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This article presents a comprehensive survey of the integration of machine learning techniques into robotic grasping, with a special emphasis on the challenges and advancements for space applications. The incorporation of artificial intelligence, particularly through deep learning, reinforcement learning, transfer learning, convolutional neural networks and recurrent neural networks, has significantly revolutionized robotic grasping. These advancements facilitate autonomous, efficient, and sophisticated manipulation in the challenging environment of outer space, transitioning from traditional mechanical grippers to sophisticated systems powered by advanced algorithms. This transition highlights the critical integration of sensory perception, grasp planning, and execution mechanisms, enhancing robots' capabilities to perceive, interact with, and manipulate objects with unprecedented precision and adaptability. The article meticulously outlines significant advancements achieved through the deployment of convolutional neural networks for visual information processing, RNNs for sequential decision-making, RL for autonomous strategy refinement, and transfer learning for leveraging pre-learned knowledge in novel tasks. These technologies address the unique challenges of space environments, such as varied textures, occlusions, microgravity conditions, and the sim-to-real gap, by enhancing sample efficiency, improving sim-to-real transfer capabilities, and integrating multimodal data for better object localization and pose estimation. Furthermore, the review explores the specific challenges faced in space robotic grasping, including handling varied textures and occlusions, adapting to unpredictable conditions, achieving real-time processing, and ensuring safety and reliability. It proposes future research directions focused on overcoming these hurdles, such as enhanced generalization through multimodal learning, robust sim-to-real transfer techniques, and the development of collaborative robotics and swarm intelligence. Critical to the development of ML models for robotic grasping are the roles of specialized datasets and simulation environments. Datasets like the Cornell Grasping Dataset and the Yale-CMU-Berkeley Object, along with simulation platforms such as Gazebo and PyBullet, provide essential resources for training, testing, and refining ML models. These tools enable researchers to simulate complex robotic systems and interactions within realistic environments, fostering rapid iterations on design and control strategies. In summary, this article offers in-depth insights into the progress, current challenges, and future prospects of machine learning techniques in robotic grasping for space exploration. It showcases significant strides made in the field and charts a path forward, emphasizing the need for innovative solutions to navigate the complexities of robotic manipulation in outer space. Through the strategic integration of advanced ML techniques, the development of adaptable and efficient robotic systems for space applications continues to advance, promising to unlock new possibilities in space exploration and beyond. • Surveys machine learning's application in space robotic grasping, noting key advances. • Highlights CNNs and RNNs' roles in robotic perception and action. • Discusses deep learning's evolution in autonomous space robotics. • Outlines future directions, emphasizing sim-to-real and multimodal learning. [ABSTRACT FROM AUTHOR]

This paper investigates the dynamic behavior of a tethered satellite system in an elliptical orbit as the tethered subsatellite is deployed from a mother satellite at an out-of-plane angle while maintaining the tether at a constant in-plane pitch angle by a predefined control force acting on the subsatellite. A variable-length pendulum model is employed to describe the purely out-of-plane tether deployment dynamics, from which an analytical tether deployment control law is derived. The stability condition of the analytical control law is examined by Floquet theory. The corresponding analytical deployment law is asymptotically stable, and the requirement for a positive tension control input is guaranteed to ensure the controllability of the tether system. Following deployment, the critical conditions for the out-of-plane libration of the tethered subsatellite to become chaotic during the station-keeping phase are examined. Finally, simulation results reveal that the proposed approach can effectively and rapidly identify periodic, quasiperiodic, and chaotic motions using bifurcation diagrams, which provides valuable insights for enhancing the stability and reliability of such tethered satellite systems. • Proposed an analytical deployment law for a purely out-of-plane tethered satellite. • Revealed nonlinear phenomena of the system during the station-keeping phase. • Explored bifurcation characteristic and chaotic windows of the system. [ABSTRACT FROM AUTHOR]

