Satellite Research Articles

Multiband photometric observations of GEO objects through Sloan filters

With the precipitous growth of the population of objects in Earth's orbit, all major space agencies and companies have made space surveillance a priority to ensure the safety of space missions. With the application of the methods of space surveillance, this article aims to characterize the population of objects in the Geostationary Earth Orbit (GEO) using optical measurements across multiple spectral bands. The study takes place in a context in which the existence of space debris poses a continuous hazard to the operations of active satellites in GEO. Photometric observations of GEO objects using Sloan filters were obtained with SCUDO, a small-aperture telescope part of the Sapienza network. Observations are divided into categories, including 11 objects: rocket bodies (4), defunct satellites (3), and active satellites (4). The spectral response of these objects has been analyzed leading to the identification of a photometric signature which was repeated for two Eutelsat satellites observed under same conditions. All the observed targets resulted in a lower magnitude in the near-infrared. Color indexes also indicate that they are redder than the Sun. This is particularly evident for SL-12 rocket bodies, whose g’-z’ reaches 1.5.

Gravity field recovery of inter-satellite links between Beidou navigation satellite system (BDS) and LEO based on geodesy and time reference in space (GETRIS)

The goal of this contribution is to construct the inter-satellite links (ISLs) between Global Navigation Satellite System (GNSS) and Low Earth Orbit (LEO) satellite to recover the Earth’s gravity field based on the concept of Geodesy and Time Reference in Space (GETRIS). Taking the constellation of the Beidou Navigation Satellite System (BDS) as an example, several types of high-low satellite-to-satellite tracking (H-L SST) modes combining BDS and GETRIS are used to research the tracking mode of high orbit satellites and the distribution of LEO satellite constellations to explore the optimal mode for gravity field recovery. The effects of multiple H-L SST modes on the accuracy of gravity field recovery are studied. In addition, the contribution of each error source is also analyzed. Finally, this study varies LEO satellite constellations to show reduced errors in the temporal gravity field solutions for the improved ISLs. The results showed that the Inclined GeoSynchronous Orbit (IGSO) satellite greatly improved the Geosynchronous orbit (GEO) satellite tracking LEO satellite mode in the high latitude regions. Compared with the Medium Earth Orbit (MEO) satellite tracking LEO satellite, the error of gravity field recovered by combining with GEO, IGSO and MEO can be reduced by 16 %. The largest error is the non-tidal signal, followed by the ocean tidal model difference, and the smallest is the instrument error. For a single LEO satellite, the combination model is more sensitive to the satellite orbital altitude, the cumulative error was decreased from 5.08 mm (550 km) to 0.33 mm (250 km). For LEO constellations, adding inclined orbit satellites can improve the accuracy of the solution to some extent. But the optimal solution can be obtained by the constellation composed of polar orbit satellites with different Right Ascension of Ascending Node (RAAN), the cumulative errors are 0.27 mm (two satellites), 0.19 mm (three satellites), and 0.19 mm (four satellites).

Interference Situational Aware Beam Pointing Optimization for Dense LEO Satellite Communication System

Recently, the low earth orbit (LEO) mega-constellation faces serious time-varying interferences due to spectrum sharing, dense deployment, and high mobility. Therefore, it is important to study the interference avoidance techniques for the dense LEO satellite system. In this paper, the interference situational aware beam pointing optimization technique is proposed. Firstly, the angle of departure (AoD) and angle of arrival (AoA) of the interfering links are obtained to represent the time-varying interference. Then, the interference avoidance problem for dense LEO satellite systems is modeled as a non-convex optimization problem, and a particle swarm optimization (PSO) based method is proposed to obtain the optimal beam pointing of the user terminal (UT). Simulations show that the relative error of the mean signal-to-interference plus noise ratio (SINR) obtained by the proposed method is 0.51%, so the co-channel interference can be effectively mitigated for the dense LEO satellite communication system.

