• Journal of Astronomy and Space Sciences
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• v.19 no.3
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• pp.197-206
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• 2002

NORAD Two Line Elements (TLE) are widely used for the increasing number of small satellite mission operations and analysis. However, due to the irregular periodicity of generation of the NORAD TLE, a new TLE that is independent of NORAD is required. A TLE type Orbit Determination (TLEOD) has been developed for the generation of a new TLE. Thus, the TLEOD system can provide an Antenna Control Unit (ACU) with the orbit determination result in the type of a TLE, which provides a simple interface for the commercialized ACU system. For the TLEOD system, NORAD SGP4 was used to make a new orbit determination system. In addition, a least squares method was implemented for the TLEOD system with the GPS navigation solutions of the KOMPSAT-1. Considering both the Orbit Propagation (OP) difference and the tendency of $B^{*}$ value, the preferable span of the day in the observation data was selected to be 3 days. Through the OD with 3 days observation data, the OP difference was derived and compared with that of Mission Analysis and Planning (MAPS) for the KOMPSAT-1. It has the extent from 2 km after sit days to 4 km after seven days. This is qualified enough for the efficiency of an ACU in image reception and processing center of the KOMPSAT-2.

• Journal of Astronomy and Space Sciences
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• v.19 no.4
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• pp.385-394
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• 2002

Satellite laser ranging is a technique for precisely measuring the range between a laser station and a satellite that is equipped with retro-reflectors. SLR technique was first used for Beacon-B satellite in 1964 with the ranging accuracy of meter level. Now the single shot have centimeter level accuracy and the normal point have mm level in ranging. In this study we developed the algorithm for precise orbit determination using SLR data and performed the orbit determination of GPS-36 satellite using the algorithm. RMS of the estimated orbit was 74cm when compared with IGS precise orbit. It is known that RMS of SLR measurement residual is below 55mm. But we were able to achieve 44mm RMS of residual throughout this study.

• Journal of Astronomy and Space Sciences
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• v.29 no.3
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• pp.275-285
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• 2012

In this study, we present preliminary results of precise orbit determination (POD) using satellite laser ranging (SLR) observations for International Laser Ranging Service (ILRS) Associate Analysis Center (AAC). Using SLR normal point observations of LAGEOS-1, LAGEOS-2, ETALON-1, and ETALON-2, the NASA/GSFC GEODYN II software are utilized for POD. Weekly-based orbit determination strategy is applied to process SLR observations and the post-fit residuals check, and external orbit comparison are performed for orbit accuracy assessment. The root mean square (RMS) value of differences between observations and computations after final iteration of estimation process is used for post-fit residuals check. The result of ILRS consolidated prediction format (CPF) is used for external orbit comparison. Additionally, we performed the precision analysis of each ILRS station by post-fit residuals. The post-fit residuals results show that the precisions of the orbits of LAGEOS-1 and LAGEOS-2 are 0.9 and 1.3 cm, and those of ETALON-1 and ETALON-2 are 2.5 and 1.9 cm, respectively. The orbit assessment results by ILRS CPF show that the radial accuracies of LAGEOS-1 and LAGEOS-2 are 4.0 cm and 5.3 cm, and the radial accuracies of ETALON-1 and ETALON-2 are 30.7 cm and 7.2 cm. These results of station precision analysis confirm that the result of this study is reasonable to have implications as preliminary results for administrating ILRS AAC.

• Journal of Positioning, Navigation, and Timing
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• v.1 no.1
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• pp.59-64
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• 2012

Precise Point Positioning (PPP) has been widely used in navigation and orbit determination applications as we can obtain precise Global Positioning System (GPS) satellite orbit and clock products. Kinematic PPP, which is based on the GPS measurements only from the spaceborne GPS receiver, has some advantages for a simple precise orbit determination (POD). In this study, we developed kinematic PPP technique to estimate the orbits of GRACE-A satellite. The comparison of the mean position between the JPL's orbit product and our results showed the orbit differences 0.18 cm, 0.54 cm, and 0.98 cm in the Radial, in Along-track, and Cross-track direction respectively. In addition, we obtained the root mean square (rms) values of 4.06 cm, 3.90 cm, and 3.23 cm in the satellite coordinate components relative to the known coordinates.

• Journal of Astronomy and Space Sciences
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• v.36 no.4
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• pp.249-264
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• 2019

In this study, the precise orbit determination (POD) software is developed for optical observation. To improve the performance of the estimation algorithm, a nonlinear batch filter, based on the unscented transform (UT) that overcomes the disadvantages of the least-squares (LS) batch filter, is utilized. The LS and UT batch filter algorithms are verified through numerical simulation analysis using artificial optical measurements. We use the real optical observation data of a low Earth orbit (LEO) satellite, Cryosat-2, observed from optical wide-field patrol network (OWL-Net), to verify the performance of the POD software developed. The effects of light travel time, annual aberration, and diurnal aberration are considered as error models to correct OWL-Net data. As a result of POD, measurement residual and estimated state vector of the LS batch filter converge to the local minimum when the initial orbit error is large or the initial covariance matrix is smaller than the initial error level. However, UT batch filter converges to the global minimum, irrespective of the initial orbit error and the initial covariance matrix.