This study proposes a new control strategy for mitigating the libration in a partial space elevator (PSE). First, a libration-free or coupling-free analytical speed function is derived by assuming no in-plane and out-of-plane libration in the cargo transportation phase. Subsequently, a thrust is applied at the PSE's end body to counter any libration during this phase. A new set of geometric measures - bending and departure angles - are introduced to characterize the libration motion in PSE's dynamic equation. Based on these measures, two separate proportional-derivative (PD) stabilizing feedback laws are proposed. These PD laws individually control the bending and departure angles by thrust at the end body to suppress the libration that deviates from the libration-free trajectory. Due to the dynamic coupling between the bending and departure modes, they dominate alternatively. Accordingly, a novel fuzzy logic control law is proposed to switch between two PD controls based on the state of these two angles. Finally, a thrust vectoring control is proposed to combine in-plane and out-of-plane thrusting into a single actuation control. The asymptotic stability of the proposed control scheme is proved by Lyapunov's stability theory. Comprehensive numerical analyses demonstrate the effectiveness of the new geometric representation of the libration and the proposed new control strategy, highlighting their ability to suppress libration with bounded control inputs efficiently. • Derived new coupling-free analytical speed function for libration-free cargo transfer trajectory. • Introduced a new set of geometric measures, bending and departure angles, to describe libration motion. • Proposed a Fuzzy logic law to switch control between bending and departure angles. • Proposed a thrust vectoring control to combine in-plane and out-of-plane thrusting into one actuation. [ABSTRACT FROM AUTHOR]

This paper develops a dual-phase control strategy based on the piecewise cooperative game method to balance the multiple competing objectives for cargo transportation by a partial space elevator in terms of orbital state stability and cargo transport efficiency and ensure final state stability. The cargo transportation is performed in the libration-free mode to facilitate the control implementation, where all libration motions are kept at zero. The new control strategy is split into phases I and II. Phase I focuses on cargo transportation and covers most cargo transfer distances. Multiple competing control objectives in this phase are balanced by the newly proposed piecewise cooperative game method. Once the remaining distance meets the preset threshold, the transportation enters phase II, which focuses on bringing the state of the partial space elevator to a stable equilibrium state. A shrinking horizon model predictive control method is used to ensure the state converges to the equilibrium point by the end of transportation. The simulation results reveal that the newly proposed dual-phase control scheme effectively balances multiple competing control objectives in the cargo transfer period. Moreover, by introducing phase II, the system can achieve a stable equilibrium state by the end of the transfer period. [ABSTRACT FROM AUTHOR]

Robotic on-orbit servicing presents the opportunity for repairing and refueling satellites and deorbiting space objects. Performing such tasks is challenging because they must be done autonomously and accurately with high robustness. Ground testing, such as air-bearing-based spacecraft simulators, is widely used to develop and validate the design and control techniques of space robotics required by modern spacecraft applications. This paper presents the development of planar air-bearing microgravity simulators with a 3-DOF robotic manipulator for autonomous spacecraft tracking, rendezvous, and capture control of a free-floating target. The system includes a pseudo-galactic star tracking system for pose determination and navigation of spacecraft simulators. A second optical tracking module was also developed to determine the pose of a target spacecraft relative to the chaser spacecraft. Path planning and PD trajectory tracking algorithms were developed for spacecraft tracking and rendezvous. The experiments successfully demonstrated that the testbed could be used to study autonomous spacecraft rendezvous and capture a tumbling spacecraft by a robotic manipulator in a space-like testing environment. • Developed air-bearing spacecraft simulators for spacecraft rendezvous control. • Developed air-bearing lifted robotic manipulator for capturing a spinning target. • Tested autonomous path planning and autonomous robotic capture by the system. [ABSTRACT FROM AUTHOR]

