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Space telescopes have been instrumental in enlightening our understanding of the universe, from the iconic Hubble Space Telescope to specialized instruments like Chandra and Kepler. Pushing the frontiers of cosmic exploration, the future of space exploration hinges on modular Large Aperture Space Telescopes (LAST), much larger than the recently launched 6.5 m James Webb Space Telescope, necessitating robotic assembly in orbit. This paper introduces a paradigm shift in astronomical observation by featuring robotic in-orbit assembly of a large aperture space telescope. This review paper starts by tracing the evolution of telescopes and presents a comprehensive overview of the state-of-the-art space telescopes. This paper then reinforces the need for LAST to address the constant clamour for higher-resolution astronomy. While current semi-autonomous robotic manipulators operate from the International Space Station, their limited walking capabilities constrain their workspace, making them unsuitable for the LAST mission. This paper presents a detailed trade-off analysis of the challenges associated with the in-orbit assembly of LAST using candidate robots to understand the technological gaps. Further, the evolution of space robotic manipulators is presented, highlighting design features, advantages, and drawbacks for in-orbit spacecraft servicing and assembly missions. To tackle design and modelling challenges for robotic systems in space, amidst the various perturbations in the extreme space environment, linear and non-linear control systems necessary for achieving ultra-high precision performance are also discussed. This paper advances the walking space manipulator technology by introducing the next generation of walking space manipulators – the End-Over-End Walking Robot (E-Walker). The dexterous and modular design of the E-Walker makes it an ideal candidate for missions involving assembly, manufacturing, servicing, and maintenance. [ABSTRACT FROM AUTHOR]

Our latest paper (Dolgikh et al., 2023) investigates the effects of UHECR propagation in a turbulent intergalactic magnetic field in the small-angle scattering regime, specifically focusing on the non-trivial caustic-like pattern that arises with strong deviation from isotropy. In this paper, we explore the effect of the observer's position on the measurement of source flux at a given distance. We examine three types of source locations, characterized by the density of cosmic rays from a given source at the observation point, which we call magnetic knots, magnetic filaments and magnetic voids. We also investigate the energy spectrum in these different cases and present simulated images of the source as it appears on the observer's telescope after propagation in the combination of intergalactic and Galactic magnetic fields. We show that hot spots in the UHECR data can arrive due to combined distortions of the source images on the intergalactic and Galactic magnetic fields. Also the fact that flux of most nearby sources is diluted in the magnetic voids affects source population studies. [ABSTRACT FROM AUTHOR]

The effect of atmospheric aerosols on the earth's radiation budget is primarily through their direct effects. Understanding aerosols' morphology and elemental composition is crucial in this context. For two years, from January 2017 to December 2018, aerosol samples (PM 10) were collected on quartz filter papers using a high-volume sampler (PM 10) in Chennai, a semi-urban coastal environment located at 12.81°N, 80.03°E. These filter papers were stored under ambient laboratory conditions and were subsequently subjected to ultrasonication using ethanol as the solvent to separate the aerosols from the filters. The extracted samples were then analyzed using scanning electron microscopy (SEM) for the morphology and energy dispersive X-ray analysis (EDX) for elemental composition. The EDX analysis of the samples revealed the presence of various elements such as carbon (C), oxygen (O), aluminum (Al), silicon (Si), sulfur (S), potassium (K), iron (Fe), magnesium (Mg), calcium (Ca), vanadium (V), bismuth (Bi), sodium (Na), chlorine (Cl), phosphorus (P), and technetium (Tc). High concentrations of carbon, oxygen, and aluminum–silicate particles indicated the presence of carbonaceous aerosols and wind-blown dust particles. Concentration-weighted trajectory (CWT) analysis was carried out to assess the transport pathways of aerosols in the region. CALIPSO overpasses during the study period were selected, and the Vertical Feature Mask (VFM) identifiers for different aerosol types were compared with the local experimental results. The findings show that CALIPSO possess a reasonably effective capability in detecting and characterizing the local aerosol types. CALIPSO detected Dusty marine, Clean marine, Elevated smoke and Polluted dust in the study area across all four seasons. These findings closely match the characteristics of such aerosol types obtained from SEM/EDX analysis, HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) modeling, and the Angstrom exponent derived from sunphotometer readings. [ABSTRACT FROM AUTHOR]

Spacecraft formation flying for interferometric observations around the 2nd Lagrange point in the Sun-Earth system (SEL2) is currently focal point in deep space exploration research, which demands high precision in relative position control of spacecraft. This paper proposes the relative motion dynamics of satellite formations around the L2 point in the port-Hamiltonian framework, and establishes a high-precision nonlinear dynamics model. PID passivity-based control (PID-PBC) is widely used in engineering. However, existing methods of PID-PBC cannot address the trajectory tracking issues in port-Hamiltonian systems. Utilizing the contraction properties of the port-Hamiltonian system, this paper proposes the trajectory tracking PID-PBC (tPID-PBC) approach, effectively resolving trajectory tracking issues for formation dynamics around L2 point in port-Hamiltonian framework. The paper details explicit solutions of the Partial Differential Equations (PDE) for the tPID-PBC method and its controller structure, and references the trajectories of interferometric observation formations, to verify the method's effectiveness through numerical simulation. The presented control approach is applicable across generic port-Hamiltonian systems, offering substantial theoretical value. [ABSTRACT FROM AUTHOR]

The paper presents the results of long-term, continuous observations of the Cherenkov light at the Yakutsk array. The Cherenkov light measurements allow one to reconstruct the longitudinal development of the shower, which is associated with both the model of hadron interactions and the mass composition of cosmic rays. The paper also provides a review of the results that are important for the physics of air showers and the astrophysics of cosmic rays, obtained over a long period of time at the Yakutsk array. [ABSTRACT FROM AUTHOR]

Remote sensing ship image detection methods have broad application prospects in areas such as maritime traffic and fisheries management. However, previous detection methods relied heavily on a large amount of accurately annotated training data. When the number of remote sensing ship targets is scarce, the detection performance of previous methods is unsatisfactory. To address this issue, this paper proposes a few-shot detection method based on global and local feature aggregation. Specifically, we introduce global and local feature aggregation. We aggregate query-image global and local features with support features. This encourages the model to learn invariant features under varying global feature conditions which enhances the model's performance in training and inference. Building upon this, we propose combined feature aggregation, where query features are aggregated with all support features in the same batch, further reducing the confusion of target features caused by the imbalance between base-class samples and novel-class samples, improving the model's learning effectiveness for novel classes. Additionally, we employ an adversarial autoencoder to reconstruct support features, enhancing the model's generalization performance. Finally, the model underwent extensive experiments on the publicly available remote sensing ship dataset HRSC-2016. The results indicate that compared to the baseline model, our model achieved new state-of-the-art performance under various dataset settings. This model presented in this paper will provide new insights for few-shot detection work based on meta -learning. [ABSTRACT FROM AUTHOR]

One of the potentially catastrophic risks to human survival is the impact of a meteorite on Earth. When a meteoroid enters the atmosphere at an ultra-high speed, a series of complex evolution processes occur, mainly including ablation, fragmentation, airburst, and ground impact. This paper proposes a new systematic dynamical method for simulating the entire process of a meteoroid entering the atmosphere. In the new method, the DEM (Discrete Element Method) model is utilized to describe the initial structure and shape of a rubble-pile meteoroid. A combination of an aerodynamic trajectory model, a thermal ablation model, and an airburst model is introduced to simulate the entry process. Particularly, the Jone-Wilkins-Lee state equation is employed to characterize the large-scale airburst phenomenon caused by the internal expansion of the meteoroid. Referring to the observational data of the Chelyabinsk meteorite event, this paper parametrically simulates the trajectories, ablation, fragmentation, and airburst, and predicts the strewn field of different-shaped meteoroids. Compared with existing debris cloud models, this method considers the shape effect of rubble-pile meteoroids and can obtain the strewn field as a side effect. Numerical validation is carried out, indicating the result of the new method is more in line with the actual scenarios. [ABSTRACT FROM AUTHOR]

