• 항공우주기술
• /
• 제11권2호
• /
• pp.19-25
• /
• 2012

정지궤도복합위성은 천리안위성에 비하여 고품질의 영상품질을 요구하며 지구센서 대신 별센서의 사용으로 인하여 고정밀의 탑재용 궤도정보생성이 요구된다. 이는 고정밀의 궤도 결정이 바탕이 되어야 한다. 천리안위성의 경우는 항공우주연구원에 설치된 추적 안테나를 이용하여 레인징을 수행하고 이를 바탕으로 궤도결정을 수행하였다. 정지궤도복합위성의 정밀한 궤도결정을 위하여 항공우주연구원에서는 축섬에 새로운 추적장비를 준비중에 있다. 본 논문에서는 대전과 축섬에 위치한 정지궤도복합위성을 가정하여 궤도결정을 수행했을 경우 궤도결정 및 예측 오차와 테이블 방식의 탑재용궤도정보 생성기의 궤도정밀도를 분석하였다. 본 논문에서는 공분산해석과 수치적인 방법을 통하여 궤도정밀도를 해석하였다. 두 해석결과를 종합하여 최종적인 궤도오차를 산출하였다.

• International Journal of Aerospace System Engineering
• /
• 제7권2호
• /
• pp.6-12
• /
• 2020

The precise prediction of future position of satellite depends on the accurate determination of orbit, which is also helpful in performing orbit maneuvers and trajectory correction maneuvers. For estimating the orbit of satellite many methods are being used. Some of the conventional methods are based on (i) Differential Correction (DC) (ii) Extended Kalman Filter (EKF). In this paper, Differential Evolution (DE) is used to determine the orbit. Orbit Determination using DC and EKF requires some initial guess of the state vector to initiate the algorithm, whereas DE does not require an initial guess since a wide range of bounds for the design unknown variables (orbital elements) is sufficient. This technique is uniformly valid for all orbits viz. circular, elliptic or hyperbolic. Simulated observations have been used to demonstrate the performance of the method. The observations are generated by including random noise. The simulation model that generates the observations includes the perturbation due to non-spherical earth up to second zonal harmonic term.

• Journal of Astronomy and Space Sciences
• /
• 제27권4호
• /
• pp.337-343
• /
• 2010

Optical observation system provides angle-only measurement for orbit determination of space object. Range measurement can be directly acquired using laser ranging or tone ranging system. Initial orbit determination (IOD) by using angle- only data set shows discrepancy according to the measurement time interval. To solve this problem, range measurement data should be added for IOD. In this study, two-site optical observation was used to derive the range information. We have observed nine geostationary earth orbit satellites by using two-site optical observation system. The determination result of the range shows the accuracy over 99.5% compared to the results from the satellite tool kit simulation. And we confirmed that the orbit determination by the Herrick-Gibbs method with the range information obtained from the two-site observation is more accurate than the orbit determination by Gauss method with the one-site observation. For more accurate two-site optical observation, a baseline should satisfy an optimal condition of length and more precise observation system needed.

• Journal of Astronomy and Space Sciences
• /
• 제36권4호
• /
• pp.249-264
• /
• 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 Astronomy and Space Sciences
• /
• 제36권3호
• /
• pp.187-197
• /
• 2019

The Optical Wide-field patroL-Network (OWL-Net) is a Korean optical space surveillance system used to track and monitor objects in space. In this study, the characteristics of four Initial Orbit Determination (IOD) methods were analyzed using artificial observational data from Low Earth Orbit satellites, and an appropriate IOD method was selected for use as the initial value of Precise Orbit Determination using OWL-Net data. Various simulations were performed according to the properties of observational data, such as noise level and observational time interval, to confirm the characteristics of the IOD methods. The IOD results produced via the OWL-Net observational data were then compared with Two Line Elements data to verify the accuracy of each IOD method. This paper, thus, suggests the best method for IOD, according to the properties of angles-only data, for use even when the ephemeris of a satellite is unknown.

