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.

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.

Geostationary Satellite Station Keeping Robustness to Loss of Ground Control

Hyung Je Woo,Bjorn Buckwalter 한국우주과학회 2021 Journal of Astronomy and Space Sciences Vol.38 No.1

For the vast majority of geostationary satellites currently in orbit, station keeping activities including orbit determination and maneuver planning and execution are ground-directed and dependent on the availability of ground-based satellite control personnel and facilities. However, a requirement linked to satellite autonomy and survivability in cases of interrupted ground support is often one of the stipulated provisions on the satellite platform design. It is especially important for a geostationary military-purposed satellite to remain within its designated orbital window, in order to provide reliable uninterrupted telecommunications services, in the absence of ground-based resources due to warfare or other disasters. In this paper we investigate factors affecting the robustness of a geostationary satellite’s orbit in terms of the maximum duration the satellite’s station keeping window can be maintained without ground intervention. By comparing simulations of orbit evolution, given different initial conditions and operations strategies, a variation of parameters study has been performed and we have analyzed which factors the duration is most sensitive to. This also provides valuable insights into which factors may be worth controlling by a military or civilian geostationary satellite operator. Our simulations show that the most beneficial factor for maximizing the time a satellite will remain in the station keeping window is the operational practice of pre-emptively loading East-West station keeping maneuvers for automatic execution on board the satellite should ground control capability be lost. The second most beneficial factor is using short station keeping maneuver cycle durations.

초소형위성체계 운용을 위한 위성궤도요소 분석 및 위성군 배치기법에 대한 고찰

이성섭 ( Soung Sub Lee ),손지혜 ( Jihae Son ),송영범 ( Youngbum Song ) 한국항행학회 2023 韓國航行學會論文誌 Vol.27 No.4

본 연구는 국가 초소형위성체계가 운용개념에 맞게 효과적으로 임무를 수행하기 위한 위성궤도요소 별 고려사항을 분석하고, 통상적으로 활용되고 있는 워커 기법 대비 지상반복궤적 궤도의 위성배치 기법에 대한 성능을 비교한다. 위성궤도요소 분석에서 는 초소형위성군의 고도 후보군, 동결궤도를 통한 궤도 이심율 및 근지점 경도의 활용, 적절한 궤도 경사각 선정의 필요성, 동일한 지상반복궤적을 비행하기 위한 위성군 배치 규칙 등을 제안한다. 이러한 분석 결과를 기반으로 지상반복궤적 궤도의 위성군 배치는 워커 기법과 비교하여 재방문 성능 분석, 글로벌 커버리지 특성, 궤도 일관성 측면에서 우월성이 검증된다. This study analyzes considerations for satellite orbit elements for the national micro-satellite system to effectively perform its mission in accordance with the operational concept, and compares the conventionally used Walker method to improve the performance of the satellite constellation method of the repeating ground track orbit. In satellite orbit element analysis, altitude candidate values of micro-satellite system, use of eccentricity and argument of perigee through frozen orbit, necessity of selection of appropriate orbit inclination, and satellite phasing rules for flying the same repeating ground track orbit are proposed. Based on these analysis results, the superiority of the constellation method of the repeating ground track orbit compared to the Walker method is verified in terms of revisit performance analysis, global coverage characteristics, and orbit consistency.

저궤도 군집 위성 간 통신 현황 및 주요 기술 동향

차홍설,김종민,임병주,이주형,고영채 한국통신학회 2022 韓國通信學會論文誌 Vol.47 No.10

Traditional satellite communication was limited to specific services such as military communication or broadcasting due to the cost and technical complexity issues. However, thanks to the recent development of satellite launch technology, it is envisaged that future satellite communication supports broadband internet services by deploying tens of thousands of satellites in Low Earth Orbit (LEO). The mega-constellation of the LEO satellite communication system consists of satellite-to-ground communication and satellite-to-satellite communication. In particular, inter-satellite link (ISL) technology for satellite-to-satellite communication is in the early stage, while satellite-to-ground communication technology is relatively mature. Thus, many countries have been getting attention to this ISL technology to accomplish low-latency and high-rate LEO satellite communication. In this paper, we summarize the current status of LEO satellite communication technology, focusing on the ISL technology while providing its future direction. 기존의 위성 시스템들은 통신서비스를 제공하기 위하여 주로 고비용의 정지궤도 위성 시스템을 이용하였기 때문에, 저비용의 이동통신 서비스를 제공하는 데에는 여러 가지 한계점이 존재해 왔다. 그러나 최근 위성 발사 기술발전으로 다수의 위성을 저비용으로 운용할 수 있음에 따라, 위성 통신이 개인 무선통신 서비스까지 지원할 수있을 것으로 전망되고 있다. 특히 저궤도 (Low Earth Orbit, LEO)에 수만 대의 위성을 배치하여 전 지구적 범위로 통신 네트워크를 제공하는 방식이 차세대 통신 분야로 여겨지고 있으며, 이를 LEO 군집 위성 통신 시스템이라고 한다. 해당 LEO 군집 위성 통신 시스템은 크게 위성-지상 간 통신과 위성-위성 간 통신으로 나누어 볼 수있는데, 이미 성숙기에 접어든 위성-지상 간 통신 기술과는 달리, 위성-위성 간 통신 (Inter Satellite Link, ISL) 기술은 선도국인 미국을 포함해 전 세계적으로 아직 태동기이다. ISL 기술은 통신 지연시간을 최소화하고 초고속데이터 통신을 실현하기 위해 필수적인 기술이다. 본 논문에서는 해당 ISL 기술을 구현하기 위한 필수 요소 기술들과 기술 현황을 요약하여 국내 위성 통신 기술 개발에 참고가 되고자 한다.

