Servicing Spacecraft Research Articles

Laser ablation induced impulse study for removal of space debris mission using small satellite

In recent years, many plans have arisen for building constellations in low Earth orbit, some of which have already provided commercial services. The number of satellites that form these constellations will exceed 10^4, and a number of these could become space debris due to accidental failure, leading to serious problems for human activities in space. Laser ablation-induced propulsion achieved by remote irradiation from the service spacecraft has been proposed as one effective method to remove such space debris and it involves effectively generating a propulsion impulse from a laser. Because most of the high-power lasers currently utilized in space applications are Nd:YAG lasers, in this study, we evaluate the characteristics of second harmonic generation (SHG), which can be generated using nonlinear crystals. The momentum coupling coefficient may be dependent on the irradiated laser wave length which has a significant difference in the ablation process such as plasma generation and heating. These effects have been investigated using an impulse measurement instrumental setup with a KD*P nonlinear crystal. As an efficient impulse generation method, the irradiation of the fundamental and SHG beams of the Nd:YAG laser at the same point was found to be more effective than the fundamental beam with the same total energy. SHG does not require additional power-consuming equipment such as additional exciters or amplifiers, but requite temperature-controlled nonlinear crystals, and impulses can be increased with minimal additional power. It turned out to be advantageous for space applications, which will require minimum power operation. Additionally, we found an additional nonlinear laser-induced impulses through the interaction of the beams.

Served space: new achievements and perspectives

The number of works aimed at developing technologies for services in space has increased significantly over the past five years. In addition to such industrial giants as Orbital-ATK, Northrop Grumman, MDA, Maxar Technologies, startups are also entering the service market that develop and demonstrate practically operating technologies. Given this trend, it is expected that maintenance in space will become a hot topic over the next few years. The article discusses the designed and operating service spacecraft of foreign countries, the state and directions of their development. Brief characteristics and capabilities of service spacecraft are given. The directions of solving the main tasks for the design and manufacture of promising service spacecraft are outlined. Satellites MEV-1 and MEV-2, manufactured by Northrop Grumman, ELSA-d, manufactured by Astroscale and SSTL, and See also OSAM-1 by Maxar Technologies, which allows robotic refueling in space and demonstrates the possibility of constructing large structures in space without direct human involvement. The results of a study carried out using available Internet sources are summarized and presented in this material. The purpose of the article is to analyze the need, ways and methods of development of services, to assess the prospects of the technologies used.

Space debris removal – Review of technologies and techniques. Flexible or virtual connection between space debris and service spacecraft

The term “space debris” refers to spacecraft not removed from orbit at the end of their service life, upper stages in the geostationary orbit region, as well as to the fragments of spacecraft and upper stages formed as a result of deliberate or accidental collision of spacecraft and upper stages with each other or with natural space debris.The problem of removing space debris from outer space is a global problem. Many countries are realizing projects on space debris cataloging, various technical means are being studied for space debris removal into graveyard orbits with parameters agreed upon by the international community. Various countries conducting space exploration have adopted special standards and guidelines for preventing the space debris formation [1,2,3,4].The report [5] emphasizes that contamination of the near-Earth space is growing steadily. The probability of spacecraft collisions with each other is significantly increasing. This can lead to the functioning spacecraft characteristics degradation and even to complete loss of performance.The article presents a brief overview of the methods and techniques that can be used to space debris removal into disposal orbits using flexible or virtual connection between space debris and service spacecraft.

Angular Trajectory Design for MR-SPS Using Bezier Shaping Approach

Solar power satellite (SPS) is a kind of large-scale on-orbit servicing spacecraft collecting solar energy in space and transmitting energy to the earth. The solar arrays of the SPS must point to the sun to collect enough solar energy and the antenna must point to the rectenna on the ground to transmit energy. But due to the limitation of the control effort, accurate solar and earth orientation may not be achieved. This paper focuses on the MR-SPS, and establishes the attitude kinematics and dynamics model of a MW-level MR-SPS. Angular trajectory based on Bezier shaping approach is generated at different time of a year to satisfy the control constraints. The simulation results demonstrate the effectiveness of the proposed method. Even if the control torque is limited to a small amount, the optimal angular trajectory can still ensure high average energy receiving efficiency.

