Integrity monitoring for precise orbit determination of LEO satellites

Due to an increasing requirement for high accuracy orbital information for low Earth orbit (LEO) satellites, precise orbit determination (POD) of LEO satellites is a topic of growing interest. To assure the safety and reliability of the applications requiring high accuracy LEO orbits in near-real-time, integrity monitoring (IM) is an essential operation of the POD process. In this contribution, the IM strategy for LEO POD in both the kinematic and reduced-dynamic modes is investigated. The overbounding parameters of the signal-in-space range error are investigated for the GPS products provided by the International GNSS Service’s Real-Time Service and the Multi-GNSS Advanced Demonstration of Orbit and Clock Analysis service. Benefting from the dynamic models used and the improved model strength, the test results based on the data of the LEO satellite GRACE FO-1 show that the average-case mean protection levels (PLs) can be reduced from about 3–4 m in the kinematic mode to about 1 m in the reduced-dynamic mode in the radial, along-track and cross-track directions. The overbounding mean values of the SISRE play the dominant role in the fnal PLs. In the reduced-dynamic mode and averagecase projection, the IM availabilities reach above 99% in the radial, along-track and cross-track directions with the alert limit (AL) set to 2 m. The values are still above 98% with the AL set to 4 m, when the duty cycle of tracking is reduced to 40%, e.g., in the case of power limits for miniature satellites such as CubeSats

A Study on Real-time GPS Precise Orbit Determination System and Message Design of GPS Precise Orbit Covariance

