Yoola Hwang

Communication, Ocean, and Meteorological Satellite Orbit Determination Analysis Considering Maneuver Scheme

Orbit determination (OD) analysis for geostationary Communications, Ocean, and Meteorological Satellite (COMS) is presented. Since the orbital longitude of COMS is close to that of satellite tracking site, geometric singularity affects observability. For OD, we fix velocity increment by the wheel off-loading maneuver, and the azimuth angle tracking bias is not estimated because of observability problem. Final epoch of the propagated OD based on different data arc length is used for two-day orbit prediction. The difference between truth and 48-hour predicted orbit that contains the OD error shows 4-18 km Root-Sum-Squares (RSS) in 3-D sense (one sigma) in spite of the singularity problem. Thus an operational Orbit Determination and prediction (ODP) system for COMS fulfills the requirement for 18 km RSS (one sigma) predicted positioning knowledge.

GEO Satellite Collision Avoidance Maneuver Strategy Against Inclined GSO Satellite

Orbit maneuver strategy for Geostationary Earth orbit (GEO) satellite is investigated to keep away from inclined geosynchronous orbit (GSO) satellite. Characteristics of inclined GSO with various combinations of eccentricity and argument of perigee are examined first. Then the close approach of inclined GSO SL-12 rocket body to GEO COMS satellite is inspected to develop a maneuver strategy for collision avoidance. Several sizes of deltavelocities are applied to the GEO satellite to check the effect of the maneuvers on separation. It is found that radial separation between the two satellites is the most important factor and the greatest separation can be achieved when the collision avoidance maneuver is executed at 12 hours before the time of closest approach.

Precise Orbit Determination of LEO Satellite Using Dual-Frequency GPS Data

다목적실용위성-5호는 2010년 발사를 목표로 고도 550km의 저궤도에 위치하게 될 것이다. 다목적실용위성-5호의 임무인 고정밀 SAR(Synthetic Aperture Radar) 영상을 처리하기 위해서는 정확한 위성의 위치(20cm) 와 속도(0.03cm/s)가 결정되어야 한다. 이러한 요구 조건은 한국 전자통신연구원에서 개발한 ETRI GNSS Precise Orbit Determination(EGPOD) 소프트웨어로 검증하였다. 0.1Hz 수신 주기의 SAC-C 위성 반송파위상 데이터로 정밀궤도결정을 수행하였다. 이중 주파수 GPS 데이터를 사용하여 수신 선호의 전리층 오차를 대부분 제거하고 이중 차분된 데이터를 생성함으로써 GPS 위성과 수신기의 공통된 시계 오차를 없앴다. 동역학 모델 접근 방법을 이용하였고, Batch Least Square Estimator(BLSE) 필터로 각 데이터 아크(arc) 에 해당하는 위성의 위치와 속도, 대기저항 계수, 태양풍 계수를 추정하였다. 또한 정밀한 동역학 모델을 위하여 모델 되지 않은 부정확한 가속도 항을 보충하는 경험 가속도를 추가하였다. 경험 가속도는 위성의 공전 주기(revolution) 당 한번씩 시선방향(radial), 진행방향(along-track), 수직방향(cross-track)으로 추정하고, 수직방향의 상수 항에 대해서는 해당 데이터 아크에 관하여 부가적으로 추정하였다. 정밀궤도결정 결과 검증을 위하여 EGPOD 소프트웨어에서 얻어진 결과와 JPL에서 제공하는 정밀궤도력(Precise Orbit Ephemeris)을 비교하였다. 【KOorea Multi-purpose SATellite(KOMPSAT)-5 will be launched at 550km altitude in 2010. Accurate satellite position(20 cm) and velocity(0.03 cm/s) are required to treat highly precise Synthetic Aperture Radar(SAR) image processing. Ionosphere delay was eliminated using dual frequency GPS data and double differenced GPS measurement removed common clock errors of both GPS satellites and receiver. SAC-C carrier phase data with 0.1 Hz sampling rate was used to achieve precise orbit determination(POD) with ETRI GNSS Precise Orbit Determination(EGPOD) software, which was developed by ETRI. Dynamic model approach was used and satellites position, velocity, and the coefficients of solar radiation pressure and drag were adjusted once per arc using Batch Least Square Estimator(BLSE) filter. Empirical accelerations for sinusoidal radial, along-track, and cross track terms were also estimated once per revolution for unmodeled dynamics. Additionally piece-wise constant acceleration for cross-track direction was estimated once per arc. The performance of POD was validated by comparing with JPLs Precise Orbit Ephemeris(POE).】

KOMPSAT-2 Precise Orbit Determination Using GPS Data

A Precise Orbit Determination (POD) has been developed for Korea multipurpose satellite-2 (KOMPSAT-2) to fulfill the requirement for 1 m positioning accuracy. The POD is resolved using single-frequency Global Positioning System (GPS) data in a dynamic filter. To compensate for the ionospheric delay by single-frequency GPS receiver, we use following techniques such as the group and phase ionosphere calibration (GRAPHIC) and scale factor estimate for international reference ionosphere-2000 (IRI-2000). Also, time drifting error of GPS receiver is estimated during the data preprocessing. The POD produced 4-hour overlapping arc position error approximately 1 m Root-Sum-Square (RMS) for 30-hour data arc, which satisfies the design requirement for KOMSAT-2. The implemented method and achieved results for the KOMPSAT-2 POD are presented. Nomenclature N = integer ambiguity 1 P = pseudorange observable on GPS L1 frequency 1 Φ = carrier phase range observable on GPS L1 frequency 0 ,t t k = tagging time of measurement for arbitrary epoch, k and minimum range epoch, 0 during the phase lock, respectively, sec ion ρ Δ = ionospheric range delay, m S R ρ = geometric range from GPS satellite transmitter to the LEO satellite receiver antenna, m ph gr e e , = measurement error for group delay and pseudorange except ionosphere error, respectively α = scale factor

