Advancing the Solar Radiation Pressure Model for BeiDou-3 IGSO Satellites

In the absence of detailed surface information, empirical solar radiation pressure (SRP) models, such as the five-parameter Empirical CODE Orbit Model (ECOM1) and its extended version-ECOM2, are widely used for modeling SRP forces acting on GNSS satellites. This study shows that the orbits of BeiDou-3 Inclined Geosynchronous Orbit satellites (IGSOs) determined with the ECOM1 model suffer from systematic once-per-revolution radial orbit errors, which can be partly reduced by the ECOM2 model. To eliminate such orbit errors, the BeiDou-3 IGSO optical coefficients are solved by using an adjustable box-wing (ABW) model and then introduced into an a priori box-wing SRP model to enhance the ECOM1 model (ECOM1 + BW). In the ABW solution, in addition to satellite body and solar panels, the contributions of the communication payloads installed on BeiDou-3 IGSO ±X panels on the SRP are also considered, which markedly improves the stability of the optical coefficient estimates. The efficiency of the developed a priori box-wing model is demonstrated through eliminated once-per-revolution radial orbit errors and decreased day boundary discontinuities. However, the orbit solutions still show significant degradations during eclipse seasons. The results of the first yaw-attitude analysis for eclipsing BeiDou-3 IGSOs show that their yaw behaviors are the same as those of BeiDou-3 CAST (China Academy of Space Technology) MEOs (Medium Earth Orbit satellites), and have been well considered in the study. This rules out the possibility that attitude errors are the potential reason for the orbit deterioration. By introducing a once-per-revolution sine term in the Sun direction (Ds term) and keeping Ds active during the Earth’s shadow transitions to the ECOM1 + BW model, the orbit performance inside the eclipse seasons is significantly improved and can be comparable to that outside the eclipse seasons

China Near Seas Combat Capabilities

The capstone U.S. Defense Department study on the future operational environment declares, China\u27s rise represents the most significant single event on the international horizon since the collapse of the Cold War. Understanding and assessing changes in China\u27s traditionally defensive naval strategy, doctrine, and force structure are of obvious importance to the U.S. Navy (USN) and other Pacific navies concerned with the possible security implications of that rise. This chapter examines the development of the Chinese navy\u27s Houbei (Type 022) fast-attack-craft force and its roles and missions in China\u27s near seas and discusses implications for the U.S. Navy and other navies in the region.https://digital-commons.usnwc.edu/cmsi-red-books/1010/thumbnail.jp

Desarrollo de algoritmos para el tratamiento de datos GNSS : su aplicación a los escenarios GPS modernizado y Galileo

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Matemáticas, Sección Departamental de Física de la Tierra, Astronomía y Astrofísica I (Geofísica y Meteorología) (Astronomía y Geodesia), leída el 24-07-2012Nowadays, the major GNSS systems are the american GPS and the russian GLONASS, however, in a near future the european project Galileo and the chinesse system COMPASS will become part of the current GNSS scenario. These systems will transmit for the first time three different frequencies, giving place to a multi-system and multi-frequency scenario which will dramatically push the boundaries of the positioning techniques. Currently, one of the most studied positioning techniques is known as Precise Point Positioning (PPP), which is aimed at estimating precise receiver position from undifferenced GNSS code and carrier phase observations and precise satellite products. In this thesis, some new and original algorithms for static PPP have been developed, which are able to deal with the future multi-system and multifrequency GNSS observations. The new algorithms have been named MAP3. In the new approach, the least squares theory is applied twice to estimate the ionospheric delay, initial ambiguities and smoothed pseudodistances from undifferenced observations, which in turn are used to recover the receiver position and its clock offset. MAP3 provides position estimations with an accuracy of 2.5 cm after 2 hours observation and 7 mm in 1 day, being at the same level as other PPP programs and even better results are obtained with MAP3 in short observation periods. Moreover, MAP3 have provided some of the first results in positioning from GIOVE observations and GPC products. In addition, these algorithms have been applied in the analysis of the influence of ionospheric disturbances on the point positioning, concluding that the presence of a high ROT (Rate of TEC), observed at equatorial latitudes, reflects a significant degradation of the point positioning from dual-frequency observations.Actualmente, los únicos sistemas globales de navegación por satélites operativos son GPS y GLONASS, sin embargo, en un futuro cercano el proyecto europeo Galileo y el sistema chino COMPASS entrarán a formar parte del actual escenario GNSS. Estos sistemas emplearán por primera vez, tres frecuencias distintas, dando lugar a un escenario multi-frecuencia que revolucionará las técnicas de posicionamiento. Entre las técnicas actuales de posicionamiento con GNSS destaca el Posicionamiento Preciso Puntual (PPP), que consiste en determinar la posición de un receptor a partir de observaciones de código y fase no differenciadas y productos precisos. En este trabajo de tesis se han desarrollado unos nuevos y originales algoritmos para PPP estático, llamados MAP3, capaces de procesar observaciones GNSS multifrecuencia y multi-sistema del futuro escenario GNSS y determinar la posición de un receptor de forma precisa y exacta. Los algoritmos MAP3 se dividen en dos partes en las cuales se ha aplicado la teoría mínimos cuadrados y se han obtenido expresiones explícitas para estimar el retraso ionosférico, ambigüedades de fase inicial y pseudodistancias suavizadas, que se emplean para determinar la posición del receptor y el offset de su reloj. MAP3 proporciona una estimación de la posición con una exactitud de 2.5 cm tras 2 horas de observación y de 7 mm tras 24 h, resultados que mejoran los obtenidos hasta el momento con otros programas para PPP en periodos cortos de tiempo. Además, MAP3 han proporcionado los primeros resultados en el posicionamiento con observaciones GIOVE y productos del GPC. Por otro lado, estos algoritmos se han aplicado al análisis de los efectos de ciertas perturbaciones ionosféricas en el posicionamiento concluyendo que la presencia de un ROT (Rate of TEC) elevado, observado en latitudes ecuatoriales, refleja una degradación significativa del posicionamiento puntual con observaciones doble frecuencia.Unidad Deptal. de Astronomía y GeodesiaFac. de Ciencias MatemáticasTRUEunpu

