Robotic On-orbit Servicing Research Articles

Semi-Analytical Model for Design and Analysis of On-Orbit Servicing Architecture

Robotic on-orbit servicing (OOS) is expected to be a key technology and concept for future sustainable space exploration. This paper develops a novel semi-analytical model for OOS system analysis, responding to the growing needs and ongoing trend of robotic OOS. An OOS infrastructure system is considered whose goal is to provide responsive services to the random failures of a set of customer modular satellites distributed in space (e.g., at the geosynchronous orbit). The considered OOS architecture comprises a servicer that travels and provides module-replacement services to the customer satellites, an on-orbit depot to store the spares, and a series of launch vehicles to replenish the depot. The OOS system performance is analyzed by evaluating the mean waiting time before service completion for a given failure and its relationship with the depot capacity. By uniquely leveraging queueing theory and inventory management methods, the developed semi-analytical model is capable of analyzing the OOS system performance without relying on computationally costly simulations. The effectiveness of the proposed model is demonstrated using a case study compared with simulation results. This paper is expected to provide a critical step to push the research frontier of analytical/semi-analytical model development for complex space systems design.

Effective Capture of Nongraspable Objects for Space Robots Using Geometric Cage Pairs

Capture and removal of space debris are challenging in robotic on-orbit servicing activities. A large portion of space debris does not possess any graspable features, which makes the conventional grippers inapplicable. To handle such nongraspable objects, a space robotic capture system is presented. A dual-arm space robot simulator that has the advantages of miniaturization and scalability is designed for ground tests. Inspired by the robotic caging, we propose a novel capture method that uses a series of hollow-shaped end-effector pairs to cage the antipodal pairs of the nongraspable objects. To apply the caging-pair method steadily, space robots need exerting a squeezing action on objects, which can be characterized by the motion and force manipulation of two robotic arms in the assigned directions. Based on the velocity and force manipulability transmission ratios, a caging compatibility index is proposed to describe the capturing ability in this manner. Via the optimization of the desired caging compatibility index, an effective algorithm is proposed to plan the near-optimal joint configurations for the pregrasping cages. Finally, both simulation studies and experimental tests are conducted to evaluate the performance of the proposed capture method.

Pose Determination for Malfunctioned Satellites Based on Depth Information

Autonomous on-orbit servicing is the future space activity which can be utilized to extend the satellite life. Relative pose estimation for a malfunctioned satellite is one of the key technologies to achieve robotic on-orbit servicing. In this paper, a relative pose determination method by using point cloud is presented for the final phase of the rendezvous and docking of malfunctioned satellites. The method consists of three parts: (1) planes are extracted from point cloud by utilizing the random sample consensus algorithm. (2) The eigenvector matrix and the diagonal eigenvalue matrix are calculated by decomposing the point cloud distribution matrix of the extracted plane. The eigenvalues are utilized to recognize rectangular planes, and the eigenvector matrix is the attitude rotation matrix from the sensor to the plane. The solution of multisolution problem is also presented. (3) An extended Kalman filter is designed to estimate the translational states, the rotational states, the location of mass center, and the moment-of-inertia ratios. Because the method only utilizes the local features without observing the whole satellite, it is suitable for the final phase of rendezvous and docking. The algorithm is validated by a series of mathematical simulations.

Tutorial Review on Space Manipulators for Space Debris Mitigation

Space-based manipulators have traditionally been tasked with robotic on-orbit servicing or assembly functions, but active debris removal has become a more urgent application. We present a much-needed tutorial review of many of the robotics aspects of active debris removal informed by activities in on-orbit servicing. We begin with a cursory review of on-orbit servicing manipulators followed by a short review on the space debris problem. Following brief consideration of the time delay problems in teleoperation, the meat of the paper explores the field of space robotics regarding the kinematics, dynamics and control of manipulators mounted onto spacecraft. The core of the issue concerns the spacecraft mounting which reacts in response to the motion of the manipulator. We favour the implementation of spacecraft attitude stabilisation to ease some of the computational issues that will become critical as increasing level of autonomy are implemented. We review issues concerned with physical manipulation and the problem of multiple arm operations. We conclude that space robotics is well-developed and sufficiently mature to tackling tasks such as active debris removal.