Launch vehicle applications require highly accurate and reliable navigation systems that can withstand the high dynamic conditions of the launch and flight phases. GNSS-aided INS (Inertial Navigation System) is the most popular solution for launch vehicle navigation. However, the accuracy of Global Navigation Satellite System (GNSS) receivers can be compromised by malicious spoofing attacks, which can result in significant safety risks and mission failure. This paper presents a method for identifying and mitigating the spoofing attacks on Global Navigation Satellite System (GNSS) receivers using the independent and simultaneous measurements of the Inertial Navigation System (INS). A state space approach is attempted in this paper with an extended Kalman Filter for identifying the spoofed signals. The well-established method of integrating INS and GNSS data for navigation accuracy improvement is taken as the baseline of this algorithm. The proposed method is an extension of a loosely coupled integration algorithm already established for fusing INS and GNSS data. The extended Kalman filter estimated position and velocity of the receiver is used along with the satellite position and velocity computed from ephemeris to find out the range and range rate of each of the satellites to the receiver. The difference between the estimated range and range rate against the measured range and range rate is considered as filter residual. The filter residuals are taken as the parameter to identify the spoofing. The threshold of filter residuals for range and range rates is the critical parameter that decides the false isolation and missing detection. The threshold is decided based on the environment in which the receiver is operated, the dynamics expected, and the noise model. The algorithms envelopment and simulation studies are done. The simulation tests are completed using a GNSS constellation simulator with spoofed signals. The INS and GNSS error model, states selection, Kalman filter design, algorithm details, simulation tests, simulation results, advantages and disadvantages of the new algorithm, and future work are covered in this paper. [ABSTRACT FROM AUTHOR]

Extended kalman filter (EKF) is widely used to integrated navigation system of global navigation satellite system (GNSS) and strapdown inertial navigation system (SINS). However, non-Gaussian noise and the uncertainty of measurement noise can seriously reduce the performance of EKF, so it is difficult to obtain an optimal GNSS/INS integration solution. At present, non-Gaussian noise processing is still a difficult issue in filter research. In this paper, an adaptive and robust maximum correntropy extended kalman filter (MCEKF) method based on Cauchy kernel function is proposed to solve the above problem. Thanks to the excellent properties of Cauchy kernel function, the proposed method can effectively avoid filter faults and has better stability. However, the performance of MCEKF depends on the select of kernel bandwidth parameter, which is a difficult problem in the engineering application of MCEKF. In this paper, the switching kernel bandwidth algorithm is employed to adaptively estimate the kernel bandwidth parameter to solve the tradeoff between convergence rate and steady-state misalignment in the MCEKF algorithm under constant kernel bandwidth. Finally, the performance of the proposed algorithm is verified by two sets of vehicle-mounted precise point positioning (PPP) and SINS tightly coupled integration experiments in urban environment. The results show that compared with EKF, the proposed method can significantly improve the positioning accuracy, that is, the PPP/SINS positioning accuracy based on GE, GR and GRE system is improved by 25.1 %, 2.5 % and 17.0 % in D196 experiment, and 23.5 %, 16.5 % and 31.8 % in D107 experiment, respectively. The velocity and attitude accuracy of the two methods are similar. The velocity errors of all schemes can reach cm/s level. The roll, pitch and heading errors of navigation-grade inertial sensor are all less than 0.12 degree. The roll and pitch errors of MEMS are less than 1.0 degree, the heading error of the G, GE, GR, and GRE systems are 1.719, 1.464, 1.676, and 1.475 degree, respectively. [ABSTRACT FROM AUTHOR]

• Designed affordable 3DOF attitude simulator. • In–house built 3-axis Helmholtz coil cage. • Identified CubeSat demonstrator parameters. • Demonstrated CubeSat self-actuation & detumbling. Spacecraft attitude determination and control systems (ADCS) stand as a pivotal factor for ensuring the success of missions. As satellite sizes continue to decrease, the need for more intelligent and efficient control algorithms becomes increasingly pronounced. In response to this imperative, we propose the development of a scaled-down testbed specifically designed for evaluating satellites (ACDS). This testbed will demonstrate effective control of a CubeSat through the use of Helmholtz coils, magnetic torquer solenoids, reaction wheels and inexpensive student-made components and available components off the shelf (COTS) in the San Diego State University SPACE Lab. Referred to as the Spacecraft Attitude Testbed (SAT), this custom-designed 3-DoF experimental attitude platform replicates the conditions experienced by a weightless satellite in space. The objective of this research paper is to improve the understanding of how to manufacture a testbed and components like those within this paper, expose some of the issues encountered and improve the outcomes for future academic testbeds. Within this study, the testbed employs torque application to magnetic torquers and reaction wheels to regulate attitude. In summary, this research endeavors to establish a comprehensive and cost-effective testbed platform dedicated to the assessment of spacecraft attitude control and determination systems. It not only seeks to enhance our understanding of advanced control algorithms but also aims to contribute valuable insights into fault detection and adaptive control strategies, ultimately bolstering the efficiency and robustness of satellite operations. [ABSTRACT FROM AUTHOR]

The new generation of remote sensing satellites improves the coverage of remote sensing imaging by improving the orbital surface and using the rotary scanning imaging technology. In this paper, a new technical scheme of rotating payload platform based on disturbance-free payload technology is proposed to adapt to the rotary scanning imaging satellite. The platform adopts the cubic Stewart configuration and uses the Lorentz force magnetic actuator as the actuator to form the satellite support module and the payload into a noncontact two-stage three-body. First, this paper uses Newton-Euler method to establish a six-degree-of-freedom dynamic model for the new rotating payload platform, and establishes a kinematic model by quaternion method. Then, according to the established kinematics and dynamics model, the control scheme of absolute pointing control of payload platform (upper platform) and relative follow-up control of kinetic energy container (middle platform) is designed. Furthermore, the six-degree-of-freedom decoupling control method of the actuator is designed. Based on this, the absolute pointing controller of the payload module and the relative position and attitude calculate controller of the kinetic energy container are designed. Finally, the research of simulation is carried out. The simulation results show that the new rotating payload platform has higher rotation pointing accuracy and stability than the traditional ultra-quiet platform, and the vibration isolation acting on the support module and the vibration absorption acting on the payload are more effective. [ABSTRACT FROM AUTHOR]

• A formation keeping control law for deorbiting debris by a laser ablation is proposed. • The analytical solution of relative motion in powered flight is derived. • The control law is robust against the uncertainties of ablation thrust and orbital perturbation. This paper proposes the formation keeping control law for deorbiting debris by a laser ablation. Laser ablation is vital technology for contactless active debris removal, where a chaser satellite with a laser system irradiates laser pulses to a target object to generate the ablation force for deorbiting. The deorbiting force decelerates the target, and the chaser must maintain its relative position and continue irradiating. In other words, both the chaser and the target are supposed to be deorbited simultaneously, where both have accelerations. Although conventional formation flying missions assume that only a chaser maneuvers, the formation flying in this paper considers that both a chaser and a target have accelerations. Thus, this paper derives the relative equations of motion between the chaser and the target in powered flight and their analytical solution using relative orbital elements. A control law based on the analytical solution is proposed, which determines the timings and directions of the laser ablation and the electrical thrust so that the formation periodically returns to a desired formation. Numerical simulations first examine the control law in two cases with different maneuver timings. Then, a Monte Carlo simulation is performed to verify the effectiveness of the control law for a variety of desired formations. [ABSTRACT FROM AUTHOR]