• Journal of Astronomy and Space Sciences
• /
• 제20권1호
• /
• pp.1-10
• /
• 2003

A precise kinematic orbit determination (P-KOD) procedure for Low Earth Orbiter(LEO) using the GPS ion-free triple differenced carrier phases is presented. Because the triple differenced observables provide only relative information, the first epoch's positions of the orbit should be held fixed. Then, both forward and backward filtering was executed to mitigate the effect of biases of the first epoch's position. p-KOD utilizes the precise GPS orbits and ground stations data from International GPS Service (IGS) so that the only unknown parameters to be solved are positions of the satellite at each epoch. Currently, the 3-D accuracy off-KOD applied to CHAMP (CHAllenging Min-isatellite Payload) shows better than 35 cm compared to the published rapid scientific orbit (RSO) solution from GFZ (GeoForschungsZentrum Potsdam). The data screening for cycle slips is a particularly challenging procedure for LEO, which moves very fast in the middle of the ionospheric layer. It was found that data screening using SNR (signal to noise ratio) generates best results based on the residual analysis using RSO. It is expected that much better accuracy are achievable with refined prescreening procedure and optimized geometry of the satellites and ground stations.

• 한국항해항만학회:학술대회논문집
• /
• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.1
• /
• pp.191-196
• /
• 2006

In GPS Positioning, the error of satellite orbit will affect user's position accuracy directly, it is important to determine the satellite orbit precise. The real-time orbit is needed in kinematic GPS positioning, the precise GPS orbit from IGS would be delayed long time, so orbit prediction is key to real-time kinematic positioning. We analyze the GPS predicted ephemeris, on the base of comparison of EKF and UKF, a new orbit prediction method is put forward based on UKF in this paper, the result shows that UKF improves the orbit predicted precision and stability. It offers a new method for others satellites orbit determination as Galileo, and so on.

• ETRI Journal
• /
• 제33권4호
• /
• pp.487-496
• /
• 2011

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.

• Journal of Astronomy and Space Sciences
• /
• 제28권3호
• /
• pp.193-201
• /
• 2011

A strategy for geostationary orbit (or geostationary earth orbit [GEO]) surveillance based on optical angular observations is presented in this study. For the dynamic model, precise analytical orbit model developed by Lee et al. (1997) is used to improve computation performance and the unscented Kalman filer (UKF) is applied as a real-time filtering method. The UKF is known to perform well under highly nonlinear conditions such as surveillance in this study. The strategy that combines the analytical orbit propagation model and the UKF is tested for various conditions like different level of initial error and different level of measurement noise. The dependencies on observation interval and number of ground station are also tested. The test results shows that the GEO orbit determination based on the UKF and the analytical orbit model can be applied to GEO orbit tracking and surveillance effectively.

• 한국항공우주학회지
• /
• 제44권9호
• /
• pp.781-788
• /
• 2016

본 논문에서는 실시간 On-board 궤도 결정 성능을 향상시키기 위해 고정밀 우주 섭동 모델을 구현하였고, 구현된 우주 섭동모델을 GNSS 수신기의 궤도 결정 로직에 적용하여 그 결과를 분석하였다. 궤도 결정 로직은 확장 칼만 필터(Extended Kalman Filter)로 구현되었고, 의사거리로 계산한 궤도(Standard Position Service)를 관측정보로 이용하였다. 궤도 결정 로직 성능 검증은 GPS 인공위성의 신호를 모사하는 GNSS 시뮬레이터를 이용하여 수행하였다. 고정밀 섭동모델의 궤도 결정 성능을 $J_2$ 항만 고려한 섭동모델의 궤도 결정 성능과 비교하여 분석한 결과, GPS 항행해의 위치 정밀도는 43.61 m($3{\sigma}$)에서 23.86 m($3{\sigma}$)로 46 % 개선되었으며 속도 정밀도는 0.159 m/s($3{\sigma}$)에서 0.044 m/s($3{\sigma}$)로 72 % 개선되어 정밀도가 향상된 것을 확인할 수 있었다.