Tube-Based Model Predictive Control with Uncertainty Identification for Autonomous Spacecraft Maneuvers

Autonomous spacecraft must be robust toward uncertainty and disturbances in the system while achieving required levels of performance. As an example, robotic servicing spacecraft must intercept target objects with potentially unknown dynamic properties during active debris removal efforts. This work presents tube-based model predictive control (MPC) with uncertainty identification as a strategy to enhance performance while maintaining robustness in autonomous maneuvers. The proposed algorithm, which is an extension of the standard tube-based MPC framework, measures and predicts the exogenous input to the system (i.e., the uncertainty) online. This in turn enables the robust tube to be shrunk and grown appropriately as the trajectory progresses in both predicted time and actual time. The algorithm is demonstrated in a simulated intercept maneuver with a tumbling target whose inertia tensor is uncertain. Results indicate two improvements over the standard tube-based algorithm: first, better performance is obtained when the initial exogenous input bounds are overconservative, and, second, there is greater flexibility in encouraging robustness when the exogenous input bounds are overly optimistic since the robust tube is updated online. As such, tube-based MPC with uncertainty identification represents an incremental step in enhancing the flexibility of autonomous spacecraft in addressing uncertain scenarios and environments.

Model predictive control for close-proximity maneuvering of spacecraft with adaptive convexification of collision avoidance constraints

This study investigated model predictive control (MPC) for close-proximity maneuvering of spacecraft. It is essential for a designed MPC to effectively handle collision avoidance between the servicer spacecraft and the client spacecraft, especially while the client is rotating. The rotating motion of the client leads to dynamic changes in the collision avoidance constraints, which increases the difficulty of optimizing the control input in the MPC framework. Therefore, this study presents a method to improve the performance and computational efficiency of MPC for rendezvous and docking with a nonrotating or rotating client. An ellipsoid is adopted to model the client’s keep-out zone (KOZ). Given the spherical KOZ of the servicer, an expanded ellipsoid is introduced to describe the KOZ for the center of mass of the servicer and modeled as a nonlinear constraint. The linearization method for reference points located at the expanded ellipsoid is adopted to convexify the nonlinear constraints. The reference points are adaptively determined according to the positions of the servicer, client, and expanded ellipsoidal KOZ. The resulting hyperplanes are then used to describe the collision avoidance constraints. By utilizing the aforementioned strategies, combined with the calculated reference points, an adaptive convex programming algorithm suitable for real-time implementation of MPC is derived. The performance of the proposed method is demonstrated through numerical simulations.

3D Reconstruction Method of Space Target on Optical Images with Wide Baseline via Neural Radiance Field

3D reconstruction of space targets using optical measurement data is an important topic in the field of space surveillance and spacecraft service in orbit. The core of current mainstream 3D reconstruction methods is to establish feature association between optical images. In space-based optical imaging scenes, the texture of target region is missing and the range of view is large, which causes great difficulties in feature extraction and matching of image sequences. Neural radiance field technology does not need to extract explicit features, and its implicit expression of 3D scenes has great potential for solving reconstruction problems in weak texture and broad baseline cases. Therefore, a novel 3D reconstruction method for a sequence of images based on neural radiance field is proposed. The proposed method breaks through the limitation of traditional 3D reconstruction methods which rely on rich texture and narrow baseline image sequences. Simulation experiments show that compared with the existing methods for space target images with weak texture and wide baseline, our method performs better in terms of accuracy and completeness.

