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• A space harpoon device based on aluminum honeycomb buffer has been designed for space debris. • The feasibility of the harpoon capture scheme was verified through ground experiments. • Aluminum honeycomb reduces the impact force and rebound speed during operation. • The adaptability of space harpoons can capture target states of different postures and materials. To address the issues of high impact and limited adaptability in capturing space debris with space harpoons, a novel harpoon capture device based on aluminum honeycomb buffering was proposed. The issue of excessive impact force for harpoons could be effectively addressed by the excellent energy-absorbing characteristics of aluminum honeycomb. A simulation model was established to analyze the penetration of space harpoons into aluminum alloy target plates using Johnson-Cook's dynamic constitutive model and fracture failure criteria. Ground experiments were conducted to validate the correctness of the simulation model. The impact of aluminum honeycomb was investigated by analyzing the simulation results of harpoons with and without aluminum honeycomb. With the introduction of aluminum honeycomb as a buffering component, the rebound velocity of the harpoon decreased by 76.2 %, and the impact force reduced by 78.6 %. Then the model was used to study the influence of different launching angles and different targets on the penetration characteristics of the space harpoon. The research findings indicate that space harpoons could successfully penetrate and capture aluminum alloy targets at a launch velocity of 53.1 m/s to 58.5 m/s, as determined through ground experiments and simulation analysis. The error in the crushing height of the aluminum honeycomb was found to be 2.19 %, while the error in the harpoon penetration depth was 9.02 %. Moreover, within a launch angle error of 10°, space harpoons also demonstrate the capability for adaptive capture of both aluminum alloy plates and aluminum honeycomb sandwich panels, with average correction capabilities of 92.5 % and 95.5 %. In conclusion, the analysis of the adaptive penetration characteristics of space harpoons provides a solid theoretical foundation and technical support for the design of harpoon capture systems. [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]

The militarization and weaponization of outer space are increasing continuously with the development of new and more advanced space weapon systems by a growing number of nations. This is a direct consequence of the high and growing strategic value of outer space for defense, security, and warfare. This paper reviews trends in space weapon systems and analyzes the implications of anti-satellite military weapons for human activities in outer space. A direct consequence of the completion of anti-satellite military tests is that the amount of orbital debris has increased significantly. We use a simple physical – economic model to illustrate how anti-satellite military tests, particularly those using direct-ascent weapons, dramatically increase the probability that the Kessler syndrome will occur. Whereas the long-run impact of low altitude anti-satellite tests is limited because of atmospheric drag, at high altitude direct-ascent anti-satellite tests are persistently harmful for human activities in space. The paper also provides a simulation of the long-run effects of a war in space. [ABSTRACT FROM AUTHOR]

Bistable composite shells are suitable candidates for deployable space structures due to high stiffness to weight ratio as well as large volume reduction. Nevertheless, impact performance of bistable composite shells conflicting with space debris have been rarely studied. In this paper deployable hybrid composites constructed with combinations of carbon–carbon, carbon–kevlar, kevlar–kevlar, high-energy-absorption graphene-reinforced polyurethane elastomers are developed, and their ballistic penetration behaviors are experimentally and computationally studied. The influences of ballistic velocity on the absorbed energy, the residual velocity and damage morphology of the targets are investigated in both deployed and coiled stable states. The results show that severe local damages were observed for the carbon–carbon and carbon–kevlar samples after penetration with various velocities even first cosmic velocity, and the sample of deployable hybrid composite shell yielded the best ballistic impact resistance. The total energy absorption performance of the hybrid composite structure was greatly improved by introducing graphene-reinforced polyurethane elastomers without losing the deployability. Additionally, investigation on the energy absorption capability of deployed laminated shells with various curvature radii indicated that the curvature radius had a significant effect on the anti-penetration performance. • Development of deployable composite shell structures. • Experimental and numerical penetration and damage analysis of deployable composite shells. • Effects of curvature radius and elastomer ply thickness on the energy absorption of deployable laminated shells. [ABSTRACT FROM AUTHOR]

We present an analytical formula to definitively restrict the orbit prediction error. In low earth orbit, millions of pieces of space debris are below 10 cm in size. One promising active debris removal (ADR) method for "lethal nontrackable (LNT)" objects is laser-based method. The recoil of laser ablation changes the orbit of the debris object. The laser must be precisely focused on the surface of the debris object. Because the relative speed of a debris object can reach 15 km/s, accurate orbit prediction is required. Our formula ensures that the laser is focused on the debris surface at the correct time and direction. We also evaluate the parameters in the formula, achieving an orbit prediction error of less than 1 cm 10 s after detecting a debris object. This formula can be used to design a specific laser ADR system for LNT. [Display omitted] • We derive a formula providing an upper bound of orbit prediction error. • The formula is applied to medium size debris in a low Earth orbit. • The orbit prediction error can be less than 1 cm within 10 s. • The formula is useful to design a debris removal system using a high-power laser. [ABSTRACT FROM AUTHOR]

In-space satellites fragmentation events contribute to the continuous growth of man-made debris. Observations of these events can provide limited information on the number and characteristics of the generated fragments, as only the largest ones can be detected with ground instrumentation. Numerical simulations replicating in-orbit fragmentation can integrate the missing information regarding fragments number, shape, and orbital distribution. In this context, this paper presents the numerical reconstruction of COSMOS 2499 break-up of January 4th, 2023. First, a digital twin of the satellite is modeled with the Collision Simulation Tool Solver, a custom semi-empirical simulation code, to replicate the explosion of an internal tank; different expansion velocities for the exploding elements are examined and the resulting fragments size and shape distributions are presented. In a second part, the effect of the attitude at the moment of the break-up on the generated debris orbital distribution is discussed. Finally, the numerical results are compared with the available data from ground observations, showing a good accordance with them. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to study active removal of rotating space debris in space, a conical harpoon was used to carry out penetration experiments on a single-axis rotating 2A12 aluminum alloy target plate at 6° / s, 12° / s and 18° / s, respectively. The velocity change curve and kinetic energy change curve of the harpoon were established. The results show that the rotation velocity of the 2A12 aluminum alloy target has little effect on the velocity change of the harpoon after the harpoon penetrates the 2A12 aluminum alloy target with different rotation speeds. Under the same initial kinetic energy E = 2738.78 J, the velocity of kinetic energy attenuation of harpoons with different initial velocities in the process of penetrating the aluminum alloy target plate is different. According to the research, the velocity of the kinetic energy attenuation of the harpoon can be arranged according to the initial velocity, as follows: 30.73 m/s > 28.38 m/s > 26.50 m/s > 24.95 m/s, which means that the greater the initial velocity, the faster the kinetic energy attenuation of the harpoon. [ABSTRACT FROM AUTHOR]