Implementation and Validation of Earth Acquisition Algorithm for Communication, Ocean and Meteorological Satellite

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

Automated Communication, Ocean, and Meteorological Satellite Operational Orbit System

This paper presents automated geostationary satellite operational orbit function for the operational orbit prediction and orbit determination using Batch type filter and Extended Kalman filter. The Extended Kalman filter is autonomously accomplished for near real-time orbit determination process to relieve operator’s load since ranging and angle-tracking data are transmitted to the Flight Dynamics Subsystem (FDS) every hour. The post-time orbit determination uses Batch type filter with more than two-day data arc length collected every hour. The orbit prediction and post-time orbit determination are performed only if operator types the start and end time as an input by Graphical User Interface (GUI) with default dynamic and estimation parameter options. We design the automated operational orbit system based on the object-oriented design using Agora Plastic® tool. The results of the propagated orbit determination for two-day simulated antenna data with 0.025-degree noise and 0.02-degree constant bias show roughly 10 km (one-sigma) Root-Sum-Squares (RSS) error using Earth gravitational model, luni-solar perturbation, and solar radiation pressure dynamic models when compared to the truth orbit in spite that COMS locates near longitude of ground station.

KOMPSAT-2 Orbit Determination Status Report

Korea-MultiPurpose-SATellite-2 (KOMPSAT-2) has been successfully operated by Mission Control Element (MCE) since the launch of July 28, 2006. The spacecraft was built by Korea Aerospace Research Institute (KARI) and the MCE system was developed by Electronics and Telecommunications Research Institute (ETRI). This paper presents status of the operational and precise KOMPSAT-2 Orbit Determination (OD) in Mission Analysis and Planning System (MAPS), one of MCE subsystems. The KOMPSAT-2 is the first satellite to perform Precise Orbit Determination (POD) using single frequency GPS data to process high resolution image data obtained from Low Earth Orbiter (LEO) satellite in Korea. Operational Orbit Determination (OOD) using GPS navigation solution data should satisfy 10 m Root-Sum-Square (RSS) in one sigma and Precise Orbit Determination (POD) is required to fulfill 1 m RSS in one sigma. In order to demonstrate the accuracy of the KOMPSAT-2 OD, OOD was compared with POD and POD was tested using orbit overlapping solution. The orbit accuracy of OOD and POD results met the given requirement, within 5-6 m RSS to the reference data and 60-75 cm RSS in orbit overlapping solution, respectively.

Automation of the flight dynamics operations for low Earth orbit satellite mission control

Automation of the key flight dynamics operations for the low Earth orbit satellite mission control is designed and implemented. The automation includes coordinate transformation, tracking data formatting, orbit determination, and orbit prediction. An object-oriented design methodology is used for design of the automation system. Graphical user interface is implemented using Trolltech QT. The automation is applied to the KOMPSAT-2 flight dynamics system for daily routine operations.

Design of the Flight Dynamics Subsystem for the COMS Satellite Ground Control System

A multi-mission geostationary Earth orbit satellite, Communications, Ocean, and Meteorological Satellite (COMS) has three payloads including Ka-band communications, geostationary ocean sensing imager, and meteorological imager. COMS Satellite Ground Control System (SGCS) is the only system for monitor and control of the satellite in orbit. In order to fulfill the mission operations of the three payloads and spacecraft bus, COMS SGCS performs telemetry reception and processing, satellite tracking and ranging command generation and transmission, satellite mission planning, flight dynamics operations, and satellite simulation. Flight dynamics function is one of most important functions in SGCS. Flight Dynamics Subsystem (FDS) operations include spacecraft orbit determination, orbit prediction, event prediction, fuel accounting, station-keeping maneuver planning, and station-relocation maneuver planning. FDS also provides COMS specific operation related functions such as wheel off-loading, oscillator updating parameter calculation, sensor interference management, and Earth acquisition parameter calculation after emergency Sun reacquisition. All of the orbit dynamics functions in FDS consider twice a day thruster based wheel off-loading operations affecting the COMS orbit. In this paper, detailed design of the FDS in COMS SGCS is presented. An object oriented analysis and design methodology is applied.

Validation of GPS Based Precise Orbits Using SLR Observations

In this study, the YLPODS (Yonsei Laser-ranging Precision Orbit Determination System) is developed for POD using SLR (Satellite Laser Ranging) NP (Normal Point) observations. The performance of YLPODS is tested using SLR NP observations of TOPEX/POSEIDON and CHAMP satellite. JPL`s POE (Precision Orbit Ephemeris) is assumed to be true orbit, the measurement residual RMS (Root Mean Square) and the orbit accuracy (radial, along-track, cross-track) are investigated. The validation of POD using GPS (Global Positioning System) raw data is achieved by YLPODS performance and highly accurate SLR NP observations. YGPODS (Yonsei GPS-based Precision Orbit Determination System) is used for generating GPS based precise orbits for TOPEX/POSEIDON. The initial orbit for YLPODS is derived from the YGPODS results. To validate the YGPODS results the range residual of the first adjustment of YLPODS is investigated. The YLPODS results using SLR NP observations of TOPEX/POSEIDON and CHAMP satellite show that the range residual is less than 10 cm and the orbit accuracy is about 1 m level. The validation results of the YGPODS orbits using SLR NP observations of the TOPEX/POSEIDON satellite show that the range residual is less than 10 cm. This result predicts that the accuracy of this GPS based orbits is about 1m level and it is compared with JPL`s POE. Thus this result presents that the YLPODS can be used for POD validation using SLR NP observations such as STSAT-2 and KOMPSAT-5.