Space Debris Removal Research Articles

Development of 6DOF Hardware-in-the-Loop Ground Testbed for Autonomous Robotic Space Debris Removal

This paper presents the development of a hardware-in-the-loop ground testbed featuring active gravity compensation via software-in-the-loop integration, specially designed to support research in autonomous robotic removal of space debris. The testbed is designed to replicate six degrees of freedom (6DOF) motion maneuvering to accurately simulate the dynamic behaviors of free-floating robotic manipulators and free-tumbling space debris under microgravity conditions. The testbed incorporates two industrial 6DOF robotic manipulators, a three-finger robotic gripper, and a suite of sensors, including cameras, force/torque sensors, and tactile tensors. Such a setup provides a robust platform for testing and validating technologies related to autonomous tracking, capture, and post-capture stabilization within the context of active space debris removal missions. Preliminary experimental results have demonstrated advancements in motion control, computer vision, and sensor fusion. This facility is positioned to become an essential resource for the development and validation of robotic manipulators in space, offering substantial improvements to the effectiveness and reliability of autonomous capture operations in space missions.

Adaptive robust fault-tolerant control of spinning tether system for space debris removal

The Spinning Tether System (STS) is currently recognized as one of the most effective and ideal platforms for removing space debris. It offers several advantages, including a non-contact mechanism, rapid deorbit capabilities, stable spinning, and a short preparation time for subsequent missions. The system primarily depends on the thrusters of the main spacecraft and the capture device for its spin-up process. Although modern technology and quality management methods strive to minimize thruster failures, the capture of debris significantly affects the STS. This impact can induce tether oscillations and cause actuator failures, thereby destabilizing the spin-up process. Given these challenges, this paper explores the design of fault-tolerant control strategies to enhance system reliability during the post-capture spin-up phase. Initially, a dynamic model using quaternions as generalized coordinates was established based on the constrained Lagrange equation. This model facilitated a detailed analysis of potential thruster failure modes. Subsequently, the optimal trajectory for the spin-up process was planned using the pseudo-spectral method, ensuring efficiency and safety in control execution. To address the identified vulnerabilities, the study introduces an adaptive robust fault-tolerant controller. This controller, based on a BLF and integrated with a nonlinear neural network disturbance observer, is designed to operate effectively under fault conditions. Numerical simulations were conducted to validate the performance of the controller, demonstrating its capability to maintain stable control of the system, both after detecting a fault signal and following an actuator failure.

Numerical and experimental study on effects of net-bullet ejection angles and initial distances on space-debris capture

The increasing volume of space debris in the outer space poses a significant threat to operational spacecraft. Hence, net capture systems have emerged as a promising technique for removing space debris. These systems operate by deploying a net to envelop and capture the debris. The effectiveness of debris capture using nets depends on ejection parameters such as speed, ejection angle, and the crucial initial distance between the net and debris. Simulations are performed to examine various scenarios of active debris removal. In addition, the experiments involved meticulously calibrated net and debris ejector systems, where bullets are utilized for net deployment by varying the angle of bullet ejection (θ). The net trajectory is determined using simplified equations of motion, while considering both the ejection dynamics and its interaction with the debris. The findings of this study reveal the correlations between the initial parameters and net performance pertaining to space debris capture. Larger ejection angles and greater distances between the net and the debris-hindered debris capture. Despite slight simultaneous net and debris ejection delays, the results of the real-world experiments validated the simulation results.

Service spacecraft for space debris removal

The problem of space debris removal from the near-Earth space is being studied in almost every country taking part in space exploration. This is due to the global threat of critical increase in the number of space debris objects predicted for the near future, in particular as a result of significant growth in demand for multi-satellite constellations for various purposes. To date, researchers have proposed a large number of different methods for space debris removal. The work presented is the development of one of the promising contactless methods of space debris removal by an ion beam. The results of modeling and optimization of physical processes in the ion source to be mounted on board a service spacecraft that is necessary for implementing the considered method of space debris removal are presented. Besides, the results of thermal modeling and thermal mapping of the ion source during its operation are presented also, and the calculation results of its output parameters are compared to experimental data, which verified the small divergence angles of the generated ion beam. To assess the prospects of using a system for contactless space debris transportation by an ion beam using the obtained data on the operating parameters of the ion source, the trajectory design and mission analysis were carried out, which revealed the feasibility of removing seven space debris objects out of the protected region in geostationary orbit by a single service spacecraft. Besides, the preliminary service spacecraft design is presented.