• A novel fault-tolerant controller has been developed for the attitude control of rigid spacecraft based on Q-learning. • This controller obviates the necessity for actuator fault data or extensive fault knowledge. • The controller stability analysis and controller implementation are discussed. This paper presents a novel active fault-tolerant control (FTC) scheme based on reinforcement learning (RL) for rigid spacecraft operating in challenging conditions with simultaneous actuator faults and external disturbances. Initially, the paper outlines the dynamics of a rigid spacecraft afflicted by actuator faults and subject to external disturbances. Subsequently, an observer is designed to swiftly detect actuator faults, ensuring a timely response to fault occurrences. An indirect fault estimator is then employed to estimate the total faults affecting the system. Based on the estimated total faults, the proposed decision mechanism switches the controller from the nominal to the fault-tolerant controller. The proposed fault-tolerant controller is model-free and utilizes the Q-learning algorithm. This Q-learning-based fault-tolerant controller can be implemented online without relying on explicit system models or actuator fault details. Notably, this innovative controller operates independently from fault detection and identification (FDI), utilizing data extracted from system trajectories. The stability of the fault-tolerant controller is established using Lyapunov techniques, providing rigorous validation of its effectiveness in maintaining system stability and achieving satisfactory performance. The performance and adaptability of the proposed approach are assessed through comprehensive simulation studies, emphasizing its capacity to enhance spacecraft fault tolerance in demanding operational scenarios. [ABSTRACT FROM AUTHOR]

• Inter-satellite links (ISL) establishment within libration point constellation for orbit determination (OD). • Analyzed the factors that affect the accuracy of establishing ISLs for OD within the constellation. • Research on the impact of ISLs building interval on OD performance. • Discusses the OD accuracy after establishing ISLs between the libration point constellation and BDS. Earth-Moon libration point navigation constellation has a merit of fully covering the cislunar space and providing navigation services with merely a small number of satellites. Furthermore, this type of constellation itself can achieve orbit determination by using only its Inter-satellite links (ISL) owing to the well-known gravitational asymmetry near the libration points. This paper adopts a representative four-satellite navigation constellation including three satellites located near the libration point L3, L4, L5, and an extra one in Distant Retrograde Orbit (DRO), and studies the orbit determination accuracy of the constellation under two conditions: establishing ISLs within itself (called Solely libration point satellites) and establishing additional ISLs with BeiDou Navigation Satellite System (BDS) (called Libration + BeiDou satellites). The simulation results indicate that, for the Solely libration point satellites scenario with the 1 m range error and solar radiation pressure (SRP) error with the level of 10% deviation between ball model and macro model, the final orbit accuracies for L3, L4, L5, and DRO satellites can respectively achieve 11.3 m, 12.7 m, 12.6 m, and 7.3 m. Reducing the link interval can significantly shorten the arc length to achieve final accuracy, whileas it has less impact on the final orbital accuracy. When the link interval is set as 240, 60, 10, and 2 min, the arc lengths at the final accuracy of better than 15 m are about 35, 29, 23, and 20 days, respectively. To balance the communication burden and the orbit determination arc length, the recommended ISL building interval is 10 min. Errors coming from range measurement model and dynamic model, in addition, are key factors in orbit determination, which can result in meters to tens of meters of orbital accuracy. For the Libration + BeiDou satellites scenario, the augmented ISLs to BDS can substantially improve constellation orbital accuracy and shorten the orbit determination arc length. When the DRO satellite attached to the Geostationary Earth Orbit (GEO), Inclined Geosynchronous Orbit (IGSO), and Medium Earth Orbit (MEO) satellites of BDS respectively, the improved accuracy are 37.1%, 61.2%, and 42.2%, while the shortened arc length are 20.1%, 28.3%, and 28.1%, respectively. The research findings presented in this paper can serve as a reference for the construction and assessment of navigation constellations in the Earth-Moon system. [ABSTRACT FROM AUTHOR]

• Sun interference is studied on the 10 year-operation of Earth observation satellite. • Impact by Sun on Geostationary Ocean Color Imager (GOCI) data reception is examined. • Sun outage is prevented by GOCI imaging time adjustment in real satellite operation. • Simulation and measurement of sun interference are compared by quantitative analysis. • Prevention from sun outage in GOCI image reception is validated by operation results. A practical approach has been studied to cope with the sun interference of Earth observation geostationary satellite and the results of 10-year satellite operation for preventing sun outage are presented with detailed analysis in this paper. The Communication Ocean Meteorological Satellite (COMS) is equipped with the Geostationary Ocean Color Imager (GOCI), which performs ocean observation mission in the geostationary orbit. After the launch of the COMS, this study was initiated to prevent image data loss due to sun interference in receiving GOCI image data at the ground station of the principle user site under the operation configuration of single satellite and single ground station. This paper fully covers the entire research and the operation process which have been conducted over the 10 years from 2011 to 2021, including unexpected changes of operational environment such as ground station antenna change and satellite longitude position change. The specific characteristics of sun interference on the COMS operation is analysed through the theoretical simulation on the strength and the occurrence time of sun interference affecting the GOCI image data reception. The simulation outcomes are used to specify trigger level, date and time of sun outage in the COMS operation. From the concept that the sun outage could be prevented by adjusting the GOCI imaging time in advance, a GOCI special operation plan was established for the practical way of the sun outage prevention that was optimized for the COMS mission and could be applied to actual satellite operation. The approach of this study is verified by confirming the success of the sun outage prevention after the execution of the GOCI special operation plan. The verification is based on the operation results of the satellite link Radio Frequency (RF) signal performance and the image reception success status which has been obtained during the 10 years of the COMS operation. And, this study shows good consistency between the simulation outcomes and the operational measurements as well as the operational flexibility that it is possible to cope with the sun outage successfully even in the unexpected operational changes during the 10 years. [ABSTRACT FROM AUTHOR]

• Commercial-of-the shelf (COTS) space qualified solenoid valves for small satellite missions are financially unviable. • Thrusters control spacecraft attitude, the response time, and parameters of the solenoid valve is critical in mission design. • A mathematical model was developed to find the optimized geometrical configuration of the solenoid valve. • This paper presents a practical solution for designing custom solenoid valves. • The developed mathematical model validated using COTS space qualified solenoid valves. Small satellites and spacecrafts use propulsion systems to stabilize their attitude, control orientation and deorbit it at the end of the mission life. The flow and thrust of the liquid propulsion system are controlled by the control valve, typically operated by solenoid. According to recent literature, space-qualified solenoid valves are expensive and financially non viable, especially for small satellite missions. In this paper, a detailed methodology is presented to design the solenoid valve dedicated for small satellites. This study includes design criteria focusing on geometrical configuration. The dynamic, and electro-magnetic models are used to characterize the solenoid valve. Dynamic modelling helps to determine the response time of valve, affecting the thruster minimum impulse bit. The physical dimensions of the designed solenoid valve are smaller than those available in commercial off-the shelf (COTS) solenoid valves. However, the efficacy of the proposed design is proven effective with the COTS space grade valve specifications, and it shows that the proposed valve consumes less power than the conventional valves. Finally, it is worth noting that despite their modest and compact physical dimensions, the proposed valve are ideal for small satellite missions. [ABSTRACT FROM AUTHOR]