Quick-response attitude takeover control using multiple servicing spacecraft based on inertia properties identification

Multi-spacecraft is essential to on-orbit servicing (OOS) which leads to spacecraft life prolongation thus reducing space debris. However, the abrupt change of inertia parameters caused by the attachment of each servicing spacecraft is a critical obstacle to the stable and high-accuracy attitude takeover control of a target spacecraft during the entire servicing process using multiple servicing spacecraft. Therefore, a quick-response attitude takeover control method based on inertia properties identification is proposed in this paper. Combining the Euler dynamical equations of combined spacecraft with space environment moment model, a novel iterative identification equation integrating inertia matrix is established to eliminate ill-conditioned identification and realize the precise identification of inertia parameters using only single sampling data for each update. With the quickly and precisely estimated inertia parameters, a Lyapunov-based attitude controller and an optimal torque allocation method are designed to actualize the high-accuracy and globally stable attitude takeover control with the minimum energy consumption. The proposed method can actualize the quick-response and stable attitude takeover control with low computational cost, even at the moment of attachment of servicing spacecraft. Hence, it is greatly appropriate for the OOS missions with multiple servicing spacecraft. The ground experiments and numerical simulations were conducted for demonstrating the feasibility and effectiveness of the proposed method. The experiment result indicated that the trajectory tracking error could converge to ±0.02° and ±0.02°/s and the parameters identification error was less than 5.5%.

Scheduling Optimization of Multiple Hybrid-Propulsive Spacecraft for Geostationary Space Debris Removal Missions

To efficiently implement space debris removal missions on geostationary Earth orbit (GEO), a scheduling optimization scheme of multiple hybrid-propulsive servicing spacecraft (SSc) is proposed. In this scheme, a many-to-many task allocation coding model is established to formulate the removal sequences of debris targets with respect to different SSc. And a hybrid-propulsive orbit transfer strategy is developed to implement the debris removal maneuvers to save the propellant consumption and removal time simultaneously via using both electric and chemical propulsion systems. Then, the multiple GEO space debris removal scheduling optimization problem is formulated to minimize the total propellant consumption by exploring the optimal removal sequences and orbit maneuver parameters, subject to the available velocity increment, removal time, and many-to-many task allocation constraints. To effectively solve the scheduling optimization problem involving discrete-continuous mixed variables, a clustering based adaptive differential evolution algorithm with potential individual reservation (CADE-PIR) is proposed. In CADE-PIR, the k-means clustering method and potential individual reservation mutation strategy are employed to promote the convergence rate and performance of exploration and exploitation. In the end, a real-world GEO space debris removal mission with multiple SSc is investigated to demonstrate the effectiveness and practicality of the proposed optimization scheme.

Time-Synchronized Tracking Control for 6-DOF Spacecraft in Rendezvous and Docking

For the short-rangerelative motion of the on-orbit service spacecraft during rendezvous and docking missions, this article improves control performance with the describable straight line convergence trajectory and reduces energy consumption by proposing and solving the spacecraft time-synchronized control problem. This problem requires that the closed-loop system of the spacecraft is finite/fixed-time stable, all nonzero elements converge synchronously, and the trajectory of the closed-loop system tends to be the describable straight line. Based on the time-synchronized stability (TSS) and fixed-time-synchronized stability (FTSS), this article proposes the TSS and FTSS controllers for the 6-degree of freedom (DOF) spacecraft to solve the problem. For the spacecraft closed-loop system under these optimization-free methods, the derivative of the state is always opposite to the direction of the state, then the system trajectory will tend to a straight line, and the redundant motion components in the direction orthogonal to the state are significantly suppressed (performance improvement), and the excess energy loss is reduced considerably. Conversely, redundant motion components will cause excess transient motion and more energy consumption. Furthermore, this article proposes the linear combination theorem of the ratio persistence property, which further enriches the theoretical tools for the time-synchronized control method. The rigorous theoretical proof and comparative simulation verify the rationality, effectiveness, and advantages of the controllers proposed.

