Capture Mission Research Articles

Compliance resistance collision control for operating a space robot to capture a non-cooperative spacecraft

Collision between the grasper and the target is unavoidable in robotic-arm-based non-cooperative spacecraft capture missions, potentially leading to various adverse effects. For instance, the impact of collision could result in a post-collision separation between the grasper and the target. Additionally, a significant impact can damage the space robot. Both post-collision separation and damage to the space robot result in the failure of the capture mission. To improve the success rate of capturing, this paper first proposes a new one-dimension (1-D) collision control method to reduce adverse effects yielded by collisions, which is named Compliance Resistance Control (CRC). Unlike existing methods, CRC aims to prevent post-collision separation while reducing the maximum contact force. Theoretical analysis validates that this method can achieve the desired objective. Then, to extend the applicability of this method to three-dimensional (3-D) capture missions, we introduce a position-based CRC control scheme. In addition, an output torque correction algorithm is designed to enhance motor response speed. Finally, numerical simulation results demonstrate the effectiveness and robustness of this strategy across various capture scenarios.

Estimation of Full Dynamic Parameters of Large Space Debris Based on Rope Net Flexible Collision and Vision

The identification of space debris’s dynamic parameters is a prerequisite for detumbling and capture operations. In this paper, a novel method for identifying dynamic parameters based on the rope net flexible collision and vision data is proposed, which combines the advantages of full dynamic parameter estimation (contact method) and safety (non-contact method). The point cloud data before and after collision is obtained by LiDAR, and the transformation matrix of point clouds and debris motion data are calculated by point cloud registration. Before the collision, using the motion model-based optimization, the real-time position of the debris center of mass is estimated. And the transformation matrix between visual and debris-fixed coordinates are calculated by the mass center position and transformation matrix of the point cloud. Then, using the debris dynamic model and parameters’ characteristics, the normalized dynamic parameters are estimated. An identification method of net node position changes based on the flexible collision characteristics of rope nets is proposed, which is used to obtain the momentum of the rope net after the collision. Based on the conservation of linear momentum and angular momentum of the satellite-net system, the true values of the mass and the principal moment of inertia of the debris are estimated. The true values of the kinetic energy and momentum can be obtained by substituting the true values of the principal moment of inertia into the normalized parameters, and the full dynamic parameters of large space debris is estimated. Simulations of identifying full dynamic parameters have been performed; the results indicate that this method can provide accurate and real-time true values of dynamic parameters for the detumbling and capture mission.

Development and evaluation of a space robot prototype equipped with a cable-driven manipulator

This research focuses on developing and evaluating a free-flying space robot equipped with a cable-driven manipulator and an adaptive gripper. First, a transmission joint comprising a pair of gears and pulleys is designed and actuated by motors located in the first link of the manipulator. Afterward, based on the kinematics and dynamics models of the robot, a mission distribution control scheme is proposed for the robot to drive its end-effector to achieve the desired position and attitude for capturing space targets. Furthermore, exploiting this strategy, considerable comparison simulations between two space robots equipped with a traditional manipulator and a cable-driven arm are conducted. Wherein, the goal position and attitude are selected through a uniform sampling method. For the same capture mission, energy consumptions of the base and manipulator as well as state errors of the base are taken as cost functions for performance evaluation. Finally, a planar target capture case study using the adaptive gripper and a spatial motion test with the help of an air-bearing simulator are carried out to demonstrate the efficiency of the presented cable-driven space robot.