Electric Sail Test Cube–Lunar Nanospacecraft, ESTCube-LuNa: Solar Wind Propulsion Demonstration Mission Concept

The electric solar wind sail, or E-sail, is a propellantless interplanetary propulsion system concept. By deflecting solar wind particles off their original course, it can generate a propulsive effect with nothing more than an electric charge. The high-voltage charge is applied to one or multiple centrifugally deployed hair-thin tethers, around which an electrostatic sheath is created. Electron emitters are required to compensate for the electron current gathered by the tether. The electric sail can also be utilised in low Earth orbit, or LEO, when passing through the ionosphere, where it serves as a plasma brake for deorbiting—several missions have been dedicated to LEO demonstration. In this article, we propose the ESTCube-LuNa mission concept and the preliminary cubesat design to be launched into the Moon’s orbit, where the solar wind is uninterrupted, except for the lunar wake and when the Moon is in the Earth’s magnetosphere. This article introduces E-sail demonstration experiments and the preliminary payload design, along with E-sail thrust validation and environment characterisation methods, a cis-lunar cubesat platform solution and an early concept of operations. The proposed lunar nanospacecraft concept is designed without a deep space network, typically used for lunar and deep space operations. Instead, radio telescopes are being repurposed for communications and radio frequency ranging, and celestial optical navigation is developed for on-board orbit determination.

COSMIC: a UK Active Debris Removal Mission

In recent years, the escalation of space activities has led to an alarming surge in space debris within low Earth orbit (LEO). This paper addresses the pressing need for Active Debris Removal (ADR), a two-pronged strategy to stabilize space debris: maintaining shorter satellite lifetimes and actively removing defunct satellites. In 2022, the UK Space Agency issued funding to explore the launch of a 2026 mission to remove uncooperative debris in LEO. Astroscale’s COSMIC (Cleaning Outer Space Mission through Innovative Capture) mission has been conceived to meet this challenge. Leveraging Astroscale’s expertise and heritage from the ELSA-M mission, which is designed for magnetically capturing prepared clients, COSMIC advances the field of ADR by transitioning from magnetic capture to robotic capture, enabling the removal of unprepared and uncooperative debris. This paper explores the development of COSMIC and its mission to pioneer institutionally funded debris removal with robotic capture, representing a significant milestone in ADR and the broader realm of space exploration. Keywords: Active Debris Removal, In-orbit Servicing, Rendezvous Proximity Operations, Spacecraft Detumbling, Robotic Capture

Large-volume LEO satellite imaging data networked transmission scheduling problem: Model and algorithm

With the current miniaturization and cost reduction trend, many small imaging satellites are deployed in low Earth orbit (LEO). Efficient scheduling of transmission links is crucial for handling the large volume of imaging data in the time-varying inter-satellite broadband communication networks. This ensures optimal utilization of inter-satellite link resources and gives rise to a novel problem known as the Large-volume LEO satellite Imaging Data Networked Transmission Scheduling Problem (LLSIDNTSP). This problem requires the integrity of the imaging data received on the ground station. A Specific Time-Evolving Graph (STEG) model is introduced to formulate this problem, while a highly effective Sequential Two-Phased Heuristic Algorithm (STPHA) is proposed to solve it. STPHA determines an optimized Contact Plan (CP) with a Contact-Fast Construction Algorithm (CFCA) in the first phase. With this CP as input, it produces an optimal transmission schedule with Linear Programming in the second phase. The CFCA incorporates a novel heuristic called Mission Residual Volume Factor(MRVF), which guides the selection of a proper inter-satellite and satellite-to-ground link at each construction step. Extensive simulation results demonstrate the effectiveness of the proposed STPHA. In particular, it can achieve the optimal solution for small-sized scenarios with one-hundredth of the computing time used by the exact solver CPLEX. Also, it is consistently better than other heuristic algorithms adapted from the literature for large-sized scenarios. Additional experimental analysis is conducted to showcase the effectiveness of the innovative components of STPHA.

