Orbit Satellite Constellation Research Articles

An Efficient Location-Based Forwarding Strategy for Named Data Networking and LEO Satellite Communications

Low Earth orbit (LEO) satellite constellations are increasingly gaining attention as future global Internet providers. At the same time, named data networking (NDN) is a new data-centric architecture that has been recently proposed to replace the classic TCP/IP architecture since it is particularly well suited to the most common usage of the Internet nowadays as a content delivery network. Certainly, the use of NDN is especially convenient in highly dynamic network environments, such as those of next LEO constellations incorporating inter-satellite links (ISL). Among other native facilities, such as inbuilt security, NDN readily supports the mobility of clients, thus helping to overcome one of the main problems raised in LEO satellite networks. Moreover, thanks to a stateful forwarding plane with support for multicast transmission and inbuilt data caches, NDN is also able to provide a more efficient usage of the installed transmission capacity. In this paper, we propose a new location-based forwarding strategy for LEO satellite networks that takes advantage of the knowledge of the relative position of the satellites and the grid structure formed by the ISLs to perform the forwarding of NDN packets. So, forwarding at each node is done using only local information (node and destination locations), without the need of interchanging information between nodes, as is the case with conventional routing protocols. Using simulation, we show that the proposed forwarding strategy is a good candidate to promote the efficient and effective future use of the NDN architecture in LEO satellite networks.

Security Performance Analysis of LEO Satellite Constellation Networks under DDoS Attack

Low Earth orbit satellite constellation networks (LSCNs) have attracted significant attention around the world due to their great advantages of low latency and wide coverage, but they also bring new challenges to network security. Distributed denial of service (DDoS) attacks are considered one of the most threatening attack methods in the field of Internet security. In this paper, a space-time graph model is built to identify the key nodes in LSCNs, and a DDoS attack is adopted as the main means to attack the key nodes. The scenarios of two-satellite-key-node and multi-satellite-key-node attacks are considered, and their security performance against DDoS attacks is also analyzed. The simulation results show that the transmission path of key satellite nodes will change rapidly after being attacked, and the average end-to-end delay and packet loss are linearly related to the number of key-node attacks. This work provides a comprehensive analysis of the security performance of LSCNs under a DDoS attack and theoretical support for future research on anti-DDoS attack strategies for LSCNs.

Integrated kinematic precise orbit determination and clock estimation for low Earth orbit satellites with onboard and regional ground observations

Many low Earth orbit (LEO) satellite constellations have been designed in recent years to provide global broadband Internet services. These constellations provide opportunities for LEO satellites to serve as navigation satellites by launching navigation signals while also being equipped with an onboard global navigation satellite system (GNSS) receiver. We propose a kinematic precise orbit determination (KPOD) and precise clock estimation (PCE) approach for LEO satellites by integrating regional ground observations and onboard observations of LEO satellites. By taking into account the LEO satellite clock bias, this approach can demonstrate the contributions of the ground and onboard observations of LEO satellites to the orbit and clock results, respectively. A composite LEO satellite constellation consisting of 168 satellites and observations from regional ground stations and LEO satellite onboard receivers are simulated considering the LEO satellite clock bias to verify the proposed approach. The results indicate that the convergence time of LEO satellite orbit determination can reach 9.38 min with the integrated KPOD (IKPOD) method, which is a reduction of 24.0% compared with the traditional KPOD method. However, the additional improvement in the LEO satellite orbit accuracy after convergence is very limited. The average root mean square (RMS) and standard deviation (STD) values of all LEO satellite clocks using the integrated PCE (IPCE) method with the participation of LEO satellite onboard observations can reach 0.27 ns and 0.15 ns, respectively. The improvements in the average RMS and STD are 42.6% and 60.5%, respectively, compared with the ground LEO PCE method. The convergence time and accuracy of LEO/GNSS precise point positioning can be improved by 44.6%, 48.3%, 26.7%, and 20.4% in the east, north, and up directions, respectively, using LEO satellite orbits and clocks from the IKPOD and IPCE methods compared with KPOD and PCE.

