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Robotic Capture and De-Orbit of a Heavy, Uncooperative and Tumbling Target in Low Earth Orbit
Abstract
This paper presents a robotic capture concept for large spacecraft in low Earth orbit (LEO) that was developed as part of the the e.Deorbit feasibility study within the scope of the clean space initiative of the European Space Agency (ESA). The defective and tumbling satellite ENVISAT has been chosen as potential target to be captured, stabilized, and subsequently de-orbited in a controlled manner. Following a thorough target analysis including potential grasping points, a robotic capture concept was developed that is based on a 7-DoF dexterous robotic manipulator, a linear two-bracket gripper, and a clamping mechanism for achieving stiff fixation between target and chaser satellites prior to the de-tumbling and execution of the de-orbit maneuver. The robotic grasp concept includes a stereo-vision camera system featuring a visual servoing algorithm for camera-in-the-loop error correction. In addition, a platform-mounted camera system is utilized for target model building as well as relative motion and pose estimation. For concept validation, visual servoing, haptic grasp and capture simulations were performed. The task-specific kinematics of the manipulator and potential joint locks as contingency events were validated and analyzed using the method of capability maps. For the complete robotic capture maneuver, an error budget was created and evaluated. Geometric analysis and haptic grasp simulations showed that the gripper design and connected grasp approach is feasible and robust. In addition, the kinematics analysis yielded a sufficient reachability, even in the case of an improbable joint lock. FE-analyses were performed to show that a high compound stiffness can be achieved by the clamping device and that all required forces can be transmitted without damaging the target’s structure. Overall, the study showed that the capture and deorbiting of ENVISAT is feasible and robust using the developed robotic concept.
... = spacecraft mass-to-area ratio 20 = oblateness coefficient of the asteroid's gravitational field 22 = ellipticity coefficient of the asteroid's gravitational field ce = orientation of ℱ c defined in ℱ e ast = perturbation force due to asteroid gravity srp = perturbation force due to solar radiation pressure ...
... However, in all cases it is of interest to minimize the effect of the manipulator motion on the attitude of the hovering spacecraft. Employing a space-based manipulator on a free-floating system has been an area of active study for several decades [20,21], with several studies tackling the problem for manipulating and controlling uncooperative bodies (e.g., [22,23,24,25]). Moreover, it is expected that the manipulator motion will require a very short duration in order to complete its operation. ...
... There is a significant commercial boost in the in-orbit services market, which is predicted to be $1 billion by 2030 (Satellite Catapult Applications, Fair-Space and Astroscale, 2021). The candidate in-orbit missions include the following: servicing and repairing high-value space assets including operational spacecraft, life extension, refueling, orbit correction, in-space assembly of space telescopes for Earth observation and astronomical observations, space-based power generation, and active debris removal, to name a few (Oda et al., 1996;Whittaker et al., 2000;Yoshida, 2001;Friend, 2008;Shengwei, 2013;Flores-Abad et al., 2014;Jaekel et al., 2015;Lee et al., 2016;Reed et al., 2016;Medina et al., 2017;Taylor et al., 2018;Li et al., 2019;Wilde et al., 2019;Jackson et al., 2020;Nair et al., 2020;Romano, 2021;Xu, 2021). Building satellite servicing and debris removal capabilities will open up bigger and longerterm markets linked to assembly and manufacturing in space (Satellite Catapult Applications, Fair-Space and Astroscale, 2021). ...
Ground-based applications of robotics and autonomous systems (RASs) are fast advancing, and there is a growing appetite for developing cost-effective RAS solutions for in situ servicing, debris removal, manufacturing, and assembly missions. An orbital space robot, that is, a spacecraft mounted with one or more robotic manipulators, is an inevitable system for a range of future in-orbit services. However, various practical challenges make controlling a space robot extremely difficult compared with its terrestrial counterpart. The state of the art of modeling the kinematics and dynamics of a space robot, operating in the free-flying and free-floating modes, has been well studied by researchers. However, these two modes of operation have various shortcomings, which can be overcome by operating the space robot in the controlled-floating mode. This tutorial article aims to address the knowledge gap in modeling complex space robots operating in the controlled-floating mode and under perturbed conditions. The novel research contribution of this article is the refined dynamic model of a chaser space robot, derived with respect to the moving target while accounting for the internal perturbations due to constantly changing the center of mass, the inertial matrix, Coriolis, and centrifugal terms of the coupled system; it also accounts for the external environmental disturbances. The nonlinear model presented accurately represents the multibody coupled dynamics of a space robot, which is pivotal for precise pose control. Simulation results presented demonstrate the accuracy of the model for closed-loop control. In addition to the theoretical contributions in mathematical modeling, this article also offers a commercially viable solution for a wide range of in-orbit missions.
... Many dysfunctional satellites are occupying valuable orbits, and potential collisions with them might create more dangerous debris. Robotic manipulators could be the key technology to enable de-orbiting of uncooperative targets like ENVISAT, as discussed in Jaekel et al. (2015). Onorbit servicing is a promising technology to try to keep the orbits clean. ...