A grasp planning algorithm under uneven contact point distribution scenario for space non-cooperative target capture

The contact point configuration should be carefully chosen to ensure a stable capture, especially for the non-cooperative target capture mission using multi-armed spacecraft. In this work scenario, the contact points on the base and on the arms are distributed on the opposite side of the target. Otherwise, large forces will be needed. To cope with this problem, an uneven-oriented distribution union criterion is proposed. The union criterion contains a virtual symmetrical criterion and a geometry criterion. The virtual symmetrical contact point criterion is derived from the proof of the force closure principle using computational geometry to ensure a stable grasp, and the geometry criterion is calculated by the volume of the minimum polyhedron formed by the contact points to get a wide-range distribution. To further accelerate the optimization rate and enhance the global search ability, a line array modeling method and a continuous-discrete global search algorithm are proposed. The line array modeling method reduces the workload of calculating the descent direction and the gradient available, while the continuous-discrete global search algorithm reducing the optimization dimension. Then a highly efficient grasping is achieved and the corresponding contact point is calculated. Finally, an exhaustive verification is conducted to numerically analyze the disturbance resistance ability, and simulation results demonstrate the effectiveness of the proposed algorithms.

Neural-network-based backstepping control for the post-capture tethered space combination using HDO

In this paper, a novel neural-network-based backstepping control method is designed for the post-capture tethered space combination system subjected to multi-source disturbances and actuator saturation. To cope with the multi-source disturbances, the so-called HDO is put forward which is capable of addressing both modeled and unmodeled disturbances. These disturbances are not necessarily matched disturbances and hence the backstepping design procedure is utilized. In virtue of the radial basis function neural networks (RBFNNs), the unknown nonlinearities is estimated. Additionally, the anti-windup technique is employed to handle the actuator saturation phenomenon which is unavoidable in the post-capture tethered space combination system. Sufficient conditions are derived to guarantee that the post-capture tethered space combination system is stabilized while carrying out the non-cooperative target capture mission. Finally, a number of numerical simulations are conducted on the post-capture tethered space combination to validate the proposed methodology.

Rapid capture trajectories from parabolic orbit with modulated radial thrust

The aim of this paper is to analyze the performance of a radially-accelerated spacecraft in a capture mission scenario, in which a space vehicle transfers from a parabolic approaching trajectory of assigned semilatus rectum to a target circular orbit around a generic celestial body. The radial propulsive acceleration provided by the spacecraft propulsion system can be modulated within a suitable given range, and the radial thrust can be either inward- or outward-directed. The transfer mission performance is analyzed in an optimal framework, by minimizing the total flight time with an indirect approach. In this context, the paper proposes a semi-analytical method to reduce the computation time required to solve the optimal control problem. Using a proper description of the spacecraft dynamics in a dimensionless form, the paper reports a set of graphs and tables that allow the designer to obtain a rapid approximation of the optimal mission performance with an accuracy consistent with that of a preliminary trajectory design. Finally, the proposed approach is used to describe the minimum time capture trajectories in a mission scenario towards Ceres.

Asteroid Capture Dynamics and Control Using a Large-Scale Flexible Net

Asteroids are scientific windows for understanding the universe while having enormous economic value. Instead of merely bringing back a small sample, capturing an asteroid into earth's orbit is one of the most promising ways to explore and subsequently exploit space. In this article, the authors study the process of capturing an asteroid using a flexible net spacecraft (FNS). The net capture dynamics, comprising the net and nonlinear contact dynamics models, are constructed for the asteroid mission. The sliding mode control is applied for designing the controllers of the FNS. Numerical simulations show that the asteroid 101955 Bennu can be fully enveloped using a spider-shaped FNS around a kilometer diameter. During the capture mission, the opening area of the FNS gradually decreases, which is much smaller than the projected area of the asteroid at the end of the capture; the elongation rate of each net thread in the FNS is far less than its material's endurable value; and the actuators in the FNS have not collided with each other, thus selfdestruction does not happen. All of these results suggest the feasibility of the FNS for the asteroid capture mission.