Efficient computation of the geopotential gradient is essential for numerical propagators, particularly in scenarios involving low Earth orbits. Conventional geopotential calculations are based on spherical harmonics series, which become computationally demanding as the degree/order increases. This computational burden can be mitigated by means of parallelized algorithms. Additionally, certain situations lend themselves to high parallelization, such as the propagation of space debris catalogs, satellite mega-constellations, or the dispersion of particles resulting from a space collision event. This paper introduces an optimized Graphics Processing Unit (GPU) implementation designed to facilitate extensive parallelization in the geopotential gradient calculation. The formulation developed in this study is not specific to any GPU. However, to illustrate the low-level optimizations necessary for an efficient implementation, we selected the Compute Unified Device Architecture (CUDA) as the dominant and de facto standard in parallel computing. Nevertheless, most of the concepts and optimizations presented in this paper are also valid for other GPU architectures. Built upon the spherical harmonic expansion using the Cunningham formulation, which is well-suited for GPU computations, our implementation offers several variants with different tradeoffs between speed and accuracy. Besides GPU double precision, we introduced a mixed precision arithmetic –a hybrid between single and double precision– that exploits GPU capabilities with a low penalty in accuracy. The proposed algorithm was implemented as a software reusable module, and its performance was evaluated against GMAT, GODOT, and Orekit astrodynamic codes. The algorithm's accuracy in double precision is comparable to such codes. The mixed precision version showed enough accuracy for LEO satellite propagation, with around 1 m difference in four days. Testing across different CUDA architectures revealed very high speed-up factors compared to a single CPU, reaching a speed-up of 645 for the mixed precision variant and 450 for the double precision one in the propagation of about 3200 objects with a geopotential of degree/order 126 × 126 using an A100 GPU device. [ABSTRACT FROM AUTHOR]

This paper presents a method for autonomous onboard mission generation of Earth observation imaging satellites based on user preferences. The paper develops a planning database to store the previous user mission requirements, and proposes a database updating algorithm to track the changes in user preferences. The paper also proposes a mission generation method based on the planning database, which predicts target priorities and imaging methods. Finally, a mission allocation strategy is used to assign newly generated missions to the appropriate satellites. Simulations results show that the proposed method can effectively improve the utilization of satellite resources and thereby obtain higher mission return. [ABSTRACT FROM AUTHOR]

• A modified far-field model (FFM) to simplify the calculation of the electromagnetic force is proposed and common interference forces of the dynamic model of Electromagnetic Formation Spacecraft (EMFS) are analyzed. • A novel proportional passive controller is designed as a nominal controller. For comparison, a saturation proportional-derivative (PD) controller is proposed. The proportional passive controller includes a damping term, which has the potential to avoid energy accumulation. The proposed proportional passive control method demonstrates good robustness and enables faster system stabilization. • Based on the observer determination of AFED, a fixed-time FTC method was developed. Although it can effectively handle unexpected failures of actuators, the design process is relatively complex [26]. The nature of actuator failures and efficiency factor information are determined before controller design, so unexpected actuator faults cannot be effectively handled [27]. Different from the FTC mentioned earlier, this paper proposes an ismc-based FTC scheme that can effectively suppress AFED without requiring a fault observer and the reconstruction of the nominal controller. This scheme combines an adaptive estimation method to estimate AFED in real-time, without requiring any information about the disturbance or actuator faults. Fault-tolerant control (FTC) is an essential consideration for the reason that the proper functioning of electromagnetic formation spacecraft (EMFS) actuators are challenged by the harsh space environment. An Integral-Type Sliding Mode Control (ISMC) scheme is proposed for actuator faults and external disturbances (AFED) caused by coil failure and external complex environment of EMFS system. Before the system state reaches the sliding mode surface, we use super-twisting algorithm to accelerate the reaching of the sliding mode surface and reduce the chattering. After reaching the sliding surface, a novel nominal proportional passive controller is proposed that integrates a damping term, thereby enhance system robustness and expediting system stabilization. Moreover, the FTC method proposed incorporates adaptive techniques to handle unknown AFED in real-time while ensuring system stability. This paper proposes a new adaptive FTC method that enhances the actuator's capability without requiring controller reconfiguration. Simulation results illustrate the effectiveness of this method for suppressing AFED in harsh space environment. [ABSTRACT FROM AUTHOR]

Over the last decade, the scientific interest in Mars drastically increased. The planned growth of the number of robotic missions, together with the sensors' increasing data acquisition capabilities and the expected crewed expeditions, entails a significant increase in data flow between the Martian assets and Earth both in volume and frequency of contact. In particular, crewed missions would lead to the need for nearly continuous communication with Martian assets. The keystone to avoid the future Martian telecommunication deadlock resides in specialising assets on specific functionalities through infrastructures. In this regard, the paper proposes a distributed Mars-based orbiting system servicing as a communication relay for any scientific and technological mission operating on the red planet's surface. The paper explores the design of a small satellites Martian constellation to maximise the surface coverage and visibility time with respect to ground users while reducing the station keeping efforts of the assets. A relatively novel proposed approach is to exploit the so-called Trans Areostationary Orbits (TASO), which allow low drift of the spacecraft with respect to Mars' surface, with an improved orbital stability than the perfectly stationary orbits. The paper aims at extending the available options by exploring trajectories that leverage the third body gravitation from the two Martian moons, Phobos and Deimos, to possibly further improve stability, coverage of the surface, communication datarates, and manoeuvres costs in general. The costs include the operative phase, as well as all the transfers from Earth to the Martian sphere of influence.As a final contribution, the paper explores the concept of Linked, Autonomous, Interplanetary Satellite Orbit Navigation (LiAISON) (Hill, 2007) for the proposed constellation configurations, to verify the possibility of reconstructing the spacecraft states through relative-only measurements. [ABSTRACT FROM AUTHOR]

• Phisically-based thermal infrared images rendering chain for artificial satellite targets. • Assessment and comparison of most relevant pixel-level VIS-TIR image fusion techniques. • Fused noisy image processing within the context of uncooperative space-craft relative navigation. State-of-the-art techniques for vision-based relative navigation rely on images acquired in the visible spectral band. Consequently, the accuracy and robustness of the navigation is strongly influenced by the illumination conditions. The exploitation of thermal-infrared images for navigation purposes is studied in the present paper, as a possible solution to improve navigation in close proximity with a target spacecraft. Thermal-infrared images depend on the thermal radiation emitted by the target, hence, they are independent from light conditions; however, they suffer from a poorer texture and a lower contrast with respect to visible ones. This paper proposes pixel-level image fusion to overcome the limitations of the two types of images. The two source images are merged into a more informative one, retaining the strengths of the distinguished sensing modalities. The contribution of this work is twofold: firstly, a realistic thermal infrared images rendering tool for artificial targets is implemented; secondly, different pixel-level visible-thermal infrared images fusion techniques are assessed through qualitative and quantitative performance metrics to ease and improve the subsequent image processing step. The work presents a comprehensive evaluation of the best fusion techniques for on-board implementation, paving the way to the development of a multispectral end-to-end navigation chain. [ABSTRACT FROM AUTHOR]