A frequent concern for robot manipulators deployed in dangerous and hazardous environments for humans is the reliability of task executions in the event of a joint failure. A redundant robotic manipulator can be used to mitigate the risk and guarantee a post-failure task completion, which is critical for instance for space applications. This paper describes methods to analyze potential risks due to a joint failure, and introduces tools for fault-tolerant task design and path planning for robotic manipulators. The presented methods are based on off-line precomputed workspace models. The methods are general enough to cope with robots with any type of joint (revolute or prismatic) and any number of degrees of freedom, and might include arbitrarily shaped obstacles in the process, without resorting to simplified models. Application examples illustrate the potential of the approach.
... A robotic spacecraft is a system capable of performing a multitude of operations in-orbit such as the maintenance and repair, assembly of large structures, refuelling and the de-orbiting of debris [1,2,3]. It can be free-floating or free-flying. ...
A robotic spacecraft, that can be used for a variety of missions in-orbit, is highly challenging to control due to the dynamic coupling between the arm and the spacecraft base. In addition to the dynamic coupling, there are internal and external disturbances that require a robust controller to be tackled. In this paper, the mission concept of a chaser controlled floating robot used for the capture of a target in-orbit is introduced where the dynamical model of the system is derived with respect to the target frame. An H∞ controller is designed for this system to first reduce the relative range between the chaser and the target then track the pre-designed trajectory for the robotic arm. The simulation results are based on a 12 degree of freedom robotic spacecraft in the presence of internal and external disturbances.
... Part of the presented research has previously been presented on the ASTRA conference ( Jaekel et al., 2015) by the first author, however, copyrights do not apply. Giorgio Panin contributed to this research during his fellowship at DLR, Institute for Robotics and Mechatronics, until June 2016. ...
This paper presents a robotic capture concept that was developed as part of the e.deorbit study by ESA. The defective and tumbling satellite ENVISAT was chosen as a potential target to be captured, stabilized, and subsequently de-orbited in a controlled manner. A robotic capture concept was developed that is based on a chaser satellite equipped with a seven degrees-of-freedom dexterous robotic manipulator, holding a dedicated linear two-bracket gripper. The satellite is also equipped with a clamping mechanism for achieving a stiff fixation with the grasped target, following their combined satellite-stack de-tumbling and prior to the execution of the de-orbit maneuver. Driving elements of the robotic design, operations and control are described and analyzed. These include pre and post-capture operations, the task-specific kinematics of the manipulator, the intrinsic mechanical arm flexibility and its effect on the arm's positioning accuracy, visual tracking, as well as the interaction between the manipulator controller and that of the chaser satellite. The kinematics analysis yielded robust reachability of the grasp point. The effects of intrinsic arm flexibility turned out to be noticeable but also effectively scalable through robot joint speed adaption throughout the maneuvers. During most of the critical robot arm operations, the internal robot joint torques are shown to be within the design limits. These limits are only reached for a limiting scenario of tumbling motion of ENVISAT, consisting of an initial pure spin of 5 deg/s about its unstable intermediate axis of inertia. The computer vision performance was found to be satisfactory with respect to positioning accuracy requirements. Further developments are necessary and are being pursued to meet the stringent mission-related robustness requirements. Overall, the analyses conducted in this study showed that the capture and de-orbiting of ENVISAT using the proposed robotic concept is feasible with respect to relevant mission requirements and for most of the operational scenarios considered. Future work aims at developing a combined chaser-robot system controller. This will include a visual servo to minimize the positioning errors during the contact phases of the mission (grasping and clamping). Further validation of the visual tracking in orbital lighting conditions will be pursued.
... These targets are non-cooperation targets; there is no cooperative marker on it. Therefore, to protect the precious and limited GEO orbit resources, effective visual measurement and capture strategy should be taken before things get worse [2][3][4][5]. ...
... On-orbit debris population in LEO is likely to increase due to collisions between existing debris [2]. Thus, missions are proposed for capturing and removing selected large space debris from orbit (see, e. g., [3]). ...
It is considered to use a manipulator-equipped satellite for performing On-Orbit Servicing (OOS) or Active Debris Removal (ADR) missions. In this paper, several possible approaches are reviewed for end-effector (EE) trajectory planning in the Cartesian space, such as application of the Bézier curves for singularity avoidance and method for trajectory optimization. The results of numerical simulations for a satellite equipped with a 7 degree-of-freedom (DoF) manipulator and results of experiments performed on a planar air-bearing microgravity simulator for a simplified two-dimensional (2D) case with a 2-DoF manipulator are presented. Differences between the free-floating case and the case where Attitude and Orbit Control Systems (AOCS) keep constant position and orientation of the satellite are also shown.
... A continuous active removal of high risk debris objects seems to be the only chance of stabilizing the orbit population and avoiding such a cascade 3,4 . Several agencies, companies and research institutions have identified this threat and investigate various technologies to solve the problem 5,6 . Those technologies are spread over various Technology Readiness Levels (TRL), with for example robotic grippers being rather advanced, but bound to specific counterpart interfaces. ...