Steering Toward the Future: The Use of Piezo Technology for Optical Intersatellite Communication

Recent years have seen a reemergence of interest and investment in low Earth orbit (LEO) satellite constellations. First proposed in the 1990s, the construction of such constellations was once the hopeful plan of companies, such as Iridium, Globalstar, Odyssey, and Teledesic [1]. Unfortunately, most of these plans never fully came to fruition as the upfront construction costs were unfeasible, and a new competing network implementing fiber optic cables was introduced. These fiber optic cable networks promised users high data rates at a fraction of the construction costs of a satellite network. Today, as worldwide data throughput and coverage requirements increase beyond the capacity of fiber optic cable networks, companies, such as SpaceX, Amazon, ViaSat, OneWeb, and Telesat, are resurrecting the idea of LEO constellations [2]. In order to avoid the fate of their predecessors, these companies must build robust constellations with reliable satellites as launching satellites comes at high costs. One of the most critical systems aboard these satellites is the communication terminal that allows each satellite to communicate with other satellites in the constellation.

Performance Evaluation of Random Access Methods for IoT-over-Satellite

Low Earth orbit (LEO) satellite constellations are currently being explored to provide global and seamless coverage for IoT-over-Satellite applications. Random access techniques require low transmission overhead providing a compatible route for IoT-over-Satellite applications, however, coming at the expense of the offered quality-of-service. In this paper, we develop a realistic uplink performance framework that incorporates many practical parameters such as the satellite availability, packet collision and interference, Doppler shift, and impairments experienced in a typical Satellite-to-Ground channel. The framework is capable of assessing multiple key performance indicators of the overall IoT-over-Satellite random access system. The performance is presented in terms of the bit error rate, packet error rate, and the energy wasted per IoT device. To emulate a realistic IoT-over-Satellite network, LoRa modulated traffic is first generated and injected into the Satellite-to-Ground channel. The results indicate high resistance to Doppler shifts even without any Doppler correction and provide some resistance to highly congested environments.

Photometric characterization and trajectory accuracy of Starlink satellites: implications for ground-based astronomical surveys

ABSTRACT Starlink is a low-Earth orbit (LEO) satellite constellation operated by Space Exploration Technologies Corp. (SpaceX) which aims to provide global satellite internet access. Thus far, most photometric observations of Starlink satellites have primarily been from citizen scientists’ visual observations without using quantitative detectors. This paper aims to characterize Starlink satellites and investigate the impact of mega constellations on ground-based astronomy, considering both the observed magnitude and two-line element (TLE) residuals. We collected 353 observations of 61 different Starlink satellites over a 16-month period and we found an average GAIA G magnitude of 5.5 ± 0.13 with a standard deviation of 1.12. The average magnitude of V1.0 (pre-VisorSat) Starlinks was 5.1 ± 0.13 with a standard deviation of 1.13. SpaceX briefly used a low-albedo coating on a Starlink satellite called DarkSat to test light pollution mitigation technologies. The brightness of DarkSat was found to be 7.3 ± 0.13 with a standard deviation of 0.78, or 7.6 times fainter than V1.0 Starlinks. This concept was later abandoned due to thermal control issues and sun visors were used in future models called VisorSats. The brightness of VisorSats was found to be 6.0 ± 0.13 with a standard deviation of 0.79, or 2.3 times fainter than V1.0 Starlinks. Over the span of the observations, we found that TLEs were accurate to within an average of 0.12 deg in right ascension and –0.08 deg in declination. The error is predominantly along-track, corresponding to a 0.3 s time error between the observed and TLE trajectories. Our observations show that a time difference of 0.3 ± 0.28 s is viable for a proposed 10 s shutter closure time to avoid Starlinks in images.

Asymmetric Differential Routing for low orbit satellite constellations

Low Earth Orbit (LEO) constellations create a network that includes the satellites (as routing nodes) connected by Inter-Satellite Links (ISLs) while the satellite terminals are dynamically connected to one or more satellites. The combination of transient, high-rate changes with high latency presents a unique challenge for designing a routing protocol that can provide guaranteed bandwidth, and support the frequent changes without packet drops. Current works focus on end-to-end routing between multiple gateways and terminals and do not provide guaranteed service.This paper addresses the problem of routing traffic from a source terminal to a destination terminal on a LEO constellation using Asymmetric Differential Routing (ADR) to plan ‘semi-fixed’ routes. ADR keeps most of the planned route fixed and only minor (differential) adjustments are required to account for handovers. Using ADR, a terminal and a gateway (GW) communicate using a fixed route with a time complexity of O(1) to account for handovers.

