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In the second part of the series of articles, the issues of the systemic organization of mathematical models for solving the problem of controlling the flows of target information in the Earth remote sensing space system are considered. A description of the interrelated mathematical models of the orbital constellation as components of the information system, the main task of which is to survey ground objects and the formation of the initial volume of information for its further processing, is presented. To calculate the time of servicing the request by the space segment, the following methods of formation are proposed: a model of the evolution of the Earth remote sensing spacecraft orbit; model for forecasting possible spacecraft correction intervals to maintain nominal orbital parameters; model for forecasting possible time intervals for on / off cycles of observation equipment; model for forecasting possible time intervals for dumping the received information to the information reception points. When calculating the cost of servicing a single request from the orbital complex, both the cost of servicing one spacecraft per unit of time and the cost of processing a single request from the ground complex were taken into account. In conclusion, a generalized form of representation of the target information flow model of the Earth remote sensing space system is proposed as an interconnected sequence of functions for changing the amount of information when an appropriate processing process (traffic change functions) is applied to it. General approaches to solving the optimization problem are considered.

The recent advances in low earth orbit (LEO) satellites enable the satellites to provide task processing capability for remote Internet-of-Things (IoT) mobile devices (IMDs) without proximal multiaccess edge computing (MEC) servers. In this article, by leveraging the LEO satellites, a novel MEC framework for terrestrial-satellite IoT is proposed. With the aid of terrestrial-satellite terminal (TST), the computation offloading from IMDs to LEO satellites is divided into two stages in the ground and space segments. In order to minimize the weighted-sum energy consumption of IMDs, we decompose the formulated problem into two layered subproblems: 1) the lower layer subproblem minimizing the latency of space segment, which is solved by sequential fractional programming with attaining the first-order optimality and 2) the upper layer subproblem that is solved by exploiting the convex structure and applying the Lagrangian dual decomposition method. Based on the solutions to the two layered subproblems, an energy-efficient computation offloading and resource allocation algorithm (E-CORA) is proposed. By simulations, it is shown that: 1) there exists a specific amount of offloading bits, which can minimize the energy consumption of IMDs and the proposed E-CORA outperforms full offloading and local computing only; 2) larger transmit power of the TST helps to save the energy of IMDs; and 3) by increasing the number of visible satellites, the ratio of offloading bits increases while the energy consumption of IMDs can be decreased.

Galileo navigation system has significantly expanded satellite constellation over the last few years and now serves with 22 satellites in three orbital planes. The development of the Galileo is not only limited to the number of satellites in the space segment, but also the quality of the IGS MGEX products produced by different Analysis Centers has increased gradually and brought up the topic of investigation of the accuracy and precision of the Galileo-only positioning. However, almost all of the studies on Galileo-only positioning in the literature have been performed with Precise Point Positioning method and comprehensive studies with the relative positioning technique are quite a few. In this study, the development of the accuracy and precision of the Galileo from 2016 to the end of 2019 (4 years) has been investigated for the first time by means of relative positioning technique. For this purpose, data of eight GNSS stations selected from the IGS MGEX network were obtained and analyzed with GAMIT/GLOBK software as GPS-only and Galileo-only, separately. Using the daily solutions obtained from both navigation systems, time series were produced and the differences between them were compared in order to reveal the Galileo accuracy. According to the results, the accuracy of the Galileo was variable during the experiment and it could be examined in three periods. The averages of 3D positioning error in the first period (2016-2017) is 14.92 mm and improved by 56%, and decreased to 6.55 mm in the second period (2017-2018), and then improvement at 23% in the third period (2018 to the end of 2019) and decrescent to level of 5.13 mm on average for all stations. Similarly, standard deviations obtained from Galileo increased during the experiment and during the 3rd period it was closed to a few mm with GPS. It was concluded that the accuracy and precision of the Galileo showed parallel development and the development was directly related to the number of satellites in the Galileo constellation, and as a result, nowadays, Galileo-derived coordinates are close to the coordinates obtained from the GPS by a few mm.

The design of Very High Throughput Satellite (VHTS) systems will be an important milestone for future telecommunications systems in the light of the ongoing integration between satellite and 5G technologies as well as with the upcoming 6 G evolution. To this end, satellite systems will be operating at EHF frequency bands, hence requiring a special attention to the overall network design in terms of ground and space segment optimisation. In particular, the mitigation of feeder link outage events through advanced prediction techniques and the exploitation of smart gateway diversity concepts will be combined with an overarching network resources’ orchestration, jointly conceived to meet the QoS requirements of the end users. In this respect, this paper proposes a novel optimisation framework able to achieve very high throughput system figures, building on an adaptive QoS management concept. The proposed framework has been compared with other existing solutions from the literature and validated by means of extensive simulation campaigns, whose collected results show significant performance improvements.