Electromagnetic formation flight technology utilizes electromagnetic force and torque between satellites to control satellites' relative position and attitude without consuming propellant, thus having broad application prospects. However, the dynamics of electromagnetic formation flying are nonlinear and strongly coupled, posing challenges to the 6-DOF control of electromagnetic formation and the magnetic dipole allocation of satellites. The frequency division multiplexing method can approximate decoupling formation dynamics by loading multi-frequency AC carriers onto satellite magnetic dipoles and is likely to achieve more control functions. A design method for AC carriers based on frequency division multiplexing is proposed to decouple formation dynamics while controlling electromagnetic force and torque. This paper further provides an analytical solution for the magnetic dipoles of the electromagnetic force/torque equations. In addition, in response to external disturbances, model uncertainty, and the inability to obtain relative velocity and angular velocity information of the formation system, this paper establishes a 6-DOF coupling model based on dual quaternion and implements tracking control using the active disturbance rejection control method. Based on the internal force characteristics of the electromagnetic formation, an expression for the equilibrium distribution of reaction wheel torque is derived to avoid some reaction wheels' rapid accumulation of angular momentum. Numerical simulation results show the effectiveness of the proposed control method. [ABSTRACT FROM AUTHOR]

In order to explore the constraint degree of GNSS and InSAR data on the Maduo earthquake under the layered earth model structure, and to understand the cause of the Maduo earthquake and the danger of the surrounding area, this paper uses D-InSAR technology to obtain the InSAR co-seismic deformation field of the Maduo earthquake on May 22,2021. Based on GNSS and InSAR data, the co-seismic slip model and fault plane stress distribution of the Maduo earthquake are jointly inverted. This paper calculates the Coulomb stress changes caused by 14 M ≥ 7 strong earthquakes co-seismic, post-seismic viscoelastic relaxation and inter-seismic tectonic stress loading of 19 fault segments in the Bayan Har block research area (96°E-106°E, 29°N-36°N) since 1900. The results show that: (1) The maximum Line Of Sight (LOS) deformation obtained based on the ascending and descending InSAR data was about 0.9 m. The maximum slip amount of GNSS + InSAR joint inversion is 4.87 m, which is located in the Dongcao Along Lake section (∼98.6°E). Combined with the stress drop distribution of the fault surface, it is found that the Maduo earthquake is dominated by strike-slip. (2) The historical strong earthquakes delayed the Maduo earthquake by nearly 103 years. The 1937 Huashixia earthquake, the 1947 Dari earthquake, the 1963 Dulan earthquake, and the 1973 Luhuo earthquake had the greatest stress unloading effect, which was equivalent to delaying the Maduo earthquake by 53 years, 21 years, 11 years, and 17 years, respectively. The cumulative Coulomb stress at the source location of the Maduo earthquake reached 0.0112 MPa. Most area of the fault sections such as the East Kunlun Fault, the Maduo-Gande Fault, the western and eastern sections of the Dari Fault, the western and eastern sections of the Qingshuihe Fault, the Ganzi-Yushu Fault, and the eastern section of the Kunlunshankou-Jiangcuo Fault are in the Coulomb stress loading area, which should be paid attention to. [ABSTRACT FROM AUTHOR]

This paper proposes a novel longitudinal reference trajectory tracking guidance framework for Mars atmospheric entry. Unlike traditional methods that require strict adherence to pre-defined safe trajectories, this guidance framework incorporates path constraints into the closed-loop tracking process to ensure safety. The framework comprises a safety module and a guidance law module. The safety module employs an online path constraints management algorithm that converts real-time path constraints into equivalent control constraints and applies them to the guidance module. The guidance law module uses the anti-saturation generalized super-twisting based sliding mode (ASGSTSM) guidance law, which provides sufficient rapidity and robustness to achieve trajectory tracking while accounting for uncertainties and control saturation. Simulation results demonstrate that the proposed guidance framework effectively ensures compliance of the entry vehicle with path constraints. The ASGSTSM guidance law exhibits notable speed and robustness, making it adaptable within the guidance framework. Particularly, in Monte Carlo simulations introducing significant uncertainty, incorporating the ASGSTSM guidance law within the guidance framework resulted in convergence in all trajectory tracking processes, whereas guidance laws in the control group led to numerous failures. Additionally, the paper offers practical principles for designing guidance laws within this universal framework. This facilitates future research to easily replace the guidance law module based on specific mission requirements. [ABSTRACT FROM AUTHOR]

Ionospheric scintillation is a common phenomenon in the equatorial, auroral, and polar areas, posing a threat to the Global Navigation Satellite System's (GNSS) operation. This ionospheric effect is thought to impact satellite signal propagation, hence, lowering positioning accuracy. Therefore, detecting ionospheric scintillation is critical in enhancing GNSS performance, particularly at low latitudes with severe amplitude scintillation. This paper investigates the effects of ionospheric scintillation on GPS signals at UNIMAS station, the East part of Malaysia. This study aims to identify the occurrence of ionospheric scintillation by calculating the index of scintillation strength during solar maximum 2014. The amplitude scintillation, which is measured in the S 4 index is obtained and classified accordingly from the data recorded at the UNIMAS station. The results have shown that strong scintillation (S 4 ≥ 0.5) occurred in the spring (April) and autumn (September and October) seasons, reaching 8 incidents. This paper also presents the diurnal, seasonal, and solar activity dependence of ionospheric scintillation. It is evident that the occurrence of amplitude scintillation is influenced by variations in solar activity, including solar flares and sunspots, as well as diurnal and seasonal changes. These findings provide valuable insights into the behaviour of the ionosphere and its impact on space-based communication and navigation systems. [ABSTRACT FROM AUTHOR]

This paper presents the novel simultaneous observations of plasma blobs, MSTIDs and plasma depletions in OI 630 nm all sky airglow images over Srinagar, India (34.1 °N, 74.8 °E) during the night of July 29, 2019, obtained using an airglow imager. Notably, the MSTID bands that followed the plasma blob interacted with a plasma depletion structure and suddenly disappeared, resulting in a reduction in the intensity of the plasma depletion. The SWARM satellite observations during the airglow observations indicated the occurrence of the plasma blob event and showed the conjugate appearance of MSTIDs in both hemispheres. The ROTI maps indicated the absence of EPBs but the occurrence of irregularities near the transition zone just before the presence of plasma blobs in airglow images and at the time of plasma irregularity detection. These observations suggest potential interactions between these phenomena, indicating that the presence of one impacts the other. This paper discusses in detail the observed ionospheric features and time evolution of the occurrences of these events, in addition to their interactions.Utilizingthe satellite observations, including SABER, INSAT-3DR and AIRS, the presence of deep convective clouds and upward propagating gravity waves near the location of the plasma blob is demonstrated, suggesting that convective-generated gravity waves could possibly trigger the formation of plasma blobs. [ABSTRACT FROM AUTHOR]