There are many problems in space debris monitoring with ground‐based telescopes, such as too many stars in the same field of view, uneven background and optical distortion in the optical system. We propose a two‐stage weak debris detection algorithm. In the first stage, wavelet transform is used to extract different components of three frames of images, and the median of corresponding components of the images is taken respectively to eliminate the influence of stars. In the second stage, an improved version of the faint space target extraction based on principal component analysis. The algorithm uses a smooth‐detection idea to extract target information. Based on a 150 mm aperture telescope, we improved the existing method of faint space debris extraction based on principal component analysis by introducing the smooth‐detection idea, and transformed the target detection problem into the separation problem of sparse matrix and low‐rank matrix. We applied a certain preprocessing consisting of wavelet‐based star removal and median pre‐filtering to keep as little noise and other contaminants as possible. After experimental measurements by observers, the algorithm demonstrated advanced detection capabilities on multiple indicators. Plain Language Summary: In recent years, space activities have gradually increased, followed by a massive increase in space debris. Due to the extremely high speeds at which space debris travels, it is difficult to control. If these high‐speed debris collide with operational satellites, they pose a significant destructive, potentially leading to the complete loss of satellite functionality. Therefore, space debris poses a major threat to satellites in orbit and other space assets. Accurately monitoring space target information and promptly executing aircraft avoidance maneuvers are effective measures to prevent collisions. In the actual observation system, the space target energy in the image is small and weak, especially in the middle and high orbit, it is difficult to extract the target information. We propose a two‐stage faint target detection algorithm. In the first stage, the influence of stars and partial noise on target detection is eliminated. In the second stage, the idea of principal component analysis is applied to extract spatial target information. It is worth noting that our aim is to build an automated space target information extraction system, so we do not apply any prior information about the space target in the algorithm. Key Points: We propose a space debris detection algorithm under complex background, which can improve the space surveillance capability of telescopesThe faint target detection technique in complex background is transformed into the separation problem of low rank matrix and sparse matrixWe use a large number of images captured by real telescopes for experiments, qualitative and quantitative analysis to reach conclusions [ABSTRACT FROM AUTHOR]

Objective: To investigate the effect of dexmedetomidine (DEX) on the polarization of alveolar macrophages induced by lipopolysaccharide (LPS) and to explore the related mechanisms. Methods: Rat alveolar macrophages NR8383 were cultured in vitro. Experiment one was divided into control group, model group (1 μg/ml LPS), DEX low, medium and high dose groups (1, 5, 10 mg/kg DEX+10 mg/kg LPS). Experiment two was divided into DEX high dose group (10 mg/kg) and DEX high dose+Colivelin (JAK2/STAT3 signaling pathway activator) group (10 mg/kg DEX+0.5 μmol/L Colivelin). The morphological changes of rat alveolar macrophages NR8383 were observed by inverted microscope; RT-PCR method was used to detect the expression levels of iNOS and Arg1 mRNA in NR8383 cells, and flow cytometry was used to detect the expression levels of CD86 and CD163 proteins in NR8383 cells; Western blot was used to detect the expression levels of surface marker proteins TNF-α, iNOS, SOCS, Arg1, TGF-β and JAK2/ STAT3 signaling pathway related proteins in NR8383 cells. Results: Compared with control group, there were a lot of cell debris in the intercellular space of NR8383 in the model group, the proportions of iNOS mRNA, CD86 positive cells, and the expression levels of TNF-α, p-JAK2/JAK2, p-STAT3/STAT3 were significantly increased, the proportions of Arg1 mRNA, CD163 positive cells, and the expression levels of SOCS and TGF-β were significantly reduced (P<0.05); compared with the model group, the NR8383 intercellular cell debris in the DEX low, medium, and high dose groups were decreased, the proportions of iNOS mRNA, CD86 positive cells, and the expression levels of TNF-α, p-JAK2/JAK2, p-STAT3/STAT3 were significantly reduced, the proportions of Arg1 mRNA, CD163 positive cells, and the expression levels of SOCS and TGF- β were significantly increased (P<0.05). The reactivation of the JAK2/ STAT3 signal pathway by Colivelin could weaken the role of DEX in LPS induced NR8383 cell polarization. Conclusion: DEX can inhibit the M1 polarization of NR8383 cells induced by LPS, which may be achieved by inhibiting the JAK2/STAT3 signaling pathway. [ABSTRACT FROM AUTHOR]

Infrasound sensing plays a critical role in the detection and analysis of bolides, offering passive, cost-effective global monitoring capabilities. Key objectives include determining the timing, location, and yield of these events. Achieving these goals requires a robust approach to detect, analyze, and interpret rapidly moving elevated sources such as bolides (also re-entry). In light of advancements in infrasonic methodologies, there is a need for a comprehensive overview of the characteristics that distinguish bolides from other infrasound sources and methodologies for bolide infrasound analysis. This paper provides a focused review of key considerations and presents a unified framework to enhance infrasound processing approaches specifically tailored for bolides. Three representative case studies are presented to demonstrate the practical application of infrasound processing methodologies and deriving source parameters while exploring challenges associated with bolide-generated infrasound. These case studies underscore the effectiveness of infrasound in determining source parameters and highlight interpretative challenges, such as variations in signal period measurements across different studies. Future research should place emphasis on improving geolocation and yield accuracy. This can be achieved through rigorous and systematic analyses of large, statistically significant samples of such events, aiming to resolve interpretative inconsistencies and explore the causes for variability in signal periods and back azimuths. The topic described here is also relevant to space exploration involving planetary bodies with atmospheres, such as Venus, Mars, and Titan. [ABSTRACT FROM AUTHOR]

Explosions or collisions of satellites around the Earth generate space debris, whose uncontrolled dynamics might raise serious threats for operational satellites. Mitigation actions can be realized on the basis of our knowledge of the characteristics of the fragments produced during the breakup event and their subsequent propagation. In this context, important information can be obtained by implementing a breakup simulator, which provides, for example, the number of fragments, their area-to-mass ratio or the relative velocity distribution as a function of the characteristic length of the fragments. Motivated by the need to analyze the dynamics of the fragments, we reconstruct a simulator based on the NASA/JSC breakup model EVOLVE 4.0 that we review for self-consistency. This model, created at the beginning of the XXI century, is based on laboratory and on-orbit tests. Given that materials and methods for building satellites are constantly progressing, we leave some key parameters variable and produce results for different choices of the parameters. We will also present an application to the Iridium–Cosmos collision and we discuss the distribution function after a breakup event. The breakup model is strongly related to the propagation of the fragments; in this work, we discuss how to choose the models and the numerical integrators, we propose examples of how fragments can disperse in time, and we study the behavior of multiple simultaneous fragmentations. Finally, we compute some indicators for detecting streams of fragments. Breakup and propagation are performed using our own simulator SIMPRO, built from EVOLVE 4.0; the executable program will be freely available on GitHub. [ABSTRACT FROM AUTHOR]