Key technologies of TianGong-2 robotic hand and its on-orbit experiments

With the development of robotics in recent years, space robotic manipulators have become a research focus on space technologies. In the TianGong-2 (TG-2) spacelab mission, a human-robot collaborative on-orbit servicing experiment was planned as one of the three key tasks. The central component of this task is the TG-2 robotic manipulator, which is a multisensory in-vehicle space robot with multiple control modes, including a 6-DOF robotic arm, a five-fingered humanoid hand, hand-eye and global cameras, and on-orbit human-machine interfaces(space mouse and cyber glove). The design purpose of TG-2 robotic task is to complete various prototypical experiments under micro-g environment to validate key technologies of space robots and on-orbit human-robot collaboration and gain experience and experimental data about robotic on-orbit servicing by assisting or cooperating with human astronauts. A variable time-scale motion plan method, which could adjusts the trajectories of the robot to reduce or eliminate the collision force between the robot collide with the environment, is developed for safe human-robot collaboration. The five-fingered hand grasp control is based on an approach coined as “coordinated grasp control based object Cartesian stiffness” for the adaptation of external forces and robust grasp. To solve the kinematic mapping from cyber glove commands to five-fingered robotic hand, a fingertip-position-based method is proposed to acquire precise solutions. The TG-2 robotic manipulator was launched to space in Sep. 15, 2016. From Oct. 27 to Nov. 13, 2016, all the planned experiments, including dynamic parameter identification, grasping floating objects and prototypical on-orbit servicing, were carried out successfully under the supervision and assistance of the two astronauts, laying foundations for the future applications of space robots.

Advanced Path Planning System of Free-Floating Space Manipulator for On-Orbit Observation

Robotic on-orbit servicing (OOS) is the key to the development of the space frontier as a major element in space infrastructure. This paper discusses the concept of OOS and introduces the categories of OOS including assembly, maintenance and upgrade. This paper also demonstrates the process of on-orbit observation. A system model for the space manipulator system is established, and the kinematic equation of such manipulator system is established as well. Point-to-point trajectory planning in joint space is also studied in this paper based on Newton-Raphson method. The approach could guarantee that the manipulator end-effector reaches the desired point. In this paper, the authors have limited discussions within the simulation and 6-DOF FFSM point-to-point planning problems, whereas the adoption of such strategy will provide the possibility and basis for further application of the space manipulator system in free-floating mode to some extent.

Adaptive estimation of attitude and angular velocity of malfunctioned satellites for on-orbit servicing

Estimating the attitude and angular velocity of a malfunctioned satellite is one of the key technologies to achieve robotic on-orbit servicing, which is a challenging space activity. In this paper, a new method of estimating attitude parameters for target satellite by using stereo-vision system is proposed. First, two sets of vectors are constructed according to the feature point coordinates in target frame and stereo-vision system frame respectively, and then the relative attitude between the target and the servicer is determined through QUEST algorithm. Secondly, a new nonlinear estimator is proposed to estimate the attitude and inertial angular momentum of the target and the angular velocity is computed according to the estimated angular momentum and attitude. The stability of the estimator is proved by using the LaSalle’s invariance principle. Thirdly, a switch rule and an adaptive regulating rule are proposed to improve the estimation performance. The former decides when to switch from the rough estimator to the precise one. The latter regulates the gain dynamically in order to reduce the influence of the varying stereo-vision noise in the precise estimating procedure. Finally, numerical simulations and an experiment are carried out to verify the validity of the proposed method.

Effects of Multivantage Point Systems on the Teleoperation of Spacecraft Docking

Rendezvous and docking with uncooperative target objects are driving capabilities for future robotic on-orbit servicing and space debris removal systems. A teleoperation system augments a robotic system with the perception, cognition, and decision capabilities of a human operator, which can lead to a more capable and more flexible telerobotic system. The ThirdEye system was developed in order to support the human operator in the complex relative navigation task of final approach and docking. It provides the operator with a flexible camera vantage point which can be positioned freely in the relevant space around and between the chaser and target spacecraft. The primary and secondary camera views, an attitude head-up display, and a trajectory prediction display are integrated into an intuitive graphical user interface. A validation study was conducted to evaluate the effects of this ThirdEye system on the performance of the teleoperation system during final approach and docking with uncooperative, rotating targets. The results of this study show that the ThirdEye system increases the overall task success rate by 15% and improves operator situation awareness, without having negative impact on the usage of system resources. The partial failure rates are decreased by 20-30%. In high-difficulty scenarios, the operator task load is increased due to the dual task of teleoperating the camera arm and the spacecraft in tandem, which leads to a minor increase in failure rate in these scenarios.

