Korea Multi-Purpose Satellite-5 (KOMPSAT-5) is the first satellite in Korea that provides 1 m resolution synthetic aperture radar (SAR) images. Precise orbit determination (POD) using a dual-frequency IGOR receiver data is performed to conduct high-resolution SAR images. We suggest orbit determination strategies based on a differential GPS technique. Double-differenced phase observations are sampled every 30 seconds. A dynamic model approach using an estimation of general empirical acceleration every 6 minutes through a batch least-squares estimator is applied. The orbit accuracy is validated using real data from GRACE and KOMPSAT-2 as well as simulated KOMPSAT-5 data. The POD results using GRACE satellite are adjusted through satellite laser ranging data and compared with publicly available reference orbit data. Operational orbit determination satisfies 5 m root sum square (RSS) in one sigma, and POD meets the orbit accuracy requirements of less than 20 cm and 0.003 cm/s RSS in position and velocity, respectively.

An operational orbit determination (OD) and prediction system for the geostationary Communication, Ocean, and Meteorological Satellite (COMS) mission requires accurate satellite positioning knowledge to accomplish image navigation registration on the ground. Ranging and tracking data from a single ground station is used for COMS OD in normal operation. However, the orbital longitude of the COMS is so close to that of satellite tracking sites that geometric singularity affects observability. A method to solve the azimuth bias of a single station in singularity is to periodically apply an estimated azimuth bias using the ranging and tracking data of two stations. Velocity increments of a wheel offloading maneuver which is performed twice a day are fixed by planned values without considering maneuver efficiency during OD. Using only single-station data with the correction of the azimuth bias, OD can achieve three-sigma position accuracy on the order of 1.5 km root-sum-square.

Earth acquisition is to solve when earth can be visible from satellite after Sun acquisition during launch and early operationud period or on-station satellite anomaly. In this paper, the algorithm and test result of the Communication, Oceanud and Meteorological Satellite (COMS) Earth acquisition are presented in case of on-station satellite anomaly status. Theud algorithms for the calculation of Earth-pointing attitude control parameters including those attitude direction vector,ud rotation matrix, and maneuver time and duration are based on COMS configuration (Eurostar 3000 bus). The coordinateud system uses the reference initial frame. The constraint calculating available time-slot to perform the earth acquisitionud considers eclipse, angular separation, solar local time, and infra-red earth sensor blinding conditions. The results of Electronicsud and Telecommunications Research Institute (ETRI) are compared with that of the Astrium software to validate theud implemented ETRI software

The flight dynamics subsystem (FDS) of a geostationary satellite ground control system conducts estimates of the orbital states, keeping within its mission box, and calculating the satellite operational parameters to be uploaded. A new FDS has been designed and implemented by dividing it into core- and bus-dependent modules for a recent Korean geostationary satellite ground control system. The core modules include orbit determination and prediction, event prediction, and station-keeping and relocation (SKR) planning; whereas the bus-dependent modules include fuel accounting, thruster modeling and maneuver reconstructions of SKR, and calculate all of the bus-dependent parameters. In particular, separate designs based on the components of the SKR planning and maneuver reconstruction using thruster modeling allow the system to be reusable and replaceable. We also designed and implemented a conjunction analysis tool and collocation control and monitoring units for multiple-satellite control. A FDS database has been developed and is managed using SQLite, which is freely distributed. The FDS is easy to develop and operate thanks to a novel separation concept introduced for the core-platform and spacecraft bus-dependent modules. It is the same concept used for operation and the graphical user interfaces (GUIs) applicable to the FDS. All of the FDS modules for new geostationary satellites have been validated through function and performance testing, and have proven to work successfully after the launch of satellites.