Twenty years of gravity observations from various satellite missions have provided unique data about mass redistribution processes in the Earth system, such as melting of Greenland's ice shields, sea level changes, ground and underground water depletion, droughts, floods, etc. The ongoing climate change underlines the urgent need to continue this kind of observations with future gravimetry missions using enhanced concepts and sensors. This paper studies the benefit of enhanced electrostatic and novel optical accelerometers and gradiometers for future gravimetry missions. One of the limiting factors in the current space gravimetry missions is the drift of the Electrostatic Accelerometers (EA) which dominates the error contribution at low frequencies (<1mHz). This study focuses on the modeling of enhanced EAs with laser-interferometric readout, so-called optical accelerometers, and on evaluating their performance for gravity field recovery in future satellite missions. In this paper, we simulate gravimetry missions in multiple scopes, applying various software modules for satellite dynamics integration, accelerometer (ACC) and gradiometer simulation and gravity field recovery. The total noise budgets of the modeled enhanced electrostatic and optical ACCs show a similar sensitivity as the ACC concepts from other research groups. Parametrization w.r.t. the weight of the test mass (TM) of ACCs and the gap between the TM and the surrounding electrode housing confirmed the fact known from previous results that an ACC with a heavier TM and a larger gap will perform better. Our results suggest that the anticipated gain of novel ACCs might at some point be potentially limited by noise from the inter-satellite laser ranging interferometry. In order to present the advantage of the novel sensors, time-variable background models and associated aliasing errors were not considered in our simulations. The utilization of enhanced EAs and optical ACCs shows a significant improvement of accuracy compared to the currently used GRACE-like EA. In addition, their benefit in double satellite pairs in a so-called Bender constellation as well as in the combination of low-low satellite-to-satellite tracking with cross-track gradiometry has been investigated. [ABSTRACT FROM AUTHOR]

• A Hp-Adaptive Pseudospectral Hybrid Optimal Algorithm is proposed. • The optimal solution of the OSIP and OPEG problem can be robustly solved by this work. • Cases with different thrust configurations and initial conditions are reported. In this paper, a Cartesian model of the orbit pursuit-evasion game under J2 perturbations is constructed, and a step-by-step solution method applicable to this problem, namely the Hp-Adaptive Pseudospectral Hybrid Optimal Algorithm, is proposed by analyzing the principle of the pseudospectral method and the costate mapping principle. We first use the hp-adaptive Radau pseudospectral method to solve the one-sided interception problem to obtain a tentative guess of the costate and then get the saddle-point solution of the game problem by solving the two-point boundary value problem through the Newton method. The numerical results show that the hybrid method proposed in this work can efficiently find the optimal trajectory of interception and the optimal control laws of the game problem and have high accuracy. In addition, the effects of J2 perturbations and the initial orbital altitude of the evader on the game results and the algorithm itself are discussed in this paper. [ABSTRACT FROM AUTHOR]

• Shared camera measurements in a dual-agent system for pose estimation using a MEKF. • Stereo-vision measurements remove range ambiguity for relative pose estimation. • Relative navigation estimation accuracy improves for proximity operations using stereo-vision measurements. This paper presents a novel autonomous relative navigation architecture for inspector spacecraft in proximity operations to a known structure in a lunar orbit. Autonomous on-orbit servicing and assembly of large space structures are at the forefront of research for advancing space exploration beyond low-earth orbit. Communication delays with ground stations and limited computational power located on the inspector spacecraft make current relative navigation methods unfeasible and in turn, make it difficult to maintain an accurate estimate of the relative position and orientation of the inspector spacecraft with respect to the structure. The proposed method utilizes the camera measurements from two identical inspector spacecraft, each equipped with a single camera, to estimate the relative position and orientation of the structure. This shared measurement strategy overcomes the deficiencies in monocular vision-based relative navigation techniques, such as the range ambiguities, as is proven in the simulated results of this paper. The proposed stereo-vision system in this work allows for a deterministic solution of the relative position and orientation from the measurements of each inspector spacecraft to the structure. The stereo-vision system was tested with a Multiplicative Extended Kalman Filter (MEKF) for each spacecraft to estimate the relative states of the structure while maintaining a fixed relative position to the structure. The performance of the proposed stereo-vision system was evaluated in terms of accuracy and reliability of the estimated relative position and orientation of two inspector spacecraft to the structure over 100 Monte Carlo simulations for three case studies. The results showed that the stereo-vision system significantly outperforms the monocular vision system even when fewer points on the structure are visible, as is the case for proximity operations. Additionally, the stereo-vision system is consistently more accurate for the relative velocity, attitude, and angular velocity states regardless of how many points are visible. The proposed stereo-vision relative navigation system has the potential to be applied autonomously in proximity operations of spacecraft for various space missions, such as rendezvous and docking, inspection, and on-orbit servicing. [ABSTRACT FROM AUTHOR]

The combination of InSAR and GNSS data can provide more accurate measurements of coseismic 3D surface deformations, which are crucial in determining earthquake source parameters. Currently, the methods for inverting coseismic 3D surface deformations by integrating GNSS and InSAR data using the strain model (SM) (e.g., Simultaneous and integrated strain tensor estimation from geodetic measurements to obtain 3D displacement maps (SISTEM), SM-VCE) simply select GNSS points based on a certain number or distance, without considering the weight influence of the spatial distribution of G NSS points on the InSAR and GNSS data fusion results. To address this issue, this paper proposes a new method that uses Voronoi diagrams analyze the contribution of GNSS points to the deformation at target points. In this paper, GNSS points with high contribution can be used to construct observation value equations and optimize the internal weight of GNSS data. The proposed approach characterizes the contribution of GNSS data to target points by analyzing the changes in the Delaunay triangulation area formed before and after the target points are added to the GNSS data. Simulation experiments reveal that the proposed method outperforms conventional methods in accuracy and completeness. The proposed method is then applied to map the coseismic 3D surface deformations of the 2020 Mw6.5 Monte Cristo Range earthquake and find that the maximum deformation in the east–west, north–south, and vertical directions is about 13 cm, 11 cm, and 24 cm, respectively. [ABSTRACT FROM AUTHOR]

• Human resources development aided the developing space program of the Philippines. • Most of the selected personnel for training came from the academia. • Trainees taken from the industry followed later to support the push for space. • Most of trained personnel opted to stay in the country to support the space program. The Philippines has experienced a shift of interest in space technology development and utilization over the past decade, culminating with the establishment of its national space agency in 2019. In cooperation with different universities in Japan, the Philippines successfully developed and launched two microsatellites, DIWATA-1 and DIWATA-2, and six nanosatellites, MAYA-1 to MAYA-6. By sending personnel to Japan and other space-faring countries, the country was able to rapidly ramp up its satellite development and utilization capabilities. In this paper, we examine and evaluate the complex human resources development efforts conducted by the country to support the creation of a local space ecosystem and ensure its long-term sustainability. Through a careful review, we identify how many people benefited from training programs, studies abroad or other forms of capacity building, and how these skilled individuals were retained in the budding Filipino space sector. Precisely, we looked at the backgrounds of the different people trained by the country, what type of training they received (funding, location, and duration), and how they are supporting the local space ecosystem at the time of writing this paper. [ABSTRACT FROM AUTHOR]

• A relative orbit design method for CubeSats flying around space station is proposed. • The CubeSat's relative orbit is used for observing feature-points on surface of space station. • The design method considers the field-of-view constraints and occlusion effect. • The method could be used for other similar constrained close-range on-orbit service missions. This paper presents a novel relative orbit design method for CubeSats flying around the space station to perform visual inspection considering the Field-Of-View (FOV) constraints and occlusion effect. Firstly, a parametric model for Periodic Relative Orbits (PROs) is established by using the well-known Clohessy-Wiltshire equations. Based on this model, the relative orbit design problem for orbital target inspection is successfully integrated into a problem of two-parameters determination, one of which is the correlation coefficient and the other is the orbital amplitude. Secondly, by categorically evaluating the range of design variables, the design method for generating feasible solutions of PROs to satisfy the FOV constraints is proposed. Thirdly, considering the existence of the occlusion effect of large space structure, this paper presents an efficient calculating method to evaluate the degree of occlusion based on the analysis of line-of-sight blockage. Then, to avoid the occlusion effect, an improved relative orbit design method is developed. Finally, the designed algorithms are testified by carrying out some typical simulations with the China Space Station as the observed object and a small CubeSat assumed to perform the required inspection mission. The results illustrate well the validity and practicability of the proposed method. [ABSTRACT FROM AUTHOR]

