Alex Ellery

Bio: Alex Ellery is an academic researcher. The author has contributed to research in topics: Teleoperation & Spacecraft. The author has an hindex of 1, co-authored 1 publications receiving 15 citations.

Tutorial Review on Space Manipulators for Space Debris Mitigation

Abstract: 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.

On the guidance, navigation and control of in-orbit space robotic missions: A survey and prospective vision

Abstract: In the first part, this article presents an overview of Guidance, Navigation and Control (GNC) methodologies developed for space manipulators to perform in-orbit robotic missions, including but not limited to, on-orbit servicing, satellite/station assembly, probing extra-terrestrial objects and space debris mitigation. Some space mission concepts are briefly mentioned, for which space robotics is discussed to be among the most practical and universal solutions. Common phases of an in-orbit robotic mission are identified as: close-range rendezvous, attitude synchronization, target identification, manipulator deployment, capture, and if needed, post-capture maneuvers. Prominent GNC methodologies that are either proposed for or applicable to each phase are extensively reviewed. In the current article, the emphasis is placed on the study of GNC methodologies utilized in attitude synchronization, manipulator deployment, and capture phases, specially the ones reported for use in the two free-floating and free-flying operating regimes of space manipulators. Kinematics and dynamics of space manipulator systems are formulated to help unifying the presentation of the main ideas behind different GNC methodologies. Using a unified notation, comparison tables and discussions provided in this paper, researchers can compare various GNC approaches and contribute to the next-generation GNC systems for space robots. In addition, this survey aids technology users to learn about in-orbit robotic missions and choose appropriate GNC technologies for specific applications. In the second part of this paper, two families of emerging control schemes based upon reinforcement learning and geometric mechanics are introduced as promising research directions in the GNC of space robotic systems. The benefits of implementing these techniques to the GNC of in-orbit robotic missions are discussed. An exclusive study of environmental disturbances affecting space manipulators and their threat to long-term autonomy concludes this article.

A review of structures, verification, and calibration technologies of space robotic systems for on-orbit servicing

Abstract: Recently, with the rapid development of aerospace technology, an increasing number of spacecraft is being launched into space. Additionally, the demands for on-orbit servicing (OOS) missions are rapidly increasing. Space robotics is one of the most promising approaches for various OOS missions; thus, research on space robotics technologies for OOS has attracted increased attention from space agencies and universities worldwide. In this paper, we review the structures, ground verification, and on-orbit kinematics calibration technologies of space robotic systems for OOS. First, we systematically summarize the development of space robotic systems and OOS programs based on space robotics. Then, according to the structures and applications, these systems are divided into three categories: large space manipulators, humanoid space robots, and small space manipulators. According to the capture mechanisms adopted, the end-effectors are systematically analyzed. Furthermore, the ground verification facilities used to simulate a microgravity environment are summarized and compared. Additionally, the on-orbit kinematics calibration technologies are discussed and analyzed compared with the kinematics calibration technologies of industrial manipulators with regard to four aspects. Finally, the development trends of the structures, verification, and calibration technologies are discussed to extend this review work.

A two-arm flexible space manipulator system for post-grasping manipulation operations of a passive target object

Abstract: Space Manipulator Systems (SMSs) are complex systems made of a platform equipped with one or more deployable robotic arms and they will be playing a major role in future autonomous on-orbit missions. The latter may as well involve manipulation operations of the target object which needs to be moved from an initial configuration to a final one suitable for the specific task under consideration. In the present study, the mission being analyzed concerns the manipulation of a passive body by means of a flexible SMS after grasping operations have been performed. The dynamics model is derived in a three-dimensional context (non-linear formulation for the rigid-body motions and linear for the elastic dynamics). The SMS involved in the investigation has two actuated seven-degree of freedom arms. Furthermore, the modeling of the grasp constraint existing between the SMS end-effectors and the target object is a critical issue which is addressed in the present paper. A combination of Jacobian Transpose and Proportional-Derivative Control is synthesized to accomplish the desired mission goals. Numerical results proving the effectiveness of the proposed strategy are presented and discussed.

A space crawling robotic bio-paw (SCRBP) enabled by triboelectric sensors for surface identification

Abstract: With the rapid development of space crawling robotics technology, tactile perception, a significant source for the robot to sense the external environment, has become the preferred solution to gather information in space. Sensors embedded in the robotic end-effector unit can collect and encode the large tactile data, allowing the robot to feel and perceive the real surroundings. Therefore, a space crawling robotic bio-paw (SCRBP) inspired by a cat paw, which performs as a compliant device and can flat the impulse force during the robot’s contact process to the target surface, is proposed in this paper. Meanwhile, a touch-sensing system embedded on SCRBP with self-powered sensors based on the triboelectric nanogenerator (TENG) technology is proposed which can provide the multi-dimensional sensation information in real time. By combining with machine learning (ML), the sensory system can be used for surface identification from the footfall process to the robot’s controller hub. In conclusion, SCRBP device proposed in this paper has obvious advantages in surface information acquisition, space adaptability, power consumption, cost, reliable signal and minimized data. Accordingly, SCRBP system shows fabulous potential in space robotics. • Inspired by the cat's paw structure and its footfall process, a space crawling robotic bio-paw (SCRBP). • Tactile perception is realized enabled by multi-dimensional sensation provided by triboelectric sensors. • By combining with machine learning (ML), the sensory system can be used for surface identification from the footfall process to the robot’s controller hub. • The mechanism developed in this paper can be an essential complement of the perception system and help space robots know more about surface information.