This paper investigates the spin rate bounds, the configuration stability subject to the solar wind fluctuations, and sail angle control of an electric solar wind sail (E-sail) by a high-fidelity tether dynamic model. This model describes the elastic deformation of tethers with inter-connected 2-noded tensile elements discretized by the nodal position finite element method. The E-sail is assumed to be an axisymmetric system spinning in the plane normal to the heliocentric ecliptic plane. The upper and lower spin rate bounds are revisited to reveal the physics that dictates these bounds and analytic expressions are provided to ensure the proper operation of E-sail. Then, the influences of the solar wind fluctuations on the configuration stability of the E-sail are investigated by parametric analysis with different E-sail configurations, sail angles, and spin rates. Finally, an alternative sail angle control strategy for the E-sail is proposed by applying control force at the remote units with a simple PD control. Numerical analysis demonstrates that the sail angle of E-sail can be controlled quickly by the control law at the remote units with a high-precision. • Derived a new theoretical lower bound of spin rate for E-sail with auxiliary tethers. • Analyzed structural dynamics of E-sail by a high-fidelity tether dynamic model. • Revealed necessity and effectiveness of auxiliary tethers by tether dynamic perspective. • Controlled sail angle by applying control forces at remote units only. [ABSTRACT FROM AUTHOR]

The partial space elevator is a space transportation system that conveys cargo by a climber moving along the tether that connects the main satellite and the end body. This work proposed a novel prescribed performance based dual-loop control strategy for configuration keeping of the partial space elevator in cargo transportation. The control loop I controls the libration angle of the climber by a newly proposed prescribed performance control law to track the desired state with bounded performance. The Lyapunov stability of the control law is proved analytically. Control loop II stabilizes the overall configuration of the PSE by applying thrust and deploying/retrieving the tether simultaneously at the end body. To enforce the constraint that the total tether length is unchanged at the end of transportation, an event-triggered loaning control algorithm is proposed to further improve the Control loop II. Numerical simulations validate the prescribed performance based dual-loop control strategy. The results show that the stable configuration of the PSE is kept effectively with no libration motion in the period of cargo transportation. • A new dual-loop control strategy to keep PSE configuration in cargo transportation. • A prescribed performance control law to keep the climber's libration angle. • An event-triggered loaning control to incorporate configuration constraint. [ABSTRACT FROM AUTHOR]

Spacecraft formation maneuvering will inevitably induce flexible vibration from flexible appendages of spacecraft such as solar array appendages or antennae, which leads to complex disturbances with unknown fundamental frequencies. To achieve high performance of spacecraft formation flying, a novel adaptive iterative learning disturbance observer based on adaptive notch filter is designed to estimate and compensate unknown multi-frequency disturbances. Different from existing results on iterative learning disturbance observer, the newly proposed observer can estimate effectively both low-frequency disturbances and high-frequency periodic disturbances. Based on the proposed observer, an output feedback pose tracking law is derived by combining the proposed velocity observer and a feedback controller in dual quaternions description. The stability of the closed-loop system is approved based on the Lyapunov framework. Finally, the effectiveness and accuracy of the proposed observer and controller are demonstrated successfully by numerical simulations. • Developed a novel adaptive iterative learning control for flexible spacecraft formation. • Developed adaptive iterative learning observer to estimate multi-frequency disturbances. • Formulated 6DOF spacecraft formation maneuvering by dual quaternions. [ABSTRACT FROM AUTHOR]

This paper describes the experimental validation of a CubeSat tether deployment design by air-bearing ground test and microgravity parabolic flight test. The tethered CubeSat mission includes two 1U CubeSats with a tape-type tether of 100 m. The tether will be deployed by pull with two CubeSats separating at a desired velocity. Various ground tests were performed to validate the designed separation velocity, estimate the internal friction force, and measure the deployed tether length. Finally, the engineering model of tether deployment system is validated by microgravity parabolic flight testing. The parabolic flight demonstrated the tether deployment system works as expected. By measuring the separation velocity of CubeSats in the parabolic flight, it reveals the internal friction is much less in the microgravity environment than the value measured on the ground. • Validation of Tape-type tether deployment system design by air-bearing ground testbed. • Validation of Tape-type tether deployment system design by microgravity parabolic flights. • Friction force in tether deployment system is much smaller in microgravity than on Earth. [ABSTRACT FROM AUTHOR]