This paper investigates the fault-tolerant attitude control problem for a spacecraft with actuator faults using an event-triggered-based concurrent-learning control (CLC) approach. A concurrent-learning controller, updating itself through previous control signal values to generate the current control signal, is studied in this paper. The concurrent-learning controller is designed under an event-triggered policy to compensate for the actuator's data transmission constraints caused by bandwidth limit. In addition, a robust fault observer is designed to facilitate the concurrent-learning controller in compensating for the actuator faults. The key feature of the given approach is in the simplicity of control structure to stabilize spacecraft attitude considering actuator faults, model uncertainty, actuators' dynamics effect, and data transmission; simulation results show the proposed approach's efficiency. [ABSTRACT FROM AUTHOR]

• Long-term trends in foF2 change remarkably with the solar activity proxy used. • F30 is the only proxy, which provides trends of the same sign for all stations. • I recommend F30 as the best solar proxy for trends of foF2 at midlatitudes. The most studied ionospheric parameter for long-term trends is foF2. The dominant factor of foF2 variability is the solar cycle, which is much stronger than the long-term trends. Therefore its effect in data must be removed. However, several decade long homogeneous measurements of the solar EUV fluxes are not available, so various solar activity proxies (solar activity indices) must be used. The aim of this paper is to study the impact of selection of different solar activity proxies on foF2 long-term trends and to find the best solar activity proxy for foF2 trends at middle latitudes. The results based on yearly average data of six midlatitude stations from four continents (1976–2014) and of six solar activity proxies show that the long-term trends in foF2 depend substantially on the solar activity proxy used, and the only solar proxy, which provides trends of the same sign for all stations and both sub-periods, is F30. Based on results of this paper and that of Laštovička and Burešová (2023) , I can recommend F30 as the best solar proxy for studying long-term trends of foF2 at middle latitudes (at least for yearly average values). [ABSTRACT FROM AUTHOR]

Access points to Heliophysics information are often poorly inter-linked to one another, making it challenging for researchers to integrate information, mature their understanding, and incorporate more complex ideas and relationships into their analyses. The authors reason this behavior to be a direct conseaquence of the lack of infrastructure for knowledge and data discovery in Heliophysics. Building an online library resource for Heliophysics addresses this gap in resources, and can also address other troublesome gaps related to community-building, such as access to help from other scientists, example analysis tutorials, and collaboration opportunities. This paper envisions a resource that better connects existing Heliophysics information and knowledge sources, the LIbrary for KnowledgE and Discovery (LIKED), which will be an online resource that interlinks information across databases (e.g., observational and publication), researcher interactions (e.g., conferences and discussion boards), and educational materials. The result is a rich and searchable environment to provide users a more productive experience for research and collaboration. In this paper, we provide the conceptual model for LIKED. We expand to detail how LIKED will serve to connect the various knowledge and research components available internationally together in an uniformly searchable manner. Finally, this work outlines various contributions the community can make towards this goal. [ABSTRACT FROM AUTHOR]

In the domain of Space Situational Awareness (SSA), the challenges related to orbit determination and catalog correlation are notably pronounced, exacerbated by data scarcity. This study introduces an initial orbit determination methodology that relies on data obtained from a single surveillance radar, with the need for fast algorithms within an operational context serving as the main design driver. The result is a linearized least-squares fitting procedure incorporating an analytically formulated approximation of the dynamics under the J 2 perturbation, valid for short-term propagation. This algorithm utilizes all available observables, including range-rate, distinguishing it from other similar methods. A significant contribution of this paper is the enhancement of estimation quality by incorporating information about the object's predicted orbital plane into the methodology, a method denoted as OPOD. The proposed methods are evaluated through a series of simulations against a classical range and angles fitting method (GTDS) to examine the effects of track length and measurement density on the quality of full state estimation, including the impact of using arcs that are too short. The OPOD methodology shows promising results throughout a wide range of scenarios. [ABSTRACT FROM AUTHOR]

This paper presents Guidance and Control (G&C) systems for multi-satellite assembly in proximity operations. The systems utilize the twistor model, which is linearized through Taylor's series. Decentralized control laws, designed using Linear Quadratic Regulator (LQR) and Model Predictive Control (MPC), are employed to track an energy-optimal trajectory generated using the Hamiltonian approach. Data exchange between satellites and their neighbors is represented using graph theory. The decentralized MPC framework is implemented using the CasADi package. To ensure collision avoidance between the satellites, a repulsive control law is designed, considering symmetric input saturation in the actuators. The proposed G&C systems are tested using a high-fidelity nonlinear satellite relative motion model that incorporates orbital perturbations. Numerical simulations are performed in a MATLAB® environment, and the results are visualized using STK®. Furthermore, a comparative study is conducted to evaluate tracking performance and fuel consumption between the two control methods. The results demonstrate that the use of an optimal trajectory reduces fuel consumption for both control algorithms. [ABSTRACT FROM AUTHOR]

In this paper, we present for the first time a comprehensive statistical study between type II radio bursts from the metric (m) to the dekameric–hectometric (DH) domain and their associated solar and space weather (SW) phenomena, namely, solar flares (SFs), sunspot (SN) configurations, filament eruptions, coronal mass ejections (CMEs), their interplanetary (IP) counterparts (ICMEs) and shocks, in situ detected particles and geomagnetic storms (GSs). The m-only and m + DH radio signatures are identified from dynamic spectra provided by the ground-based RSTN stations distributed over the globe together with Wind/WAVES satellite data. The DH-only type IIs are adopted from a ready catalog based on Wind/WAVES spacecraft data. We perform the temporal and spatial association between the radio emission and the listed above activity events during solar cycle (SC) 24, separately for the three sub-categories, m-only, m + DH and DH-only type IIs. A quantitative assessment on the occurrence rates is presented as a function of the strength of the specific SW phenomena: highest rates are obtained with CMEs, SFs, filament eruptions, and SN configurations, whereas a much weaker relationship is found with ICMEs, IP shocks, energetic particles, and GSs. The potential of the obtained rates to be used in empirical or physics-based models for SW forecasting is discussed. [ABSTRACT FROM AUTHOR]

• 3D recursive kinematics is introduced for the dynamic modeling of the multi-flexible-link space manipulators. • The general expressions of the dynamic boundary conditions are derived based on 3D recursive kinematics. • The difference between the results of the time-varying modes and time-invariant modes is investigated. This paper presents a dynamic modeling method for the multi-flexible-link space manipulators under time-varying dynamic boundary conditions. This method is based on 3D recursive kinematics and is applicable to the space manipulators with an arbitrary number of flexible links. The elastic deflection of the flexible links is described by using the Assumed Mode Method (AMM). The general expressions of the dynamic boundary conditions are derived by combining the Newton-Euler equation with 3D recursive kinematics. Based on 3D recursive kinematics, the dynamic model suitable for space manipulators with an arbitrary number of flexible links is established. For the multi-flexible-link manipulator systems, the movement of the links will alter the mass distribution of the system, resulting in the time-varying modes of the links. The difference between the results of the time-varying modes and time-invariant modes are investigated. Numerical simulations are performed to verify the adaptability of the proposed dynamic modeling method to different manipulators. Simulation results shows that the results of time-varying modes are in good agreement with those of time-invariant modes, and the simulation calculation time of time-invariant modes is less than that of time-varying modes. For the above reasons, the time-invariant modes are sufficient and it is unnecessary to update the modes. [ABSTRACT FROM AUTHOR]