정지궤도 위성의 자동운용을 위한 위치결정 시스템의 개념연구

이상철(Sang-Cherl Lee),주광혁(Gwanghyeok Ju),김방엽(Bang-Yeop Kim),박봉규(Bong-Kyu Park) 한국항공우주학회 2005 韓國航空宇宙學會誌 Vol.33 No.11

현재 240여기의 상업용 정지궤도 통신위성이 운용 중에 있지만, GPS 동의 위치항법 위성의 고도보다 높을 뿐만 아니라 나쁜 가시성으로 인하여 중궤도 위치항법시스템을 사용할 수 없으므로 반드시 지상관제소에 의해 추적되어야 한다. 또한 지상관제소에서 관측할 경우 정지궤도 위성은 거의 움직이지 않는 것처럼 보이기 때문에 수 미터급의 정지궤도 위성의 위치결정 정밀도를 높이기 위해서 충분히 멀리 떨어진 2곳 이상의 추적안테나를 사용하여야 한다. 따라서 본 논문에서는 정지궤도 위성의 궤도결정과 자동운용을 위해서 정지궤도 고도보다 높은 2일 주기의 원형궤도를 사용하는 GSPS(Geostationary Satellite Positioning System)을 제안하였다. GSPS는 지상추적소에서 정밀하게 위치가 결정된 자기 자신의 위치정보 및 시각정보, 보정데이터와 정지궤도 위성의 운용을 위한 명령을 GSPS 위성에 전송하여 정지궤도위성에 위치정보를 제공하는 기능을 한다. Even more than 240 commercial geostationary communication satellites currently on orbit at the higher location than the GPS orbit altitude perform their own missions only by the support of the ground segment because of weak visibility from GPS. In addition, the orbit determination accuracy is very low without using two or more dedicated ground tracking antennas in intercontinental ground segment, since the satellite hardly moves with respect to the ground station. In this paper, we propose the GSPS(Geostationary Satellite Positioning System) in circular orbits of two sidereal days period higher than the geosynchronous orbit for orbit determination and autonomous satellite operation. The GSPS is conceived as a ranging system in that unknown positions of a geostationary satellite can be acquired from the known positions of the GSPS satellites. Each GSPS satellite transmits navigation data, clock data, correction data, and geostationary satellite command to control a geostationary satellite.

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.

Geostationary Satellite Station Keeping Robustness to Loss of Ground Control

Woo, Hyung Je,Buckwalter, Bjorn The Korean Space Science Society 2021 Journal of astronomy and space sciences Vol.38 No.1

For the vast majority of geostationary satellites currently in orbit, station keeping activities including orbit determination and maneuver planning and execution are ground-directed and dependent on the availability of ground-based satellite control personnel and facilities. However, a requirement linked to satellite autonomy and survivability in cases of interrupted ground support is often one of the stipulated provisions on the satellite platform design. It is especially important for a geostationary military-purposed satellite to remain within its designated orbital window, in order to provide reliable uninterrupted telecommunications services, in the absence of ground-based resources due to warfare or other disasters. In this paper we investigate factors affecting the robustness of a geostationary satellite's orbit in terms of the maximum duration the satellite's station keeping window can be maintained without ground intervention. By comparing simulations of orbit evolution, given different initial conditions and operations strategies, a variation of parameters study has been performed and we have analyzed which factors the duration is most sensitive to. This also provides valuable insights into which factors may be worth controlling by a military or civilian geostationary satellite operator. Our simulations show that the most beneficial factor for maximizing the time a satellite will remain in the station keeping window is the operational practice of pre-emptively loading East-West station keeping maneuvers for automatic execution on board the satellite should ground control capability be lost. The second most beneficial factor is using short station keeping maneuver cycle durations.