We present numerical simulations of planetary systems in star clusters with different initial stellar densities, to investigate the impact of the density on debris disc dynamics. We use lps+ to combine N -body codes nbody6++gpu and rebound for simulations. We simulate debris discs with and without a Jupiter-mass planet at 50 au, in star clusters with |$N=$| 1k–64k stars. The spatial range of the remaining planetary systems decreases with increasing N. As cluster density increases, the planet's influence range first increases and then decreases. For debris particles escaping from planetary systems, the probability of their direct ejection from the star cluster decreases as their initial semimajor axis (⁠|$a_0$|⁠) or the cluster density increases. The eccentricity and inclination of surviving particles increase as cluster density increases. The presence of a planet leads to lower eccentricities and inclinations of surviving particles. The radial density distribution of the remaining discs decays exponentially in sparse clusters. We derive a general expression of the gravitational encounter rate. Our results are unable to directly explain the scarcity of debris discs in star clusters. Nevertheless, given that many planetary systems have multiple planets, the mechanism of the planet-cluster combined gravitational influence on the disc remains appealing as a potential explanation. [ABSTRACT FROM AUTHOR]

The Meteosat Third Generation - Imager 1 satellite, launched on 13 December 2022, features the first Lightning Imager instrument, a high-speed optical camera providing near real-time lightning detection over Europe and Africa. This study demonstrates that signatures of fireballs (i.e. bright meteors) can be detected in Lightning Imager data. We describe a method to analyse this data to determine the timing, light signal, and trajectory of fireballs, highlighting the instrument's usefulness for bright meteor observation and proposing avenues for further research. By using known fireball locations and timings from external sources, the Lightning Imager data can be filtered to isolate 'lightning events' induced by the meteor. From this data set, the fireball light curve is computed by aggregating signal increases measured by instrument pixels. A trajectory is then deduced using a weighted average of pixel locations based on observed intensity. Three examples of fireballs detected by the Lightning Imager are presented, including a man-made meteor from space debris re-entry, with estimated timing, light curves, and trajectories. [ABSTRACT FROM AUTHOR]

The EPFL Spacecraft Team (EST) is working on the Constellation of High-Performance Exospheric Science Satellites (CHESS) mission, which aims to launch a constellation of two CubeSats in 2027. These CubeSats will study the chemical composition of Earth's exosphere using time-of-flight mass spectrometry. To downlink the collected scientific data, the satellites will utilise a custom X-band transceiver, presented in this paper, operating in the amateur frequency range of 10.45 GHz to 10.50 GHz. The proposed transceiver architecture employs Software-Defined Radio (SDR) technology and can be easily adapted for different use cases. This modular approach has the potential to be suitable for future spacecraft missions, such as active debris removal or lifetime extension services, where flexible communication systems are required. • Hybrid SDR architectures enable versatile telecom systems for space missions. • IOD/IOV missions let students follow the entire life cycle of a space project. • Short development/prototyping cycles maximise the lessons learned in student teams. [ABSTRACT FROM AUTHOR]

The increasing space debris population in critical orbits due to spacecraft failure dictates the need for action. On-Orbit Servicing (OOS) has been proposed as a method for mitigating this trend by repairing existing space assets. The development of large servicing spacecraft has been given significant attention. In this paper, we are approaching the problem with a new paradigm for a servicing spacecraft by proposing a CubeSat class servicer equipped with a one-degree-of-freedom (DoF) robotic arm. Considering the OOS context, we choose the Orbital Replacement Unit (ORU) installation on a target spacecraft as a challenging benchmark task for the proposed servicer configuration. To carry out this task, we formulate and compare performance of four controllers to achieve coordinated control of both the CubeSat and the robotic arm for the installation task. We start with a basic PD controller and progress to the more advanced impedance controller, Model Predictive Control (MPC) and Model Predictive Impedance Control (MPIC) designs. The controllers are evaluated and compared across several relevant metrics for the ORU installation and their merits for practical implementation are discussed. • Comparative analysis of model-based controllers against traditional control methods. • Monte Carlo simulations used to test robustness of the controllers. • Novel, mechanically simple CubeSat servicer for simulated ORU installation. • MPC, PD controllers show similar success rates, MPC requires higher control efforts. [ABSTRACT FROM AUTHOR]

The article considers the mission design problem for removal of large space debris objects from near-Earth orbits. It is assumed that a single active spacecraft-collector (SC) should de/re-orbit several objects. The upper planning level calls for a scenario that specifies the type of repeating operations of an SC. Despite the apparent diversity of these scenarios, they can be reduced to two variants of objects removal to disposal orbits (DOs). In variant I, transfers between objects are effected by an SC with detachable propulsion modules (PMs) onboard. Once the next-in-line object is captured, one module is accommodated on its surface, and, after demating, this PM ensures the relocation of the object to a DO. In variant II, the SC operates as a tug vehicle and transfers the object to DO on its own, and then returns to the next object. A reasonable choice of the removal variant depends on the SC launch mass which should be compared for the same number of de/re-orbited derelict targets. To this end, one should estimate the SC dry mass, the payload mass, and the SC propellant mass. Each of these three terms is nonlinear and depends explicitly on each other, the mass of the captured object, and on the SC maneuvers. Analytical models are proposed for estimation of the SC launch mass for each of the two removal variants. It is also shown that there exists an altitude optimality boundary (the radius of a spherical layer) above which the removal variant II is more advantageous than variant I. Such models are constructed based on several assumptions capable of breaking the iterative search of the SC launch mass. The position of the altitude optimality boundary depends on seven input parameters of the mission: the SC dry mass; the PM dry mass; the mass of the object, the required variation of the semi-major axis Δ a to reach the DO, the number of objects removed by a single SC, the average Δ V for a transfer between two objects, and the effective exhaust velocity of SC main engine. In the present paper, four types of objects are considered: heavy and light LV stages in low orbits, upper stages in GEO and GNSS regions. By choosing concrete objects of study one can substantially reduce the solution space by excluding the impossible combinations of input data. By using the developed SC launch mass models, it is possible to formulate removal recommendations for concrete groups of space debris objects. These models were shown as being adequate on the examples of Elsa-M and MRV projects which are due to be implemented in the next one-two years. • Upper planning level for large space debris active removal is considered. • Analytical models are proposed for estimation of the launch mass of an SC aimed at handling several objects. • Two variants of removal of launch vehicle stages and upper stages to disposal orbits are studied. • It is shown that there exists an altitude optimality boundary between these variants. • Recommendations on removal variant for objects located in low, medium, and high Earth orbits are given. [ABSTRACT FROM AUTHOR]