Three-Dimensional Particle Tracing Analysis of a Rotational Magnetic Sail

A magnetic sail is a propellantless propulsion system that has great potential in long-term space travel. It utilizes the interaction between the solar wind and the magnetic field generated by a high-current coil. However, the requirement of a large-sized coil with a high working current limits its practical application. To reduce the coil size while maintaining the thrust, a rotational magnetic sail is proposed and analyzed using the three-dimensional particle tracing method. The results show that the magnetic sail thrust significantly increases with the rotational speed and is influenced by plasma parameters. Moreover, the sail achieves the maximum thrust and the most stable attitude when the magnetic moment vector is perpendicular to the particle impact direction. The analysis implies that the rotational magnetic sail can shrink to about a minimum of 20% and approximately 1% of the size of a static magnetic sail in the solar wind and low Earth orbit, respectively, while maintaining the same thrust.

Experimental Investigation on the Influence of Observation Angle on the Spectral Characteristics of Minerals in the Visible-Near Infrared Range

The analysis of the factors affecting the spectral characteristics of rock minerals is the basis of improving the accuracy of quantitative inversion of spectral minerals. Hyperspectral remote sensing has advantages and development potential in the quantitative inversion of minerals, but it is limited by many constraints and influencing factors in the process of remote sensing recognition of rock and mineral spectral information. In practical application, satellite earth observation is affected by terrain fluctuation, which leads to some deviation of observation Angle. At the same time, vertical samples are often used in the experiment to reduce the spectral experimental error. Therefore, the spectral observation Angle plays an important role in determining the composition of rock and ore. In order to study the effect of different observation angles on the reflectance spectra of minerals, the spectral reflectance spectra were analyzed in the visible near-infrared (0.4-2.5μm) band to explore the variation rules. First, common quartz, orthoclase and plagioclase minerals were sliced and polished to make block samples with fixed roughness values. The incident Angle of light source was fixed, and the influence of different observation angles on the visible near-infrared spectral characteristics of minerals was analyzed by changing the Angle of emergence and azimuth. Secondly, through the qualitative and quantitative analysis of the results and the mechanism analysis, it can be concluded that the effect of zenith Angle on spectral reflectance is the same under different observation azimuth angles. The observed zenith Angle has a great influence on the spectral reflectance, which is reflected in the fact that the reflectance of mineral samples gradually increases with the increasing of the zenith Angle to reach the peak value within 30°~50°, and then gradually decreases. The spectral reflectance at 0°-360° azimuth is symmetrical, and the spectral reflectance is oscillatory, and the reflectance at 180° azimuth is the highest. The overall situation gradually increases from 0°-180° spectral reflectance, and gradually decreases from 180°-360° spectral reflectance. With the change of observation Angle, the peak and trough of the reflectance of the sample are basically located in the same band position. It is of great significance to realize the accurate division of rock mining area and to exploit mineral resources reasonably and efficiently.

Depositing gradient thickness silver film on CNF/rGO/polyimide surface to form a sandwich structure for efficient electromagnetic interference shielding

Deployable satellites in space are exposed to high-frequency electromagnetic interference (EMI) for long periods of time, resulting in shortened lifetimes, so there is an urgent need for supportive electromagnetic shielding materials. To address this limitation, our team has developed innovative ultrathin carbon nanofiber/reduced graphene oxide/polyimide (CNF/rGO/PI) composites. It has excellent strength, shape memory properties, thermal stability and wide temperature range tolerance. Among them, polyimide with 4 % CNFs and 4 % rGO (CGPI44) has the best performance. Gradient-thick Ag films are deposited on both sides of the CGPI44 substrate by magnetron sputtering to form sandwich structure composites. With a sputtered Ag thickness of only about 5 μm and a total thickness of 0.146 mm, the material exhibited an extremely high electrical conductivity and excellent EMI shielding effectiveness (SE) of up to 112 dB in the 8.2–12.4 GHz band. Finite element analysis is performed to calculate the electric field strength and energy distribution. By providing a feasible scheme for highly effective shielding of high-frequency EMI, this approach will promote research on magnetron-sputtered polymer composites in the field of electromagnetic shielding.