Sidereal filtering for multi-GNSS precise point positioning and deformation monitoring

PhD ThesisFor earthquake and tsunami early-warning, it is crucial that displacements resulting from earthquakes are recorded with speed and accuracy. Traditional methods based on seismometer data often suffer from errors during integration which results in the maximum displacement not being accurately recorded. In contrast, Global Navigation Satellite Systems (GNSS) can measure permanent static displacement directly; however it too is subject to errors, the main error of which is multipath. Multipath can lead to errors in the measurement of small displacements or mask the displacement completely. Multipath is dependent on the geometry of the GNSS constellation orbits and the antenna’s surrounds. GPS satellites have an orbital period of half a sidereal day with a near-sidereal repeating ground track. Similarly, the GLONASS constellation geometry repeats about once every eight sidereal days thus the satellite-reflector geometry will repeat with these same periods. By accurately determining the repeat periods it is possible to remove the multipath error by analysing data from the previous repeat periods. This method is known as sidereal filtering and can be used to improve the precision of GNSS coordinate time series and hence improve displacement measurements. This thesis looks to find the optimum geometry repeat period for the GLONASS constellation, which was found to be 689248 s and combine GPS and GLONASS for observation domain near-sidereal filtering. GLONASS-only filtering improves GLONASS coordinate solution standard deviations, on average, by 22.3%, 18.1% and 17.6% in the East, North and Up, whereas GPS and GLONASS combined filtering improves GPS and GLONASS standard deviations by 21.2%, 23.4% and 25.1%. The average maximum stability improvement, in terms of Allan deviation for all components is approximately 21.0% for GLONASS-only and 29.0% for combined filtering. Combined filtering produces more stable coordinate time series for averaging intervals over a few hundred seconds. It also reduces coordinate time series standard deviations and thus aids the measurement of small coordinate displacements and reduces the number of false alarms by half during displacement detection. Filtering improves the accuracy and precision of displacement estimates on average by about 2 mm, in terms of the difference between filtered and unfiltered RMSD and mean displacement values.UK Natural Environment Research Council (NERC

Undifferenced and Uncombined GNSS Time Transfer and its Space Applications

This thesis presents a framework for developing a state-of-the-art undifferenced and uncombined (UDUC) time transfer technique for space applications. It addresses challenges in GNSS time transfer, such as multi-frequency signal modelling, satellite clock estimation, and hardware delay variations. The thesis introduces the UDUC POD method for GNSS time transfer in space and explores the feasibility of constructing a LEO-based space-time reference. This PhD dissertation is among the first to investigate the UDUC GNSS time transfer

RUSSIA AND CHINA IN SPACE: SECURITY AND DEFENSE CAPABILITIES. IMPLICATIONS OF BILATERAL COOPERATION.