A Computation Offloading Strategy in LEO Constellation Edge Cloud Network

With the rise of a new generation of low Earth orbit (LEO) satellite constellations and the advancement of the 6G network, satellite–terrestrial integrated Internet of Things (IoT) in the future will achieve global coverage through the integration of LEO constellation, and extend computing to the edge of the network through the deployment of edge computing services in LEO constellation so as to meet the demand of mass connection and low latency data processing. The LEO constellation network of the future will be an edge cloud network combining network and computing. In this paper, we propose a computation offloading strategy for the combined optimization of energy and computational load in a LEO constellation edge cloud network (hereinafter referred to as LEO-ECN). First, we establish the LEO-ECN system model, in which the user task can be offloaded to the satellite through the multi-hop path. Then, a cost model considering energy consumption and load calculation is proposed. Finally, a joint optimization problem to minimize energy consumption and balance the LEO-ECN load is established, which is a convex optimization problem. The simulation result demonstrates that, compared with the benchmark strategy, our proposed strategy has better performance and can improve the computing resource utilization of LEO-ECN.

Implications of a growing spaceflight industry: Climate change

The global impacts of the spaceflight industry have historically been viewed as limited in scope, without significant growth, and therefore not requiring regulatory attention. As a result, little scientific attention has been paid to the impacts of rocket launches and space debris reentries on climate and stratospheric ozone. However, the space industry has recently seen revolutionary change and growth with the development of new heavy lift rockets, deployments of large low earth orbit satellite constellations, and the introduction of new space-based data services. As the visibility of a rapidly growing spaceflight industry increases, so will the public's interest to understand how spaceflight affects climate, the role it plays in the broader scope of greenhouse gas emissions, and the global response to climate change. Though recent scientific research has answered a few outstanding questions about spaceflight's climate impacts, science and technology advancements and prospects for growth have raised many more so that, in a relative sense, knowledge of spaceflight's climate impacts has declined. Scientific uncertainties, coupled with increased rocket launches and space debris reentries, mean that a space policy based on the assumption of limited global impacts is no longer appropriate. Policymakers will require a comprehensive assessment of the global consequences of spaceflight in order to make effective and informed decisions to guide spaceflight development in coming decades. Stakeholders across the space industry should recognize the urgency of the need to organize and properly fund a vigorous program of scientific research in order to understand the global impacts of spaceflight. Such a science based policy would forestall unwarranted regulation and ensure regulatory impartiality where regulation is unavoidable.

Technical assessment of an equatorial Low Earth orbit satellite constellation for Egypt

Egypt, the region’s agricultural powerhouse, has the largest irrigation area among the eleven Nile Basin countries. Meanwhile, the demand for water and irrigation management is becoming necessary. The Internet of Things (IoT) plays a key role in smart agriculture and water management to cope with modern water scarcity. This paper presents the methodology of design and assessment of a small IoT satellite constellation providing continuous coverage over Egypt and decides on the optimal location for ground stations to serve IoT sector in Egypt. Moreover, it evaluates the latency analysis and handover time for such constellation.It is shown that a constellation of 9 satellites in a circular equatorial Low Earth Orbit (LEO) can provide continuous coverage for Egypt. The latency analysis showed that two ground stations in southernmost Egypt will provide the optimal latency for such constellation.

Cooperative multigroup multicast beamforming for cache‐enabled ultra‐dense low earth orbit satellite constellation networks

SummaryThe ultra‐dense low earth orbit (LEO) satellite constellation (UD‐LSC) networks are expected to be incorporated in future wireless networks, particularly 6G networks, to provide global wireless access with enhanced data rates. This paper investigates the downlink multigroup multicast transmission for UD‐LSC networks, in which LEO satellites provide the multicast service for ground users with full frequency reuse. Moreover, in‐network caching, as a key enabling technology of information‐centric networking, is brought into UD‐LSC networks to achieve both bandwidths saving and delay reduction. However, the multicast capacity is constrained by the signal to interference and noise ratio (SINR) of bottleneck users in each multicast group. Besides, the high‐speed movement of LEO satellites makes cache placement and updating more challenging than ground networks with immobile base stations. To track these problems, we first propose a cache‐enabled multi‐satellite cooperation framework and formulate the multicast transmission problem and the content caching problem. Then, to reduce the average content delivery delay (CDD) of ground users, we propose a cooperative multicast beamforming and transmission‐aware dynamic caching (CMB‐TDC) algorithm based on the sample average approach and successive convex approximation. Simulation results show that the proposed CMB‐TDC algorithm can improve the multicast capacity, and then the average CDD is reduced for UD‐LSC networks.