Multiple GEO satellites on-orbit repairing mission planning using large neighborhood search-adaptive genetic algorithm

This paper proposes a novel large neighborhood search-adaptive genetic algorithm (LNS-AGA) for many-to-many on-orbit repairing mission planning of geosynchronous orbit (GEO) satellites with mission deadline constraint. In the many-to-many on-orbit repairing scenario, several servicing spacecrafts and target satellites are located in GEO orbits which have different inclination, right ascension of ascending node (RAAN) and true anomaly. Each servicing spacecraft need to rendezvous with target satellites to perform repairing missions under limited fuel. The mission objective is to find the optimal servicing sequence and orbit rendezvous time of each servicing spacecraft to minimize total Δv cost of all servicing spacecrafts with all target satellites repaired. Firstly, a time-dependent orbital rendezvous strategy is proposed, which can handle the mission deadline constraint. Besides, it is also cost-effective compared with the existing strategy. Based on this strategy, the many-to-many on-orbit repairing mission planning model can be simplified to an integer programming problem, which is established based on the vehicle routing problem with time windows (VRPTW) model. In order to efficiently find a feasible optimal solution under complicated constraints, a hybrid adaptive genetic algorithm combining the large neighborhood search procedure is designed. The operations of “destroy” and “repair” are used on the elite individuals in each generation of the genetic algorithm to enhance local search capabilities. Finally, simulation results under several different scenarios show the effectiveness and superiority of the presented algorithm and orbital rendezvous strategy.

Autonomous obstacle avoidance strategies in the mission of large space debris removal using potential function

Debris removal problem has become a consensus of international communities with the dramatically increase of space debris. When the service spacecraft (Servicer) carries out debris removal operations, there may exist collision threaten from other small objects which fly around the target debris. In this paper, autonomous collision avoidance strategies using improved potential function are studied, which drive the Servicer to rendezvous with the large debris and avoid obstacles around the trajectory. Firstly, the repulsive potential for static obstacles is constructed based on the relative position vector. Considering the necessary of avoidance of dynamic obstacles, the relative velocity vector between the Servicer and dynamic obstacles in space is introduced to design the repulsive potential for dynamic obstacles. Also, the corresponding control law is derived to drive the Servicer to approach the large debris. Finally, numerical simulations are performed to validate the effectiveness and stability of the obstacle avoidance strategy for debris removal.

On-ground validation of a CNN-based monocular pose estimation system for uncooperative spacecraft: Bridging domain shift in rendezvous scenarios

The estimation of the relative pose of an inactive spacecraft by an active servicer spacecraft is a critical task for close-proximity operations, such as In-Orbit Servicing and Active Debris Removal. Among all the challenges, the lack of available space images of the inactive satellite makes the on-ground validation of current monocular camera-based navigation systems a challenging task, mostly due to the fact that standard Image Processing (IP) algorithms, which are usually tested on synthetic images, tend to fail when implemented in orbit. In response to this need to guarantee a reliable validation of pose estimation systems, this paper presents the most recent advances of ESA’s GNC Rendezvous, Approach and Landing Simulator (GRALS) testbed for close-proximity operations around uncooperative spacecraft. The proposed testbed is used to validate a Convolutional Neural Network (CNN)-based monocular pose estimation system on representative rendezvous scenarios with special focus on solving the domain shift problem which characterizes CNNs trained on synthetic datasets when tested on more realistic imagery. The validation of the proposed system is ensured by the introduction of a calibration framework, which returns an accurate reference relative pose between the target spacecraft and the camera for each lab-generated image, allowing a comparative assessment at a pose estimation level. The VICON Tracker System is used together with two KUKA robotic arms to respectively track and control the trajectory of the monocular camera around a scaled 1:25 mockup of the Envisat spacecraft. After an overview of the facility, this work describes a novel data augmentation technique focused on texture randomization, aimed at improving the CNN robustness against previously unseen target textures. Despite the feature detection challenges under extreme brightness and illumination conditions, the results on the high exposure scenario show that the proposed system is capable of bridging the domain shift from synthetic to lab-generated images, returning accurate pose estimates for more than 50% of the rendezvous trajectory images despite the large domain gaps in target textures and illumination conditions.

