In-orbit Servicing Research Articles

Close-Proximity Operations Design, Analysis, and Validation for Non-Cooperative Targets with an Application to the ClearSpace-1 Mission

This paper addresses the design, analysis, and validation of safe close-proximity operations around uncooperative targets, with an application to the ClearSpace-1 (CS-1) mission. It is focused on the areas of Guidance, Navigation, and Control (GNC), and Mission Analysis, due to their criticality for the success and safety of this kind of operation. The relevance of the concepts, of the GNC solutions, and their validation is demonstrated for the case study of CS-1, a reference mission for the rendezvous, capture, and de-orbiting of an uncooperative target (i.e., the VESPA payload adapter). It is shown how the design approach can be adopted for the Concept of Operations of CS-1, covering the definition of keep-out zones, corridors, and GO/NO GO criteria, for assessing the passive safety of trajectories, and for the incorporation of active safety strategies. The analysis is adopted for functional chains such as the Navigation and Control, and the combination of a prototyping and a high-fidelity simulator is adopted for directed Model-in-the-Loop Monte-Carlo campaigns. The outcomes are intended to support the industry in the development of Close-Proximity Operations similar to that of CS-1. These can be adopted in a wide variety of missions, including Active Debris Removal and In-Orbit Servicing. In particular, the adopted concepts are a key contribution to the standardization of Close-Proximity Operations for non-cooperative rendezvous missions, and act towards a sustainable and safe commercial application.

Pose Estimation for Cross-Domain Non-Cooperative Spacecraft Based on Spatial-Aware Keypoints Regression

Reliable pose estimation for non-cooperative spacecraft is a key technology for in-orbit service and active debris removal missions. Utilizing deep learning techniques for processing monocular camera images is effective and is a hotspot of current research. To reduce errors and improve model generalization, researchers often design multi-head loss functions or use generative models to achieve complex data augmentation, which makes the task complex and time-consuming. We propose a pyramid vision transformer spatial-aware keypoints regression network and a stereo-aware augmentation strategy to achieve robust prediction. Specifically, we primarily use the eight vertices of a cuboid satellite body as landmarks and the observable surfaces can be transformed by, respectively, using the pose labels. The experimental results on the SPEED+ dataset show that by using the existing EPNP algorithm and pseudo-label self-training method, we can achieve high-precision pose estimation for target cross-domains. Compared to other existing methods, our model and strategy are more straightforward. The entire process does not require the generation of new images, which significantly reduces the storage requirements and time costs. Combined with a Kalman filter, the robust and continuous output of the target position and attitude is verified by the SHIRT dataset. This work realizes deployment on mobile devices and provides strong technical support for the application of an automatic visual navigation system in orbit.

Safe Guidance Scheme for Proximity Operations Forced Motion

Autonomous spacecraft proximity operations represent a key enabler for future mission architectures such as in-orbit servicing, active debris removal, object inspection, and in-orbit assembly. This work addresses safety concepts for the relative trajectory guidance design applicable to challenging proximity operations in the close-range domain. The relative orbital element framework is used to formulate safety checks that improve the trajectory’s robustness in case of chaser’s malfunctions or loss of control. Particularly, concepts of passive abort safety and active collision safety are applied to the trajectory design to maintain the chaser outside keep-out zones. These definitions are included within a guidance algorithm that exploits sequential convex programming to efficiently solve the fixed final time safety-constrained close-range rendezvous problem. Test cases of reconfiguration between stable relative orbits and synchronization to a rotating hold point are presented, highlighting the advantages in using these new safety concepts in terms of safety, trajectory insight, and formulation efficiency.

Electro-Optical Relative Navigation for Inspection and Rendezvous in the SpEye Mission

The execution of autonomous in-orbit servicing operations is expected to play a crucial role to preserve and enhance satellites’ performance, as well as to ensure a sustainable use of outer space. In this respect, several research efforts are dedicated to addressing the technological challenges that characterize the development of an autonomous guidance, navigation, and control system. In this framework, the Space Eye (SpEye) mission, funded by the Italian Space Agency, aims to demonstrate safe and inexpensive on-orbit inspection of a target satellite using a CubeSat-based free-flying nanosatellite. This paper, which stems from the phase A mission study, describes the high-level architectural design of its electro-optical-based relative navigation subsystem, employing multisensor algorithmic approaches based on the combination of visual, laser, and Differential Global Navigation Satellite System measurements. A dedicated environment is developed for the simulation of measurements from the relative navigation suite (including a synthetic image generator), allowing a preliminary performance assessment of the proposed algorithmic approaches.

