the ground based navigation test using extended kalman filtering

This paper considers the error analysis of the ground based navigation test of the strapdown type inertial navigation system. Using an extended Kalman filter, the biases in the inertial sensor are estimated in the static condition of the laboratory environment and the dynamic condition by the test car where another highly accurate instrument is carried to provide target states. The results show that the gyro bias estimates of the filter are within 0.2 deg/hr and the accelerometer biases are within 0.1 mg.

Stage Separation Analysis of Launch Vehicle Using Monte Carlo Simulation

This paper addresses Monte-Carlo simulation analyses for the stage separation of the general launch vehicle. The stage separation event of the launch vehicle occurs during a very short time and is related with many dynamic parameters. The stage separation is a critical event in that the launch fails if there is a collision during the stage separation. The stage separation analyses was conducted for the general launch vehicle to confirm the separation without collision within the designed clearance in case of the random input parameters. This paper presents the stochastic results of the stage separation of the launch vehicle using the Monte-Carlo simulation.

Performance Analysis of a Precise Explicit Guidance Algorithm for Space Launch Vehicles

This paper considers one of the explicit guidance algorithms, which has been proposed by Jaggers, to determine the closed-loop guidance algorithm for upper stages of a 3-staged space launch vehicle. Its commanded thrust vector is closer to the optimal solution when compared with that obtained by using the well-known Powered Explicit Guidance (PEG), which has been developed through the Space Shuttle program. Its performance is evaluated here by applying for guidance of the launcher during the second and third stages. Furthermore, to generate more precise guidance commands, it is attempted not to use the approximate formulas for the derivation of the original guidance law, and it is shown that performance is improved in comparison with the original.

Attitude Controller Design and Test of Korea Space Launch Vehicle-I Upper Stage

This paper introduces the upper stage attitude control system of KSLV-I, which is the first space launch vehicle in Korea. The KSLV-I upper stage attitude control system consists of two electro-hydraulic actuators and a reaction control system using cold nitrogen gas. A proportional, derivative, and integral controller is designed for the electro-hydraulic thrust vectoring system, and Schmidt trigger ON/OFF controllers are designed for the reaction control system. Each attitude controller is designed to have enough stability margins. The stability and performance of KSLV-I upper stage attitude control system is verified via hardware in the loop tests. Hardware in the loop tests are accomplished for perturbed flight conditions as well as nominal flight condition. The test results show that the attitude control loop of KSLV-I upper stage is very stable and the attitude controllers perform well for all flight conditions. Attitude controllers designed in this paper have been successfully applied to the first flight of KSLV-I on August 25, 2009. The flight test results show that all attitude controllers of the KSLV-I upper stage performed well and satisfied the accuracy specifications even during abnormal flight conditions.