• Journal of Aerospace System Engineering
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• v.9 no.2
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• pp.57-62
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• 2015

The satellite orbit is continuously changing due to space environment. Especially for low earth orbit, atmospheric drag plays an important role in the orbit altitude decay. Recently, solar activities are expected to be high, and relevant events are occurring frequently. In this paper, analysis on the impact of geomagnetic storm on LEO satellite orbit is presented. For this, real flight data of KOMPSAT-2, KOMPSAT-3, and KOMPSAT-5 are analyzed by using the daily decay rate of mean altitude is calculated from the orbit determination. In addition, the relationship between the solar flux and geomagnetic index, which are the metrics for solar activities, is statistically analyzed with respect to the altitude decay. The accuracy of orbit prediction with both the fixed drag coefficient and estimated one is examined with the precise orbit data as a reference. The main results shows that the improved accuracy can be achieved in case of using estimated drag coefficient.

• Journal of Astronomy and Space Sciences
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• v.28 no.3
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• pp.183-192
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• 2011

The current study analyzes the effects of the scaling parameters of the batch unscented transformation on precision satellite orbit determination. Satellite laser ranging (SLR) data are used in the orbit determination algorithm, which consists of dynamics model, observation model and filtering algorithm composed of the batch unscented transformation. TOPEX/Poseidon SLR data are used by utilizing the normal point (NP) data observed from ground station. The filtering algorithm includes a repeated series of processes to determine the appropriate scaling parameters for the batch unscented transformation. To determine appropriate scaling parameters, general ranges of the scaling parameters of ${\alpha}$, ${\beta}$, k, $\lambda$ are established. Depending on the range settings, each parameter was assigned to the filtering algorithm at regular intervals. Appropriate scaling parameters are determined for observation data obtained from several observatories, by analyzing the relationship between tuning properties of the scaling parameters and estimated orbit precision. The orbit determination of satellite using the batch unscented transformation can achieve levels of accuracy within several tens of cm with the appropriate scaling parameters. The analyses in the present study give insights into the roles of scaling parameters in the batch unscented transformation method.

• Journal of Astronomy and Space Sciences
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• v.34 no.2
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• pp.139-151
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• 2017

This paper presents an overview of deep space orbit determination software (DSODS), as well as validation and verification results on its event prediction capabilities. DSODS was developed in the MATLAB object-oriented programming environment to support the Korea Pathfinder Lunar Orbiter (KPLO) mission. DSODS has three major capabilities: celestial event prediction for spacecraft, orbit determination with deep space network (DSN) tracking data, and DSN tracking data simulation. To achieve its functionality requirements, DSODS consists of four modules: orbit propagation (OP), event prediction (EP), data simulation (DS), and orbit determination (OD) modules. This paper explains the highest-level data flows between modules in event prediction, orbit determination, and tracking data simulation processes. Furthermore, to address the event prediction capability of DSODS, this paper introduces OP and EP modules. The role of the OP module is to handle time and coordinate system conversions, to propagate spacecraft trajectories, and to handle the ephemerides of spacecraft and celestial bodies. Currently, the OP module utilizes the General Mission Analysis Tool (GMAT) as a third-party software component for high-fidelity deep space propagation, as well as time and coordinate system conversions. The role of the EP module is to predict celestial events, including eclipses, and ground station visibilities, and this paper presents the functionality requirements of the EP module. The validation and verification results show that, for most cases, event prediction errors were less than 10 millisec when compared with flight proven mission analysis tools such as GMAT and Systems Tool Kit (STK). Thus, we conclude that DSODS is capable of predicting events for the KPLO in real mission applications.

• Aerospace Engineering and Technology
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• v.11 no.2
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• pp.149-157
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• 2012

In this paper, the performance of the sequential filter for a space debris collision management system is analyzed by using the flight data of KOMPSAT-2. To analyze the performance of the sequential filter, the results of batch filter used in the orbit determination system of the KOMPSAT-2 ground station is used as reference data. The overlap method is also used to evaluate the orbit accuracy. This paper shows that the orbit determination accuracy of the sequential filter is similar to that of the KOMPSAT-2 ground station, but dissimilar characteristics exist due to the filter difference. In addition, it is also shown that the orbit determination accuracy is order of 1m root mean square by using 30 hour GPS navigation solutions and 6 hour comparison period for the overlap method.

• Aerospace Engineering and Technology
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• v.12 no.2
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• pp.123-130
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• 2013

Many countries tried to design the collision risk management system to protect their own satellites from collision probability due to the space debris. In this situation, KARI(Korea Aerospace Research Institute) is developing the KARISMA(KARI Conjunction Risk Management System) to protect our operating satellites from these space debris. The quality of this system is depending on the accuracy of orbit determination for the space debris which has collision risk. Therefore, this system must treat many kinds of measurement data types to estimate the orbit of space debris. In this paper, to handle the radar observation data widely used for these space debris, the orbit determination system was applied with simulated radar tracking data for the KOMSAT-2 which has precise orbit determination data.