Young-Keun Chang

High-Accuracy Image Centroiding Algorithm for CMOS-Based Digital Sun Sensors

The digital sun sensor calculates the incident sunlight angle using the sunlight image registered on a CMOS image sensor. In order to accomplish this, an exact center of the sunlight image has to be determined. Therefore, an accurate estimate of the centroid is the most important factor in digital sun sensor development. The most general method for determining the centroid is the thresholding method, and this method is also the simplest and easy to implement. Another centering algorithm often used is the image filtering method that utilizes image processing. The sun sensor accuracy using these methods, however, is quite susceptible to noise in the detected sunlight intensity. This is especially true in the thresholding method where the accuracy changes according to the threshold level. In this paper, a template method that uses the sunlight image model to determine the centroid of the sunlight image is suggested, and the performance has been compared and analyzed. The template method suggested, unlike the thresholding and image filtering method, has comparatively higher accuracy. In addition, it has the advantage of having consistent level of accuracy regardless of the noise level, which results in a higher reliability.

Development of the HAUSAT-2 nanosatellite for low-cost technology demonstration

This paper addresses the development and design of the HAUSAT-2 (Hankuk Aviation University SATellite-2) which is nano class ultra-small satellite, being developed by SSRL (Space System Research Lab.) of Hankuk Aviation University. As a spin-off result, the HAUSAT-2 project can offer graduate and undergraduate students great opportunities to be able to understand the satellite design process, analysis, manufacturing, assembly, integration, test, launch and operation and also provides practical experience as a team member. The main mission objectives of the HAUSAT-2 satellite are to study the scope of activities and ecology of animals using Animal Tracking System (ATS) and collect the space information data from Electric Plasma Probe (EPP) as a space science payload. The HAUSAT-2 satellite is being designed to be compatible with a LEO with attitude 650 /spl sim/ 800 km sun synchronous orbit during design mission life which is expected to be 2 years. The HAUSAT-2 is a nano-satellite which is less than 25kg of mass with 30 cm /spl times/ 30 cm /spl times/ 38 cm hexahedron configuration. The three-axis stabilization is being implemented with pitch bias momentum method. Sun sensors and magnetometer manufactured by SSRL will provide attitude.

HAUSAT-2 nanosatellite ADCS performance analysis and commissioning

The HAUSAT-2 is a 25kg class nanosatellite which is being developed by graduate students at the Space System Research Laboratory (SSRL). The HAUSAT-2 implements a pitch bias momentum method for 3-axis stabilization, consisting of one momentum wheel in pitch axis and 3-axis magnetic torquers. 2-axis sun sensors, a 3-axis magnetometer, and a star tracker are used to determine the attitude. This paper describes two primary attitude control modes and control performances to perform the following functions: 1) initial acquisition (initial attitude acquisition mode), 2) 3-axis stabilization (mission mode). In addition to two operation modes, momentum wheel start-up method was also simulated using MATLAB. For detumbling the satellite, the initial mode uses a momentum wheel and magnetic torquers with B-dot control law. The mission mode also uses a momentum wheel and magnetic torquers to maintain 3-axis stabilization. A momentum wheel will have to be started from rest before it is fully operated. If the wheel speed is suddenly increased to nominal wheel RPM, the angular momentum produced can cause instability to satellites body. In this paper, effective wheel start-up method of ultra-small satellite equipped with momentum wheel and magnetic torquers has been studied. Also, a momentum dumping method using magnetic torquers was considered.

DEVELOPMENT OF ULTRA-LIGHT 2-AXES SUN SENSOR FOR SMALL SATELLITE

This paper addresses development of the ultra-light analog sun sensors for small satellite applications. The sun sensor is suitable for attitude determination for small satellite because of its small, light, low-cost, and low power consumption characteristics. The sun sensor is designed, manufactured and characteristic-tested with the target requirements of FOV (Field of View) and pointing accuracy of . Since the sun sensor has nonlinear characteristics between output measurement voltage and incident angle of sunlight, a higher order calibration equation is required for error correction. The error was calculated by using a polynomial calibration equation that was computed by the least square method obtained from the measured voltages vs. angles characteristics. Finally, the accuracies of 1-axis and 2-axes sun sensors, which consist of 2 detectors, are compared.