Η παρούσα διπλωματική εργασία παρέχει μια εις βάθος ανάλυση των πτυχών άμυνας και ασφάλειας των ρωσικών και κινεζικών διαστημικών προγραμμάτων. Εξετάζει τις πολιτικές και τις προτεραιότητες των δύο χωρών στο διάστημα, τις στρατηγικές τους για τη χρήση διαστημικών πόρων και τις προοπτικές τους για διεθνή συνεργασία. Η μελέτη επικεντρώνεται σε στρατιωτικές εφαρμογές της διαστημικής τεχνολογίας, συμπεριλαμβανομένων των δορυφορικών αμυντικών συστημάτων και των αντί-δορυφορικών όπλων. Λαμβάνει επίσης υπόψη τις γεωπολιτικές επιπτώσεις των διαστημικών προγραμμάτων αυτών των δύο χωρών. Η Κίνα είναι μια ανερχόμενη δύναμη σε γεωπολιτικό, οικονομικό και τεχνολογικό επίπεδο, αμφισβητώντας την παγκόσμια κυριαρχία των ΗΠΑ. Η συνεργασία της με τη Ρωσία έχει καθοριστική στρατηγική σημασία. Η εισβολή της Ρωσίας στην Ουκρανία έχει αλλάξει το γεωπολιτικό τοπίο, προκαλώντας μετατοπίσεις στις διεθνείς οικονομικές, στρατιωτικές και τεχνολογικές συμμαχίες. Η παρούσα εργασία εξετάζει αυτές τις εξελίξεις και τις αναμενόμενες διεθνείς επιπτώσεις τους για τη διαστημική βιομηχανία και τη συνεργασία μεταξύ διαστημικών οργανισμών, ιδιαίτερα μετά την επιβολή των δυτικών κυρώσεων κατά της Ρωσίας.This thesis provides an in-depth analysis of the defense and security aspects of the Russian and Chinese space programs. It examines the countries’ policies and priorities in space, their strategies for utilizing space assets, and their prospects for international collaboration. The study focuses on military applications of space technology including satellite defense systems and anti-satellites weapons. It also considers the geopolitical implications of the space programs of these two countries. China is a rising power in geopolitics, economics, and technology, challenging the global dominance of the U.S. Its collaboration with Russia holds significant strategic importance. The invasion of Ukraine by Russia has shifted the geopolitical landscape, triggering changes in economic, military, and technological alliances. This thesis examines these developments and their expected international implications for the space industry and collaboration among space organizations, particularly after the imposition of Western sanctions against Russia

Reconfigurable satellite constellations for geo-spatially adaptive Earth observation missions

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 145-151).Continuously increasing demand for Earth observation in atmospheric research, disaster monitoring, and intelligence, surveillance and reconnaissance (ISR) has been met by responsive architectures such as unmanned aerial systems (UAS) or artificial satellites. Space-based architectures can provide non-dominated design solutions on the utility-cost curve compared to alternate architectures through the use of two approaches: (1) reducing satellite manufacturing and launch costs and (2) introducing reconfigurability to the satellite constellations. Reconfigurable constellations (ReCons) enable fast responses to access targets of interest while providing global monitoring capability from space. The wide-area coverage and fast responses provided ReCon can complement high-resolution imagery provided by UAS. A newly proposed ReCon framework improves the model fidelity of previous approaches by utilizing Satellite Tool Kit (STK) simulations and Earth observation mission databases. This thesis investigates the design and optimization of ReCon in low Earth orbits. A multidisciplinary simulation model is developed, to which optimization techniques are applied for both single-objective and multi-objective problems. In addition to the optimized baseline ReCon design, its variants are also considered as case studies. Future work will potentially co-optimize ReCon and UAS-like systems.by Sung Wook Paek.S.M

Interference Management and System Optimization with GNSS and non-GNSS Signals for Enhanced Navigation