Deep Learning Aided Routing for Space-Air-Ground Integrated Networks Relying on Real Satellite, Flight, and Shipping Data

Current maritime communications mainly rely on satellites having meager transmission resources, hence suffering from poorer performance than modern terrestrial wireless networks. With the growth of transcontinental air traffic, the promising concept of aeronautical ad-hoc networking relying on commercial passenger airplanes is potentially capable of enhancing satellite-based maritime communications via air-to-ground and multihop air-to-air links. In this article, we conceive space-air-ground integrated networks for supporting ubiquitous maritime communications, where the low earth orbit satellite constellations, passenger air-planes, terrestrial base stations, ships, serve as the space, air, ground, and sea layer, respectively. To meet heterogeneous service requirements, and accommodate the time-varying and self-organizing nature of space-air-ground integrated networks, we propose a deep learning aided multi-objective routing algorithm, which exploits the quasi-predictable network topology and operates in a distributed manner. Our simulation results — based on real satellite, flight, and shipping data in the North Atlantic region — show that the integrated network enhances the coverage quality by reducing the end-to-end delay and by boosting the end-to-end throughput, as well as improving the path-lifetime. The results demonstrate that our deep learning aided multi-objective routing algorithm is capable of achieving near pareto-optimal performance.

Gateway Placement in Integrated Satellite–Terrestrial Networks: Supporting Communications and Internet of Remote Things

Low Earth orbit (LEO) satellite constellations have become a promising architecture to integrate with terrestrial networks for facilitating communications and Internet of Remote Things (IoRT) services through gateways. Nevertheless, different gateway locations may have various channel conditions and service demands due to differentiated atmospheric conditions, populations, and number of terminal devices required by IoRT services in different areas. Besides, the gateway placement scheme further affects the service coverage performance and the access performance of the network to service demands. Therefore, gateway placement plays a pivotal role in improving network capabilities in the integrated system of LEO satellites and terrestrial networks (ISoLS-TNs). Motivated by the aforementioned facts, in this article, we first formulate the gateway placement problem in ISoLS-TNs as a multiobjective optimization problem to maximize the total revenue of service data demand within coverage while minimizing the average access distance and the number of deployed gateways. In order to enhance network resource utilization and assure local information confidentiality, a distributed resource allocation (DRA) mechanism based on the alternating direction method of multipliers (ADMMs) algorithm is designed to calculate the total revenue of service data demand within coverage. Furthermore, we propose a genetic-based gateway placement algorithm with the ADMM for DRA. Finally, through massive simulations based on real data, we validate the effectiveness of the proposed algorithm in improving resource utilization and coverage performance of the network. In addition, the results also bring lights on the relationship between service data demand distribution and gateway location preference.

Time Difference Detection of Atomic Clock-Based Reference Signal from a CubeSat in Orbit

Satellite signal delays and errors depend on the amount of ionosphere Total Electron Content (TEC) in the signal path. The measurement of TEC has been mostly done using Global Navigation Satellite System (GNSS) signals. Signals from a satellite orbiting in lower altitude with lower frequencies than GNSS may provide more precise measurement of Total Electron Content (TEC). Space Precision Atomic Clock Timing Utility Mission (SPATIUM) is a program to do three-dimensional ionosphere mapping by a satellite constellation in Low Earth Orbit (LEO) measuring TEC with Ultra High Frequency (UHF) radio signals. The first technology demonstration satellite called SPATIUM-I, a 2U CubeSat, was deployed from the International Space Station in October 2018. The satellite emits a 467-MHz reference signal generated by a chip scale atomic clock. The signal is Spread Spectrum (SS)-modulated with 250 chips in 4 ms. This paper explains the methodologies and their results of detecting the signal time delay on the ground using a Software-Defined Radio (SDR). To improve the precision, a Global Positioning System (GPS) clock was used to put a time stamp on the satellite signal every 1 s. The time difference of two consecutive signals is the key method for deriving the TEC difference between two signal paths.

Scalable routing in low-Earth orbit satellite constellations: Architecture and algorithms

Low-Earth orbit satellite constellations (LEO-SCs) are attractive for provisioning global, high-speed and low latency Internet access services. Due to the fast movement of satellites and the lack of inter-satellite links (ISLs), the LEO-SC topology is highly dynamic. Applying shortest path routing directly to LEO-SCs may suffer from poor scalability and frequent route changes. In this paper, a scalable two-layer routing architecture is first proposed. Based on it, two stable routing algorithms, delay-bounded routing (DBR) and delay-aware routing (DAR), are designed to minimize route changes. DBR is flow-based. It provides bounded network latency but at the cost of a larger forwarding table. DAR is destination-based. Although network latency is not bounded, we show that the further reduction in route changes is significant and the increase in average latency is minimal.