A technique for assessing the market of advanced global telecommunication networks, including the space segment, as global coverage communication megaconstellations is considered. According to our results, the worldwide traffic consumption by 5G mobile devices by 2022 will be almost 8.5 EB/month. The possible cost of deploying a megaconstellation of communications to provide broadband Internet access at any place in the world can range from $5 to $50 billion, depending on service requirements. We have shown that modern and prospective space communications constellations can be integrated into a new-generation global telecommunication infrastructure. Deployment of a constellation of 600 or more devices with a cost of almost $10 billion can provide traffic transit from base stations in remote areas delivering the population with broadband Internet through 5G networks.

Robotic exploration of the solar system using small satellites (SmallSats) is gaining popularity because of SmallSats’ lower cost and faster development cycle compared to primary science missions. A potential obstacle for deployment of SmallSats in deep space is the limitation associated with the communications link imposed by SmallSats' frugal power and antenna size. These technical limitations constrain the range and throughput of SmallSats and may impact their navigation performance. To allow SmallSats to play a greater role in deep space science endeavors, we propose an enhanced communications architecture that will lessen the communications disparity between larger, more expensive missions and SmallSats. The objectives of the study are to define a communications architecture, in-flight and flight-to-ground, that is needed for planetary SmallSats, both standalone or in support of a larger mission; and to develop a guideline for primary spacecraft that would communicate with ride-along SmallSats. This work treats the space segment and the ground network as a whole to provide for improvements not only via investments in technology, but also via improvements in operational procedures. The study includes reviews of current communication concepts, technologies, and procedures, as well as an assessment of navigation needs, evaluation of the communication architecture performance for a range of destinations and applications, and identification of any gaps in capability. The study product is a set of recommendations to space agencies and the planetary SmallSat community. The main thrust of these recommendations is investment in technology, such as radios, antennas, protocols, and methodologies. The concepts for improving communications capability of deep space SmallSats are discussed in a series of three articles, Improving Small Satellite Communications in Deep Space. In this article, Part I, we discuss SmallSat direct-to-Earth links, as well as SmallSat communications equipment. In Part II, we discuss navigation topics, proximity links and networks, and the use of the communications channel for science observations. We present the ground network in Part III. Definitions and assumptions are provided here in Part I.

Developments in technologies, attitudes and investment are transforming the space environment, achieving greater accessibility for an increasing number of parties. New and proposed constellations will increase the in-orbit satellite population by the order of thousands, expanding the threat landscape of the space industry. This article analyses past satellite security threats and incidents to assess the motivations and characteristics of adversarial threats to satellites. The ground and radio frequency communications were the most favoured targets; however, the boom of satellites constellations in the upcoming years may shift this focus towards the space segment which must be addressed. Key technology advancements and open issues in the satellite industry related to security and operational requirements are also discussed.

Metop is the space segment of the EUMETSAT Polar System (EPS), which provides real-time data to several European meteorological services as well as to the National Oceanic and Atmospheric Administration (NOAA) and other international agencies. The third Metop satellite, Metop-C, was launched on 7 November 2018 and shall enter in operations in few months, once the on-going commissioning of the meteorological products is completed. Each Metop satellite was designed to operate at least five years. A sequential deployment of the satellites was foreseen to achieve the target mission duration of 15 years, replacing an old one at end of life with a newer one; thanks to the excellent performances of the launchers and of the platform itself, and to continuous improvements to the fuel management, it was possible to extend the operational life of each satellite by a factor of three, still maintaining enough fuel to perform safe de-orbiting operations (foreseen for Metop-A, launched in 2006, at the end of 2021). This provided the opportunity to develop in 2012 (after Metop-B launch) dual-satellite products, which now, with the arrival of Metop-C, can evolve to tri-satellite; several decisions, concerning the selection of launch date and time as well as commissioning and operational locations, had to be been taken to achieve the target configuration; the analyses leading to these decisions are discussed here.

An analysis of a number of tasks that need to be solved during the war in the southeastern region of our country requires a meaningful study of world experience in the use of reconnaissance and dual-purpose satellites in local wars and armed conflicts of the present on different military operations. This will help to specify the tasks and determine the features and conditions for the use of reconnaissance satellites in the interests of information support for the preparation and conduct of hostilities. The aim of the article is to systematize, on the basis of world experience, the tasks, features and conditions of the use by foreign states of space-based reconnaissance and surveillance means to solve the tasks of information support for military operations in local wars and armed conflicts of our time. On the basis of the analysis of world experience, the use of reconnaissance satellites in the system of providing combat actions on the examples of known local wars and armed conflicts of the late XX – early XXI centuries has been investigated: Iraq, 1991; Yugoslavia, 1999; Afghanistan, 2001; Iraq, 2003; Syria since 2014. The attention was paid to the peculiarities of the use of space reconnaissance craft, which were inherent in each of the local wars, taking into account the relevant arena of war, space reconnaissance capabilities of the states that took part in them. Information is given about orbital groups of spacecrafts that performed reconnaissance tasks in the interests of ground troops in different ranges of wavelengths of the electromagnetic spectrum. Conclusions regarding space reconnaissance trends are made, as well as the prospects for the development of the space segment in the system of providing future military struggle. The experience of local wars and military conflicts indicates that space reconnaissance is a necessary and most important element of the state’s infrastructure, which has modern armed forces. The use of reconnaissance spacecraft is precisely that critical factor that provides advance and advantage in armed conflicts in advance.