Space debris poses a great threat to space stations. When a collision hazard is detected, the space station's orbit should be adjusted. An alternative approach is to apply collision avoidance measures that consist in creating an external impact on the space debris object to change its orbit and increase the miss distance slightly. Such an impact can be carried out using a ground-based or orbital laser, through the use of nano-tugs thrusters, or by placing a cloud of particles in the path of the object. This study proposes to use the plume of a thruster of an active spacecraft called an Ion Beam Interceptor. When a potential collision is detected, the interceptor undocks from the space station, approaches the space debris object and directs an ion beam, which is generated by the spacecraft's thrusters, at it. Hitting into the surface of the object, the particles of the ion beam exert a force effect on it, which leads to the required change in the orbit. After the completion of the maneuver, the interceptor returns to the space station for refueling and servicing. The objective of the study is a preliminary assessment of the feasibility and effectiveness of the proposed approach of protecting a space station from space debris impact using an active spacecraft. A mission profile of the space station protection is proposed. A series of numerical simulations are performed to determine mission parameters and fuel costs. Based on an analysis of the orbits of space objects located near the space station, the maximum angle between the orbital planes of the dangerous object and the station are determined at which it is advisable to use the Ion Beam Interceptor. The developed concept also allows to implement just-in-time collision avoidance measures for space debris objects whose orbital planes are close to the plane of the space station. • The concept of the Ion Beam Interceptor spacecraft designed to protect the space station from a predicted collision is developed. • A series of calculations were carried out to analyze the possibility of protecting the international space station from potentially dangerous objects. • The developed mission can be effectively used to protect the International Space Station from objects whose orbit is deviated from the station's orbit by no more than 0.23 rad. • The concept makes it possible to implement just-in-time collision avoidance measures for space debris objects in the above range of orbits in LEO. [ABSTRACT FROM AUTHOR]

Space debris are a tangible risk for satellites in Earth orbits. Indeed, in the last decades fragmentation events have generated a large number of uncontrolled objects that have made the debris population grow. Modelling the space debris environment is becoming a fundamental task to evaluate the vulnerability of operational satellites, the probability of accidental collisions with uncontrolled objects, and the evolution of the debris population. With this aim, remote and in-situ measurements provide valuable data to tune the space debris population models and improve their reliability. While large satellites can be observed and tracked from ground, the sub-millimeter debris population requires in-situ measurements. In this context, in-orbit impact sensors are a key technology to obtain information about the sub-mm space debris environment. In this framework, a small-scale impact sensor sized to be integrated in a 2U CubeSat is being developed at the University of Padova. The sensor consists of a multitude of thin, conductive stripes arranged on a thin film of non-conductive material. When a debris hits the sensor, one or more stripes are severed, and the impact is detected. Moreover, the sensor design ensures low power consumption, making it feasible for CubeSat space missions. This work presents the latest outcomes obtained from the development of the sensor. Specifically, structural analyses are performed to assess that the sensor can withstand the launch loads, as well as thermal analyses to confirm its endurance capability with in-orbit temperatures. The number of expected impacts during the mission is predicted through orbital propagation, using state-of-the-art debris environment modelling tools. Finally, the paper presents a functional shooting test and vibration tests, executed onto a development model of the sensor, which verify its functionality and validate a Technology Readiness Level (TRL) of 4. • Space-borne sensor for in-situ monitoring of space debris. • Resistive impact sensor based on thin films and flexible PCB technology. • Thermal and structural analyses of CubeSat-sized impact sensor. • Vibrational test and functional test campaigns on a development model. [ABSTRACT FROM AUTHOR]

Space objects monitoring data represents the foundation of any Space Traffic Management system, as it provides inputs both for operational needs (e.g. collision avoidance), but also to space debris models to assess the status and evolution of the debris environment. The current paper provides an overview of current techniques used for space object observation, ranging from radar to in-situ system, together with a survey of emerging technologies and recommendations for evolution in view of observed trends in space operations (e.g. need for improved collision avoidance data, increase in rideshare missions, development of active debris removal and servicing missions). • An overview about observation techniques to monitor and track space debris. • Reviews on-going developments. • Provides recommendations for improved trackability. [ABSTRACT FROM AUTHOR]

Constraint Programming is a classical artificial intelligence paradigm characterised by its flexibility for the modelling of complex problems. In the field of space operations, this approach has been successfully used for mission planning and scheduling. This manuscript proposes a framework that leverages the strengths of Constraint Programming for the preliminary analysis of space missions, introducing some modifications to tailor it to the application at hand. Specifically, it uses constraint propagation and search techniques to thoroughly explore the configuration space of a mission in an efficient manner. Consequently, it is able to quantify the performance of precomputed mission choices with respect to the mission requirements, as well as generate new ones that optimise such performance. The proposed methodology has been particularised for two application cases involving active debris removal missions for large constellations in low Earth orbit, namely, a chaser case and a mothership case. The chaser case considers a servicing satellite that rendezvouses with the failed satellites of the constellation and directly transports them to a disposal orbit. The mothership case comprises a servicing satellite that installs deorbiting kits in each of the failed satellites, except for the one removed in the last place. This way, the servicing satellite will only transport this object, while the deorbiting kits will carry out the disposal of the rest of them. This methodology has been successfully used to evaluate a preliminary mission analysis of both application cases developed under ESA's Sunrise project. [ABSTRACT FROM AUTHOR]

With the increase of the complexity of space environment and the improvement of satellite maneuverability, the satellite maneuver game has become the focus of space research. In view of the need for pre-observation during debris removal or on-orbit maintenance missions, a scenario of observation and counter-observation similar to the pursuit-evasion game is proposed. In this paper, the impulsive observation and counter-observation game (OCOG) of two satellites is comprehensively investigated using a multi-objective optimization method. A sequential decision impulsive maneuver model is constructed and the impulsive OCOG is transformed into a bilateral optimization problem in terms of multiple constraints such as maneuverability, illumination angle, and fuel consumption, etc. To determine the optimal impulsive maneuvers for both satellites, the ring topology multi-objective particle swarm optimization (RTMOPSO) is designed. This novel algorithm uses adjacent particles to form multiple small populations to make the population converge in multiple directions during the optimization process, avoiding the single convergence of the population. Compared with non-dominated sorting genetic algorithm II (NSGA-II) and self-organized speciation based multi-objective particle swarm optimization (SSMOPSO) in the OCOG scenario, proposed method always has superiority in the game. Additional simulation is conducted and shows that the proposed algorithm is also applied for the case of non-maneuvering satellites. This research provides an effective maneuver strategy for future space game. [ABSTRACT FROM AUTHOR]