학위논문(박사)--서울대학교 대학원 :공과대학 기계항공공학부,2020. 2. 기창돈.This study developed a centimeter-level real-time GPS precise orbit determination system for precise navigation and proposed an efficient message design of providing covariance. Global navigation satellite system is a typical navigation system that utilizes a number of satellites to provide the user's location and time. User performs navigation using satellite position and satellite time information. The orbit and clock error of a satellite contains meter-level errors and affects the user's position. Therefore, real-time precise orbit information of a centimeter-level is essential for real-time precise navigation applications such as drones, autonomous vehicles, and artificial intelligence vehicles. In addition, since the covariance of real-time precision orbit can be utilized to improve the user's position accuracy, fault detection, and calculate the level of position error, a system is needed to estimate the precise orbit and covariance. A real-time orbit determination system can estimate covariance of precise orbits using orbit dynamics and globally distributed network observations. The existing real-time orbit determination estimates the orbit error and clock error of the satellite together, but in this study, double differential measurements are used to estimate the orbit information separated from the clock error. This provides information in orbit alone, allowing relative navigation users to use it. Also, in addition to Earth's gravity, solar and lunar gravity, solar radiation pressure, gravitational field variation by tidal effect, and general relativity effects are analyzed and considered precisely. Most perturbations are well modeled, but in the case of solar radiation, estimates should be made in real-time as an environmentally sensitive component. To this end, the effects by earth and moon shadows were analyzed, and orbit determination taking into account the effects of the moon's shadow. The performance of a developed real-time precise orbit determination system was verified with IGS final orbit. 3D error and radius direction error are RMS 8cm and 2cm, respectively. Using this, the user expects to be able to improve navigation performance by utilizing precise orbits and to use covariance information to calculate the user's positional error level. Furthermore, it proposed an efficient way to provide covariance estimated in real-time GPS precision orbital determination system. Covariance of precise orbit information is highly utilized such as monitoring integrity and improving user location performance. However, since no product is currently providing orbit full covariance information, the covariance is estimated using the real-time precise orbit determination system established in this study and the provision method is proposed. The estimated covariance analyzed the interaxial correlation in the various coordinate systems, suggesting a coordinate system to ignore the interaxial correlation. The proposed measure could reduce the number of messages by 33 %, rather than providing the entire covariance information. The proposed covariance provision was evaluated at orbit confidence level in measurement and user confidence level in position error. Users' confidence level has been reduced to 30% since the satellite orbit's confidence level using covariance provides up to 55% more information than previously. As such, it is expected that