Resource allocation algorithm for space-based LEO satellite network based on satellite association

Baochao Liu,Lina Wang 한국인터넷정보학회 2024 KSII Transactions on Internet and Information Syst Vol.18 No.6

As a crucial development direction for the sixth generation of mobile communication networks (6G), Low Earth Orbit (LEO) satellite networks exhibit characteristics such as low latency, seamless coverage, and high bandwidth. However, the frequent changes in the topology of LEO satellite networks complicate communication between satellites, and satellite power resources are limited. To fully utilize resources on satellites, it is essential to determine the association between satellites before power allocation. To effectively address the satellite association problem in LEO satellite networks, this paper proposes a satellite associationbased resource allocation algorithm. The algorithm comprehensively considers the throughput of the satellite network and the fairness associated with satellite correlation. It formulates an objective function with logarithmic utility by taking the logarithm and summing the satellite channel capacities. This aims to maximize the sum of logarithmic utility while promoting the selection of fewer associated satellites for forwarding satellites, thereby enhancing the fairness of satellite association. The problems of satellite association and power allocation are solved under constraints on resources and transmission rates, maximizing the logarithmic utility function. The paper employs an improved Kuhn-Munkres (KM) algorithm to solve the satellite association problem and determine the correlation between satellites. Based on the satellite association results, the paper uses the Lagrangian dual method to solve the power allocation problem. Simulation results demonstrate that the proposed algorithm enhances the fairness of satellite association, optimizes resource utilization, and effectively improves the throughput of LEO satellite networks.

GPS 궤도오차의 기저선 거리에 따른 시선각 벡터 투영오차 분석

장진혁(JinHyeok Jang),안종선(JongSun Ahn),부성춘(Sung-Chun Bu),이철수(Chul-Soo Lee),성상경(SangKyung Sung),이영재(Young Jae Lee) 한국항공우주학회 2017 韓國航空宇宙學會誌 Vol.45 No.4

오늘날 다양한 나라에서 위성항법시스템을 운용, 개발하고 있다. 또한 GNSS의 성능향상을 위해 정지궤도위성을 이용하는 SBAS가 운용 중에 있다. 가장 대표적으로 사용되는 SBAS는 미국에서 개발한 GPS의 WAAS이다. SBAS에서는 사용자에게 정확성, 가용성, 연속성, 무결성을 보장하기 위해 다양한 알고리즘이 사용되고 있다. 이 중 위성에 대한 무결성을 보장하기 위한 알고리즘이 있다. 이 알고리즘은 위성오차를 추정하고 보정정보를 생성하여 사용자에게 제공한다. 여기서 위성궤도오차를 3차원으로 추정하게 된다. 이렇게 위성궤도오차를 3차원으로 추정하기 위해서는 기준국 배치가 중요하게 된다. 기준국의 배치가 넓을수록 시선각 벡터가 넓게 분포되어 추정 정확도가 향상될 수 있다. 여기서 대표적 SBAS 운영국인 미국과 한국의 지역적 특성으로 인한 분석을 수행하고자 한다. 한국은 미국에 비해 매우 협소한 지리적 특성을 가지고 있다. 따라서 3차원 위성궤도오차 추정 기법을 그대로 사용하기 어렵다. 본 논문에서는 협역지역에서 위성궤도오차를 3차원으로 추정하는 것이 아닌 스칼라로 값으로 사용하는 방식을 제안한다. 제안하는 기법은 기준국(Reference)과 위성간의 시선각 (LOS, Line-Of-Sight) 벡터에 궤도오차를 투영한 스칼라 값을 이용하는 것이다. 이 방식을 이용하여 정상상태, 고장상태의 한국과 미국지역에서 기저선 거리에 따른 오차 변화를 확인하도록 한다. 이 오차변화 차이를 비교하여 제안하는 기법의 사용 가능성을 제시한다. Recently, many nations are operating and developing Global Navigation Satellite System (GNSS). Also, Satellite Based Augmentation System (SBAS), which uses the geostationary orbit, is operated presently in order to improve the performance of GNSS. The most widely-used SBAS is Wide Area Augmentation System (WAAS) of GPS developed by the United States. SBAS uses various algorithms to offer guaranteed accuracy, availability, continuity and integrity to its users. There is algorithm for guarantees the integrity of the satellite. This algorithm calculates the satellite errors, generates the correction and provides it to the users. The satellite orbit errors are calculated in three-dimensional space in this step. The reference placement is crucial for this three-dimensional calculation of satellite orbit errors. The wider the reference placement becomes, the wider LOS vectors spread, so the more the accuracy improves. For the next step, the regional features of the US and Korea need to be analyzed. Korea has a very narrow geographic features compared to the US. Hence, there may be a problem if the three-dimensional space method of satellite orbit error calculation is used without any modification. This paper suggests a method which uses scalar values to calculate satellite orbit errors instead of using three-dimensional space. Also, this paper proposes the feasibility for this method for a narrow area. The suggested method uses the scalar value, which is a projection of orbit errors on the LOS vector between a reference and a satellite. This method confirms the change in errors according to the baseline distance between Korea and America. The difference in the error change is compared to present the feasibility of the proposed method.