No abstract

Satellite operating agencies are constantly monitoring conjunctions between satellites and space objects. Two line element (TLE) data, published by the Joint Space Operations Center of the United States Strategic Command, are available as raw data for a preliminary analysis of initial conjunction with a space object without any orbital information. However, there exist several sorts of uncertainties in the TLE data. In this paper, we suggest and analyze a method for estimating the uncertainties in the TLE data through mean, standard deviation of state vector residuals and covariance matrix. Also the estimation results are compared with actual results of orbit determination to validate the estimation method. Characteristics of the state vector residuals depending on the orbital elements are examined by applying the analysis to several satellites in various orbits. Main source of difference between the covariance matrices are also analyzed by comparing the matrices. Particularly, for the Korea Multi-Purpose Satellite-2, we examine the characteristics of the residual variation of state vector and covariance matrix depending on the orbital elements. It is confirmed that a realistic consideration on the space situation of space objects is possible using information from the analysis of mean, standard deviation of the state vector residuals of TLE and covariance matrix.

Korea Aerospace Research Institute (KARI) has been conducting the satellite mission operations for Korea Multi-Purpose Satellite (KOMPSAT) series. Flight dynamics functions of KOMPSAT series operation include comprehensive orbital analysis and mission planning support as well as orbit data distribution for image processing by conducting Operational Orbit Determination (OOD), Orbit Prediction (OP), Orbit Maneuver Planning (OMP), Ground Track Maintenance (GTM) and Precision Orbit Determination (POD). Precise orbit of KOMPSAT series was estimated and released on a daily basis. POD processing of KOMPSAT was using the Global Positioning System (GPS) measurements including pseudo-range and carrier phase measurement data from onboard GPS receivers. In flight dynamics operations, the accuracy of POD was evaluated by the root-mean square error of daily POD ephemeris in comparison with previous POD ephemeris using overlapping method. But, sometimes, POD accuracy does not meet its requirements due to the various erroneous sources, which include data unavailability or defective data in GPS ephemeris and International GNSS Service (IGS) Station information. In this paper, exceptional cases of POD processing are thoroughly analyzed to reduce data latency for robustness of software in terms of satellite operations. For this purpose, flight dynamics team rebuilds the POD processing flow in more efficient way and add an additional correction steps to provide the quality-controlled orbit ephemeris. The high-fidelity proven capabilities for POD processing provided by commercial software such as MicroCosm and in-house algorithms are extensively used for this purpose. Finally, POD data accuracy of KOMPSAT series is improved and data latency is reduced than previous workflow. It could be reference to setup an operational strategy for the POD processing in terms of robust orbit data processing and rapid data provision.

No abstract

This paper describes the orbital dynamics operation results for the launch and early operations phase (LEOP) of KOMPSAT-3, which was successfully launched on May 18, 2012. At the initial phase, operational orbit determination was carried out using ground tracking data and GPS navigation solution. And, both in-plane and out-of plane maneuvers were executed in order to change the orbit from the injection orbit to the mission orbit. In addition, the accuracy of precise orbit determination was indirectly evaluated by overlapping method using GPS raw data of KOMPSAT-3 and international GNSS service data from worldwide-distributed ground stations. Currently, KOMPSAT-3 is operated in pre-defined mission orbit, and its various kinds of orbit data are generated and distributed to support the normal mission operations.