In the last few decades, Global Navigation Satellite System (GNSS) has become an indispensable element in our society. Currently, GNSS is used in a wide variety of sectors and situations, some of them offering critical services, such as transportation, telecommunications, and finances. For this reason, and combined with the relative ease an attack on the GNSS wireless signals can be performed nowadays with an Software Defined Radio (SDR) transmitter, GNSS has become more and more a target of wireless attacks of diverse nature and motivations. Nowadays, anyone can buy an interference device (also known as a jammer device) for a few euros. These devices are legal to be bought in many countries, especially online. But at the same time, they are illegal to be used. These devices can interfere with signals in specific frequency bands, used for services such as GNSS. An outage in the GNSS service at a specific location area (which can be even a few km2) could end up in disastrous consequences, such as an economical loss or even putting lives at risk, since many critical services rely on GNSS for their correct functioning. Fundamentally, this thesis focuses on developing new methods and algorithms for interference management in GNSS. The main focus is on interference detection and classification, but discussions are also made about interference localization and mitigation. The detection and classification algorithms analyzed in this thesis are chosen from the point of view of the aviation domain, in which additional constraints (e.g., antenna placement, number of antennas, vibrations due to movement, etc.) need to be taken into account. The selected detection and classification methods are applied at the pre-correlation level, based on the raw received signal. They apply specific signal transforms in the digital domain (e.g., time-frequency transformations) to the received signal. With such algorithms, interferences can be detected at a level as low as 0 dB Jamming-to-Signal Ratio (JSR). The interference classification combines transformed signals with previously trained signals Convolutional Neural Network (CNN) and/or Support Vector Machine (SVM) to determine the type of interference signal among the studied ones. The accuracy of such a classification methodology is above 90%. Knowing which signal causes interference we can better optimize which mitigation and localization algorithm we should use to obtain the best mitigation results. Furthermore, this thesis also studies alternative positioning methods, starting from the premise that GNSS may not always be available and/or we are certain that we can not rely on it due to some reason such as high or unmitigated interferences. Therefore, if one needs to get a Position Velocity and Time (PVT) solution, one would have to rely on alternative signals that could offer positioning features, such as the cellular network signals (i.e. 4G, 5G, and further releases) and/or satellite positioning based on Low Earth Orbit (LEO) satellites. Those systems use presumably different frequency bands, which makes it more unlikely that they will be jammed at the same time as the GNSS signal. In this sense, positioning based on LEO satellites is studied in this thesis from the point of view of feasibility and expected performance