This paper explores a new control strategy to suppress the libration of a partial space elevator by applying torque control at the climber only. The control torque at the climber is generated by reaction wheels. A new dynamic model of the partial space elevator is developed by integrating the attitude dynamics of the climber into the classical two-piece dumbbell model. The influence of the climber attitude motion on the libration motion of the partial space elevator is analyzed with and without the control torque at the climber. Based on the characteristics of the system dynamics, a novel reaction wheel control strategy is proposed to suppress both the libration of the elevator and the climber attitude motion. Such a new control strategy is implemented by an optimal control scheme. The simulation results validate the effectiveness of the proposed control strategy, which provides a new alternative method to stabilize the libration of the partial space elevator for fast transfer of cargo with constant speeds. To avoid the adverse effect on the reaction wheel due to the frequent switch of rotation direction, a control strategy by two unidirectional reaction wheels is proposed to achieve the same control effect, where the reaction wheels rotate in only one direction. • Include attitude dynamics of climber into the dynamic model of partial space elevator. • Suppress the libration of partial space elevator by applying control torque at the climber only using reaction wheel. • Study control input by one and two reaction wheels and associated advantage and disadvantage. [ABSTRACT FROM AUTHOR]

This paper proposes a novel concept of looped tether transportation system with multiple climbers for highly efficient transportation of payloads. It is formed by connecting two parallel tether transportation systems or partial space elevators with multiple climbers per tether at upper and lower ends. A high-fidelity and accurate model for the system is built up to capture the high order flexural modes of tethers based on the nodal position finite element method in the arbitrary Lagrangian-Eulerian description. Numerical analysis is conducted to understand the dynamic characteristics of the looped tether transportation system compared to the tether transportation system with a single tether. The results show that the high-order flexural modes of tethers must be considered in the system's engineering analysis. The analysis also shows the interaction between two tethers caused by climbers on different tethers moving in different directions could be beneficial. It will reduce the overall libration of the system while keeping the magnitude of tether tension comparable to the tether transportation system with a single tether. In addition, the analysis of high order flexural modes of tether indicates that there exists a risk of tether collision in the payload transportation, which indicates again the necessity to include the high order flexural modes of tether in the analysis. Finally, the study shows the risk of tether collision could be avoided by optimizing the number of climbers per tether, the climber's moving profiles, and the distance between climbers using the optimal control methodology. • A novel looped space tether transportation system with multiple climbers is proposed. • A high-fidelity finite element model is developed by arbitrary Lagrangian-Eulerian description. • Advantages and disadvantages of the novel system are analyzed by the high-fidelity model. [ABSTRACT FROM AUTHOR]

This paper investigates the dynamic characteristics of thrust-induced sail plane coning and attitude motion of an electric solar wind sail (E-sail) by considering high-order modes of flexible elastic tethers. The tethers of the E-sail are assumed elastic and discretized into inter-connected 2-noded tensile elements using the nodal position finite element method, while the central spacecraft and the remote units are simplified as lumped masses. The E-sail is assumed in the heliocentric ecliptic orbital plane at a distance of 1 au from the Sun. The influences of the propulsive force models and the initial E-sail orientation on the dynamic characteristics of the sail plane coning and attitude motion of E-sail are analyzed. The current work derives an analytic expression of the coning motion frequency under the assumption of small coning angle. Through parametric analyses, the current work shows that the magnitude of the propulsive force significantly influences the increment magnitude of the E-sail's orbital radius while has little effect on the angles of sail and thrust angles and the E-sail spin rate. The parametric analyses also show that the initial E-sail orientation significantly influences the thrust vector and the variation of sail angle. Finally, the relationships of the sail and thrust angles, as well as the dimensionless acceleration of the E-sail, are given in polynomial expressions by curve-fitting of simulation results of E-sails with the consideration of coning motion. The relationships are compared with the previous results of E-sails without including coning motion. It shows the coning motion has negligible effect on the macro dynamic behaviors of E-sail. • Investigated thrust-induced sail plane coning and attitude motion of E-sail. • Considered high-order modes of elastic tethers using nodal position finite element method. • Derived analytic expression of frequency of periodic coning motion of sail plane. [ABSTRACT FROM AUTHOR]