The increase in the number of space activities in recent decades has led to a concomitant increase in space debris in orbit around Earth. Space debris pose a risk not just for specific satellites, but also on a systemic level, as a collision cascade can result in the near-Earth orbits becoming unusable. In turn, this would entail a loss of the services currently provided through satellites. The international community has recognised this risk. Despite this, states are reluctant to negotiate and conclude international legal rules to address the proliferation of space debris. This article explores a root cause of this discrepancy. It argues that while law is typically seen as the regulator of uncertainty, international law's regulation of outer space – under the interests of global capital investors – is directed by principles that support processes of commodification (i.e., the freedom of use), rather than principles that manage the risks associated with the proliferation of space debris as these would constrain (or are perceived to constrain) the expansion of capital (e.g., the precautionary principle). Therefore, international law – at the level of principles – is a co-producer of uncertainty. This conclusion is reached by exploring the proliferation of space debris through Ulrich Beck's world risk society and by incorporating capital and economic power into his work. This inclusion reveals (i) that it is the accumulation of capital that generates risks and (ii) that capital exploits the socially constructed nature of risk to legitimise its expansion. International law – as both a regulator and co-producer of uncertainty – plays an essential role in legitimising these processes. [ABSTRACT FROM AUTHOR]

A numerical method has been presented to simulate hypervelocity impacts on metal targets. The target is a rectangular prism and is positioned at various inclined angles relative to the impact direction, while four different projectiles such as square prism, triangular prism, truncated cone, and ogival shape are chosen. This numerical model employs an open-source code, MPM3D-F90, which is based on the Material Point Method. In order to enhance flexibility of the code for defining projectiles and target bodies in the material domain, a preprocessor is developed to create a variety of geometrical shapes for a given volume. In addition to supplementing and defining various geometrical bodies, this tool also simplifies the preprocessing process to create the user's specific preferences for the problem. To demonstrate the utility of the preprocessor tool and investigate the influence of geometry on hypervelocity impacts, simulations are conducted using various projectile and target configurations. The analysis results reveal that the structure of the debris cloud formations, scattering behavior of the ejected particle from both front and rear faces, and penetration depth measures are significantly influenced by the projectile shape and impact angles. [ABSTRACT FROM AUTHOR]

The post-capture control of tethered debris can be challenging due to its unresponsive and uncooperative nature. Often, control of debris may require knowledge of the moments of inertia, which are usually unknown. This study applies an Unscented Kalman Filter to estimate the attitude, angular rates, and principal moments of inertia of debris captured via a tether. The filter utilizes tension and pixel-coordinate measurements of various landmarks on the debris to achieve estimation. Due to the translational and rotational motion of the debris, landmarks can be occluded or exit the field of view of the camera. Different control profiles are applied to the chaser to investigate the effects of the tension in the tether and of the visibility of chosen landmarks. It is found that large tension in the tether does not provide more accurate estimates, but that prolonging transient tether behavior improves the accuracy and precision of moment of inertia estimates. It is further observed that lower tension magnitudes with longer visibility times of landmarks make estimation of the inertia parameters possible with fewer tracked landmarks. [ABSTRACT FROM AUTHOR]

Knowledge of the spin state of space objects is critical for effectively planning operations such as collision avoidance and debris removal. One such passive method for assessing the spin rate and spin-axis of debris is through the use of passive brightness measurements known as “light curves.” Astronomers have derived physics-based algorithms for retrieving spin state via light curve analysis. These algorithms convert the relative spin state into an inertial spin state by accounting for the motions of the observation telescope, the space object, and the sun. A major downside of these theories, however, is that the resulting cost functions for operational deployment are highly non-linear. The intractable nature of the spin state estimation problem opens the door for solution via Machine Learning (ML) models. Typical “black box” ML algorithms do not rely on scientific theory, but rather are trained on large data-bases to learn how to solve a task in a manner that is obscured from the operator. While ML models can be effective for making predictions that out-perform human-derived algorithms, they also have the potential to derive solutions that either violate known physical constraints or are non-generalizable to new data instances. This is in particular a concern for many Space Domain Awareness (SDA) problems that are rooted in the physical theory of the motions of orbiting bodies. To overcome the limitations of both physical theory and “black box” ML models for spin state retrieval, we leverage a hybrid approach: the physics-guided ML model. This concept uses a physics-based loss function in the learning objective of the ML model in order to guide the model towards making predictions that not only exhibit low prediction error with respect to training data but are also physically consistent with astronomer-derived theories. Towards this end, we introduce a new physically derived equation for relating the inertial spin state to observations of relative spin rates. We then show that this equation can be used as a loss function for training ML models. We present a time-variant ML model for the retrieval of spin state that substantially outperforms both randomized numerical optimization approaches as well as temporally-invariant ML methods such as Convolutional Neural Networks. Finally, we provide initial evidence that training of the time-variant ML model with our physics-based loss function is more stable and generalizes more effectively to unseen (i.e. “out-of-distribution”) data instances. We believe that this paper provides promising avenues for merging big-data ML approaches with the robust physical theory of the SDA field. [ABSTRACT FROM AUTHOR]

Space non-cooperative target recognition is crucial for on-orbit servicing. Multi-satellite cooperation has great potential for broadening the observation scope and enhancing identification efficiency. However, there is currently a lack of research on recognition methods tailored for multi-satellite cooperative observation. In this paper, we propose a novel space non-cooperative target recognition method to identify satellites and debris in images from multi-satellite observations. Firstly, we design an image-stitching algorithm to generate space-wide-area images. Secondly, we propose a two-stage multi-target detection model, a lighter CNN model with distance merge threshold (LCNN-DMT). Specifically, in the first stage, we propose a novel foreground extraction model based on a minimum bounding rectangle with the threshold for distance merging (MBRT-D) to address redundant detection box extraction for satellite components. Then, in the second stage, we propose an improved SqueezeNet model by introducing separable convolution and attention mechanisms for target classification. Moreover, due to the absence of a public multi-target detection dataset containing satellites and debris, we construct two space datasets by introducing a randomized data augmentation strategy. Further experiments demonstrate that our method can achieve high-precision image stitching and superior recognition performance. Our LCNN-DMT model outperforms mainstream algorithms in target localization accuracy with only 0.928 M parameters and 0.464 GFLOPs, making it ideal for on-orbit deployment. [ABSTRACT FROM AUTHOR]

