Hae-Yeon Kim

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.

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

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.

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.

ANALYSIS OF COMS-1 NORTH-SOUTH STATION KEEPING METHOD

The perturbations caused by the Sun and the Moon are predominantly out-of-plane effects causing a change in the inclination and in the right ascension of ascending node of a geostationary satellite. Due to the change of the inclination, subsatellite latitude of the geostationary satellite has a daily variations of the same magnitude of the inclination. Therefore we need a facility to control the orbital inclination and right ascension of ascending node for maintaining the satellite position in specified subsatellite latitude boundary using thrusters. In this paper we studied North-South station keeping strategies of the COMS-1 such as Track-Back Chord Target (TBCT) method, Maximum Compensation Target (MCT) method and Minimum Fuel Target (MFT) method. We accomplished those North-South station keeping maneuvers for one year starting from December 2008. The required velocity increments to maintain the satellite are estimated as MCT 52.6065m/s, TBCT 52.2383m/s, MFT 51.5428m/s, respectively. We demonstrated that TBCT and MFT methods are proper to North-South station keeping for COMS-1. MFT method showed the minimum required velocity increments whereas TBCT traced narrow inclination boundary area for North-South station keeping.

ANTENNA POINTING TO THE GEO SATELLITE USING CONVERTED NORAD TLE FROM OSCULATING ORBITAL ELEMENTS

Antenna pointing analysis for a geostationary satellite has been performed for using the NORAD Two-Line-Elements (TLE) converted from osculating Keplerian orbital elements. In order to check the possibility of the reception of the satellite signal, the antenna offset angles have been derived for the Communications, Ocean, and Meteorological Satellite (COMS) which carries out weekly East-West and North-South station-keeping maneuvers and twice a day thruster assisted momentum dumping. Throughout the analysis, it is shown that the use of converted NORAD TLE simplifies the antenna pointing related interfaces in satellite mission control system. For a highly eccentric transfer orbit cases, further analysis presents that the converted NORAD TLE from near apogee gives more favorable results.

North-South Station-Keeping Maneuver Planning for COMS

Communication, Ocean, and Meteorological Satellite (COMS) Flight Dynamics Software (FDS) provides spacecraft orbit related flight dynamics support. In this paper, North-South Station Keeping (NSSK) maneuver planning, one of the important spacecraft flight operations, is performed using Maximum Compensation Target (MCT), Track-Back Chord Target (TBCT), and Minimum Fuel Target (MFT) strategies, respectively. The NSSK simulation result for one year appears that COMS is well maintained within 0.05° limit boundary for all strategies. However, calculated yearly required velocity increments and consumed fuel shows that TBCT and MFT strategy are appropriate to COMS NSSK maneuver.