This paper studies the dynamic characteristics of an electric solar wind sail (E-sail). A high-fidelity multiphysics model is developed by the nodal position finite element method to investigate the coupling effects of orbital and self-spinning motions of the E-sail, and the interaction between the axial/transverse elastic motions of tether and the Coulomb force. Furthermore, parametric study is conducted to better understand these coupling effects. The simulation results show that the coupling effects have a significant impact on the dynamic behavior of E-sail and the induced thrust. Furthermore, the analysis indicates a strong dependence of the thrust on sail and coning angles of E-sail even in the case of small sail angle. Finally, the influence of the initial self-spin rate and the sail angle on the dynamic behavior of a flexible E-sail is investigated. It shows that a high spin rate is needed to hold the geometrical configuration of the E-sail, and the difference in the orbital maneuvering is distinct when the E-sail inclines to the incident solar wind. It implies that a suitable control strategy should be employed to accomplish the thrust vectoring for the orbit maneuvering. The analysis provides an effective and robust way to design the E-sail in the mission planning phase. • Developed high-fidelity multiphysics model for electric solar wind sail. • Revealed coupling effect of orbital and self-spin motion of E-sail. • Studied interaction between axial/transverse motion of tether and Coulomb force. • Studied influence of initial self-spin rate & sail angle on flexible E-sail dynamics. • High spin rate is needed to hold the geometrical configuration of E-sail. [ABSTRACT FROM AUTHOR]

Abstract This paper develops control laws for the deployment of tethered spacecraft systems with an explicit non-negative velocity constraint using invariance principle of control systems. It addresses a class of space tether deployment control problems where the tether is deployed out only. This implies the tether deployment velocity must be always positive and approaches to zero at the end of deployment. This non-negative velocity constraint is explicitly satisfied in the proposed tension control laws by transforming it into an invariance property of control system. Two control laws with nonlinear feedback are derived with two complementary manifolds. The Lyapunov stability of the control laws is proved and the controllability of the tethered spacecraft system with tension input is analyzed. Finally, the effectiveness of control laws is demonstrated by numerical simulation. Highlights • Developed control law for monotonic deployment of tethered spacecraft systems. • Satisfied non-negative deployment velocity explicitly by invariance principle. • Proved controllability of tethered spacecraft systems and stability of control law. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a predictive visual servo kinematic control scheme for a robotic manipulator with the eye-in-hand configuration to perform autonomous capture of a non-cooperative space target with unknown motion. The unknown motion is estimated by an integrated algorithm of the photogrammetry and adaptive extended Kalman filter, in which the eye-in-hand configuration of the vision system improves the accuracy of the motion estimation as it approaches the target. Based on the vision feedback, a dynamic trajectory of robotic manipulator is planned in real time at each sampling instant and the end-effector of the manipulator moves towards the predicted position of the target at the next time instant incrementally. In this way, the multiple solutions problem of inverse kinematics in the joint space is effectively avoided and the robotic manipulator could intercept the non-cooperative target for a fast rendezvous. Validation experiments are performed on a custom built robotic manipulator with an eye-in-hand configuration. The experimental results demonstrate the effectiveness and robustness of the proposed control scheme. Highlights • A predictive incremental kinematic controller is presented for autonomous robotic capture. • The stability of the predictive kinematic controller has been proved. • The multiple solutions problem of inverse kinematics is effectively avoided. • Validation experiments are performed on an eye-in-hand robotic manipulator. [ABSTRACT FROM AUTHOR]