Dynamic Closing Point Determination for Space Debris Capturing via Tethered Space Net Robot

Tethered space net robot (TSNR) is treated as one of the most promising space debris capturing methods. To perform a successful net capture mission, it is necessary to determine the net closing point for four maneuvering units to make the net fully close around the debris. In the previous studies, a fixed point (FP) is provided as the position for maneuvering units to converge. However, the FP cannot be easily given, especially for the situation that the debris does not contact in the center of the net and the debris in the state of tumbling. In this article, we propose a method to determine the “dynamic closing point” (DCP), which is a dynamic position moving with the motion of the four maneuvering units and suitable for maneuvering units to converge. First, the dynamic model of TSNR is derived. Then, the “DCP” is defined based on the position of the four maneuvering units. Taking a cylindrical target as the example, the DCP and FP are chosen as the different net closing methods to show the net closing performance of TSNR. The simulation results verify that the proposed DCP is more efficient and fuel-saving.

MROS: runtime adaptation for robot control architectures

Known attempts to build autonomous robots rely on complex control architectures, usually implemented with the Robot Operating System (ROS). Runtime adaptation is needed in these systems, to cope with component failures and with contingencies arising from dynamic environments – otherwise these affect the reliability and quality of the mission execution. Existing proposals on how to build self-adaptive systems in robotics usually require a major re-design of the control architecture and rely on complex tools unfamiliar to the robotics community. Moreover, they are hard to reuse across applications. This paper presents MROS: a model-based framework for runtime adaptation of robot control architectures based on ROS. MROS uses a combination of domain-specific languages to model architectural variants and capture mission quality concerns, and an ontology-based implementation of the MAPE-K and meta-control visions for runtime adaptation. The experiment results obtained applying MROS in two realistic ROS-based robotic demonstrators show the benefits of our approach in terms of the quality of the mission execution, and MROS's extensibility and reusability across robotic applications.

Dynamics and control of a bio-inspired Stewart platform

Collision and strong impacts take place in mission of the on orbit capture of non-cooperative spacecraft. So, it is necessary to design a vibration isolation system with efficient vibration isolation performance. A Stewart vibration isolation platform based on the bio-inspired isolation system is proposed in this paper. The characteristics of the novel bio-inspired Stewart platform realizes the vibration isolation protection of the serving spacecraft during the capture mission. The dynamic model of the vibration isolation platform is established by Lagrange's equations. The fidelity of the established dynamic model is verified via a comparison of the theoretical simulation and the ADAMS simulation. Comparisons between the presently proposed vibration isolation platform and the traditional spring-mass-damper type Stewart vibration isolation platform demonstrates the advantages of the present platform. The effects of system parameters on the isolation performance of the present platform are thoroughly investigated. The feedback linearization control method is used to control the present platform which overcomes the drift motion that occurs in the passive isolation case. The results show that the novel bio-inspired Stewart platform has excellent vibration isolation performance, which provides a promising way for the vibration isolation of the non-orbit capture mission.

A trajectory optimization method with frictional contacts for on-orbit capture

Using space robots to perform capture missions are challenging problems due to potential contacts. Most state-of-the-art techniques sidestep contacts by separating a capture mission into pre- and post-capture phases, and assuming the end-effector fixes to the target instantaneously. In this paper, frictional contacts have been taken into consideration, and a corresponding trajectory optimization method is developed. The frictional contact is formulated as two sets of complementarity constraints for the compression phase and the decompression phase. The direct method for trajectory optimization with complementarity constraints is established. The combination mechanism based on the sequential quadratic programming is proposed to solve resultant highly complex optimization problems, which can provide local optimal trajectories for space robots. The method is verified via numerical simulations of a planar dual-arm space robot capturing a spinning target, and results illustrate its great performance and potential usability on other scenarios.

