Orbit Determination of High-Earth-Orbit Satellites by Satellite Laser Ranging

오형직,박은서,임형철,이상률,최재동,박찬덕 한국우주과학회 2017 Journal of Astronomy and Space Sciences Vol.34 No.4

This study presents the application of satellite laser ranging (SLR) to orbit determination (OD) of high-Earth-orbit (HEO) satellites. Two HEO satellites are considered: the Quasi-Zenith Satellite-1 (QZS-1), a Japanese elliptical-inclinedgeosynchronous- orbit (EIGSO) satellite, and the Compass-G1, a Chinese geostationary-orbit (GEO) satellite. One week of normal point (NP) data were collected for each satellite to perform the OD based on the batch least-square process. Five SLR tracking stations successfully obtained 374 NPs for QZS-1 in eight days, whereas only two ground tracking stations could track Compass-G1, yielding 68 NPs in ten days. Two types of station bias estimation and a station data weighting strategy were utilized for the OD of QZS-1. The post-fit root-mean-square (RMS) residuals of the two week-long arcs were 11.98 cm and 10.77 cm when estimating the biases once in an arc (MBIAS). These residuals were decreased significantly to 2.40 cm and 3.60 cm by estimating the biases every pass (PBIAS). Then, the resultant OD precision was evaluated by the orbit overlap method, yielding three-dimensional errors of 55.013 m with MBIAS and 1.962 m with PBIAS for the overlap period of six days. For the OD of Compass-G1, no station weighting strategy was applied, and only MBIAS was utilized due to the lack of NPs. The post-fit RMS residuals of OD were 8.81 cm and 12.00 cm with 49 NPs and 47 NPs, respectively, and the corresponding threedimensional orbit overlap error for four days was 160.564 m. These results indicate that the amount of SLR tracking data is critical for obtaining precise OD of HEO satellites using SLR because additional parameters, such as station bias, are available for estimation with sufficient tracking data. Furthermore, the stand-alone SLR-based orbit solution is consistently attainable for HEO satellites if a target satellite is continuously trackable for a specific period.

QZS-1 위성의 SLR 기반 궤도 결정 및 분석

오형직,김영록,박찬덕,박상영 한국항공우주학회 2013 한국항공우주학회 학술발표회 논문집 Vol.2013 No.11

Satellite Laser Ranging(SLR)을 이용한 항법위성의 정밀궤도결정은 위성의 위치결정 정밀도가 임무의 요구 조건에 중요한 역할을 담당하는 위성항법시스템에서 유용하게 사용되는 궤도 결정 전략이다. 본 연구는 한국형 항법위성의 자체적 SLR 정밀궤도결정 기술 확보를 위한 선행연구로, 일본의 지역적 위성항법 시스템 Quasi-Zenith Satellite System 의 기술적 검증을 위한 첫 번째 위성인 QZS-1 의 SLR 기반 궤도 결정을 수행하였다. 일주일의 추정기간 동안 총 네 곳의 관측소에서 관측한 결과를 활용하여 후처리 알고리즘을 적용하였고, 추정 정밀도를 자체적으로 검증하기 위한 방법으로 궤도 중첩(overlap) 방법을 사용하였다. 그 결과 겹친(overlap) 기간 동안 관측 값과 추정 값 간의 잔차 평균이 6.49 cm 인 궤도 결정 결과를 얻을 수 있었고, 3 차원 차이는 평균 56.04 m 였다. Precise orbit determination of navigation satellite using Satellite Laser Ranging is one of the useful orbit determination strategies due to the importance of state determination accuracy in Navigation Satellite System. As a preliminary research for SLR precise orbit determination technology development of Korean Navigation Satellite System, this research presents precise orbit determination of QZS-1, the first satellite of Japan’s Quasi-Zenith Satellite System for technical validation. Orbit determination range is set to one week, and post-processing algorithm is applied using observation data of four SLR tracking sites. Also, orbit overlap strategy is applied to verify the orbit determination accuracy For the overlapped period, the residual of observation and estimation values was 6.49 cm, and the 3-dimensional error was 56.04 m by average.

경추강내 신경장관낭종 1예 : Case Report

오형직,성기원,성우현,박영섭,이재수,최창락 대한신경외과학회 1990 Journal of Korean neurosurgical society Vol.19 No.6

A case of neurenteric cyst within the cervical canal is reported. He has been suffered from gradual aggrevated quardriparesis since 4 months. On spine C-T scan and cervical myelographic examimnation, intradural extramedullary mass was detected. And so total laminectomy of C₄, C_(5) and C_(6) was performed. We could diagnose by the pathological findings.