Risk Assessment of a Large Constellation of Satellites in Low-Earth Orbit

This paper aims to assess the risk of mission termination for a large constellation of satellites in a low-Earth orbit. Many large constellations will be deployed to provide broadband network services using thousands of satellites. There is concern that such large constellations will have a serious impact on the long-term sustainability of outer space activities due to the rapid increase in population. First, therefore, the authors conducted an assessment under nominal activities (referred to as “business-as-usual”) on the basis of a prediction by ESA’s MASTER-2009 and NASA standard breakup model 2001 revision. The assessment found that nearly one catastrophic collision may happen in a large constellation, generating more than two million fragments as small as 1 mm in size. Second, the authors conducted a further assessment assuming a hypothetical collision of a satellite in a large constellation using the NASA standard breakup model and a spherical finite element model adopted in ESA’s MASTER-2009. In consequence, another catastrophic collision may happen to a large constellation, generating approximately a half-million fragments as small as 1 mm in size. Therefore, such catastrophic collisions and resulting secondary collisions should be prevented for large constellations.

Radar sensing of the sea surface using small spacecraft

The possibility of using a constellation of small spacecraft as receiving satellites, when “highlighting” the sea surface from existing (navigational, communication) or specially created spacecraft—to form a wide-area (about 1 000 km) radar survey zone at a given resolution (about 10 m)—is under consideration. Such a constellation could provide operational monitoring of fast-moving atmospheric cyclones, measuring directly the parameters of storm waves (altitude and orbital velocity)—which would replace the existing constellation of microwave scatterometers, providing operational monitoring of the World Ocean surface in the 3 H (H—altitude of the satellite’s orbit) field of view with a resolution of about 10 km—but with calibration of the received images by wind speed and direction, which leads to huge errors when trying to introduce altitude calibration in the Small spacecraft have many advantages over large satellites. For example, they are relatively inexpensive to build, take minimal time from design to launch, are easily modified to solve a specific problem, and create less radio interference. The approach under consideration consists in redistribution of tasks to be solved between the constellation of satellites in orbit. High orbiting navigation satellites, for example, can be used as transmitter carriers (of the illumination of the surface) that use the necessary broadband signal with acceptable periodicity. Receivers of reflected signals are placed on board small spacecraft, and at formation of wide-band radar image of sea surface with necessary resolution ∼10 m (that only on order exceeds acceptable on small spacecraft size of receiving antennas)—in flight direction is necessary to use synthesized aperture of receiving antenna. This work has the character of “staged” research.

Toward Practical Entanglement-Based Satellite FSO/QKD Systems Using Dual-Threshold/ Direct Detection

We propose a new implementation of the BBM92 protocol for satellite continuous-variable quantum key distribution (CV-QKD) systems using the dual-threshold/direct detection (DT/DD) scheme. The proposed system is less complex and therefore possibly cheaper than current discrete-variable (DV) and CV-QKD ones using coherent detection receivers. We model and analyze the performance of the proposed system in the context that a satellite distributes secret keys to two legitimate users. The analytical results are derived by considering channel loss, atmospheric turbulence-induced fading, and receiver noises. The Gaussian beam model is considered to evaluate the impact of geometric spread on the signal received by legitimate users and the possibility of being eavesdropped. Based on the design criteria for the system and analytical results, we investigate the feasibility of a case study for the Japan QKD network using the existing low-Earth orbit (LEO) satellite constellation.

Service Coverage for Satellite Edge Computing

Recently, increasing investments in satellite-related technologies make the low earth orbit (LEO) satellite constellation a strong complement to terrestrial networks. To mitigate the limitations of the traditional satellite constellation “bent-pipe” architecture, satellite edge computing (SEC) has been proposed by placing computing resources at the LEO satellite constellation. Most existing works focus on space-air-ground integrated network architecture and SEC computing framework. Beyond these works, we are the first to investigate how to efficiently deploy services on the SEC nodes to realize robustness aware service coverage with constrained resources. Facing the challenges of spatial-temporal system dynamics and service coverage-robustness conflict, we propose a novel online service placement algorithm with a theoretical performance guarantee by leveraging Lyapunov optimization and Gibbs sampling. Extensive simulation results show that our algorithm can improve the service coverage by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.3\times $ </tex-math></inline-formula> compared with the baseline.

Universal Broadband Assessment of Low Earth Orbit Satellite Constellations: Evaluating Capacity, Coverage, Cost, and Environmental Emissions

Universal Broadband Assessment of Low Earth Orbit Satellite Constellations: Evaluating Capacity, Coverage, Cost, and Environmental Emissions