This paper presents the design and test of a docking mechanism that is based on mushroom-shaped dry
adhesives as well as a theoretical assessment of highest achievable adhesion. The presented mechanism is
adaptable to different target geometries, reusable, switchable, and robust to loads in any direction with espect to the target surface. The design of the mechanism is based on a detailed trade-off of different concepts to apply the adhesives, supporting the most suitable design for the requirements on which the trade-off is based.
Tests have been conducted with an engineering model in a laboratory environment. Preliminary tests
have already shown the functionality of the mechanism to attach to a smooth planar object, lift, move, and subsequently release it without applying strong disturbing forces. In additional tests, the influence of curvature, load angle and macroscopic contact splitting on the mechanism’s adhesion has been analyzed.
... On the one hand, a clamping system [20] using "tentacles" can be used to completely clasp the target. On the other hand, a robotic gripper system [23] can be utilized to get hold of the target at a specific position on the surface. Such mechanical systems feature the advantage of being capable of repeating the docking process if necessary. ...
The number of objects in the space debris population increased noticeably in the last couple of years. Pieces
from fragmentation incidents play a significant role in this connection. Simulations show that strategies, such
as post mission disposal (PMD) or active debris removal (ADR), are efficient measures to stabilize the
population in orbit. Especially, ADR can compensate for an uncontrolled growth of the population, if objects
with a high risk of collision will be removed. According lists with high priority objects were developed in the
past and Russian Zenit upper stages and the European ENVISAT can be found on top of the lists.
Even though, unmanned ADR missions were not accomplished, yet, most of the mission phases (such as
phasing, rendezvous, re-entry et cetera) are well known from other projects. The docking or capture phase is
scientifically interesting, since the debris object is uncontrolled and does not exhibit according interfaces. Thus, the challenge is to capture a tumbling object which was not designed to support a docking maneuver. Current approaches for capturing such objects rely, for example, on harpoons, nets, or robotic arms. Risks are involved which are either based on a limited number of docking tries or on the compatibility with the object structure. The Institute of Space Systems (IRAS) at Technical University of Braunschweig currently follows another approach, which is supposed to support docking to arbitrary high risk objects. Biologically inspired switchable dry adhesives, so called gecko materials, imitate the capabilities of geckos to adhere to (almost) any surface and disconnect as necessary. A docking mechanism is being developed that is based on the gecko material. This paper shows the use spectrum of gecko materials in aerospace engineering and depicts initial estimations for a docking approach. Further, an overview of test environments at IRAS is given, that allows for investigating the docking approach at high priority objects.
The paper discusses dynamic requirements for designing ground manipulator platforms that can be utilized to verify the performance of controllers developed for space manipulators. Dimensional analysis is used to formalize the dynamic equivalence conditions and control scaling laws between a given space manipulator and the ground manipulator to be designed, such that the space manipulator and the designed ground manipulator are dynamically equivalent. Given that, unlike its space counterpart, the ground manipulator may not have the complete six degrees of freedom for its base and it must function under the gravity effects, as well as manufacturing imprecisions in building the ground manipulator, the sensitivity of dynamic equivalence conditions to the above factors is analyzed. Further, an error compensation scheme based on the feedback linearization technique is developed to make the closed-loop ground manipulator have similar joint movements to those of the space manipulator under its controller. As a result, ground-based verification experiments can be performed for the controllers that will operate on the space manipulator. The design of a ground manipulator with the error compensation scheme for a specific space manipulator is illustrated through simulations, and it is shown how the performance of a PID controller for the space manipulator can be verified using the designed ground manipulator.
Non-cooperative capture using a free-flying robot is anticipated for space debris removal and on-orbit servicing. However, a pre-flight testing strategy is not established in this advanced case as navigation in non-cooperative capture involves contact behavior. In this paper, we present an experimental verification strategy for on-orbital non-cooperative capture, involving contact dynamics, which leads towards final HIL testing. In the preliminary experimental verification, a single point collision using 2D air-floating testbed and a prospective simulator (GAZEBO) is modeled, and the collision properties are verified to match between hardware and simulation testing.
We present a tracking controller for the rendezvous of a robotic chaser satellite to a free-tumbling target satellite in the presence of uncertainty in the predicted target motion, applicable in real-time. The maneuver to be controlled is modeled on the e.Deorbit scenario. The path followed by the chaser in the orbital frame is based on a prediction of the target motion and is provided by a motion planner. For the robust control of the maneuver, a linear tube-based robust model predictive controller is proposed, which will guarantee feasibility and stability for a predefined uncertainty in the target motion. The control problem is itself linear, permitting controller formulation using the linear framework. However, the relation between the uncertainties of the maneuver participants is nonlinear, which complicates the controller design. The controller is evaluated in simulation, the results of which depict its effectiveness for a realistic uncertainty boundary
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