Orbital debris with equivalent size of 1∼10 cm is hard to be detected and its number is huge, which is the most harmful to on-orbit spacecraft while there is still no effective removal means. Inspired by vacuum cleaner, applying the conductive property of orbital debris and the physical law that variable magnetic flux would induce eddy current on the surface of a conductive material, this paper put forward a novel approach of 'along orbit debris self-collecting with rotating constant magnetic dipole array'. Based on dynamic modeling, self-collecting feasibility and control capability analysis, evolution law of relative orbital motion with induced magnetic force derivation, and on-orbit debris magnetic collecting numerical simulation, this novel approach has been verified and the corresponding requirements of magnetic collector are put forward. In addition, this paper also gave how to use several key parameters to adjust the region of along orbit debris self-collecting, and pointed out several problems needing to be researched in-depth for actual application. [ABSTRACT FROM AUTHOR]

Bayesian filtering provides an effective approach for the orbit determination of a non‐cooperative target using angle measurements from multiple CubeSats. However, existing methods face challenges such as low reliability and limited estimation accuracy. Two distributed filtering algorithms based on factor graphs employed in the sub‐parent and distributed cluster spacecraft architectures are proposed. Two appropriate factor graphs representing different cluster spacecraft structures are designed and implement distributed Bayesian filtering within these models. The Gaussian messages transmitted between nodes and the probability distributions of variable nodes are calculated using the derived non‐linear Gaussian belief propagation algorithm. Gaussian messages propagate from the deputy spacecraft to the chief spacecraft in the sub‐parent spacecraft architecture, demonstrating that the estimation accuracy converges to the centralised extended Kalman filter (EKF). Simulation results indicate that the algorithm enhances system robustness in observation node failures without compromising accuracy. In the distributed spacecraft architecture, neighbouring spacecraft iteratively exchanges Gaussian messages. The accuracy of the algorithm can rapidly approach the centralised EKF, benefiting from the efficient and unbiased transmission of observational information. Compared to existing distributed consensus filtering algorithms, the proposed algorithm improves estimation accuracy and reduces the number of iterations needed to achieve consensus. [ABSTRACT FROM AUTHOR]

Aiming at the leakage problem of the fluid loop system for the thermal control system of spacecraft caused by the impact of micro-meteoroid and orbital debris, we investigate the dependence of the leak rate, pressure drop and flow characteristics before and after leaking on leak position, inlet pressure, and leaking aperture, calculated in a straight pipeline with single leakage, using stationary and transient three-dimensional computational fluid dynamics simulations with commercial software (FLUENT). The working fluid adopts single-phase water without gravity. It is found that the pressure increases obviously near the leak point, which is caused by the local peak of pressure. As the length between the leak point and the inlet becomes larger, the local peak of pressure and the dimensionless leak rate are smaller. When the inlet pressure increases, the leaked mass flow rate increases; however, the ratio of the leaked flow rate to inlet flow rate decreases. Furthermore, it is observed that the dependence of dimensionless leaking rate on dimensionless leaking aperture has a scaling relation with the scaling exponent approximating to 2, which may be related to the proportion of the vortex formed by the backward flow at the leak hole, the amplitude, and the affected length along the pipe of the local peak of pressure. This study is instructive and meaningful to the leak detection and plugging of fluid loop in space. [ABSTRACT FROM AUTHOR]

Eliminating space debris in valuable Earth orbits is an urgent challenge for the sustainable development of outer space, and active removal is considered the most effective measure for debris elimination. In terms of legal jurisdiction, any country intending to remove space debris belonging to other countries undergoes a legality review encompassing obligations and liabilities. According to the fundamental principles of international space law, both threatened and capable countries possess the right to actively remove identifiable space debris of foreign nations, subject to strict legal obligations towards the registry country unless authorized by the United Nations, granted an agreement on jurisdiction transfer of debris, or justified by emergency necessity. Moreover, active removal may result in third-party space objects or personnel damage, imposing a substantial liability burden that could restrict space operation. Henceforth, it is imperative to establish a more rational legal regime for space liability allocation purposes. The international community can establish a mechanism for liability sharing and cross-waiver agreements among relevant countries while also considering potential fund establishment, involvement of non-governmental entities in cost-sharing efforts, and promoting commercial recycling initiatives as potentially motivating measures towards active removal. • Existing liability regimes in space law lack flexible mechanisms for sharing the liability of removing space debris. • Excessive international obligations and responsibilities imposed on removal countries discourage their active engagement in removal operations. • An international mechanism facilitating liability allocation negotiations before and after active removal is imperative. [ABSTRACT FROM AUTHOR]

This paper discusses the processes which should be taken to establish debris indices that assess the orbital environmental impact of spacecraft or missions in orbit. The first process is establishing a methodology and criteria for evaluating an impact on the orbital environment. This study proposed an assessment method to evaluate the cumulative environmental changes during an evaluation period. It evaluated the impact of an uncontrolled LC mission abandoned in orbit. This study used Near-Earth Orbital Debris Environment Evolutionary Model (NEODEEM), an orbital environmental evolutionary model that Kyushu University and JAXA developed. The second process is the debris index formulation. This study considered four steps to establish the debris index. To reveal the establishing process of a debris index, this study used debris indexes as candidates which consider expected number of fragments generated from an object. The calculated debris index values were compared to the impact on the environment assessed by the evolutionary model to see if there was any correlation. Further, this study conducted numerical simulations of un-controlled large-constellation satellites abandoned in low earth orbit in different scenarios, and of active debris removals of large intact objects by NEODEEM. This paper discusses the applicability of proposed environmental assessment methods and the debris index. • Two processes to establish a debris index are proposed. • A methodology and criteria for evaluating environmental impacts is discussed. • Four steps to formulate a debris index is discussed. • Correlations between debris indexes and environmental impacts are compared. [ABSTRACT FROM AUTHOR]

In the framework of Space Traffic Management (STM) the growing number of space debris and the consequent increased risk of collisions have become a topic of great interest. Moreover, the difficulty of detecting and characterizing a Resident Space Object (RSO) in terms of orbital parameters makes this research field very challenging. In most cases the available observations have a very short duration and an accurate estimation of the orbit is very difficult. This paper introduces the Initial Orbit Determination via Artificial intelligence (IODA) algorithm, a reliable and accurate orbit estimator combining metaheuristic and artificial intelligence frameworks to perform precise orbit determination from Very Short Arcs (VSAs). Starting from an initial orbit estimate derived through an Artificial Bee Colony (ABC) algorithm, a Physics Informed Extreme Learning Machine is employed to increase the accuracy of the predicted orbit. Results on simulated data have shown the robustness of the algorithm to random parameters initialization and a percentage of success of 89% of retrieving the reference orbit with an error under 1 km and 0.01 km/s on the initial target's state. • Description of an AI-based orbit determination tool from very short arcs. • Combination of meta-heuristic and machine learning techniques for accurate orbit estimation. • Tests on simulated data for robustness against random parameters initialization. • Montecarlo simulation on simulated data for robustness against random mission scenarios. [ABSTRACT FROM AUTHOR]