the provision of covariance will improve the availability of precision navigation systems by reducing user confidence In this paper, it is expected that not only the real-time precise orbit determination system will be secured, but the system verification using actual data will be carried out so that it can be utilized in the real-time orbit determination system of the future Korean-type satellite navigation system. In addition, the proposed covariance provision could contribute to improved user location performance and integrity monitoring.최근 실시간 사용자의 정밀 위치를 활용한 드론, 자율주행 차량, 인공지능 자동차 등의 어플리케이션이 증가함에 따라, 실시간 GPS 정밀 궤도에 관한 관심이 높아지고 있다. 실시간 정밀궤도는 실시간 사용자의 위치 정확도를 개선할 수 있고, 정밀 궤도의 공분산은 사용자의 위치 정확도 향상, 고장 감지, 위치 신뢰 수준 계산 등에 활용될 수 있어 정밀 궤도뿐 아니라 정밀 궤도의 공분산을 제공할 수 있는 시스템이 요구되고 있다. 따라서, 본 연구에서는 센티미터 수준의 정밀 궤도 및 공분산 정보를 제공할 수 있는 실시간 GPS 정밀 궤도 결정 시스템을 개발하고 효율적인 공분산 제공 방안을 제안한다. 실시간 GPS 정밀 궤도 결정 시스템은 정밀 궤도 예측 기술과 섭동 모델 변수 추정, 자료 처리 필터 등의 복합 시스템이다. 본 논문은 확장형 칼만필터를 기반으로 실시간 GPS 정밀 궤도 결정 시스템을 구현하여, 실시간 정밀 궤도 및 정밀 궤도 공분산을 추정한다. 기존 실시간 궤도 결정 연구는 위성의 궤도 오차와 시계오차를 함께 추정하지만, 본 연구에서는 이중차분 측정치를 활용하여 궤도 단독의 정보를 제공한다. 또한, GPS 위성 환경의 궤도 섭동력인 태양과 달의 중력, 태양 복사압, 조석에 의한 중력장 변화, 일반 상대성 효과의 크기를 분석하여, 궤도 환경을 분석했다. 이 때, 지구 및 달 그림자 환경을 분석하여, 다양한 궤도 환경에서 궤도 결정 성능을 분석했다. 개발된 실시간 정밀 궤도 결정 시스템의 성능은 IGS 후처리 정밀 궤도와 비교하여 3D 오차는 위성 평균 RMS 8cm, 반경 방향으로 2cm 수준으로 검증하였고, 추정된 궤도의 공분산 정보는 오차의 확률 분포 및 누적 확률분포를 활용하여, 잘 반영함을 확인했다. 더 나아가 실시간 GPS 정밀 궤도 공분산의 특징을 분석하고, 효율적인 공분산 제공 방안을 제안했다. 실시간 GPS 정밀 궤도의 신뢰수준은 사용자 위치 안전을 위한 무결성, 가용성 등의 분야에서 활용도가 높다. 현재 정밀 궤도의 신뢰수준은 일반적으로 User range accuracy로 제공되고 있으나, 최근 궤도 오차의 전체 공분산을 제공하는 방안이 제안되고 있다. 정밀 궤도의 전체 공분산은 사용자 위치 성능 개선, 고장 감지 성능 향상, 가용성 증가 등의 성능 향상이 예측되고 있다. 그러나, 현재까지 실시간 궤도 전체 공분산을 제공하고 있는 제품이 없고, 향후 전체 공분산을 제공하기 위해 관련 연구가 필요한 상황이다. 본 연구에서 다양한 좌표계에서 실시간 GPS 정밀 궤도의 축간 상관관계를 분석함으로써 축간 상관관계를 무시할 수 있는 방안을 제안했다. 제안된 방안은 전체 공분산 정보를 제공을 위한 메시지 량을 33% 감소시킬 수 있고, 시뮬레이션을 통해 기존 방법 대비 위성 궤도의 측정치 내 오차 신뢰 수준의 크기는 55%, 사용자의 위치 신뢰 수준의 크기는 30% 수준으로 감소함을 확인했다. 따라서, 제안된 방법은 전체 공분산 제공을 위한 메시지량을 줄이고, 정밀 항법 시스템의 가용성을 개선시킬 수 있을 것으로 기대된다. 본 논문은 실시간 GPS 정밀 궤도 결정 시스템을 정밀하게 구현하여, 국내 실시간 GPS 정밀 궤도 결정 시스템의 성능을 센티미터 수준으로 향상시켰으며, 효율적인 궤도 공분산 제공방안을 제안했다. 실시간 구조와 실시간 GPS 정밀 궤도 결정의 기반 기술은 향후 한국형 위성항법 시스템의 실시간 궤도 결정에 활용될 수 있을 것으로 기대한다. 또한 제안된 공분산 제공 방안은 GPS 뿐 아니라 다양한 위성항법 시스템의 공분산 제공 파라미터를 효율적으로 제공함으로써 사용자 위치 성능 향상 및 무결성 감시 등에 기여할 수 있을 것으로 기대한다.1장. 서 론 １ 1. 연구 동기 및 목적 １ 2. 연구 동향 ３ 1) 실시간 GPS 정밀 궤도 결정 시스템 ４ 2) 실시간 정밀 궤도 신뢰수준 제공 연구 ６ 3. 연구 내용 및 방법 ７ 4. 연구 결과의 기여도 ８ 2장. 실시간 GPS 정밀 궤도 결정을 위한 기본 요소 １０ 1. GPS 시스템 １０ 1) GPS 시스템 개요 １０ 2) GPS 측정치 １１ 3) GPS 측정치 기타 오차 요소 １３ 2. IGS ２０ 3. 시간계 및 좌표계 ２２ 1) 시간계 ２２ 2) 좌표계 ２５ 4. GPS 위성 동역학 ２７ 1) 지구의 중력 ２８ 2) 3체 중력 ２９ 3) 태양 복사압 (Solar radiation pressure) ３０ 4) 지구 복사압 ３４ 5) 조석에 의한 중력장 변화 (Tidal effect) ３４ 6) 상대성 효과 ３６ 3장. 실시간 GPS 위성 정밀 궤도 결정 시스템 ３８ 1. 개요 ３８ 2. GPS 측정치 관측 모델 ４４ 3. EKF 필터 ４６ 4. 궤도 전파 모델 ５０ 5. 수치 적분 모델 ５２ 6. 알고리즘 효율화 ５４ 4장. 실시간 GPS 정밀 궤도 결정 계산 및 검증 ５５ 1. GPS 궤도 환경 분석 ５５ 1) 지구 그림자 ５６ 2) 달 그림자 ６０ 2. 실시간 GPS 정밀 궤도 결정 시스템 검증 결과 ６３ 1) 데이터 처리 환경 ６３ 2) 실시간 GPS 정밀 궤도 결정 시스템 계산 결과 ６４ 3) 달 그림자 모델 영향 분석 ６９ 5장. 실시간 정밀 항법 사용자를 위한 공분산 제공 방안 설계 ７７ 1. 궤도 공분산의 축간 상관관계 분석 ７７ 1) 다양한 좌표계에서 궤도 공분산 분석 ７８ 2) 시간에 따른 축간 상관관계 ８３ 3) RSW와 RAC 좌표계의 축간 상관관계 ８６ 4) 효율적인 제공방안 설계 ８８ 5) 공분산 제공 방법 별 비교 ９２ 2. 실시간 정밀 항법 사용자를 위한 정밀 궤도 공분산 제공 방안 및 효과 ９７ 1) 사용자 위치 신뢰 수준과 궤도 오차 신뢰수준 ９７ 2) 궤도 신뢰 수준 제공 방법의 종류 １０１ 3) 위치에 따른 궤도 신뢰수준 분석 １０３ 4) 위치에 따른 사용자 위치 신뢰수준 분석 １０９ 6장. 결론 및 향후 과제 １１２ 1. 결론 １１２ 2. 향후 과제 １１３ 참고 문헌 １１７Docto