A background suppression detector array for fast neutron measurement in space science study

A compact detector array with a symmetrical structure was designed and developed for the measurement of fast neutron flux in space radiation environments by the recoil proton method. It consists of seven solid-state detectors and a hydrogen-containing conversion layer, which can effectively eliminate the background from the charged particles and gamma rays. The performances for fast neutron measurements in the low Earth orbit and on the lunar surface have been simulated by Geant4 software. The signals from recoil protons can be well distinguished in a complex radiation environment. The accuracy of fast neutron flux measurement can be improved with a higher signal-to-noise ratio. Utilizing this array, a neutron spectrometer for low Earth orbit applications was constructed and was launched on board the “Weiming-1” CubeSat at the beginning of 2024.

Magnetic Shielding Implementation in the Small Satellite Reaction Wheel

Low Earth orbit satellites face challenges from Earth's magnetic field, causing attitude disturbances. Attaining a magnetic-dipole-free satellite is crucial. Layout optimization and in-orbit dipole compensation are common methods, but layout optimization can be impractical. In contrast, in-orbit dipole compensation struggles with rapidly changing magnetic dipoles like those from reaction wheel motors. This research proposes an alternative solution using Mu-metal, known for shielding against magnetic exposure. This shield can be applied to trap the magnetic field generated by the motors. Ground tests evaluated this approach. First, it determined the minimum distance between the magnetometer and the shield for accurate measurements with minimal interference, with the result of 10 cm as the least affected distance, particularly important for small satellite layout design. Second, it assessed the shield's effectiveness in trapping the motor-generated magnetic field. Tests showed a significant reduction in magnetic field magnitude and up to a 95% reduction in field fluctuations when the motor is activated. This research offers a practical solution for small satellite layout design, addressing the challenges posed by their compact dimensions. Mu-metal shielding proves effective for mitigating rapidly changing magnetic dipoles and enhancing magnetic cleanliness in low Earth orbit.

Detecting climate‐related shifts in lakes: A review of the use of satellite Earth Observation

AbstractClimate change exerts a profound impact on lakes, eliciting responses that range from gradual to abrupt transitions. When reaching critical tipping points, the established lake dynamics stand to undergo substantial modifications, setting off a chain reaction that reverberates through the entire ecosystem. This lake shift ripples into related ecosystem services and even influences the well‐being of human communities. Despite the importance of lake shifts, we lack a systematic overview of their occurrence, mainly due to the lack of systematic data at the global scale. We reviewed the literature focusing on climate‐related lake shifts and assessed how satellite Earth Observation (EO) has contributed to the research topic, and what we can unlock from this novel data. Our results show that EO data are used in only 9% of studies on lake shifts, although this fraction has increased since 2012. EO data is most commonly used to assess shifts in surface extent, ice coverage, or phytoplankton phenology. These variables are directly observable and the spatio‐temporal resolution of EO satellites is of great advantage. But lake shifts can also be identified indirectly from EO data, as in the example of the vertical mixing of lake water, which can be described on the basis of surface patterns. In all possible applications, we expect increasing use of EO satellites in the future, including the development of early warning systems that promise to provide timely alerts regarding impending lake shifts, thus serving as a vanguard against abrupt alterations that could ripple through interconnected ecosystem services.