Spacecraft protection against man-made and natural space debris particles

Classification of space objects according to their size, mass and density is presented. Methods developed for assessing the degree of near-Earth space contamination by space debris are reviewed briefly. General principles of providing passive and active protection for spacecraft are analyzed. Based on the developed model of particle motion under the conditions of electrodynamic armor, the areas of its efficient application are specified. It is shown that the current level of development of structural materials and high-pulse energy storage devices does not fully ensure the possibility of their full-scale efficient use in spacecraft protection systems. It is stated that it is necessary to develop additional measures to ensure the space flight safety, for example, by developing service spacecraft on the basis of unified space platforms, the primary purpose of which would be the active removal of space debris.

Less fuel strategies for space debris removal in Low Earth Orbit

This paper proposes less fuel strategies for space debris removal. To mitigate the risk of space debris cost-efficiently, multi-rendezvous missions are under development. On the other hand, multi-rendezvous missions often require changing orbital planes of removal satellites, which requires a huge amount of ΔV. Therefore, this study focuses on exploiting the J2 perturbation force as an auxiliary force and aims to establish maneuver rules that minimize ΔV consumption while maximizing the benefit of the J2 perturbation. The J2 perturbation equation is explored analytically, which clarifies whether the change in the semi-major axis or the inclination dominates the efficiency of the exploitation. A straightforward criterion is extracted which determines the efficient maneuver based on the initial inclination of the satellite.

CubeSats for space debris removal from LEO: Prototype design of a robotic arm-based deorbiter CubeSat

Space debris has become a growing problem, and various studies indicate that the population of space objects has reached a critical density in low Earth orbits (LEO). Therefore, removing debris from the LEO is key to stabilizing the growth of space objects and making some of the orbits reusable for future launches. Deorbiting larger debris objects using miniaturized satellites, CubeSats is both economically viable and requires relatively less time for design & deployment. In this paper, we present a system-level study of orbital debris removal from LEO using CubeSats, detailing various existing debris tracking, rendezvous, capture, and deorbit mechanisms. A deep learning-based object detection algorithm has been utilized to improve the accuracy of detecting and localizing debris. We also present a discussion on the CubeSat-compatible capture & deorbit mechanisms identified from our study and an upper bound on the debris mass that can be deorbited from a given LEO orbit using CubeSats. We aim to demonstrate a case study for the orbital decay analysis of a CubeSat deorbiting the XSat, a microsatellite launched by Singapore. We detail the design of a 27U CubeSat deorbiter prototype equipped with a pair of robotic arms to capture the XSat. This analysis considers active deorbiting using Hall-effect thrusters, for which the required delta-V & propellant mass have also been computed.

Implementing Scalable Solutions for Space Debris Mitigation

Abstract: Collision of space debris present in the LEO (Low Earth Orbit) poses a serious threat to the current operational space missions as well as to the future utilization of the LEO space. These also result in major environmental impairment and significant economic losses due to damage to satellites and space stations. It thus becomes imperative to develop effective strategies and design and build systems which can aid in the removal of both small and large debris. This paper investigates the various existing space debris mitigation models such as ElectroDynamic Debris Eliminator (EDDE), ESA’s Space Harpoon, Laser Ablation, and JAXA’s Electrodynamic tether. A useful comparison is drawn amongst these different techniques while evaluating their efficiency within the framework of methods for space debris capture and removal. The advantages and drawbacks of these technologies are discussed through examples, previous and ongoing projects. The paper also aims to briefly introduce a novel concept for debris mitigation and to motivate more rigorous research in this area.

A Trajectory Planning Method for Capture Operation of Space Robotic Arm Based on Deep Reinforcement Learning

Abstract In order to deal with the complex dynamics and control problems involved in space debris removal, a trajectory planning technique for a spatial robotic arm based on twin delayed DDPG (TD3) in deep reinforcement learning is proposed, and it can accomplish an end-to-end control effect comparable to that of human hand gripping objects. The trajectory planning method for capturing space debris by a floating-base space robotic arm is realized using a space robotic arm task simulation platform built on MuJoCo and using trajectory planners, trajectory trackers, and joint and end-effector control strategies formulated with seven different weighted reward functions. This makes it easier to complete spacecraft in-orbit servicing and maintenance missions. The experiment results demonstrate that the capture strategy can maintain a capture success rate of more than 99%, and debris capture can be mostly finished in three stages when taking the stability of the floating base into consideration by continuously modifying the trajectory.

Altitude optimality boundary of two variants of large space debris removal to disposal orbits

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 Δa to reach the DO, the number of objects removed by a single SC, the average ΔV 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.

Obligations and liabilities concerning the active removal of foreign space debris: A global governance perspective

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.