The 26th Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting

This document is a compilation of technical papers presented at the 26th Annual PTTI Applications and Planning Meeting. Papers are in the following categories: (1) Recent developments in rubidium, cesium, and hydrogen-based frequency standards, and in cryogenic and trapped-ion technology; (2) International and transnational applications of Precise Time and Time Interval technology with emphasis on satellite laser tracking, GLONASS timing, intercomparison of national time scales and international telecommunications; (3) Applications of Precise Time and Time Interval technology to the telecommunications, power distribution, platform positioning, and geophysical survey industries; (4) Applications of PTTI technology to evolving military communications and navigation systems; and (5) Dissemination of precise time and frequency by means of GPS, GLONASS, MILSTAR, LORAN, and synchronous communications satellites

Performance of Receiver Autonomous Integrity Monitoring (RAIM) for Maritime Operations

The use of GNSS in the context of maritime applications has evolved during the past. The International Maritime Organization (IMO) has defined and published requirements for those applications. Comparing the requirements on the one hand specified by ICAO and on the other hand by IMO, significant differences get obvious. A major focus is on the evaluation of the performance of the integrity algorithms. Also concept drivers are discussed

EGNOS 1046 maritime service assessment

The present contribution evaluates how the European Geostationary Navigation Overlay System (EGNOS) meets the International Maritime Organization (IMO) requirements established in its Resolution A.1046 for navigation in harbor entrances, harbor approaches, and coastal waters: 99.8% of signal availability, 99.8% of service availability, 99.97% of service continuity and 10 m of horizontal accuracy. The data campaign comprises two years of data, from 1 May 2016 to 30 April 2018 (i.e., 730 days), involving 108 permanent stations located within 20 km of the coast or in islands across the EGNOS coverage area, EGNOS corrections, and cleansed GPS broadcast navigation data files. We used the GNSS Laboratory Tool Suite (gLAB) to compute the reference coordinates of the stations, the EGNOS solution, as well as the EGNOS service maps. Our results show a signal availability of 99.999%, a horizontal accuracy of 0.91 m at the 95th percentile, and the regions where the IMO requirements on service availability and service continuity are met. In light of the results presented in the paper, the authors suggest the revision of the assumptions made in the EGNOS Maritime Service against those made in EGNOS for civil aviation; in particular, the use of the EGNOS Message Type 10.This research was funded by the European GNSS Agency within the framework Integration of the Fundamental Elements, Contract GSA/OP/12/16/Lot1/SC1, and the APC was funded by the Spanish Ministry of Science, Innovation and Universities Project RTI2018-094295-B-I00.Peer ReviewedPostprint (published version

Integration of ARAIM technique for integrity performance prediction, procedures development and pre-flight operations

Advanced Receiver Autonomous Integrity Monitoring (ARAIM) is a new Aircraft Based Augmentation System (ABAS) technique, firstly presented in the two reports of the GNSS Evolutionary Architecture Study (GEAS). The ARAIM technique offers the opportunity to enable GNSS receivers to serve as a primary means of navigation, worldwide, for precision approach down to LPV-200 operation, while at the same time potentially reducing the support which has to be provided by Ground and Satellite Based Augmented Systems (GBAS and SBAS). Previous work analysed ARAIM performance, clearly showing the potential of this new architectures to provide the Required Navigation Performance down to LPV 200 approach procedures. However, almost all of the studies have been performed with respect to fixed points on a grid on the Earth’s surface, with full view of the sky, evaluating ARAIM performance from a geometrical point of view and using nominal performance in simulated scenarios which last several days. Though, the operational configuration was not examined; attitude changes from manoeuvres, obscuration by the aircraft body and shadowing from the surrounding environment could all affect the incoming signal from the GNSS constellations, leading to configurations that could adversely affect the real performance. In this research, ARAIM performances in simulated operational configurations are presented. Four different algorithms were developed that integrate the ARAIM technique for performance prediction analysis. These algorithms could usefully be implemented: • In the design of instrument approach procedures. The algorithms could be used to improve the procedure of the development of new instrument approaches, reducing time, effort and costs. • In the aircraft Flight Management Systems. The algorithms could support the pilots in the pre-flight briefing, highlighting possible integrity outage in advance and allowing them to select a different approach or making them aware of the need to utilise additional positioning systems. Increased awareness and better pre-flight planning could ultimately improve the safety of flights and contribute to the safe introduction of GNSS as a viable positioning method for instrument approach. The results showed that the aircraft attitude and the surrounding environment affect the performance of the ARAIM algorithm; each satellite lost generates a peak in the performance parameters that depends on the total number of satellites in view, their relative geometry and on the number of satellites lost at the same time. The main outcome of this research is the identification that the ideal scenario would be to have a tri-constellation system that provides at the same time high redundancy, reliability and increased safety margin

