Low Earth Orbit Research Articles

Augmentation message design for LEO-enhanced precise positioning: In-orbit performance assessment

Recent advancements in low earth orbit (LEO) navigation augmentation systems, such as the CENTISPACETM system developed by Beijing Future Navigation Tech Co., Ltd, have significantly reduced the convergence time of GNSS precise point positioning (PPP). To facilitate LEO-enhanced precise positioning, we developed a comprehensive set of LEO augmentation messages, including GNSS/LEO state-space representation (SSR) parameters. These messages were validated through onboard tests using real LEO augmentation observations. To expedite cold start times, the GNSS orbit SSR is based on a polynomial model, while LEO orbits are modeled using classic GNSS broadcast ephemeris with additional perturbation parameters. GNSS and LEO clock are predicted by a linear model. The designed LEO augmentation messages were validated by LEO-augmented PPP calculations. The average convergence time with LEO SSR messages was 4.8 min, revealing an improvement of 71.3 % over GNSS PPP and aligning closely with the 5.1 min achieved through post-processing.

A Clustering Scheduling Strategy for Space Debris Tracking

The number of spacecraft and space debris, particularly in low Earth orbit, is rapidly escalating, heightening the demand for rational and effective satellite allocation strategies to alleviate the strain on satellite monitoring and tracking systems. In this paper, a clustering scheduling strategy is proposed for satellites equipped with sensors tasked with monitoring a substantial amount of space debris. To address the challenge of excessive space debris, a dynamic and static clustering division scheme is introduced, leveraging target characteristics in conjunction with the nearest neighbor clustering algorithm. Furthermore, to enhance scheduling efficiency, four performance indicators are proposed to guide the generation of a resource allocation scheme using Genetic Algorithm and Simulated Annealing. Simulation results demonstrate that the clustering scheduling strategy effectively clusters a large number of space debris, while the scheduling scheme demonstrates better balance, comprehensiveness, and efficiency. The Genetic Algorithm and Simulated Annealing exhibit superior performance compared to their counterparts across various orbital inclinations and altitudes. Notably, in a specific simulation scenario related to constellations, the Genetic Algorithm and Simulated Annealing achieve a performance enhancement of 13.48% compared to the Genetic Algorithm and an improvement of 8.73% compared to Simulated Annealing.

Dimensioning Space-Air-Ground Integrated Networks for In-Flight 6G Slice Orchestration

In this study, we present an in-depth analysis of communication services for commercial airline passengers, focusing on the challenges posed by increasing internet traffic demand. We explore the integration of satellite, airborne, and terrestrial networks, emphasizing the roles of Low Earth Orbit (LEO) satellites, High-Altitude Platform Station (HAPS), and Terrestrial Aviation Network (TAN)-based services. Our contribution includes a theoretical model for optimizing resource allocation and capacity planning in non-terrestrial wireless networks, using a bipartite graph approach and linear programming techniques. The model shows adaptability and efficiency, providing key insights through numerical analysis. Leveraging a detailed air traffic dataset, a machine learning-based aggregation method, and real-world network parameters, our research addresses current challenges, such as scalable network capacity dimensioning in high-density airspaces and meeting the demand for quality of service by robust resource provisioning, and advances the design of communication networks for Space–Air–Ground Integrated Network (SAGIN). Numerical results from European airspace suggest that complementing TAN and LEO satellite networks with HAPS-based services will be essential as airline passengers adopt ground-level internet usage patterns.

Passive Metasurface-Based Low Earth Orbit Ground Station Design

Passive Metasurface-Based Low Earth Orbit Ground Station Design

Single-epoch power positioning method for multi-beam LEO communication satellites

Low Earth Orbit (LEO) communication satellites offer reduced signal loss, fast movement, multi-beam, typically providing single coverage. This paper introduces a novel multi-beam power positioning method for low-orbit single-satellite, addressing the slow convergence and low accuracy of Doppler positioning. It establishes a power observation equation system, initializes with the nearest neighbor algorithm, and refines with the least squares method. Monte Carlo simulations indicate that with good initial values, the method converges in under 10 iterations, achieving 88.06% availability at 20° elevation with errors of 5,331 m (vertical) and 8,798 m (horizontal), and a timing error of 205 μs. At 70° elevation, all users converge with errors of 1,614 m and 1,088 m, and a timing error of 31.3 μs, demonstrating high power positioning availability. The statistical results show that power positioning users can obtain the positioning accuracy of kilometers and the timing accuracy of microseconds, which meets initial timing needs under strong confrontation, enhancing the medium and high orbit satellite navigation.