Convex-Optimization-Based Model Predictive Control for Space Debris Removal Mission Guidance

A convex-optimization-based model predictive control (MPC) algorithm for the guidance of active debris removal missions is proposed in this work. A high-accuracy reference for the convex optimization is obtained through a split-Edelbaum approach that takes the effects of J2, drag, and eclipses into account. When the spacecraft deviates significantly from the reference trajectory, a new reference is calculated through the same method to reach the target debris. When required, phasing is integrated into the transfer. During the mission, the phase of the spacecraft is adjusted to match that of the target debris at the end of the transfer by introducing intermediate waiting times. The robustness of the guidance scheme is tested in a high-fidelity dynamic model that includes thrust errors and misthrust events. The guidance algorithm performs well without requiring successive convex iterations. Monte Carlo simulations are conducted to analyze the impact of these thrust uncertainties on the guidance. Simulation results show that the proposed convex-MPC approach can ensure that the spacecraft can reach its target despite significant uncertainties and long-duration misthrust events.

Dynamic modeling of a sliding ring on an elastic rod with incremental potential formulation

Abstract Mechanical interactions between rigid rings and flexible cables find broad application in both daily life (hanging clothes) and engineering system (closing a tether-net). A reduced-order method for the dynamic analysis of sliding rings on a deformable one-dimensional (1D) rod-like object is proposed. In contrast to the conventional approach of discretising joint rings into multiple nodes and edges for contact detection and numerical simulation, a single point is used to reduce the order of the model. To ensure that the sliding ring and flexible rod do not deviate from their desired positions, a new barrier function is formulated using the incremental potential theory. Subsequently, the interaction between tangent frictional forces is obtained through a delayed dissipative approach. The proposed barrier functional and the associated frictional functional are C2 continuous, hence the nonlinear elastodynamic system can be solved variationally by an implicit time-stepping scheme. The numerical framework is initially applied to simple examples where the analytical solutions are available for validation. Then, multiple complex practical engineering examples are considered to showcase the effectiveness of the proposed method. The simplified ring-to-rod interaction model has the capacity to enhance the realism of visual effects in image animations, while simultaneously facilitating the optimisation of designs for space debris removal systems.

Multi-Debris Capture by Tethered Space Net Robot via Redeployment and Assembly

This paper presents an advanced multiple pieces of debris capture method for the tethered space net robot. A novel capture strategy that integrates redeployment and self-assembly techniques is introduced. With this strategy, the net robot self-assembles to close the net pocket and quickly maneuvers to nearby target debris. Upon reaching its target, the robot redeploys the net for debris capture. Central to this approach is the development of a capturing model that accurately describes the state function of the deployed net and incorporates an effective dragging method to counteract debris bouncing. To enable this multiple pieces of debris capture, an attitude consensus controller and a capture controller are designed using a finite-time scheme and terminal sliding mode, respectively. Numerical simulations reveal limitations in capturing multiple pieces of debris by existing design of tethered space net robots, where debris has the propensity to bounce out of a fully deployed net during multicapture attempts. The proposed strategy effectively mitigates these challenges, minimizing debris bounce and ensuring dependable multiple pieces of debris capture. Overall, the findings offer valuable insights to enhance the efficiency of active space debris removal missions.

Intelligent and robust control of space manipulator for sustainable removal of space debris

This study focuses on enhancing the control precision and efficiency of a two-degree-of-freedom (2-DOF) space manipulator used for active space debris removal. The unpredictable space environment introduces large uncertainties, which introduces unique challenges beyond the capabilities of a standalone computed torque controller and degrades control performance. To address this problem, a robust controller is developed, integrating traditional techniques such as sliding mode and computed torque control with a Neural Network framework. This synergy leverages both methods' strengths—conventional controls' accuracy and Neural Network's adaptability. The integration of Neural Network-based sliding mode control complements the robustness of computed torque control by actively mitigating uncertainties and disturbances inherent in the space environment. The 2-DOF manipulator's state variables model the system dynamics, necessitating accurate relative motion estimation between the manipulator and debris. The global asymptotic stability of the developed algorithm is demonstrated through the Lyapunov theorem, guaranteeing error convergence to zero. The convergence, stability, precision, tracking errors, and responsiveness of the controller have been analysed and validated by the MATLAB Simulink simulations. The novel approach's performance effectiveness is substantiated by numerical simulations and a comparative analysis with conventional computed torque control. Outcomes highlight the superior precision and efficiency in manipulator tracking the trajectory, validating the integrated controller's potential for successful active space debris removal.

Game theory based finite-time formation control using artificial potentials for tethered space net robot

The Tethered Space Net Robot (TSNR) is an innovative solution for active space debris capture and removal. Its large envelope and simple capture method make it an attractive option for this task. However, capturing maneuverable debris with the flexible and elastic underactuated net poses significant challenges. To address this, a novel formation control method for the TSNR is proposed through the integration of differential game theory and robust adaptive control in this paper. Specifically, the trajectory of the TSNR is obtained through the solution of a real-time feedback pursuit-evasion game with a dynamic target, where the primary condition is to ensure the stability of the TSNR. Furthermore, to minimize tracking errors and maintain a specific configuration, a robust adaptive formation control scheme with Artificial Potential Field (APF) based on a Finite-Time Convergent Extended State Observer (FTCESO) is investigated. The proposed control method has a key advantage in suppressing complex oscillations by a new adaptive law, thus precisely maintaining the configuration. Finally, numerical simulations are performed to demonstrate the effectiveness of the proposed scheme.