Using Software Defined Network (SDN) in space systems gainsmore focus nowadays. SDN can increase the reliability in satellitecommunication. Many researchers concluded that using SDN in satellitecommunication for both ground segment and space segment, improvespace system reliability. The satellite ground station network has beenalways the backbone of the Space System. From this point of view, thereliability and performance guarantee of this network is mandatory.With the introduction of SDN in the field of satellite communications,greater capabilities have been expected to be achieved, in addition tothe big reduction of operational and capital expenses in deploying andmanagement of satellite ground network equipment. In this paper, theadvantages of using SDN for handover between satellite ground stations(Site Diversity) to ensure higher reliability for the system and to increaseits performance and throughput are discussed. Some scenarios have beenimplemented and shown in this paper to demonstrate the great potentialof using SDN in ground stations handover and to help make decisions incase of link anomalies.

Using the modified algorithm for calculating the ambiguity function, we consider the method of estimation of the mutual time delay of wideband signals, which are recorded by multiposition systems for determining the radiation-source location with the help of the space segment. It is based on the extraction of narrowband channels from the received signals and their further optimal quasi-coherent processing. The criterion of reliability and efficiency of the estimated mutual time delay by the proposed method is studied.

Low earth orbit (LEO) satellite systems, an important part of the next generation of global communication systems, have the advantages of low transmission delay, low satellite cost and low launch cost. The construction of an LEO satellite network with global coverage has become the direction of future space network transmission development. Although extensive research has been conducted on the routing of LEO satellite networks, most papers focus on only space segment routing, with little attention paid to the route between the satellite and ground station. This paper introduces the transmission scenario of ground station switching with connected satellites and analyzes the problem of data packet loss caused by ground station and satellite communication link switching. Two optimization strategies based on static routing and dynamic routing are proposed as solutions to the problem of data packet loss, with software-simulated test results showing that both approaches can effectively avoid packet loss.

Funding Information: This work was supported by the Jane and Aatos Erko Foundation (JAES) and by the Teknologiateollisuus 100-year Foundation in the INCUBATE project. This work was also partly supported by the Academy of Finland, under the project ULTRA (328226, 328214). Publisher Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. Future autonomous transportation is one of the most demanding application areas in terms of connectivity, as it has to simultaneously meet stringent criteria that do not typically go hand in hand, such as high throughput, low latency, high coverage/availability, high positioning and sensing accuracies, high security and robustness to interferences, etc. In order to meet the future demands of challenging applications, such as applications relying on autonomous vehicles, terrestrial networks are no longer sufficient and are to be augmented in the future with satellite-based networks. Among the emerging satellite networks, Low Earth Orbit (LEO) networks are able to provide advantages over traditional Medium Earth Orbit (MEO) and Geo-Stationary Earth Orbit (GEO) networks in terms of signal latency, cost, and performance. Nevertheless, several challenges exist in LEO system design, which have not been fully addressed in the existing literature. In particular, the problem of LEO-system optimization of design parameters is a multi-dimensional problem with many aspects to be considered. This paper offers a comprehensive survey of the LEO-system design parameters, of the challenges in LEO system design process, and of the optimization methods for satellite communication, positioning, and sensing applications, as well as a summarizing discussion on the design considerations for LEO-based networks to support future autonomous transportation.