Vibration suppression for post-capture spacecraft via a novel bio-inspired Stewart isolation system

In the process of on-orbit capture mission, some undesirable vibrations arising from the relative motions between the servicing spacecraft and the target are inevitable, which can make the post-capture combined spacecraft unstable or even tumbling. Therefore, suppressing post-capture vibrations is critical to mission success. In this work, a novel bio-inspired X-shape structure-based Stewart isolation platform (XSSIP) system is first proposed to install between the satellite platform and the capture mechanism. It can suppress the post-capture vibrations of a free-floating spacecraft subjected to the impulsive or periodic external forces. Beneficial nonlinear stiffness and nonlinear damping characteristics with the existence of X-shape structure can be acquired, which is helpful to achieve much better vibration isolation performance in multiple directions. Different from the traditional ground vibration isolation system, the dynamic equations of the 6-DOF under-constrained system in the weightless environment of space are established by Lagrange's principle. Influences on vibration isolation performance of the XSSIP system incurred by different structural parameters are systematically studied under either periodic or impulsive excitations. In addition, ADAMS simulation is conducted to verify the accuracy and feasibility of the theoretical model. Compared with the traditional spring-mass-damper (SMD)-based Stewart isolation platform system, the XSSIP system possesses an obvious advantage and offers a highly efficient passive way for suppressing post-capture vibrations of the floating spacecraft.

On-board passive-image based non-cooperative space object capture window estimation

This paper proposes a novel capture window estimation framework for non-cooperative space object capture mission. The proposed approach is developed by taking into account the following facts: 1) only one monocular camera onboard the capturer satellite is available; 2) the a-priori knowledge of resident space objects (RSOs) is strictly limited; 3) the capture window estimation framework is independent from the capture modes. The relative state between the observed space object and capturer is formulated in a probabilistic manner through solving the admissible region from passive-images. Then, the probability and probability rate of a target entering the capture zone are efficiently characterized, leading to a complete RSO capture window estimation architecture. Finally, the entire algorithm is validated by a Monte Carlo simulation and an experimental trial, results from which demonstrate the effectiveness of the proposed approach in terms of estimation accuracy and reliability.

Effective motion planning strategy for space robot capturing targets under consideration of the berth position

Although many motion planning strategies for missions involving space robots capturing floating targets can be found in the literature, relatively little has discussed how to select the berth position where the spacecraft base hovers. In fact, the berth position is a flexible and controllable factor, and selecting a suitable berth position has a great impact on improving the efficiency of motion planning in the capture mission. Therefore, to make full use of the manoeuvrability of the space robot, this paper proposes a new viewpoint that utilizes the base berth position as an optimizable parameter to formulate a more comprehensive and effective motion planning strategy. Considering the dynamic coupling, the dynamic singularities, and the physical limitations of space robots, a unified motion planning framework based on the forward kinematics and parameter optimization technique is developed to convert the planning problem into the parameter optimization problem. For getting rid of the strict grasping position constraints in the capture mission, a new conception of grasping area is proposed to greatly simplify the difficulty of the motion planning. Furthermore, by utilizing the penalty function method, a new concise objective function is constructed. Here, the intelligent algorithm, Particle Swarm Optimization (PSO), is worked as solver to determine the free parameters. Two capturing cases, i.e., capturing a two-dimensional (2D) planar target and capturing a three-dimensional (3D) spatial target, are studied under this framework. The corresponding simulation results demonstrate that the proposed method is more efficient and effective for planning the capture missions.

Experiments and simulation of a net closing mechanism for tether-net capture of space debris

This research addresses the design and testing of a debris containment system for use in a tether-net approach to space debris removal. The tether-net active debris removal involves the ejection of a net from a spacecraft by applying impulses to masses on the net, subsequent expansion of the net, the envelopment and capture of the debris target, and the de-orbiting of the debris via a tether to the chaser spacecraft. To ensure a debris removal mission's success, it is important that the debris be successfully captured and then, secured within the net. To this end, we present a concept for a net closing mechanism, which we believe will permit consistently successful debris capture via a simple and unobtrusive design. This net closing system functions by extending the main tether connecting the chaser spacecraft and the net vertex to the perimeter and around the perimeter of the net, allowing the tether to actuate closure of the net in a manner similar to a cinch cord. A particular embodiment of the design in a laboratory test-bed is described: the test-bed itself is comprised of a scaled-down tether-net, a supporting frame and a mock-up debris. Experiments conducted with the facility demonstrate the practicality of the net closing system. A model of the net closure concept has been integrated into the previously developed dynamics simulator of the chaser/tether-net/debris system. Simulations under tether tensioning conditions demonstrate the effectiveness of the closure concept for debris containment, in the gravity-free environment of space, for a realistic debris target. The on-ground experimental test-bed is also used to showcase its utility for validating the dynamics simulation of the net deployment, and a full-scale automated setup would make possible a range of validation studies of other aspects of a tether-net debris capture mission.