소아기 두개강내 뇌지주막 낭종의 외과적 치료

오형직,박영섭,이상원,박춘근,백민우,김문찬,강준기,송진언 대한신경외과학회 1989 Journal of Korean neurosurgical society Vol.18 No.7-12

14 supratentorial and 6 infratentorial arachnoid cysts, diagnosed and treated at Kangnam St Mary's Hospital from 1983 to 1988, are reported. The most common presenting symptoms in children were craniomegaly, delayed development, increased ICP and neurlolgical focal signs. Neuroradiological examination included plain skull X-ray, brain CT and metrizamide CT or isotope study. Therpeutic criteria according to the clinical and radiological findings were reviewed. The results were as follows ; 1) The patient below age of 2 yrs who's brain had a potent ability of growth should be operated in any case for reducing mass effect. 2) In sylvian lesion, Type Ⅱ and Ⅲ according to the classification of Galassi were well treated with C-P snunt. 3) In infratentorial lesion, all patients had hydrocephalus and the patient who had communicated with subarachnoid space in metrizamide CT were well treated with V-P shunt and who not communicated with subarachnoid space was well treated with Y-shunt. 4) We had good results by fenestration above the age of 3 yrs and by C-P shunt under the age of 2 yrs in supratentorial lesion.

Validation of Geostationary Earth Orbit Satellite Ephemeris Generated from Satellite Laser Ranging

오형직,박은서,임형철,이상률,최재동,박찬덕 한국우주과학회 2018 Journal of Astronomy and Space Sciences Vol.35 No.4

Validation of Geostationary Earth Orbit Satellite Ephemeris Generated from Satellite Laser RangThis study presents the generation and accuracy assessment of predicted orbital ephemeris based on satellite laser ranging (SLR) for geostationary Earth orbit (GEO) satellites. Two GEO satellites are considered: GEO-Korea Multi-Purpose Satellite (KOMPSAT)-2B (GK-2B) for simulational validation and Compass-G1 for real-world quality assessment. SLR-based orbit determination (OD) is proactively performed to generate orbital ephemeris. The length and the gap of the predicted orbital ephemeris were set by considering the consolidated prediction format (CPF). The resultant predicted ephemeris of GK-2B is directly compared with a pre-specified true orbit to show 17.461 m and 23.978 m, in 3D root-mean-square (RMS) position error and maximum position error for one day, respectively. The predicted ephemeris of Compass-G1 is overlapped with the Global Navigation Satellite System (GNSS) final orbit from the GeoForschungsZentrum (GFZ) analysis center (AC) to yield 36.760 m in 3D RMS position differences. It is also compared with the CPF orbit from the International Laser Ranging Service (ILRS) to present 109.888 m in 3D RMS position differences. These results imply that SLR-based orbital ephemeris can be an alternative candidate for improving the accuracy of commonly used radar-based orbital ephemeris for GEO satellites.ing This study presents the generation and accuracy assessment of predicted orbital ephemeris based on satellite laser ranging (SLR) for geostationary Earth orbit (GEO) satellites. Two GEO satellites are considered: GEO-Korea Multi-Purpose Satellite (KOMPSAT)-2B (GK-2B) for simulational validation and Compass-G1 for real-world quality assessment. SLR-based orbit determination (OD) is proactively performed to generate orbital ephemeris. The length and the gap of the predicted orbital ephemeris were set by considering the consolidated prediction format (CPF). The resultant predicted ephemeris of GK-2B is directly compared with a pre-specified true orbit to show 17.461 m and 23.978 m, in 3D root-mean-square (RMS) position error and maximum position error for one day, respectively. The predicted ephemeris of Compass-G1 is overlapped with the Global Navigation Satellite System (GNSS) final orbit from the GeoForschungsZentrum (GFZ) analysis center (AC) to yield 36.760 m in 3D RMS position differences. It is also compared with the CPF orbit from the International Laser Ranging Service (ILRS) to present 109.888 m in 3D RMS position differences. These results imply that SLR-based orbital ephemeris can be an alternative candidate for improving the accuracy of commonly used radar-based orbital ephemeris for GEO satellites.

Improved GPS-based Satellite Relative Navigation Using Femtosecond Laser Relative Distance Measurements

오형직,박한얼,이광원,박상영,박찬덕 한국우주과학회 2016 Journal of Astronomy and Space Sciences Vol.33 No.1

This study developed an approach for improving Carrier-phase Differential Global Positioning System (CDGPS) based realtime satellite relative navigation by applying laser baseline measurement data. The robustness against the space operational environment was considered, and a Synthetic Wavelength Interferometer (SWI) algorithm based on a femtosecond laser measurement model was developed. The phase differences between two laser wavelengths were combined to measure precise distance. Generated laser data were used to improve estimation accuracy for the float ambiguity of CDGPS data. Relative navigation simulations in real-time were performed using the extended Kalman filter algorithm. The GPS and laser-combined relative navigation accuracy was compared with GPS-only relative navigation solutions to determine the impact of laser data on relative navigation. In numerical simulations, the success rate of integer ambiguity resolution increased when laser data was added to GPS data. The relative navigational errors also improved five-fold and two-fold, relative to the GPS-only error, for 250 m and 5 km initial relative distances, respectively. The methodology developed in this study is suitable for application to future satellite formation-flying missions.