Development of Progressively Earth-Independent Medical Operations to Enable NASA Exploration Missions.

Introduction -The National Aeronautics and Space Administration's (NASA's) transition from operations in low-Earth orbit to long-duration missions to the Moon and Mars necessitates the development of progressively Earth-independent medical operations (EIMO) to support crews and reduce overall mission risk. Previous work has defined and laid the foundation for EIMO, but further development of the concept is required to prepare for future exploration missions. Methods -NASA's Exploration Medical Capability element organized a series of 5 technical interchange meetings from 2023 to 2024, which included internal (NASA) and external subject-matter experts in human spaceflight, health technology, and austere medicine to create a framework for developing the technologies and procedures necessary to maintain human health and performance in a progressively Earth-independent fashion. Results -The EIMO technical interchange meetings provided a forum for a field of experts and stakeholders to better understand gaps between current approaches to medical care in low-Earth orbit and the innovations needed to maintain the health and performance of astronauts on long-duration deep-space missions. These discussions were recorded, analyzed, and collated into reports that can inform the maturation of EIMO concepts. Conclusions -Multidisciplinary input from experts with experience in human spaceflight, health technology, and austere medicine is critical when planning for long-duration exploration missions. Innovations such as probabilistic risk assessment tools, extended reality devices, and advanced clinical artificial intelligence capabilities have been identified as high-value targets that can enhance inflight medical autonomy while maintaining appropriate workload balance and crew safety. By further developing the EIMO paradigm, NASA aims to identify areas of future work, research, and collaboration to reduce overall risk on future human spaceflight missions into deep space.

Autonomous Docking Manoeuvre Testing in the Framework of the ERMES Experiment

Abstract The rise of the “New Space Economy” has expanded access to low-Earth orbits for commercial, non-profit, and educational entities. This has driven significant growth in the small satellite market, offering a low-cost solution for various missions. Autonomous proximity operation systems for small satellites are actively studied for their wide-ranging applications. Experimental Rendezvous in Microgravity Environment Study (ERMES) is a student project, which aimed at testing an autonomous docking manoeuvre between two free-flying CubeSats mock-ups in a reduced gravity environment. The manoeuvre is characterized by an active Chaser and cooperative Target approach. In particular, the Chaser is equipped with a cold gas propulsive system based on expendable $$\hbox {CO}_{2}$$ CO 2 cartridges for three-dimensional manoeuvering, whereas the Target has a set of reaction wheels for attitude control. The magnetic post-manoeuvre connection is achieved thanks to a dedicated miniaturized docking interface. Moreover, the reduced gravity conditions have been achieved by participating in the European Space Agency (ESA) $$79^{th}$$ 79 th Parabolic Flight Campaign thanks to the selection in the ESA Fly Your Thesis! Programme 2022 (FYT). This article provides an overview of the ERMES experiment, discussing its main objectives and key design solutions. It first describes the design of the Guidance Navigation and Control subsystems of the two mock-ups, then discusses the results of the parabolic flight campaign, and finally focuses on the analysis of a specific parabolic test, where the Chaser was able to dock by recovering a high overall misalignment.

Can the low earth orbit enhanced GNSS (LeGNSS) achieve the expected Precise Point Positioning (PPP) solutions in urban canyons?

ABSTRACT Low Earth Orbit (LEO) satellites are expected to improve Global Navigation Satellite System (GNSS) Precise Point Positioning (PPP) by providing rapid geometric variations. While centimeter-level PPP accuracy has been achieved in open-sky conditions, the effectiveness of LEO-enhanced GNSS (LeGNSS) in urban canyons, where signal blockage is frequent, remains uncertain. This paper investigates LeGNSS PPP performance in such environments, focusing on the impact of interrupted-phase observations. Results show that signal blockage significantly affects accuracy, while repairing interruptions improves precision. However, in dense urban areas or at higher speeds, this repair process becomes challenging, limiting performance.