Contributions to GNSS-R earth remote sensing from nano-satellites

Premi extraordinari doctorat UPC curs 2015-2016, àmbit de CiènciesGlobal Navigation Satellite Systems Reflectometry (GNSS-R) is a multi-static radar using navigation signals as signals of opportunity. It provides wide-swath and improved spatio-temporal sampling over current space-borne missions. The lack of experimental datasets from space covering signals from multiple constellations (GPS, GLONASS, Galileo, Beidou) at dual-band (L1 and L2) and dual-polarization (Right Hand Left Hand Circular Polarization: RHCP and LHCP), over the ocean, land and cryosphere remains a bottleneck to further develop these techniques. 3Cat-2 is a 6 units (3 x 2 elementary blocks of 10 x 10 x 10 cm3) CubeSat mission ayming to explore fundamentals issues towards an improvement in the understanding of the bistatic scattering properties of different targets. Since geolocalization of specific reflections points is determined by the geometry only, a moderate pointing accuracy is still required to correct for the antena pattern in scatterometry measurements. 3Cat-2 launch is foreseen for the first quarter 2016 into a Sun-Synchronous orbit of 510 km height using a Long March II D rocket. This Ph.D. Thesis represents the main contributions to the development of the 3Cat-2 GNSS-R Earth observation mission (6U CubeSat) including a novel type of GNSS-R technique: the reconstructed one. The desing, development of the platform, and a number of ground-based, airborne and stratospheric balloon experiments to validate the technique and to optimize the instrument. In particular, the main contributions of this Ph.D. thesis are: 1) A novel dual-band Global Navigation Satellite Systems Reflectometer that uses the P(Y) and C/A signals scattered over the sea surface to perform highly precise altimetric measurements (PYCARO). 2) The first proof-of-concept of PYCARO was performed during two different ground-based field experiments over a dam and over the sea under different surface roughness conditions. 3) The scattering of GNSS signals over a water surface has been studied when the receiver is at low height, as for GNSS-R coastal altimetry applications. The precise determination of the local sea level and wave state from the coast can provide useful altimetry and wave information as "dry" tide and wave gauges. In order to test this concept an experiment has been conducted at the Canal d'Investigació i Experimentació Marítima (CIEM) wave channel for two synthetic "sea" states. 4) Two ESA-sponsored airborne experiments were perfomed to test the precision and the relative accuracy of the conventional GNSS-R. 5) The empirical results of a GNSS-R experiment on-board the ESA-sponsored BAXUS 17 stratospheric balloon campaign performed North of Sweden over boreal forests showed that the power of the reflected signals is nearly independent of the platform height for a high coherent integration time. 6) An improved version of the PYCARO payload was tested in Octover 2014 for the second time during the ESA-sposored BEXUS-19,. This work achieved the first ever dual-frequency, multi-constellation GNSS-R observations over boreal forests and lakes using GPS, GLONASS and Galileo signals. 7) The first-ever dual-frequency multi-constellation GNSS-R dual-polarization measurements over boreal forests and lakes were obtained from the stratosphere during the BEXUS 19 using the PYCARO reflectometer operated in closed-loop mode.Global Navigation Satellite Systems Reflectometry (GNSS-R) es una técnica de radar multi-estático que usa señales de radio-navegación como señales de oportunidad. Esta técnica proporciona "wide-swath" y un mejor sampleado espacio-temporal en comparación con las misiones espaciales actuales. La falta de datos desde el espacio proporcionando señales de múltiples constelaciones (GPS, GLONASS, Galileo, Beidou) en doble banda (L1 y L2) y en doble polarización (RHCP y LHCP) sobre océano, tierra y criosfera continua siendo un problema por solucionar. 3Cat-2 es un cubesat de 6 unidades con el objetivo de explorar elementos fundamentales para mejorar el conocimiento sobre el scattering bi-estático sobre diferentes medios dispersores. Dado que la geolocalización de puntos de reflexión específicos está determinada solo por geometría, es necesario un requisito moderado de apuntamiento para corregir el diagrama de antena en aplicaciones de dispersometría. El lanzamiento del 3Cat-2 será en Q2 2016 en una órbitra heliosíncrona usando un cohete Long March II D. Esta tesis representa las contribuciones principales al desarrollo del satélite 3Cat2 para realizar observación de la tierra con GNSS-R incluyendo una nueva técnica: "the reconstructed-code GNSS-R". El diseño, desarrollo de la plataforma y un número de experimentos en tierra, desde avión y desde globo estratosférico para validar la técnica y optimizar el instrumento han sido realizados. En particular, las contribuciones de esta Ph.D. son: 1) un novedoso Global Navigation Satellite Systems Reflectometer que usa las señales P(Y) y C/A después de ser dispersadas sobre la superficie del mar para realizar medidas altimétricas muy precisas. (PYCARO). 2) La primera prueba de concepto de PYCARO se hizo en dos experimentos sobre un pantano y sobre el mar bajo diferentes condiciones de rugosidad. 3) La disperión de las señales GNSS sobre una superfice de agua ha sido estudiada para bajas altitudes para aplicaciones GNSS-R altimétricas de costa. La determinación precisa del nivel local del mar y el estado de las olas desde la costa puede proporcionar información útil de altimetría e información de olas. Para hacer un test de este concepto un experimento en el Canal d'Investigació i Experimentació Marítima (CIEM) fue realizado para dos estados sintéticos de rugosidad. 4) Dos experimentos en avión con esponsor de la ESA se realizaron para estudiar la preción y la exactitud relativa de cGNSS-R. 5) Los resultados empíricos del experimento GNSS-R en BEXUS 17 con esponsor de la ESA realizado en el norte de Suecia sobre bosques boreales mostró que la potencia reflejada de las señales es independiente de la altitud de la plataforma para un tiempo de integración coherente muy alto. 6) Una versión mejorada del PYCARO fue testeada en octubre del 2014 por segunda vez durante el BEXUS 19 que también fue patrocidado por la ESA. Este trabajo proporcionó las primeras medidas GNSS-R sobre bosques boreales en doble frecuencia usando varias constelaciones GNSS. 7) Las primeras medidas polarimétricas (RHCP y LHCP) de GNSS-R sobre bosques boreales también fueron conseguidas durante el experimento BEXUS 19.Award-winningPostprint (published version

Advanced Location-Based Technologies and Services

Since the publication of the first edition in 2004, advances in mobile devices, positioning sensors, WiFi fingerprinting, and wireless communications, among others, have paved the way for developing new and advanced location-based services (LBSs). This second edition provides up-to-date information on LBSs, including WiFi fingerprinting, mobile computing, geospatial clouds, geospatial data mining, location privacy, and location-based social networking. It also includes new chapters on application areas such as LBSs for public health, indoor navigation, and advertising. In addition, the chapter on remote sensing has been revised to address advancements