Resource-Constrained Constellation Scheduling for Rendezvous and Servicing Operations

This paper addresses the rendezvous and proximity operations constellation assignment problem by developing a responsive utility function for tasking a constellation of low Earth orbit satellites to several spacecraft servicing tasks. The paper develops the utility function that considers both score of servicing resident space object spacecraft in conjunction with the associated cost. A highly capable and operationally relevant task allocation method, called the consensus-based bundle algorithm, is leveraged for distributed processing and task allocation. This paper demonstrates that this methodology provides a robust technique for rendezvous and proximity operations scheduling within resource-constrained agent constellations.

Viability of On-Orbit Servicing Spacecraft to Prolong the Operational Life of Satellites

This research paper is an extensive literature review and data analysis on the viability of on-orbit servicing (OOS) spacecraft to prolong the operational life of satellites. A systematic analysis of the Union of Concerned Scientists (UCS) Satellite Database found that Sentinel 1A and 1B orbit at approximately the same height as Landsat 7 (∼700 km) and have a collective propellant mass (MProp) of 308 kg which is less than Landsat 7′s 544 kg. The On-orbit Servicing, Assembly and Manufacturing (OSAM) 1 spacecraft has the capacity to refuel both Sentinels as an alternative option to Landsat 7. For OSAM 1 to refuel Landsat 7, it is $261.91 M cheaper than replacement and the more economically viable and sustainable option. OSAM 1 will mitigate the immediate problem of space debris. However, a new model of standardized cooperative satellites with external plug-in interfaces could facilitate both planned and unplanned upgrades, modifications and repairs for changing missions and technology updates for the future.

Control of an Orbital Manipulator with Reaction Wheels for On-orbit Servicing

In on-orbit servicing missions, a spacecraft equipped with a manipulator arm grasps a client satellite. Afterwards, the momentum-dumping phase follows and the manipulator can be utilized for servicing tasks. Once the momentum has been dumped, a desired manipulator configuration and base attitude may be needed for initializing a servicing phase such as berthing. The proposed approach prioritizes the attitude maintenance of the servicer spacecraft, and reconfigures the manipulator arm with the grasped client satellite in the nullspace of the servicer's attitude. The approach utilizes the redundancy in rotational degrees of freedom, provided by reaction wheels, to decouple the manipulator reconfiguration task from the attitude of the servicer-base. The proposed controller shows convergence of the attitude and joint-level task, independent of kinematic singularities of the manipulator arm. Additionally, the problem of speed saturation of the reaction wheels is tackled by increasing the damping torques as a function of the wheel speed. Simulation results verify the effectiveness of the proposed control approach.

Two-level Game Based Multi-arm On-orbit Servicing Spacecraft Path Planning

针对在轨服务多臂航天器系统高精度的位姿协同要求及其运动过程中的避障约束，提出一种基于机械臂末端（腕关节）和肘关节的双层博弈多臂路径规划方法。研究建立了多臂运动学模型，在博弈论基础上建立多臂的博弈模型；给出了双层博弈的基本算法流程及其纳什均衡解的求解策略；以动目标多臂围捕为场景进行仿真分析，验证所提出算法末端精确跟踪抓取和肘部避障能力的有效性和实用性。所得结果可为多臂在轨服务航天器的智能化路径规划与控制提供新的解决方案。

Direct visual servoing and interaction control for a two-arms on-orbit servicing spacecraft

A direct visual-servoing algorithm for control of a space-based two-arm manipulator is proposed in this paper. The algorithm can be utilized in a two-arm manipulators configuration, where one of the arms performs the manipulation and the second arm is dedicated to the observation of the target zone of manipulation. The algorithm utilizes both visual features extracted from onboard cameras and force and torque measured at the manipulator's end-effector to control the movements of the manipulator during on-orbit servicing operations. The algorithm takes into account the relative dynamics of the bodies involved, it relies on images taken independently from de-localized cameras, e.g. at the end-effector of a second manipulator, and it integrates an impedance control for the compensation of eventual contact reactions when the end effector touches and operates the target body. The analytical derivations demonstrate the stability of the algorithm and incorporate an impedance compliance strategy into an optimal framework formulation. Simulations results in two different scenarios have been presented to show the adequate behavior of the presented approach in on-orbit-servicing operations.