Advances in Space Robot On-orbit Servicing for Non-cooperative Spacecraft

With the development of space robot and rendezvous docking technologies,on-orbit servicing is expected to play an increasingly important role in spacecraft life-extension,capacity improvement and space debris removal.So far, the spacecrafts already existed in orbit and the space debris are generally non-cooperative,i.e.neither any artificial marks used for the measurement nor grappling fixtures applied to the capture are mounted on the target.Therefore,robotic onorbit servicing for non-cooperative spacecrafts has been a hotspot of research in recent years.In this paper,firstly,the characteristics of the on-orbit servicing for non-cooperative spacecrafts are analyzed,and the possible apphcations of mis technology are introduced.Secondly,the achievements of the main space powers are reviewed,and the key technologies of non-cooperative on-orbit servicing are summarized.Finally,the research prospects are presented.

Standards in the space industry: Looking back, looking forward

Spaceflight is ingrained in the imagination as a state-of-the-art technology. Its level of sophistication and intricacy is unparalleled.The space industry, with its large budgets and few producers, has been able to maintain a craft mentality in the face of the hi-tech ethos of mass production. One striking example of this craft mentality is a relative lack of industry-wide standards for the design and operation of satellites. This article discusses standards-setting in the space industry, suggesting that thus far the industry has often resisted imposing standards in favor of customization. Given the maturation of on-orbit servicing technology and future shift from astronautassisted repair to semi-autonomous robotic repair, the lack of interoperability standards is increasingly problematic. How, what, and when to standardize, as well as who makes this decision, is an organizational question that has significant consequences for the future of satellite design and the operation of the space industry. It is thus important to be mindful of the current context of outer space and spaceflight, as well as to consider which lessons from human on-orbit servicing may provide insights for the development of a robotic on-orbit servicing infrastructure.

The case for robotic on-orbit servicing of spacecraft: Spacecraft reliability is a myth

This paper presents some of the results of an 18-month study into robotic on-orbit servicing (OOS) by the authors for the German Aerospace Center (Deutsches Zentrum fur Luft und Raumfahrt (DLR)), which leads the world in this area of space technology development. Rather than dealing with technology issues, however, we deal with issues concerning the potential market (the “demand” side) for OOS. We present the case that robotic OOS is not only commercially feasible, but also even more strongly assert that it is essential. We consider in particular the recent high incidence of on-orbit failures in geostationary telecommunications platforms. We present the sobering statistics of such failures, and determine that only OOS can mitigate these and future failures. OOS represents the first space-based commercial opportunity that serves the space industry itself rather than Earth-oriented applications more typical of commercial space activities, and to that end provides the basis for future space infrastructure development.

On-Orbit Upgrade and Repair: The Hubble SpaceTelescope Example

From the Hubble Space Telescope (HST) example, a model of a serviceable scientific mission is developed to study on-orbit repair and upgrading, including spacecraft repair, payload instrument upgrading, and bus subsystems upgrading. Mission utility is measured by the onboard payload instrument discovery efficiency. A Monte Carlo simulation is used to model uncertainty in the arrival of new technologies, random spacecraft failures, and catastrophic failures of a servicing operation. The value of the option to repair and upgrade, as well as the impact of different design choices, is investigated using actual data from the HST manned servicing missions. The main differences between manned and unmanned servicing missions are then analyzed in an attempt to derive conclusions for robotic on-orbit servicing of scientific missions. In light of the cases examined, designing for serviceability exclusively for satellite repair does not seem very valuable. In contrast, upgrading can significantly increase mission utility especially if the technology embedded in the serviceable modules is evolving rapidly. Technology upgrades via on-orbit servicing have been identified as a very promising concept. Large increases in mission utility can be realized for a cost significantly lower than the cost of replacing the whole satellite.

Space Robotics

In this second of three short papers, I introduce some of the basic concepts of space robotics with an emphasis on some specific challenging areas of research that are peculiar to the application of robotics to space infrastructure development. The style of these short papers is pedagogical and the concepts in this paper are developed from fundamental manipulator robotics. This second paper considers the application of space manipulators to on-orbit servicing (OOS), an application which has considerable commercial application. I provide some background to the notion of robotic on-orbit servicing and explore how manipulator control algorithms may be modified to accommodate space manipulators which operate in the micro-gravity of space.

An engineering approach to the dynamic control of space robotic on-orbit servicers

Robotic on-orbit servicing is the key to the commercial development of a space robotics infrastructure. A major technical difficulty has been the problem of control of the robotic manipulators mounted onto a freeflying platform in space. The problem of control is directly related to the fact that manipulator motions exert reaction effects on the mounting spacecraft. A solution to this problem is outlined-one in which no fuel is expended and that demands no excessive computational resources that would otherwise preclude real-time performance.