LOCATIONS OF TRIANGULAR EQUILIBRIUM POINTS OF THE RESTRICTED THREE-BODY PROBLEM WITH POYNTING-ROBERTSON DRAG AND VARIABLE MASSES

The restricted three-body problem (R3BP) is a fascinating problem that has been receiving attentions of astronomers and scientists because of its vast implications in diverse scientific fields, including among others; celestial mechanics, galactic dynamics, chaos theory and molecular physics. In this paper, we examine the locations of the triangular equilibrium points of the R3BP with Poynting-Robertson (P-R) drag forces and variable masses. The primaries are assumed to vary under the unified Mestschersky law and their dynamics defined by the Gylden-Mestschersky equation, while the smaller primary is assumed to be a radiation emitter with P-R drag. The dynamical equations are obtained for both the non-autonomous with variable coefficients and autonomized system with constant coefficients. Further, the locations of the triangular points of the autonomized systems are obtained using perturbation method. It is seen that the positions are defined by the mass parameter, radiation pressure and P-R drag of the smaller primary. The triangular points of the non-autonomous equations are obtained with help of the Mestschersky transformation, and differ from those of the autonomized system due to a function of time. The equilibrium points have several applications in space missions, satellites constellations and station-keeping.

The Spectral Characterization of Novel Spacecraft Materials in the Low Earth Orbit Environment

The Spectral Characterization of Novel Spacecraft Materials in the Low Earth Orbit Environment

Access authentication via blockchain in space information network.

Space Information Network (SIN) has significant benefits of providing communication anywhere at any time. This feature offers an innovative way for conventional wireless customers to access enhanced internet services by using SIN. However, SIN's characteristics, such as naked links and maximum signal latency, make it difficult to design efficient security and routing protocols, etc. Similarly, existing SIN authentication techniques can't satisfy all of the essentials for secure communication, such as privacy leaks or rising authentication latency. The article aims to develop a novel blockchain-based access authentication mechanism for SIN. The proposed scheme uses a blockchain application, which has offered anonymity to mobile users while considering the satellites' limited processing capacity. The proposed scheme uses a blockchain application, which offers anonymity to mobile users while considering the satellites' limited processing capacity. The SIN gains the likelihood of far greater computational capacity devices as technology evolves. Since authenticating in SIN, the technique comprises three entities: low Earth orbit, mobile user, and network control centre. The proposed mutual authentication mechanism avoids the requirement of a ground station, resulting in less latency and overhead during mobile user authentication. Finally, the new blockchain-based authentication approach is being evaluated with AVISPA, a formal security tool. The simulation and performance study results illustrate that the proposed technique delivers efficient security characteristics such as low authentication latency, minimal signal overhead and less computational cost with group authentication.

TinyGS vs. SatNOGS: A Comparative Analysis of Open-Source Satellite Ground Station Networks

In recent years, two of the largest open-source ground station (GS) networks capable of enabling Earth–satellite communication have emerged: TinyGS and SatNOGS. These open-source projects enable anyone to build their own GS inexpensively and easily, integrate into a GS network, and receive data from satellites listed in the database. Additionally, it enables satellite developers to add satellites to the databases of these projects and take advantage of this GS network to receive data from the satellites. This article introduces the TinyGS and SatNOGS projects and conducts a comparative analysis between them. Generally, the TinyGS project seems to have simpler implementation as well as lower associated costs. In a deeper analysis, it was observed that on the 29 July 2023, the TinyGS project had a higher number of online GSs and a more favorable geographic distribution. On the other hand, the SatNOGS project managed to communicate and decode a larger number of satellites up to 29 July 2023. Additionally, in both projects, it was noted that frequencies between 436 and 437 had the highest number of satellites with decoded data. Ultimately, the choice between these projects depends on critical parameters defined by the reader.

Deep learning‐based space debris detection for space situational awareness: A feasibility study applied to the radar processing

AbstractThe increasing number of space objects (SO), debris, and constellation of satellites in Low Earth Orbit poses a significant threat to the sustainability and safety of space operations, which must be carefully and efficiently addressed to avoid mutual collisions. The space situational awareness is currently addressed by an ensemble of radar and radio‐telescopes that detect and track SO. However, a large part of space debris is composed of very small and tiny metallic objects, very difficult to detect. The authors demonstrate the benefits of using deep learning (DL) architectures for small space object detection by radar observations. TIRA radio telescope has been simulated to generate range‐Doppler maps, then used as inputs for object detection exploiting You‐Only‐Look‐Once (YOLO) frameworks. The results demonstrate that the object detection by using YOLO algorithms outperform conventional target detection approaches, thus indicating the potential benefits of using DL techniques for space surveillance applications.