Theoretical Proof and Implementation of Digital Beam Control and Beamforming Algorithm for Low Earth Orbit Satellite Broadcast Signal Reception Processing Terminal

Compared to analog beamforming, digital beamforming offers better self-calibration and lower sidelobe performance, which has a profound impact on improving low Earth orbit receiver performance. The Digital Beamforming (DBF) module in the low Earth orbit satellite broadcast signal reception terminal can use digital phase shifting to compensate for the phase differences caused by path and spatial distance variations due to inconsistent Radio Frequency (RF) channel delays. This compensation ensures in-phase summation, thereby achieving maximum energy reception in the desired direction. Although DBF has gained widespread attention in the radar field due to its unique functions and advantages, its application is limited by beamforming accuracy and gain. Therefore, with the development of DBF technology, how to improve its accuracy and gain has also attracted extensive attention both domestically and internationally. To address this issue, this paper proposes a beamforming method based on a cap-shaped array for low Earth orbit satellite broadcast signal reception and processing terminals. The method combines prior information and spatial domain search for beam control, and employs a lookup table for beam synthesis. It derives formulas for the Signal-to-Noise Ratio, noise figure, processing flow of the beamforming network, and the determination of beamforming weights for the spherical antenna array. The paper presents a beam control approach that combines prior information with spatial domain search, along with an implementation process for beam synthesis using a lookup table. It also details the corresponding Field-Programmable Gate Array (FPGA) implementation process. Finally, the beamforming algorithm is experimentally validated, and error analysis is conducted. The experimental results show that the measured beamforming sensitivity at all incident angles is below −133 dBm and the G/T values are all greater than −9 dB/K, the beam uniformity at three operating frequencies is less than 3°, and the measured errors in pitch and azimuth angles are both below 2°. The beam pointing error is also below 2°.

Efficient AOA Estimation and NLOS Signal Utilization for LEO Constellation-Based Positioning Using Satellite Ephemeris Information

As large-scale low Earth orbit (LEO) constellations continue to expand, the potential of their signal strength for positioning applications should be fully leveraged. For high-precision angle of arrival (AOA) estimation, current spectrum search algorithms are computationally expensive. To address this, we propose a method that downscales the 2D joint spectrum search algorithm by incorporating satellite ephemeris a priori information. The proposed algorithm efficiently and accurately determines the azimuth and elevation angles of NLOS (non-line-of-sight) signals. Furthermore, an NLOS virtual satellite construction method is introduced for integrating NLOS satellite data into the positioning system using previously estimated azimuth and elevation angles. Simulation experiments, conducted with a uniform planar array antenna in environments containing both LOS (line-of-sight) and NLOS signals, demonstrate the effectiveness of the proposed solution. The results show that the azimuth determination algorithm reduces computational complexity without sacrificing accuracy, while the NLOS virtual satellite construction method significantly enhances positioning accuracy in NLOS environments. The geometric dilution of precision (GDOP) improved significantly, decreasing from values exceeding 10 to an average of less than 1.42.

Simulation of satellite and optical link dynamics in a quantum repeater constellation

Quantum repeaters and satellite-based optical links are complementary technological approaches to overcome the exponential photon loss in optical fibers and thus allow quantum communication on a global scale. We analyze architectures which combine these approaches and use satellites as quantum repeater nodes to distribute entanglement to distant optical ground stations. Here we simulate dynamic, three-dimensional ground station passes, going beyond previous studies that typically consider static satellite links. For this, we numerically solve the equations of motion of the dynamic system consisting of three satellites in low Earth orbit. The model of the optical link takes into account atmospheric attenuation, single-mode fiber coupling, beam wandering and broadening, as well as adaptive optics effects. We derive analytical expressions for the Bell state measurement and associated error rates for quantum memory assisted communications, including retrieval efficiency and state coherence. We consider downlink and uplink architectures for continental and intercontinental connections and evaluate the impact of satellite altitude and inter-satellite distance on the expected entanglement swapping rate. Our simulation model enables us to design different orbital configurations for the satellite constellation and analyze the annual performance of the quantum repeater under realistic conditions.

Challenges and opportunities offered by geostationary space observations for air quality research and emission monitoring

Abstract Space-borne remote sensing of atmospheric chemical constituents is crucial for monitoring and better understanding global and regional air quality. Since the 1990s, the continuous development of instruments onboard low-Earth orbit (LEO) satellites has led to major advances in air quality research by providing daily global measurements of atmospheric chemical species. The next generation of atmospheric composition satellites measures from the geostationary Earth orbit (GEO) with hourly temporal resolution, allowing the observation of diurnal variations of air pollutants. The first two instruments of the GEO constellation coordinated by the Committee on Earth Observation Satellites (CEOS), the Geostationary Environment Monitoring Spectrometer (GEMS) for Asia and the Tropospheric Emissions: Monitoring of Pollution (TEMPO) for North America, were successfully launched in 2020 and 2023, respectively. The European component, Sentinel-4, is planned for launch in 2025. This work provides an overview of satellite missions for atmospheric composition monitoring and the state of the science in air quality research. We cover recent advances in retrieval algorithms, the modeling of emissions and atmospheric chemistry, data assimilation, and the application of machine learning based on satellite data. We discuss the challenges and opportunities in air quality research in the era of GEO satellites, and provide recommendations on research priorities for the near future.