Dual-Use “New Space”: US Experience

The article explores the growing involvement of private space companies in military activities, with a primary focus on the United States. It delves into the specific contributions of private entities to national defense missions, particularly in the militarization of outer space. The authors analyze the strategic interests of government agencies in integrating non-state actors to enhance space capabilities, such as communication, Earth observation, situational awareness, and in-orbit servicing. The paper also assesses the potential implications of these trends for international security, highlighting the complexities that arise from the blurred lines between civil and military space operations. It points to the creation of the U.S. Commercial Augmentation Space Reserve (CASR), an initiative aimed at enhancing defense through commercial space partnerships, and discusses the operational and strategic challenges of managing vast satellite constellations. Additionally, the article reflects on the security risks posed by the militarization of commercial space infrastructure, examining the potential consequences for geopolitical stability and the future of space conflict management. Finally, it suggests that further research and regulatory measures are necessary to mitigate the military threats linked to the New Space

Future activities in the near-earth space in the face of ever-increasing space traffic

The increasing launch rate of spacecraft, particularly due to the deployment of large constellations and miniaturized satellites in Low Earth Orbit (LEO), has led to a significant rise in space traffic and debris. This paper examines emerging technologies and strategies for future Space Traffic Management (STM) to ensure sustainable operations in space. Key focus areas include the use of artificial intelligence (AI) for enhanced Collision Avoidance (CA) systems, the development of advanced Space Surveillance and Tracking (SST) capabilities, and Active Debris Removal (ADR) techniques to mitigate the growing risks associated with space debris. Additionally, the paper explores the potential of in-orbit servicing, re-entry services, and the exploitation of Very Low Earth Orbits (VLEO) and cislunar space. The integration of these technologies and practices is essential to manage the anticipated growth in space activities while minimizing collision risks and ensuring the long-term sustainability of the space environment.

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.

Anti-creep pretension determination of a mesh reflector antenna for long term surface accuracy retention

During the in-orbit service, mesh reflector antennas inevitably withstand the long-term creep behavior, resulting in changes in material properties and loss of cable tensions, thus decreasing the structural stiffness and surface accuracy. Pretension design plays an important role for mesh reflector antennas in achieving high surface accuracy, and different levels of pretension also affect the antenna’s creep behavior in the time dimension, which can be actively utilized to improve stability of the antenna surface accuracy. In this paper, we present an anti-creep pretension determination method for mesh reflector antennas to improve the surface accuracy stability. The creep model in the discretized time domain is adopted to describe the cable creep behavior. The time-related nonlinear equilibrium equation of the mesh reflector antenna is established with the force density method. The time-related tangent stiffness matrix is derived and adopted to solve the nonlinear equilibrium equation by the Newton-Raphson method, providing an effective way to analyze the antenna creep phenomenon in the discretized time domain. Aiming to minimize the long-term peak value of the time-variant surface error, the pretension schemes are generated and optimized. Finally, this approach is effectively applied to a thirty-unit mesh reflector antenna and its feasibility and effectiveness are verified.

Future in-orbit servicing operations in the space traffic management context

This paper provides a concise yet informative overview on future operations in near-Earth space including in-orbit servicing, assembly, manufacturing, and the use of space tugs, in the frame of the space traffic management context. After providing a general definition of these activities, the significant impact that they will have in the space domain from an economic perspective is highlighted. Past achievements in terms of orbital demonstrations are then recalled, leading to the identification of the most critical technological challenges which need to be addressed to improve reliability, frequency, and robustness of servicing operations. A summary of the most critical next steps and recommendations is finally provided.