DEEP LEARNING FOR SPACE DEBRIS REMOVAL

The advances in deep learning have revolutionized the field of artificial intelligence. These advances, as well as new tasks and requirements in space exploration, have led to an increased interest in these deep learning methods among space scientists and practitioners. The problems of controlling the attitude and relative motion of spacecraft are considered for both traditional and new missions, such as contactless space debris removal. Both supervised and reinforcement learning is used to solve such problems based on various architectures of artificial neural networks, including convolutional ones. The possibility of using deep learning together with methods of control theory is analyzed to solve the considered problems more efficiently. The difficulties that limit the application of these methods for space applications are highlighted. The necessary research directions for solving these problems are indicated.

Generation of Secondary Space Debris Risks from Net Capturing in Active Space Debris Removal Missions

Mitigation strategies to eliminate existing space debris, such as with Active Space Debris Removal (ASDR) missions, have become increasingly important. Among the considered ASDR approaches, one involves using a net as a capturing mechanism. A fundamental requirement for any ASDR mission is that the capture process itself should not give rise to new space debris. However, in simulations of net capturing, the potential for structural breaking is often overlooked. A discrete Multi-Spring-Damper net model was employed to simulate the impact of a 30 m × 30 m net travelling at 20 m/s onto an ESA Envisat mock-up. The Envisat was modelled as a two-rigid-body system comprised of the main body and a large solar array with a hinge connection. The analysis revealed that more than two significant substructures had a notable likelihood of breaking, prompting the recommendation of limiting the impacting velocity. The generation of secondary space debris indicates that net capturing is riskier than previously assumed in the literature.

Application of Article 25 of the Draft Articles on Responsibility of States for Internationally Wrongful Acts

As human exploration and use of outer space increases, the problem of space debris becomes more acute. The accumulation of space debris poses a huge threat to the exploration and use of outer space and may also affect the Earth's atmosphere and the environment. International organizations encourage national and non-governmental organizations to take initiatives in removing space debris. However, current international space law does not contain comprehensive rules governing the active removal of space debris of other States, which does not allow establishing the legality of such actions in international law. In the context of the Draft Articles on Responsibility of States for Internationally Wrongful Acts (ARS), it would be useful to clarify the issue of State responsibility for the active removal of space debris of other States. This article uses the literature review method and the case analysis method. In particular, a detailed analysis of the application of the relevant provisions of ARS was conducted, which provides useful ideas for solving the problem of space debris and regulating space activities. It was noted that it is necessary to improve the legal system and that the active removal of space debris of other States should be discussed on a case-by-case basis. If the country to which the space debris belongs clearly does not consent to other countries to clean up its space debris, then continuing to clean up the space debris of other countries should be determined to be an internationally wrongful act. However, after a country takes the initiative to clean up the space debris of other countries, it can also declare a state of emergency to eliminate the illegality of its actions depending on the specific circumstances, thereby promoting the active participation of countries in cleaning up space debris and protecting the space environment.

Space Debris Capture - About New Methods of Tethered Space Net Opening by Tubular Booms

Abstract Nowadays, space debris is one of the main subjects of discussion regarding satellites in Earth's orbit. Right now, there are about 26,000 orbiting satellites and only few of these satellites are operational. Recently, the Polish space sector has been strongly growing and delivering instruments working in space. The first part of this paper describes the several space instruments designed in the Space Research Centre Polish Academy of Science (SRC PAS). Instruments such as SWI, RPPWI, LPPWI, Ebox or Pre-boxes have been created for a mission to Jupiter named “JUICE”. After fulfilling their scientific mission, these instruments can increase the amount of debris in space. This is one of the reasons for taking up the topic of space debris reduction and the use of technical solutions used in this mission for the proposed solution presented later. The second part of this paper describes the new methods related to space debris. The activities can be related to the space debris removal programmes. The paper describes two methods developed by Polish scientists used for removal of space debris. One of them is the new capture method and mechanism designed for it. The special mechanism is based on tubular boom application for opening the net, to capture the space debris. The main parts of the mechanism are mechanisms which have been used in the JUICE space mission. The paper describes the main idea for these new methods, and for the design part prepared the strength confirmation by structural analysis. The main function of the mechanism has been verified by simulations and tests performed in laboratories.