The TianQin mission for gravitational wave detection consists of three drag-free spacecrafts deployed in geocentric orbits, and forms an equilateral triangle configuration. In this paper, we investigate lunar flyby transfers to the TianQin configuration. Firstly, a preliminary design method of lunar flyby transfers is proposed in the patched-conic model. Then, lunar flyby transfers in the ephemeris model are constructed through the multiple shooting method. Numerical computation shows that compared to the traditional Hohmann transfer, the lunar flyby transfer can save about 12 % of fuel, but its time of flight increases to about 11 days. For the initial deployment of the TianQin configuration, we propose two methods, the phasing method and the direct insertion method. The phasing method uses the phase adjustment when the three spacecraft reach the target orbit. Numerical calculation indicates that the fuel costs of the three spacecraft are identical to that of the nominal transfer, and the total time of flight is about 17 days. Then, the Jet transport tool is applied to find appropriate separation impulses to design the direct insertion orbits. Numerical computation shows that compared to the phasing method, the fuel cost of the direct insertion method is slightly larger than that of the phasing method, but the time of flight of the former is about 5 days shorter than that of the latter. [ABSTRACT FROM AUTHOR]

Aiming at the micrometeoroid/orbital debris (MMOD) collision problem for space structures, this paper proposes a self-sensing aluminum/aramid hybrid laminate for detection of MMOD collision event and identification of its associated damage. A co-curing method is used to fabricate the hybrid laminate while carbon nanotube (CNT) film and flexible printed circuit (FPC) are embedded in the laminate as sensing layer. By injecting tiny currents into the CNT film before and after MMOD collision and collecting the corresponding boundary voltages, electrical resistance tomography (ERT) is employed to reconstruct tomographic image of the conductivity change caused by MMOD collision and provide information about the damage. Experimental studies have conducted to perform ballistic high velocity impacts to simulate MMOD collision to three self-sensing hybrid laminates. The results have demonstrated that, the CNT film has good sensing performance, and the reconstructed image of conductivity changes can reflect the location and approximate size of the damage, validating the effectiveness of the proposed self-sensing hybrid laminate and providing a new way for space structures to detect MMOD collisions. [ABSTRACT FROM AUTHOR]

• Development of model predictive control for FFSM system based-on Probabilistic ensemble neural network. • Reduction of the modeling error effect in control by model variance. • Demonstration of different missions for a 3-DOF FFSM. Precise control of a free-floating space manipulator (FFSM) is of a great challenge due to the strong dynamic and kinematic coupling between its arms and base. This paper presents a model-based reinforcement learning framework for precise control of FFSMs with dynamics unknown. Dynamic behavior of an FFSM is predicted by a probabilistic ensembles neural network (PENN) trained off-line. The PENN employs probabilistic neural networks to handle aleatoric uncertainty, which is further combined with ensemble method to capture epistemic uncertainty, and used to plan action sequences on-line under the model predictive control framework. Unlike model-free methods which train a particular policy to pursue maximum reward for the corresponding task, this framework allows the same trained PENN to be applied to various tasks with task-specified reward function. Results of numerical experiments demonstrate the fast and robust performance of the proposed framework for both angular and end-effector position control. [ABSTRACT FROM AUTHOR]

• Analyzed key factors in real-world satellite constellation tracking of time-sensitive moving targets. • Introduced PDA-GA, employing dual adaptive and parallel mechanisms to enhance genetic algorithm efficiency. • Demonstrated the effectiveness of our approach through rigorous experiments in simulated scenarios. The evolution of satellite surveillance technology, bolstered by advanced onboard intelligent systems and enhanced attitude maneuver capabilities, has thrust mission scheduling and execution into the spotlight as a prominent and dynamic research field in recent years. As the demand intensifies for mission scheduling and execution to transition from static ground targets to time-sensitive moving targets, conventional scheduling methods often fall short of delivering satisfactory results for continuously tracking these dynamic targets with constellation. The paper introduces a rapid yet efficacious satellite constellation task assignment method, termed the Parallel Dual Adaptive Genetic Algorithm (PDA-GA), for the task assignment of multiple moving target tracking. Specifically, the dual adaptive mechanism isolates the genetic algorithm's sensitivity to parameters, while the parallel mechanism increases the evolutionary process's computation speed by deploying complex computations to the GPU. Based on the meticulous analysis of the relevant factors that need to be considered in real tracking scenarios, the proposed PDA-GA can improve the search quality and efficiency of the task assignment solution. We conduct an extensive array of contrast and ablation experiments to showcase the performance and efficiency of PDA-GA in conjunction with autonomous attitude control algorithms across five simulated tracking scenarios. Furthermore, to enable high-fidelity simulation of tracking scenarios, we introduce the Constellation Target Tracking Environment (CTTE), which is equipped with a physics engine and algorithms for multi-satellite task assignment and single-satellite attitude control. This endeavor lays a foundation for future research endeavors focused on autonomous tracking of multiple time-sensitive moving targets within large-scale constellation. [ABSTRACT FROM AUTHOR]

Undifferenced and Uncombined Precise Point Positioning (UPPP) currently stands as a prominent research area, where the integration of high-precision ionospheric products holds the potential to substantially enhance accuracy and convergence performance in UPPP. Presently, the majority of external ionospheric constraints for UPPP rely on Global Ionospheric Maps (GIM). However, the accuracy and resolution of GIM fall short, imposing significant limitations on the positioning performance of UPPP. Consequently, this paper introduces the application of Computerized Ionospheric Tomography based on Machine Learning (CIT-ML) to enhance UPPP performance (PPP-CIT-ML). In this approach, we convert the three-dimensional electron density of CIT-ML into vertical total electron content (VTEC), and then it is compiled into ionospheric grid files essential for UPPP. Simultaneously, the traditional ionospheric tomography methods based on the improved algebraic reconstruction technique (IART) is also employed for UPPP (PPP-CIT-IART), alongside the ionospheric grid files broadcasted by the Center for Orbit Determination in Europe (CODE) for UPPP (PPP-CODE), where PPP-CIT-IART and PPP-CODE are used as the reference methods to test the performance of PPP-CIT-ML. In Static and Kinematic UPPP, compared to PPP-CODE, PPP-CIT-IART demonstrated average improvements in positioning accuracy and convergence performance by over 10% and 7%, respectively. PPP-CIT-ML showed average improvements in positioning accuracy and convergence performance by over 26% and 28%, respectively. The extrapolated ionospheric electron density (IED) applied to UPPP (ECIT-ML-PPP) and compared with PPP-CODE displayed average improvements in positioning accuracy by over 21% and convergence performance by over 26%. Compared with PPP-CIT-IART, ECIT-ML-PPP displayed average improvements in positioning accuracy and convergence performance by over 6% and 21%, respectively. These findings highlight that ionospheric error correction information obtained through ionospheric tomography significantly enhances the positioning accuracy and convergence performance of UPPP. Moreover, the performance enhancement achieved through machine learning-based ionospheric tomography is more pronounced. This study provides preliminary validation for the feasibility of applying machine learning-based ionospheric tomography results to navigation positioning. [ABSTRACT FROM AUTHOR]