Мінімаксна модель транспортних операцій екстреного орбітального обслу-говування на сонячно синхронних орбітах

Heliosynchronous orbits are attractive for space system construction. As a result, the number of spacecraft operating therein is constantly increasing. To increase their efficiency, timely on-orbit servicing (both scheduled and emergency) is needed. Emergency on-orbit servicing of spacecraft is needed in the case of unforeseen, emergency situations with them. According to available statistical estimates, emergency situations with serviced spacecraft are not frequent. Because of this, serviced spacecraft must be within the reach of a service spacecraft for a long time. In planning emergency on-orbit servicing, the following limitations must be met: the time it takes the service spacecraft to approach any of the serviced spacecraft must not exceed its allowable value, and the service spacecraft’s allowable energy consumption must not be exceeded. This paper addresses the problem of searching for emergency on-orbit servicing that would be allowable in terms of time and energy limitations and would meet technical and economical constraints. The aim of this work is to develop a mathematical constrained optimization model for phasing orbit parameter choice, whose use would allow one to minimize the maximum time of transport operations in emergency on-orbit servicing of a spacecraft group in the region of heliosynchronous orbits. The problem is solved by constrained minimax optimization. What is new is the formulation of a minimax (guaranteeing) criterion for choosing phasing orbit parameters that minimize the maximum time of emergency on-orbit servicing transport operations. In the minimax approach, the problem is formulated as the problem of searching for the best solution such that the result is certain to be attained for any allowable sets of indeterminate factors. The proposed mathematical model may be used in planning emergency on-orbit service operations to minimize the maximum duration of emergency on-orbit servicing transport operations due to a special choice of the service spacecraft phasing and parking orbit parameters.

Control of a service satellite during its mission on space debris removal from orbits with high inclination by implementation of an ion beam method

The largest population of space debris is observed in the low-Earth-orbit region with altitudes of 600–1000 km and inclinations of 80–100°. As follows from the predictive calculations, space debris removal from this region exactly is of the first priority. For this reason, our article discusses the problems of controlling the motion of service spacecraft – space debris object cluster when the space debris object is removed from a low orbit with high inclination. In the conceptual design of the spacecraft presented hereinafter, the electric propulsion system contains two electric propulsion thrusters of stationary plasma thruster type, each of which is mounted with the possibility of independent rotation respect to two mutually perpendicular directions. An ion beam injector forms an ion beam with 65 mN of thrust. Spacecraft motion control, including the thrust vector control, is provided by coordinated rotation of thrusters. For such concept, a strategy and an algorithm for controlling the motion of the spacecraft center of mass are proposed, which are based on the control of the spacecraft lateral and longitudinal motion that is understood as the control of the relative distance between the spacecraft and the space debris object. The strategy of spacecraft lateral motion control assumes that due to the thrusters' rotation the spacecraft should be displaced in such a way that the vector of the relative range between the spacecraft and the space debris object coincides with the direction of the transversal of the orbital coordinate system. For the practical implementation of the control, an algorithm has been developed for controlling the thrusters' rotation to create the required values of the spacecraft acceleration projections. The mathematical model includes the equations of motion of the spacecraft center of mass taking into account the aerodynamic deceleration. The solar panels' orientation to the Sun is provided by the spacecraft roll rotation relative to its longitudinal axis and turning the solar panels relative to their axis of rotation. The change in the ion beam momentum transfer is considered using a simple simulation model. Mathematical modeling was performed for the following parameters of the initial orbit: altitude: 800 km; eccentricity: 0.0005; and inclination: 900. For the proposed control algorithm, a range of possible thrust of a single thruster was 51–60 mN. The simulation results show that the proposed control can be used to remove space debris object from low orbits with high inclination, taking into account the roll spacecraft rotation to keep the solar panels’ orientation to the Sun.