Spitzer shutdown may affect asteroid capture mission

Spitzer shutdown may affect asteroid capture mission

Terminal spacecraft rendezvous and capture with LASSO model predictive control

The recently investigated ℓasso model predictive control (MPC) is applied to the terminal phase of a spacecraft rendezvous and capture mission. The interaction between the cost function and the treatment of minimum impulse bit is also investigated. The propellant consumption with ℓasso MPC for the considered scenario is noticeably less than with a conventional quadratic cost and control actions are sparser in time. Propellant consumption and sparsity are competitive with those achieved using a zone-based ℓ1 cost function, whilst requiring fewer decision variables in the optimisation problem than the latter. The ℓasso MPC is demonstrated to meet tighter specifications on control precision and also avoids the risk of undesirable behaviours often associated with pure ℓ1 stage costs.

Lorentz-Augmented Jovian Orbit Insertion

The Lorentz force acting on a statically charged body moving with respect to a rotating magnetic field is evaluated as a means of capture into a Jovian orbit. This study offers insight into the classes of captures available as a function of the spacecraft's charge-to-mass ratio and approach conditions. A range of these parameters is simulated using low-order magnetosphere and gravity models and a bang-off controller. The results suggest that charge-to-mass ratios on the order of 0.1 C/kg are required to capture a spacecraft with a hyperbolic equatorial approach to an orbit similar to that of Jupiter's moon Europa. The Lorentz-augmented-orbit architecture is related to a similar technology: electrodynamic tethers. Using a high-order magnetic field and gravity model, we recreate a sample electrodynamic-tether Jovian capture mission using Lorentz-augmented orbits with a charge-to-mass ratio of 0.0975 C/kg over 2.5 years. We conclude that Lorentz-augmented-orbit maneuvers are capable of reducing a spacecraft's energy and eccentricity into a bounded circular Jovian orbit for typical mission requirements. A simple feasibility study suggests that Lorentz-augmented-orbit spacecraft designs capable of Jovian orbit insertion are challenging, but likely possible.

Dynamic Balance Control of Multi-Arm Free-Floating Space Robots

This paper investigates the problem of the dynamic balance control of multi-arm free-floating space robot during capturing an active object in close proximity. The position and orientation of space base will be affected during the operation of space manipulator because of the dynamics coupling between the manipulator and space base. This dynamics coupling is unique characteristics of space robot system. Such a disturbance will produce a serious impact between the manipulator hand and the object. To ensure reliable and precise operation, we propose to develop a space robot system consisting of two arms, with one arm (mission arm) for accomplishing the capture mission, and the other one (balance arm) compensating for the disturbance of the base. We present the coordinated control concept for balance of the attitude of the base using the balance arm. The mission arm can move along the given trajectory to approach and capture the target with no considering the disturbance from the coupling of the base. We establish a relationship between the motion of two arm that can realize the zeros reaction to the base. The simulation studies verified the validity and efficiency of the proposed control method.

Iterative Explicit Guidance for Low Thrust Spaceflight

A retargeting procedure is developed for use as a nonlinear low thrust guidance scheme. The selection of a control program composed of a sequence of inertially fixed thrust-acceleration vectors permits all trajectory computations to be made with closed form expressions, and allows the controls to be represented by constant parameters, thrust-acceleration vectors and thrusting times. By requiring each trajectory to be time optimal, the guidance problem is transformed into a parameter optimization problem which is solved by the conjugate gradient method. The scheme is applied to a low thrust capture mission, and the results of computer simulations are presented.