Impact of space systems capabilities and their role as critical infrastructure

The cyber domain has led to growth in current satellite capabilities, which have become essential due to the increased use of both civil and military critical infrastructure (CI) management systems. In recent decades, outer space has proven to be an increasingly critical sector for the international management of commercial CI, with private operators acting on both multi- and transnational levels. However, the space domain is characterised by not only opportunities but also risks and threats. As the security implications of space were not sufficiently considered at the beginning of the space era, some of the predominant risks currently extend into the commercial sphere. These risks must be considered to ensure the resilience of connected CIs in outer space. Security is a vital issue in the cyber and space domains and should be considered in every phase of a space system's life cycle, from the development and manufacturing of space assets to their deployment and end of life. This involves CI in several sectors, each of which exhibits different but interrelated risks. For example, telecommunications and location systems increasingly require the use of CI, which creates a fragile interdependence that is extremely vulnerable to threats. This paper underlines the importance of recognising space systems as CI and emphasises the need for a better integration of these assets in a system-of-systems analysis. The consequences of global satellite disruption on terrestrial CI are used to support this view. In such a disruptive scenario, mitigation measures based on in-orbit servicing or responsive space capabilities, for example, would allow CI to be restored to first ensure national security followed by commercial activities. Moreover, this paper provides an overview of the legal and policy aspects of using space systems’ capabilities in CI to better understand their implications and encourage the development of recommendations.

Redundant Space Manipulator Autonomous Guidance for In-Orbit Servicing via Deep Reinforcement Learning

The application of space robotic manipulators and heightened autonomy for In-Orbit Servicing (IOS) represents a paramount pursuit for leading space agencies, given the substantial threat posed by space debris to operational satellites and forthcoming space endeavors. This work presents a guidance algorithm based on Deep Reinforcement Learning (DRL) to solve for space manipulator path planning during the motion-synchronization phase with the mission target. The goal is the trajectory generation and control of a spacecraft equipped with a 7-Degrees of Freedom (7-DoF) robotic manipulator, such that its end effector remains stationary with respect to the target point of capture. The Proximal Policy Optimization (PPO) DRL algorithm is used to optimize the manipulator’s guidance law, and the autonomous agent generates the desired joint rates of the robotic arm, which are then integrated and passed to a model-based feedback linearization controller. The agent is first trained to optimize its guidance policy and then tested extensively to validate the results against a simulated environment representing the motion synchronization scenario of an IOS mission.

Mission analysis and guidance and control for the SpEye inspection CubeSat

The space community is moving forward with the development of in-orbit servicing and removal technologies to enable the circular economy in space and improve future space missions’ scientific and commercial return and space environment exploitation. The application of nanosatellites to carry out proximity operations presents an additional opportunity to support various novel and cost-effective distributed mission architectures. The SpEye CubeSat mission, funded by the Agenzia Spaziale Italiana in the framework of the Alcor Program, aims at demonstrating inspection and rendezvous guidance navigation and control capabilities of a nanosatellite in close-proximity of the satellite carrier in a low Earth orbit environment. This paper focuses on the design of the SpEye mission and on the guidance and control strategies to enable its technological demonstrations. Particular attention is placed on the safety aspects of trajectory design, considered of paramount importance for the robust autonomous operations of a low-cost CubeSat in proximity to another satellite.

Dynamic Modeling and Improved Nonlinear Model Predictive Control of a Free-Floating Dual-Arm Space Robot

With the increasing demand for space missions, space robots have become the focus of research and attention. As a typical representative, the free-floating dual-arm space robot has the characteristics of multiple degrees of freedom, a floating base, and dynamic coupling between the manipulator and the base, so its modeling and control are very challenging. To address these challenges, a novel dynamic modeling and control method is proposed for a free-floating dual-arm space robot. First, an explicit dynamic model of a free-floating dual-arm space robot is established based on the explicit canonical multi-rigid-body dynamic modeling theory and combined with the concept of a dynamic equivalent manipulator. The establishment process of this model is not only simple and canonical to avoid the definition and calculation of many intermediate variables, but the symbolic result expression of the model also has the characteristics of iteration, which is convenient for computer automatic modeling. Next, aiming at addressing the problem of trajectory tracking and the base attitude stability of a free-floating dual-arm space robot with parameter perturbation and external disturbance, an improved nonlinear model predictive control method introducing the idea of sliding mode variable structure is proposed. Theoretical analysis shows that the proposed controller has better robustness than the traditional nonlinear model predictive controller. Then, an in-orbit service task is designed to verify the effectiveness of the proposed dynamic modeling and control strategy of the free-floating dual-arm space robot. Finally, the dynamic modeling and control methods proposed are discussed and summarized. The proposed methods can not only realize the tracking of the desired trajectory of the arms of the free-floating space robot, but can also realize the stable control of the base of the free-floating space robot. This paper provides new insights into the difficult problems regarding the dynamics and control of free-floating dual-arm space robots.