Influence of Proton Irradiation on Thin Films of AZO and ITO Transparent Conductive Oxides—Simulation of Space Environment

Transparent conductive oxides are essential materials for many optoelectronic applications. For new devices for aerospace and space applications, it is crucial to know how they respond to the space environment. The most important issue in commonly used low-Earth orbits is proton radiation. This study examines the effects of high-energy proton irradiation (226.5 MeV) on thin films of aluminium-doped zinc oxide (AZO) and indium tin oxide (ITO). We use X-ray diffraction and electron microscopy observations to see the changes in the structure and microstructure of the films. The optical properties and homogeneity of the materials are determined by spectrophotometry and spectroscopic ellipsometry (SE). Analysis of the chemical states of the elements with X-ray photoelectron spectroscopy (XPS) gives insight into what proton irradiation changes at the surface of the oxides. All measurements show that ITO is less influenced than AZO. The proton energy and fluence used in this study simulate about a hundred years in low Earth orbit. This research demonstrates that both transparent conductive oxide thin films can function under simulated space conditions, with ITO showing superior resilience. The ITO film was more homogenous in terms of the total thickness measured with SE, had fewer defects and adsorbates present on the surface, as XPS analysis proved, and did not show a difference after irradiation regarding its optical properties, transmission, refractive index, or extinction coefficient.

Secrecy Analysis of LEO Satellite-to-Ground Station Communication System Influenced by Gamma-Shadowed Ricean Fading

The Low Earth Orbit (LEO) small satellites are extensively used for global connectivity to enable services in underpopulated, remote or underdeveloped areas. Their inherent broadcast nature exposes LEO–terrestrial communication links to severe security threats, which always reveal new challenges. The secrecy performance of the satellite-to-ground user link in the presence of a ground eavesdropper is studied in this paper. We observe both scenarios of the eavesdropper’s channel state information (CSI) being known or unknown to the satellite. Throughout the analysis, we consider that locations of the intended and unauthorized user are both arbitrary in the satellite’s footprint. On the other hand, we analyze the case when the user is in the center of the satellite’s central beam. In order to achieve realistic physical layer security features of the system, the satellite channels are assumed to undergo Gamma-shadowed Ricean fading, where both line-of-site and scattering components are influenced by shadowing effect. In addition, some practical effects, such as satellite multi-beam pattern and free space loss, are considered in the analysis. Capitalizing on the aforementioned scenarios, we derive the novel analytical expressions for the average secrecy capacity, secrecy outage probability, probability of non-zero secrecy capacity, and probability of intercept events in the form of Meijer’s G functions. In addition, novel asymptotic expressions are derived from previously mentioned metrics. Numerical results are presented to illustrate the effects of beam radius, satellite altitude, receivers’ position, as well as the interplay of the fading or/and shadowing impacts over main and wiretap channels on the system security. Analytical results are confirmed by Monte Carlo simulations.

RF System Advancements for Satellite and Space Communications: Integrating AI with High-Frequency and Hybrid Systems

With the rapid evolution of satellite communications, the use of advanced radio frequency (RF) systems has become pivotal in addressing emerging challenges. High-frequency bands, such as millimeter-wave (mmWave) and terahertz (THz), enable high-throughput data transmission but introduce new complexities such as Doppler shifts and signal degradation. Hybrid satellite-terrestrial networks are expanding the possibilities for 5G and 6G backhauls, while low Earth orbit (LEO) constellations improve latency- sensitive applications. This paper explores RF system advancements, including beamforming, MIMO, and AI-driven optimizations. Additionally, it discusses challenges like energy efficiency, atmospheric attenuation, and spectrum management. The paper concludes with insights into future trends such as quantum RF systems, deep- space communications, and reconfigurable intelligent surfaces. Keywords – Satellite Communications, RF Systems, Millimeter-Wave, Terahertz, Beamforming, AI-Driven Optimization, Hybrid Networks, Non-Terrestrial Networks (NTN), Cognitive Radios, Network Slicing, LEO Satellites, 5G/6G Backhaul, Doppler Mitigation, Energy-Efficient RF.