Laser ablation technology enables contactless debris removal, providing the advantages of safety and cost efficiency. To deorbit space debris using laser ablation, the attitude motion of the debris must be controlled in advance. Although a previous study derived an attitude control procedure, it empirically determines control gains and is easily affected by assumed preconditions. To solve this problem, this paper proposes an improved attitude control law using laser ablation. Previous methods use feedback control based on the angular velocity error and error quaternions to obtain a reference torque. By analogy with a magnetic attitude control law, this study designs a reference torque based on the angular momentum errors and presents theoretical condition for designing the control gains. Numerical examples using the proposed control law are conducted to control the target attitude from a random initial rotation of 1 rpm to an arbitrary attitude, which verify the effectiveness of the proposed method. Furthermore, the position, direction, and magnitude uncertainties of laser irradiation are introduced to numerically examine their effects on the control accuracy under environmental disturbances. • Conventional attitude control method by laser ablation is improved. • The effective control gains can be set theoretically by applying the concept of magnetic attitude controller. • The designed control gains depend on the rate of target rotation. • The method is effective under laser uncertainties and environmental disturbances. [ABSTRACT FROM AUTHOR]

We present theoretical estimates of the electrical charge and electrostatic surface potentials on debris objects orbiting in the LEO and GEO regions of the Earth's ionosphere. The estimates are obtained using analytic calculations based on an improved Orbital Motion Limited model as well as through numerical Particle-In-Cell simulations using the open-source SPIS code. A variety of shapes, sizes, and material compositions of the debris objects are considered, including HAMR objects with a high area-to-mass ratio and objects composed of insulating and conducting material patches. In the GEO region, we consider the charging arising from photo-emission effects and the impact of energetic charged particle beams associated with solar flares. We discuss the nature of the debris-induced collective excitations in the plasma and their potential use for debris detection. • Measurement of charge and surface potential on space debris in LEO and GEO regions. • Comparison of debris charging using OML theory and Particle-In-Cell simulations. • Collective excitations due to charged debris. [ABSTRACT FROM AUTHOR]

Can a satellite dodge a collision with untracked orbiting debris? Can a satellite dodge collision with a tracked object, making only the avoidance manœuvers actually required to avoid collision, despite the uncertainties of predicted conjunctions? Satellite-borne radar may distinguish actual collision threats from the much greater number of near misses because an object on a collision course has constant bearing, which may be determined by interferometric detection of the radar return. A large constellation of such radars may enable the determination of the ephemerides of all cm-sized debris in LEO. • Space debris on a collision path has a constant bearing from a threatened satellite. • Satellite-borne radar interferometry can identify such debris. • This may enable evading actual collision threats. [ABSTRACT FROM AUTHOR]

There is a growing risk to aircraft in flight from collisions with debris produced by the breakup of uncontrolled rocket bodies and satellites during atmospheric reentry. On one hand, the aviation industry has grown to almost 39 million flights per year, with a 63 % increase between 2004 and 2019. On the other hand, the number of successful rocket launches more than doubled between 2015 and 2023, from 87 to 212, respectively. During those 212 launches in 2023, 128 rocket bodies were abandoned in orbit, left to reenter uncontrollably. Such uncontrolled space object reentries are hard to predict, making mitigation measures difficult. In November 2022, a reentering Long March 5B rocket caused the closure of airspace over Europe, delaying 645 flights and having a plausible economic impact of millions of Euros. There are international and domestic laws that might enable the recovery of economic losses resulting from uncontrolled reentries, but such losses should not be allowed to occur in the first place. Instead of leaving the location of a reentry to chance, controlled reentries can be achieved with existing technologies and mission designs, directing reentries away from areas of high aircraft traffic. Moving to a controlled reentry regime would create a cost to space operators – but that cost is currently being externalized to the aviation industry. Multilateral solutions to create a controlled reentry regime should be pursued, as recommended in the 2023 Montreal Recommendations on Aviation Safety and Uncontrolled Space Object Reentries, before there is a tragedy caused by an aircraft collision with debris from a rocket body or satellite. • As the number of rocket launches and commercial aircraft flights increase, the probability of a catastrophic collision between an aircraft and reentering space debris is also growing. • Technologies and mission designs exist to enable all rocket bodies to be returned to Earth in a controlled manner, eliminating the casualty risk. • From a broad economic perspective, space companies are externalizing some of their risks and costs and imposing them on the aviation industry. • States are liable for damage caused by reentering space objects and could be liable for the economic costs caused by precautionary airspace closures. • The 2023 Montreal Recommendations offer actionable steps to reduce the risk of collisions between space debris and aircraft. [ABSTRACT FROM AUTHOR]

Heaterless hollow cathodes are a promising solution for reaching a good cathodic contact in electrodynamic tether systems. However, these cathodes cannot keep the plasma discharge if the electric current I C is below a threshold I m i n. If the tether is short, and to save power and expellant, an appropriate command strategy is needed to ensure that the cathode is triggered in conditions satisfying I C > I m i n . This study investigates four command strategies, including two fully autonomous approaches (one based on satellite position and the other on local plasma density) and two strategies involving ground segment access, differing in command generation location (ground segment and on-board computer). The success rates of the four strategies were studied though numerical simulation and for the specific scenario of the E.T.PACK demonstration mission. The results demonstrate that, as compared to continuous operation of the hollow cathode, the proposed strategies reduce propellant wastage by a factor between 5 and 10. The strategy requiring ground segment access and with the onboard computer making the command decision has the highest success rate (94%). Among the autonomous configurations, the strategy based solely on local plasma density achieves the highest success rate (69%). Additionally, the impact of sensor accuracy on success rates was assessed via Monte Carlo analysis. The command strategy relying on plasma density measurement is the most sensitivity strategy, with a 10% decrease in success rate due to sensor uncertainty. • Four strategies for commanding the hollow cathode of short electrodynamic tethers are proposed. • Duty cycle and rate of success are used to assess the performance of the strategies. • The two strategies involving contact with the ground segment have the best performance. • The two autonomous strategies only involve one onboard sensor and provide acceptable performance. [ABSTRACT FROM AUTHOR]

The Federal Aviation Administration (FAA) is developing new design procedures to extend airport pavement life beyond 20 years based on the concept of serviceability: the measure of how well a pavement fulfills user expectations. A key element is a new distress megaindex called serviceability level (SL) whose components represent independent aspects of airport pavement serviceability: low foreign object damage (FOD) potential, low skid potential, and smoothness. This research validates the assumption of independence previously used to develop a probability-based form for SL. Independence greatly simplifies the mathematics of the new form, in particular, the ability to decompose a pavement condition model into multiple relatively simple submodels. Friction is shown to not correlate to the other two components. FOD and roughness are conditionally independent with a latent variable of crack and spall density. Conditional independence means the proposed SL formulation is generally valid but requires that FOD and roughness measurements or predictions be made at the same time using the same assumptions. [ABSTRACT FROM AUTHOR]