Guidance and Control for Safe Contactless Plume Impingement Operations to Detumble an Uncooperative Spacecraft

In recent years, the interest in proximity operations to uncooperative and non-collaborative objects has been growing and and demanding for specific technology advances to tackle these challenging cases of in-orbit servicing and removal missions. Indeed, these architectures hold a crucial role in guaranteeing future sustainable and efficient space operations. One of the main challenges of conducting robotic operations with a chaser in close proximity to an uncooperative object stems from its rotational motion. A tumbling motion of a large target object may require a costly and complex synchronisation of the servicer relative trajectory to the capture point and hinder the safety of operations due to rotating appendages. In this paper, the plume impingement strategy is employed to control the target’s tumbling motion in a contactless fashion, thus guaranteeing feasible approach and capture operations. Specifically, guidance and control strategies to be employed during this delicate and complex operation are devised, focusing on improving the safety of the trajectory while maximising the efficiency of the impingement effect during proximity flight. Simulations discuss the detumbling of a satellite of a large constellation, critically comparing delta-v cost, trajectory safety and overall time of operations.

COSMIC: a UK Active Debris Removal Mission

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

Impact of Haptic Feedback in High Latency Teleoperation for Space Applications

Remote manipulation is a key enabler for upcoming space activities such as in-orbit servicing and manufacture (IOSM). However, due to the large distances involved, these systems encounter unavoidable signal delays which can lead to poor performance and users adopting a disjointed, ‘move-and-wait’ style of operation. We use a robot arm teleoperated with a haptic controller to test the impact of haptic feedback on delayed (up to 2.6 s: Earth-Moon communications) teleoperation performance for two example IOSM-style tasks. This user study showed that increased latency reduced performance in all of metrics recorded. In real-time teleoperation, haptic feedback showed improvements in success rate, accuracy, contact force, velocity, and trust, but, of these, only the improvements to contact forces and moving velocity were also seen at higher latencies. Accuracy and trust improvements were lost, or even reversed, at higher latencies. Results varied between the two tasks, highlighting the need for further research into the range of task types to be encountered in teleoperated space activities. This study also provides a framework by which to explore how features other than haptic feedback can impact both performance and trust in delayed teleoperation.

Real-time high-precision baseline measurement of satellite formation flying based on GNSS

With the establishment of the Chinese space station, a series of space science missions will be conducted in its vicinity. One of the extended tasks for the in-orbit service of space station is the formation flying of small satellites centered around the space station. Satellite formations can perform simultaneous three-dimensional observations of the space station, generating three-dimensional images and monitoring and assessing the status of critical components of the space station. The real-time and accurate relative position measurement is one of the key issues in formation flying. It is a fundamental prerequisite for maintaining and reconfiguring formation configurations, collision avoidance and safety assurance. GNSS-based relative positioning is a low-cost and high-precision measurement method, which is not constrained by light, weather, or relative attitude of satellites. This study introduces a novel approach to determine the relative position of satellites based on single-epoch Global Navigation Satellite System (GNSS) carrier phase difference measurements. Unlike traditional methods, the proposed technique eliminates the need for precise ephemeris and clock bias files and does not require historical observation data. The algorithm avoids the complexity associated with full cycle ambiguity jumps, facilitating real-time, high-precision calculations of relative position baseline vectors. Special attention is given to the influence of Geostationary Earth Orbit (GEO) satellites in the BeiDou Navigation Satellite System (BDS), and measures are taken to mitigate their impact on measurement accuracy by adjusting their observation weights. Our newly developed GNSS-based real-time measurement module, designed for high-quality GNSS signal reception and data communication, was tested on terrestrial and simulated low-orbit platforms. Remarkably, over baselines ranging from 10 m to 9.3 km, while traditional pseudorange differential measurements showed errors up to 1.5571 m, our proposed method consistently held errors under 5 cm and ensured computational speeds within 0.1 s per epoch. High-dynamic zero-baseline tests further validated its potential, with errors less than 1 cm. The innovations encapsulated in this work, resonating with the evolving trends of miniaturized and scalable satellites, present a cost-efficient and real-time solution for inter-satellite relative position measurement. This promises a new horizon in satellite formation technology, with future endeavors focusing on on-orbit experiments.