This paper proposes a robust finite element Kalman filter for the state estimation of flexible space tether systems, which are critical for space exploration and satellite missions. Due to the limited access to placing sensors along the flexible tether to measure them directly, the measurement of the state of these systems is challenging. To address this, a fully expandable, scalable, and robust approach is developed that fuses position/velocity sensors at tether ends, distributed fiber optic strain measurement along the tether, and a position/velocity estimation by a finite element-based Kalman filter to estimate the state of the tether system. The proposed estimator is mathematically proven to be observable, stable, and robust. The effectiveness of the estimator is demonstrated through numerical simulations of a space tether system in orbit, and the method can be extended to any flexible body system. The results of the simulations show that the proposed approach can accurately estimate the state of the tether system, even in the presence of disturbances and noise. • Expandable, scalable FE-Kalman state estimator for flexible space tether systems. • Data fusion with tether end position/velocity, distributed fiber optic strain measure, and estimated internal position/velocity. • Mathematically proven observability, stability, and robustness to noise of the estimator. [ABSTRACT FROM AUTHOR]

This paper studies the control of spacecraft rendezvous with attitude stable or spinning targets in an elliptical orbit. The linearized Tschauner-Hempel equation is used to describe the motion of spacecraft and the problem is formulated by model predictive control. The control objective is to maximize control accuracy and smoothness simultaneously to avoid unexpected change or overshoot of trajectory for safe rendezvous. It is achieved by minimizing the weighted summations of control errors and increments. The effects of two sets of horizons (control and predictive horizons) in the model predictive control are examined in terms of fuel consumption, rendezvous time and computational effort. The numerical results show the proposed control strategy is effective. [ABSTRACT FROM AUTHOR]

This paper developed a new multiphysics finite element method for the elastodynamic analysis of space debris deorbit by a bare flexible electrodynamic tether. Orbital motion limited theory and dynamics of flexible electrodynamic tethers are discretized by the finite element method, where the motional electric field is variant along the tether and coupled with tether deflection and motion. Accordingly, the electrical current and potential bias profiles of tether are solved together with the tether dynamics by the nodal position finite element method. The newly proposed multiphysics finite element method is applied to analyze the deorbit dynamics of space debris by electrodynamic tethers with a two-stage energy control strategy to ensure an efficient and stable deorbit process. Numerical simulations are conducted to study the coupled effect between the motional electric field and the tether dynamics. The results reveal that the coupling effect has a significant influence on the tether stability and the deorbit performance. It cannot be ignored when the libration and deflection of the tether are significant. [ABSTRACT FROM AUTHOR]

This paper presents a real-time, vision-based algorithm for the pose and motion estimation of non-cooperative targets and its application in visual servo robotic manipulator to perform autonomous capture. A hybrid approach of adaptive extended Kalman filter and photogrammetry is developed for the real-time pose and motion estimation of non-cooperative targets. Based on the pose and motion estimates, the desired pose and trajectory of end-effector is defined and the corresponding desired joint angles of the robotic manipulator are derived by inverse kinematics. A close-loop visual servo control scheme is then developed for the robotic manipulator to track, approach and capture the target. Validating experiments are designed and performed on a custom-built six degrees of freedom robotic manipulator with an eye-in-hand configuration. The experimental results demonstrate the feasibility, effectiveness and robustness of the proposed adaptive extended Kalman filter enabled pose and motion estimation and visual servo strategy. [ABSTRACT FROM AUTHOR]