Determination of the effects of GPS failures on aviation applications

Imperial Users onl

On the Mobility of Small Aperture Telescopes for Initial Orbit Determination and Apparent Magnitude Derivation of Low Earth Satellites

Maintaining Space Domain Awareness (SDA) of satellites in low Earth orbit (LEO) requires effective methods of tracking and characterization. Optical measurements of these objects are generally sparse due to limited access intervals and high angular rates. Light pollution and geographic obstructions may also preclude consistent observations. However, a mobile small aperture telescope grants the ability to minimize such environmental effects, thereby increasing capture likelihoods for objects within this regime. By enhancing LEO satellite visibility in this way, extensive orbital and visual data are obtainable. An 8-inch Meade LX200GPS telescope equipped with a Lumenera SKYnyx2-0M CCD camera comprises the system that conducted observations of LEO. From 22 sessions spanning four months, 76 objects were imaged to provide a data set of 313 streak frames for initial orbit and photometric analyses. An Assumed Circular Orbit formulation provided considerable refinements in semimajor axis and eccentricity, up to one order of magnitude, when compared to a Gauss Extended method. Regarding the use of initial orbits for future pass predictions, the Assumed Circular Orbit angular positions indicated improvements up to 97.4% in accuracy and 65.7% in consistency over Gauss Extended. A photometric study placed the brightest observed visual magnitude at 3.60 mag, and the faintest visible at 9.47 mag. By converting brightness to a physical size, detected objects were approximately 23.8 meters at the largest and 40.6 centimeters at the smallest. Angles and brightness measurements of LEO satellites with mobile platforms may thus benefit the SDA effort

Integration of ARAIM technique for integrity performance prediction, procedures development and pre-flight operations

Advanced Receiver Autonomous Integrity Monitoring (ARAIM) is a new Aircraft Based Augmentation System (ABAS) technique, firstly presented in the two reports of the GNSS Evolutionary Architecture Study (GEAS). The ARAIM technique offers the opportunity to enable GNSS receivers to serve as a primary means of navigation, worldwide, for precision approach down to LPV-200 operation, while at the same time potentially reducing the support which has to be provided by Ground and Satellite Based Augmented Systems (GBAS and SBAS). Previous work analysed ARAIM performance, clearly showing the potential of this new architectures to provide the Required Navigation Performance down to LPV 200 approach procedures. However, almost all of the studies have been performed with respect to fixed points on a grid on the Earth’s surface, with full view of the sky, evaluating ARAIM performance from a geometrical point of view and using nominal performance in simulated scenarios which last several days. Though, the operational configuration was not examined; attitude changes from manoeuvres, obscuration by the aircraft body and shadowing from the surrounding environment could all affect the incoming signal from the GNSS constellations, leading to configurations that could adversely affect the real performance. In this research, ARAIM performances in simulated operational configurations are presented. Four different algorithms were developed that integrate the ARAIM technique for performance prediction analysis. These algorithms could usefully be implemented: • In the design of instrument approach procedures. The algorithms could be used to improve the procedure of the development of new instrument approaches, reducing time, effort and costs. • In the aircraft Flight Management Systems. The algorithms could support the pilots in the pre-flight briefing, highlighting possible integrity outage in advance and allowing them to select a different approach or making them aware of the need to utilise additional positioning systems. Increased awareness and better pre-flight planning could ultimately improve the safety of flights and contribute to the safe introduction of GNSS as a viable positioning method for instrument approach. The results showed that the aircraft attitude and the surrounding environment affect the performance of the ARAIM algorithm; each satellite lost generates a peak in the performance parameters that depends on the total number of satellites in view, their relative geometry and on the number of satellites lost at the same time. The main outcome of this research is the identification that the ideal scenario would be to have a tri-constellation system that provides at the same time high redundancy, reliability and increased safety margin