Temperature dependence of atomic‑oxygen irradiation mechanism of hydrogenated diamond-like carbon film

Hydrogenated diamond-like carbon (H-DLC) films are effective lubricants for aerospace moving parts, but the service of H-DLC is severely threatened by atomic oxygen (AO) in low Earth orbit (LEO). The interaction between AO and H-DLC strongly depends on ambient temperature; however, the interactive mechanism has not been fully understood. In this study, we report different temperature dependences of AO irradiation behavior on H-DLC film. Under the AO irradiation with low energy, the increase in ambient temperature can only increase the surfacial oxidation; while, the effect of temperature under high AO irradiation energy is more significant, resulting in the transition from the surficial oxidation to continuous carbon removal. Subsequent analysis of the AO trajectories shows that the different repulsion mechanisms of the H-DLC surface against high and low energy AO result in the different temperature dependence. For AO incident with low energy, the incident AO cannot touch the H-DLC surface anymore due to the repulsion of the surfacial oxygen in the later irradiation stage. Nevertheless, high energy AO could overcome the repulsion of oxidized surface to contact the H-DLC surface, the increase in temperature can continuously promote the AO irradiation on the H-DLC surface.

Non-Cooperative LEO Satellite Orbit Determination Using Single Station for Space-Based Opportunistic Positioning

Space-based opportunistic positioning is a crucial component of resilient positioning, navigation, and timing (PNT) systems, and it requires the acquisition of orbit information for non-cooperative low Earth orbit (LEO) satellites. Traditional methods for orbit determination (OD) of non-cooperative LEO satellites have difficulty in achieving a balance between reliability, hardware costs, and availability duration. To address these challenges, this study proposes a framework for single-station orbit determination of non-cooperative LEO satellites. By utilizing signals of opportunity (SOPs) captured by a single ground station, the system performs initial orbit determination (IOD), precise orbit determination (POD), and orbit prediction (OP), enabling the long-term determination of satellite positions and velocities. Under the proposed framework, the reliability and real-time performance are dependent on the initial orbit determination and the orbit calculation based on the dynamical model. To achieve initial orbit determination, a three-step algorithm is designed. (1) An improved search method is employed to estimate a coarse orbit using single-pass Doppler measurements. (2) Data association is conducted to obtain multi-pass Doppler observations. (3) The least squares (LS) is implemented to determine the initial orbit using the associated multi-pass Doppler measurements and the coarse orbit. Additionally, to enhance computational efficiency, two fast orbit calculation algorithms are devised. These algorithms leverage the numerical stability of the Runge–Kutta integrator to reduce computations and exploit the strong correlation among nearby time intervals of orbits with small eccentricities to minimize redundant calculations, thereby achieving orbit calculation efficiently. Finally, through positioning experiments, the determined orbits are demonstrated to have accuracy comparable to that of two-line elements (TLE) updated by the North American Aerospace Defense Command (NORAD).

Cloud-edge collaborative computing offloading and resource allocation optimization in LEO satellite network

Satellite edge computing can provide communication and computing services to areas lacking ground network coverage, enhancing the computational capabilities of terrestrial users. However, due to the relatively limited computational resources available on satellites, cloud-edge collaborative computing in Low Earth Orbit (LEO) satellite communication scenarios emerges as a more optimal solution. In this paper, a cloud-edge collaborative offloading algorithm based on Deep Deterministic Policy Gradient (DDPG) algorithm is proposed to solve the offloading decision and resource allocation problems. The optimization problem is modeled as Markov decision process, and the comprehensive delay and energy consumption cost of computing tasks completed by ground users are optimized. Simulation results validate that the proposed algorithm has good convergence properties and lower comprehensive cost than processing all tasks locally and offloading all tasks to LEO satellites.