Development of Mission Analysis and Design Tool for ISR UAV Mission Planning

The optimized flight path planning which is appropriate for UAV operation with high performance and multiplex sensors is required for efficient ISR missions. Furthermore, a mission visualization tool is necessary for the assessment of MoE(Measures of Effectiveness) prior to mission operation and the urgent tactical decision in peace time and wartime. A mission visualization and analysis tool was developed by combining STK and MATLAB, whose tool was used for UAV ISR mission analyses in this study. In this mission analysis tool, obstacle avoidance and FoM(Figure of Merit) analysis algorithms were applied to enable the optimized mission planning.

TRL Impact on Development Schedule and Cost in the Aerospace Project

TRL has a direct impact on development schedule and cost in the system or technology development projects. If TRL capability of development organization for specified CTEs can be accurately assessed and the impact of TRL on development schedule and cost are analyzed as detailed as possible, the risk of development schedule delay and cost increase can be minimized during the development process. This paper describes analysis results of TRL impact on development schedule and cost in the aerospace project. The development schedule and cost change are quantitatively estimated for the TRL improvement in the Unmanned Aerial Vehicle(UAV) system development program.

Development of SEDT(System Engineering Design Tool) for Small Satellite Conceptual Design

SEDT(System Engineering Design Tool) has been developed for small satellite conceptual design with an aim to verifying the nanosatellite HAUSAT-2 design. The program can calculate the mass and power of whole satellite system having specific mission and estimate the system cost based on mission and user requirements. It is containing various analysis data of more than 200 small satellites. The database will provide the trend analysis results of the small satellites which will become important design factors. This tool has also been verified by applying more than 10 small satellite data through case studies.

DEVELOPMENT OF SYSTEM ENGINEERING DESIGN TOOL (SEDT) FOR SMALL SATELLITE CONCEPTUAL DESIGN

Although satellites are getting smaller and the development duration is getting shorter, it still takes a long time to conduct a satellite conceptual design. The System Engineering Design Tool (SEDT) has been developed to effectively and efficiently design small satellites, which are in the range between 10kg (nanosatellite) and 200kg (microsatellite) to minimize the amount of labor involved. The present SEDT consists of five design blocks and has some characteristics different from system engineering tools previously developed. First of all, it adopts top-down design methodology which induces the architecture of distributed design. SEDT has also implemented the subsystem design process which is connected in series. It enables the design order of satellite system based on design parameters of satellite database constructed from over 200 small satellites launched between 1990 and 2004, which can improve the data reliability as a design reference. SEDT incorporates system budgets, mass and power, as verification parameters, and some characteristic trend equations. SEDT can do the conceptual system/subsystem design, analyze the design output, and predict the ROM development cost in accordance with user’s requirements. Specially, the SEDT implements GUI to provide convenience to the users.

Space Simulation Test and Thermal Verification of HAUSAT-2 STM (Structural-Thermal Model) by Using Surface Heaters

This study addresses space simulation test results and thermal modelling verification of HAUSAT-2 nanosatellite STM (Structural-Thermal Model). The thermal modelling of the HAUSAT-2 has been modified in accordance with test results. Thermal analysis results were repeatedly compared with test results for modified thermal modelling. It is verified that the analysis results for modified thermal modelling agree well with test results. Some surface heaters were implemented to simulate solar illumination for HAUSAT-2 Thermal Vacuum/Balance Test. A low-cost and effective thermal test methodology, which is applicable to ultra-small satellite system, was proposed and verified by test results in this study.

HAUSAT-2 SATELLITE RADIATION ENVIRONMENT ANALYSIS AND SOFTWARE RAMMING CODE EDAC IMPLEMENTATION

This paper addresses the results of HAUSAT-2 radiation environment and effect analyses, including TID and SEE analyses. Trapped proton and electron, solar proton, galactic cosmic ray models were considered for HAUSAT-2 TID radiation environment analysis. TID was analyzed through total dose-depth curve and the radiation tolerance of TID for HAUSAT-2 components was verified by using DMBP method and sectoring analysis. HAUSAT-2 LET spectrum for heavy ion and proton were also analyzed for SEE investigation. SEE(SEU, SEL) analyses were accomplished for MPC860T2B microprocessor and K6X8008T2B memory. It was estimated that several SEUs may occur without SEL during the HAUSAT-2 mission life(2 years). Software Hamming Code EDAC has been implemented to detect and correct the SEU. In this study, all radiation analyses were conducted by using SPENVIS software.