Orbit Determination of Korea Regional Navigation Satellite System Using Inter-Satellite Links and Ground Observations

최정민,오형직,박찬덕,박상영 한국항공우주학회 2017 International Journal of Aeronautical and Space Sc Vol.18 No.2

This study presents the orbit determination (OD) of a candidate Korea Regional Navigation Satellite System (KRNSS) using both inter-satellite links (ISLs) and ground observations. The candidate constellation of KRNSS is first introduced. The OD algorithm based on both ISL and ground observation is developed, and consists of three main components: dynamic model for Korean navigation satellites, measurement model for ISLs and ground observations, and the batch least-square filter for estimating OD parameters. As numerical simulations are performed to analyze the OD performances, the present study focuses on investigating the effects of ISL measurements on the OD accuracy of KRNSS. Simulation results show that the use of ISLs can considerably enhance the OD accuracy to one meter (design preference) under certain distributions of ground stations.

Effective Strategy for Precise Orbital and Geodetic Parameter Estimation Using SLR Observations for ILRS AAC

김영록,오형직,박상영,박찬덕,박은서,임형철,Kim, Young-Rok,Oh, Jay,Park, Sang-Young,Park, Chandeok,Park, Eun-Seo,Lim, Hyung-Chul 한국천문학회 2012 天文學會報 Vol.37 No.2

In this study, we propose an effective strategy for precise orbital and geodetic parameter estimation using SLR (Satellite Laser Ranging) observations for ILRS AAC (Associate Analysis Center). The NASA/GSFC GEODYN II software and SLR normal point observations of LAGEOS-1, LAGEOS-2, ETALON-1, and ETALON-2 are utilized for precise orbital and geodetic parameter estimation. Weekly-based precise orbit determination strategy is applied to process SLR observations, and Precise Orbit Ephemeris (POE), TRF (Terrestrial Reference Frame), and EOPs (Earth Orientation Parameters) are obtained as products of ILRS AAC. For improved estimation results, selection strategies of dynamic and measurement models are experimently figured out and configurations of various estimation parameters are also carefully chosen. The results of orbit accuracy assessment of POE and precision analysis of TRF/EOPs for each case are compared with those of existing results. Finally, we find an appropriate strategy for precise orbital and geodetic parameter estimation using SLR observations for ILRS AAC.

Laser-based Relative Navigation Using GPS Measurements for Spacecraft Formation Flying

이광원,오형직,박한얼,박상영,박찬덕 한국우주과학회 2015 Journal of Astronomy and Space Sciences Vol.32 No.4

This study presents a precise relative navigation algorithm using both laser and Global Positioning System (GPS) measurements in real time. The measurement model of the navigation algorithm between two spacecraft is comprised of relative distances measured by laser instruments and single differences of GPS pseudo-range measurements in spherical coordinates. Based on the measurement model, the Extended Kalman Filter (EKF) is applied to smooth the pseudo-range measurements and to obtain the relative navigation solution. While the navigation algorithm using only laser measurements might become inaccurate because of the limited accuracy of spacecraft attitude estimation when the distance between spacecraft is rather large, the proposed approach is able to provide an accurate solution even in such cases by employing the smoothed GPS pseudo-range measurements. Numerical simulations demonstrate that the errors of the proposed algorithm are reduced by more than about 12% compared to those of an algorithm using only laser measurements, as the accuracy of angular measurements is greater than 0.001° at relative distances greater than 30 km.

위성간 상대거리 관측을 이용한 한국형 위성항법시스템의 실시간 궤도결정

신기해,오형직,박상영,박찬덕 한국항공우주학회 2015 한국항공우주학회 학술발표회 논문집 Vol.2015 No.4

본 논문에서는 한국형 위성항법시스템(Korea Regional Navigation Satellite System, KRNSS)의 지상국이 궤도력을 위성으로 송신할 수 없는 경우에 대비한 독립적/실시간 궤도 결정을 다룬다. 한국형 위성항법 시스템의 후보 위성군으로 지구정지궤도(Geostationary Orbit, GEO) 위성 3기와 타원경사지구동기궤도(Elliptical Inclined Geosynchronous Orbit, EIGSO) 위성 4기를 고려한다. 위성간 상대거리 관측(Inter-satellite Link, ISL)과 확장 칼만 필터(Extended Kalman Filter, EKF)를 사용하여 실시간 궤도결정을 수행한다. 확장 칼만 필터의 성능에 영향을 주는 주요 행렬들에 대한 체계적인 분석을 수행한 뒤, 위성간 상대거리 관측의 오차 수준이 0.3~0.7m일 경우 m급 궤도결정 정밀도를 달성할 수 있음을 확인하였다. This paper presents stand-alone/real-time orbit determination of Korea Regional Navigation Satellite System(KRNSS) when ground station fails to transmit ephemeris to satellites. Three geostationary orbit(GEO) satellites and four elliptical inclined geosynchronous orbit(EIGSO) satellites are considered to form a candidate KRNSS. Inter-satellite links are used as observation data, and extended Kalman filter(EKF) is applied as real time estimation method. Parametric analysis of EKF-related matrices is presented, and simulation results show that 0.3~0.7m observation accuracy can achieve meter-level orbit determination.