• Hybrid mission planning of on orbit refueling and debris removal is addressed. • A robust model considering hybrid uncertainty is proposed. • A novel stochastic expectation model is developed to quantify mission uncertainty. • Comparison simulations are conducted on these two mission planning models. This article proposes two optimization models to solve the multi-satellite on-orbit hybrid service mission planning problem under uncertainty. During the process of on-orbit refueling and debris removal, two categories of uncertainties are taken into account. These uncertainties have an impact on the mass of the service satellite as well as its fuel consumption during the orbit transfer. The two-stage orbit transfer strategy is given to save fuel for maneuvering, which also determines the directed graph between target orbits of satellites or debris. The stochastic expectation model is to get the service sequence with the optimal average benefit, while the robust model considers the worst situation and gives the optimal minimum benefit. Simulations of GEO satellites in orbit are conducted to demonstrate the impact of various models on handling uncertain tasks. [ABSTRACT FROM AUTHOR]

The growth of both operational satellites and orbital debris is creating the requirement for more robust Space Surveillance and Tracking (SST)-related applications. These systems necessarily must leverage ground-based sensors (optical and radar) to realise higher performance solutions. In this context, the European Union Space Surveillance and Tracking (EUSST) consortium groups European national agencies and institutions, and is in charge of carrying out the following services: conjunction analysis, fragmentation analysis and re-entry prediction, and the Italian Air Force is in charge of the latter two. In this framework, the Italian SST Operational Centre (ISOC) has recently upgraded its system to the ISOC Suite, an integrated platform providing multiple functions and services in the SST domain. This paper presents the orbit determination functions provided by the novel ISOC Suite. First, a statistical index is computed to assess the measurements correlation to a catalogued object. If it is successful, the object predicted orbit is refined through measurements according either to batch or sequential filters; otherwise these are used to refine a first estimate of the target orbital state computed according to dedicated methodologies. After the presentation of the prototypal software architecture, the ISOC Suite performance are assessed and discussed both in terms of synthetic and real data. [ABSTRACT FROM AUTHOR]

According to the theory of atmospheric transmission, the atmospheric optical characteristics of a 700 mm laser ranging telescope system are obtained by the inversion of the experimental data through the telescopic multi-elevation method, and a modified model of the ranging equation of laser diffuse radar is proposed. The variation in the Aerosol Optical Depth and atmospheric transmittance under the multi-elevation method, visibility and the oblique transmission atmospheric stratification model are analyzed and discussed. The model is numerically simulated and compared with the measured data of some space debris. The results show that the relative errors of the average echo photon number obtained by the multi-elevation method are less than 15%, and the average relative errors are 4.643% and 7.934%, respectively. The model improves the calculation accuracy of the laser ranging radar equation to a certain extent. [ABSTRACT FROM AUTHOR]

Recent challenges in space access include cost optimization and space debris reduction. The European Space Agency has envisioned the evolution of in-orbit transportation involving re-usable service vehicles, moving payloads from high parking orbits to their target orbits. This concept for orbital infrastructure requires de-risking activities and the development of building blocks, such as standardized interfaces and communication. Mastery of close-proximity operations and docking is essential for the new transportation system. This new branch of space operations represents a good opportunity to introduce more sustainable propulsion solutions, especially given the high costs and uncertain future of hydrazine and its derivatives. IOSHEX, a service spacecraft to be equipped with a green propulsion system utilizing 98% hydrogen peroxide, serves as a reference. This paper presents a design concept for this propulsion system, including trade-off analyses, calculations, and a three-dimensional model integrated with IOSHEX. [ABSTRACT FROM AUTHOR]

This paper focuses on the active removal of spent upper stages from LEO using de-orbiting devices. It proposes a method of regulating aerodynamic loads on the target during its re-entry by utilizing the features of spatial attitude motion. A mathematical model of the re-entry process is developed, and numerical simulations are conducted, demonstrating that the nature of the attitude motion during the descent influences the load factors and, thus, the breakup altitude. It is shown that the respective de-orbiting devices should control both the initial tumbling and spin of the target to achieve different mission outcomes, such as minimizing the debris footprint size or maximizing the breakup altitude. [ABSTRACT FROM AUTHOR]

One of the effects of space activities is the creation of space debris that can endanger either the space environment or the Earth’s environment. In response to concerns regarding a swift escalation in space debris, Russia tested its Anti-Satellite (ASAT) Weapon by deploying the PL-19 Nudol missile against its satellite, Cosmos 1408, generating space debris. This situation certainly raises the question of how to protect the environment in space and whether international environmental law that provides a legal framework for protection in the world can also be applied in outer space. This article offers a new perspective on implementing international law to protect the space environment. This study adopts normative juridical research methods by utilizing a statute and case approach to analyze the research. The analysis showed that space debris generated from ASAT Weapon testing activities by Russia is regarded as harmful contamination under Article IX of OST under the interpretation of the term through the method of interpretation regulated in the 1969 VCLT because these activities produce long-lived space debris. Further, Russia violated the principles of environmental protection in space by failing to fulfill the obligations contained in these principles, such as taking precautionary measures and international consultations before carrying out such test activities.

Abstract Bayesian filtering provides an effective approach for the orbit determination of a non‐cooperative target using angle measurements from multiple CubeSats. However, existing methods face challenges such as low reliability and limited estimation accuracy. Two distributed filtering algorithms based on factor graphs employed in the sub‐parent and distributed cluster spacecraft architectures are proposed. Two appropriate factor graphs representing different cluster spacecraft structures are designed and implement distributed Bayesian filtering within these models. The Gaussian messages transmitted between nodes and the probability distributions of variable nodes are calculated using the derived non‐linear Gaussian belief propagation algorithm. Gaussian messages propagate from the deputy spacecraft to the chief spacecraft in the sub‐parent spacecraft architecture, demonstrating that the estimation accuracy converges to the centralised extended Kalman filter (EKF). Simulation results indicate that the algorithm enhances system robustness in observation node failures without compromising accuracy. In the distributed spacecraft architecture, neighbouring spacecraft iteratively exchanges Gaussian messages. The accuracy of the algorithm can rapidly approach the centralised EKF, benefiting from the efficient and unbiased transmission of observational information. Compared to existing distributed consensus filtering algorithms, the proposed algorithm improves estimation accuracy and reduces the number of iterations needed to achieve consensus.