On the first test of the Weak Equivalence Principle in low Earth orbit

On the first test of the Weak Equivalence Principle in low Earth orbit

LEO-SOP Differential Doppler/INS Tight Integration Method Under Weak Observability

The utilization of low Earth orbit (LEO) satellites’ signals of opportunity (SOPs) for absolute positioning and navigation in global navigation satellite system (GNSS)-denied environments has emerged as a significant area of research. Among various methodologies, tightly integrated Doppler/inertial navigation system (INS) frameworks present a promising solution for achieving real-time LEO-SOP-based positioning in dynamic scenarios. However, existing integration schemes generally overlook the key characteristics of LEO opportunity signals, including the limited number of visible satellites and the random nature of signal broadcasts. These factors exacerbate the weak observability inherent in LEO-SoOP Doppler/INS positioning, resulting in difficulty in obtaining reliable solutions and degraded positioning accuracy. To address these issues, this paper proposes a novel LEO-SOP Doppler/INS tight integration method that incorporates trending information to alleviate the problem of weak observability. The method leverages a parallel filtering structure combining extended Kalman filter (EKF) and Rauch–Tung–Striebel (RTS) smoothing, extracting trend information from the quasi-real-time high-precision RTS filtering results to optimize the EKF positioning solution for the current epoch. This approach effectively avoids the overfitting problem commonly associated with directly using batch data to estimate the current epoch state. The experimental results validate the improved positioning accuracy and robustness of the proposed method.

Ground and Space (LEO) Based GNSS Ionospheric Detection Using Chapman Function Constraint

AbstractLimited by the number and location distribution of ground stations, the ground based ionospheric detection using Global Navigation Satellite Systems (GNSS) technology suffers from low accuracy and poor reliability in some regions. To improve the performance of the global ionospheric model, this study combines the Continuously Operating Reference Station and the Low Earth Orbit (LEO) Satellite observation to conduct the ground and space‐based (G/SBased) joint ionospheric detection technique. With reference to the ionospheric radar data of the global ionospheric radio observatory, the performance of the G/SBased GNSS joint ionospheric detection technique was tested in quiet and disturbed geomagnetic environments. Results show that in the ground and space based joint mode, the distribution of ionospheric puncture points (IPPs) is uniform, thus effectively avoiding the problem of IPPs blank in the absence of ground stations. In the quiet geomagnetic environment, the ionospheric detection of the G/SBased joint mode has a remarkable performance improvement compared with the ground GNSS mode, with an average improvement of 55.51%. In the geomagnetically disturbed environment, the G/SBased joint mode still has high consistency with the ionospheric radar results, and the detection performance is better than that of the ground GNSS mode. This research shows that combining with ground GNSS and LEO satellite observation data can substantially provide the performance of GNSS ionospheric total electron content detection and can provide good data support for the construction of a global ionospheric refinement model.

Probabilistic Explanations for Entropic Knowledge Extraction for Automated Satellite Component Detection

The escalating risk of collisions and the accumulation of space debris in Low Earth Orbit (LEO) has reached critical concern due to the ever-increasing number of spacecraft. Addressing this crisis, especially in dealing with noncooperative and unidentified space debris, is of paramount importance. This paper contributes to efforts in enabling autonomous swarms of small chaser satellites for target geometry determination and safe flight-trajectory planning for proximity operations in LEO. Our research explores on-orbit use of the You Only Look Once v5 object detection model trained to detect satellite components. Although this model has shown promise, its inherent lack of interpretability hinders human understanding, a critical aspect of validating algorithms for use in safety-critical missions. To analyze the decision processes, we introduce Probabilistic Explanations for Entropic Knowledge extraction (PEEK), a method that utilizes information theoretic analysis of the latent representations within the hidden layers of the model. Through both synthetic and hardware-in-the-loop experiments, PEEK illuminates the decision-making processes of the model, helping to identify its strengths, limitations, and biases.

Bridging Maritime Communication Gaps: The Role of LEO Satellites in Expanding Global Connectivity

ABSTRACT Direct device -to-device is the latest and potentially the biggest opportunity in the telecom business as the gap between satellite and ground communication is narrowing. Respectively, the telecom companies and mobile network operators are interested in increasing the coverage of their telecom networks which will boost the quality of services and will increase the revenues as well. In this regard, Low-earth-orbit (LEO) satellite mega-constellations, such as SpaceX Starlink, are under fast deployments and promise broadband Internet to remote areas that terrestrial networks cannot reach. This paper will investigate the opportunities and challenges facing the LEO mega-constellation and satellite networks in the maritime industry.