Equivalent Continuum Modeling for Flexible Slender Quadrilateral Truss Structure

A space in-orbit service simulation experiment platform is a type of equipment platform that allows spacecraft such as satellites and deep-space explorers to be adequately ground tested before launch. The function of the crane system is to drive the target spacecraft to perform a large-scale movement. This study focuses on the dynamics of a space in-orbit service simulation experiment platform with suspension rope and column quadrilateral truss structure as connecting devices. A space in-orbit service simulation experiment platform with a column quadrilateral truss structure as a connecting device is studied, modeled as a crane system–column quadrilateral truss structure–target spacecraft system. For the column quadrilateral truss structure, the equivalent beam model is used to make it equivalent based on the Timoshenko beam theory. The required equivalent stiffness parameters are determined and adjusted. The relative error between the finite element model and the corrected equivalent beam model of the column quadrilateral truss structure is no more than 4.7%. The results indicate that the accuracy of the modified equivalent beam model is sufficient. The improved equivalent beam model has excellent precision according to numerical calculations, and the derived equivalent stiffness parameters may be employed directly in dynamic modeling.

PROTECTION OF THE SPACE ENVIRONMENT AND SUSTAINABLE DEVELOPMENT AS A PARADIGM FOR THE DEVELOPMENT OF SPACE LEGISLATION

Managing human activity in outer space requires a mixture of tools, including technology, economics, and law. Though technology and economics are of prime importance, the space sector needs a clear, coherent, and adequately granular regulatory environment that ensures its sustainable development and also serves sustainability on Earth. No doubt the law can be a tool for introducing sustainability into the space sector’s daily life. To serve as such, law should be almost as dynamic and agile as the space activity and space environment. The space law should not only be descriptive, but it should also address new concepts such as in-orbit servicing, asteroid mining, etc. By doing so, it should also embrace the technical aspects of space activities even if they are not mandatory by international law. The lawmakers, especially national legislators, must also not be afraid to tackle new areas. The primary duty of national governments is to enhance safety and minimize risk in all, traditional and emerging space ventures, both in material and financial contexts that do not only directly affect their citizens and their assets, but also the environment, which obviously serve the entire society in an inclusive way and on a long-term basis. The purpose of this paper is to provide a voice in the discussion on the concept of sustainable development of space activities and suitability of the existing space regulatory framework. In order to draw some conclusions, it seems necessary to analyse the notion of sustainability against the existing legal framework, so as to state whether it is still up to date in this respect and whether it may contribute to materializing the sustainable development of the space sector. In particular, it is interesting to consider whether the liability regime, including the notion of damage and prerequisites of claims for compensation as adopted in the Liability Convention may still serve its purpose and answer the needs of the shift in the priorities of space exploration. Finally, I intend to consider the possibility of drawing on principles from other branches of law, including in particular, environmental law and insurance law and practice, in order to build legal mechanisms to implement the demands of sustainable development of space. Thus, among other issues, the topic of space environmentalism as well as the coherence of space and earth sustainability instruments will be analysed.

Sustainable management of space activity in low Earth orbit

ABSTRACT This paper extends the analysis initiated by Rouillon [2020. “A Physico-economic Model of Low Earth Orbit Management.” Environmental and Resource Economics 77 (4): 695–723. https://doi.org/10.1007/s10640-020-00515-z] of the externality caused by space debris. Satellite operators make choices about the design and launch of satellites, while in-orbit servicing firms supply efforts to remove space debris. Focusing on the long-term orbital state, we compare two management regimes. The open access equilibrium occurs when the orbit is a common resource. The optimal policy maximizes the net present value generated periodically by the space industry. We investigate economic instruments capable of effectively regulating space activity. We show that the combination of an ad valorem tax, a launch tax, and a market for removal effort certificates can provide the right incentives. A numerical application using a realistic calibration illustrates our results.