Global navigation satellite systems (GNSSs) have been booming in recent years, and the space segment of all four of the GNSSs, including BDS (BDS-3/BDS-2), Galileo, GPS, and GLONASS, has almost been fully deployed at present. The single point positioning (SPP) technology, which is widely used in satellite navigation and low-accuracy positioning, can benefit from the multi-GNSS integration, but the additional intersystem bias (ISB) parameters should be introduced to ensure the compatibility among different GNSSs. In this study, the ISB estimates derived from four-system integrated SPP are carefully characterized, and the performance enhancement attributed to a priori ISB constraints by prediction for position solutions under open sky and constrained visibility environments is rigorously evaluated. The results indicate that the ISB between BDS-3 and BDS-2 cannot be ignored. The daily ISBs show step changes when encountering the replacement of receiver types, while it is not the case for the receiver firmware versions. The daily ISBs are roughly consistent for the stations equipped with the same type of receivers. The short-term stability of epochwise ISBs for GLONASS, Galileo, BDS-2, and BDS-3 with respect to GPS can be 2.335, 1.262, 1.741, and 1.532 ns, respectively, whereas the corresponding long-term stability for daily ISBs can be 1.258, 1.288, 2.713, and 2.566 ns, respectively. The single-day prediction accuracy of daily ISBs for GLONASS, Galileo, BDS-2, and BDS-3 with respect to GPS can be 1.055, 0.640, 1.242, and 0.849 ns, respectively. The improvements on positioning accuracy after introducing a priori ISB constraints can be over 20% at an elevation mask of 40° and 50° with a time span of ISB prediction of a day. As to the availability, it is only 64.0% for traditional four-system SPP under a cutoff elevation of 50°, while the corresponding availability is increased to approximately 90.0% after considering a priori ISB constraints. For completeness, the characteristics of ISBs estimated with the low-cost u-blox M8T receiver and the Xiaomi Mi8 smartphone as well as the contribution of a priori ISB constraints to the multisystem SPP solutions with these devices are also investigated.

Onboard satellite clocks are the basis of Global Navigation Satellite Systems (GNSS) operation, and their revolution periods are at the level of 2 per day (about 12 h) in the case of the Medium Earth Orbit (MEO) satellites. In this work, the authors analysed the entire BeiDou Navigation Satellite System (BDS) space segment (BDS-2 and BDS-3) in terms of the occurrence of periodic, repetitive signals in the clock products, and checked if they coincide with the orbital periods or their multiples. The Lomb-Scargle (L-S) power spectrum was used as a tool to determine the periods present in the BDS clock products, allowing for analyses based on incomplete input data; in this case, the incomplete data were the phase data with jumps and outliers removed. In addition, continuous wavelet transform (CWT) was used to produce a time−frequency representation showing the more complex behaviour of the satellite clock products. As shown in the case of geostationary and geosynchronous inclined orbit satellites, the main period was 23.935 h, while for the Medium Earth Orbit it was 12.887 h, with the BDS satellite orbital period being 12 h 53 m (12.883 h). Some effects connected with reference clock swapping are also visible in the power spectrum. The conducted analyses showed that the BDS-2 satellite clocks have much higher noise than the BDS-3 satellite clocks, meaning that the number of designated periods is greater, but their reliability is significantly lower. BDS-3 satellites have only been in operation for a very short time, thus this is the first analysis to include this type of data. Moreover, such a wide and complex analysis has not been carried out to date.

ESA’s Next Generation Gravity Mission (NGGM) is a candidate Mission of Opportunity for ESA–NASA cooperation in the frame of the Mass Change and Geosciences International Constellation (MAGIC). The mission aims at enabling long-term monitoring of the temporal variations of Earth’s gravity field at relatively high temporal (down to 3 days) and increased spatial resolutions (up to 100 km) at longer time intervals. This implies also that time series of GRACE and GRACE-FO can be extended towards a climate series. Such variations carry information about mass change induced by the water cycle and the related mass exchange among atmosphere, oceans, cryosphere, land and solid Earth and will complete our picture of global and climate change. The main observable is the variation of the distance between two satellites measured by a ranging instrument. This is complemented by accelerometers that measure the nongravitational accelerations, which need to be reduced from ranging measurements to obtain the gravity signal. The preferred satellite constellation comprises one satellite pair in a near-polar and another in an inclined circular orbit. The paper focuses on the orbit selection methods for optimizing the spatial sampling for multiple temporal resolutions and then on the methodology for deriving the engineering requirements for the space segment, together with a discussion on the main mission parameters.

Internet of Space Things (IoST) is a challenging paradigm, which is currently attracting great interest from the scientific and industrial communities. IoST is based on the integration of the space segment into the global Internet of Things (IoT) infrastructure. In the relevant literature, reference is generally made to multiple constellations of nanosatellite platforms, used to enable IoT services on a global scale, including also disadvantaged and poorly infrastructured areas. In this paper, we focus on multi-tenant IoT scenarios, wherein multiple CubeSats constellations are enabled to offer services by exploiting a dynamic federation model. The objective is to efficiently provide services in an IoST scenario by leveraging an effective cooperation strategy originally designed for terrestrial IoT networks, the Mobile-IoT-Federation-as-a-Service (MIFaaS) paradigm. We extend this vision to IoT satellite networks in order to allow a constellation of satellites to effectively execute tasks through a tight cooperative behaviour with other CubeSats constellations. The reported performance evaluation studies show that better performance, in terms of percentage of tasks successfully completed, can be achieved through the implementation of the proposed cooperation paradigm.