The paper presents a tension control law to stabilize the motions of a Tethered Space-Tug system during its deorbiting process by regulating the tension in the tether. The tension control law is designed on a basis of two straightforward ideas, i.e., the potential energy shaping and the damping injection. The law is expressed in an analytical feedback form in terms of only the tether length without the need of the feedback of full state information. Meanwhile, the requirements of measuring velocities are removed with the aid of a dynamic extension technique based on the feedback interconnection of Euler-Lagrange systems. The positive and bounded tension constraint is taken into consideration explicitly by including a pair of special saturation terms in the feedback control law. The relative motions of the space-tug and the debris are described with respect to a local non-inertial orbital frame of reference, whereas the orbital motion equations of the system are formulated in terms of the modified equinoctial elements of the orbit. Finally, the effectiveness of the proposed scheme is demonstrated via numerical case studies. [ABSTRACT FROM AUTHOR]

This paper investigates the tracking and control problem of a spacecraft rendezvous with a non-cooperative and tumbling space target subject to parametric uncertainty and unknown external disturbances. The kinematics and dynamics of spacecraft position and attitude are described by dual quaternions. A novel adaptive sliding mode disturbance observer is proposed to track the pose of non-cooperative tumbling target without need for upper bounds of first and second derivatives of lumped disturbance. Based on the proposed observer, a finite time sliding mode control is developed in term of dual quaternion. Different from existing sliding mode control schemes, the conditions on the controller parameters bounds are relaxed. The stability and robustness of the overall closed-loop control is proved by the Lyapunov framework. The robustness and effectiveness of the proposed control scheme are validated by numerical simulations in comparison with existing approaches. • Track and control of spacecraft rendezvous with non-cooperative and tumbling targets. • Adaptive sliding mode disturbance observer. • Dual quaternion description of kinematics and dynamics of spacecraft. [ABSTRACT FROM AUTHOR]

This paper studies the libration suppression of a moon-based partial space elevator in the Earth-Moon three-body system. The elevator is connected to the Moon surface by a tether and a space station is connected to the free end of tether as the end body. One or multiple climber(s) can move along the tether to transfer cargos between the Moon and the end body. A high-fidelity dynamic model is derived to describe the motion of the climber(s), the end body and the flexible tether by the combination of rigid body dynamics and nodal position finite element method. The validity of the proposed model and the effect of element discretization along the tether on the dynamic behaviour of the elevator are investigated through numerical simulations. To ensure the stability and satisfy the mission constraints in the cargo transfer period, an optimal control based on the high-fidelity model is employed to regulate the control input with limited magnitude. Case studies show that by adjusting the thrusts on the end body reasonably, the libration of the Moon-based partial space elevator can be suppressed with limited control input effectively. • A novel looped Moon-based Partial Space Elevator with multiple climbers is proposed. • A high-fidelity dynamic model is developed by finite element method for the modeling and libration control. • Optimal control is applied successfully with the finite element method to suppress libration. [ABSTRACT FROM AUTHOR]

This paper investigates spacecraft orbital boost maneuver by a fully insulated electrodynamic tether using a coupled multiphysics dynamic model that considers electric-magnetic-dynamic energy coupling. The current-potential characteristics of the electrodynamic tether is described by a simplified analytical model, where revised Parker-Murphy model is employed to evaluate electric current generation at plasma contactors together with libration dynamics of tether. The 13th-order Earth's magnetic field model is used to account influence of inhomogeneity of Earth's magnetic field on orbital parameters of electrodynamic tether system, especially in inclined orbits. Parametric analysis has been conducted for orbital boost maneuver from 400 km to 1,200 km at four different orbital inclinations. The results show that (i) the orbit of electrodynamic tether system will change from circular to elliptical orbits, especially in inclined orbits, (ii) the voltage of onboard power supply at the anode affect electric current generation, (iii) the coupled multiphysics model is necessary to characterize the interaction of electrodynamic tether with the surrounding space environment and the controllability of electric current in electrodynamic tether, (iv) the motion of orbital boost maneuver by electrodynamic tether is stable, which is different from the deorbit by electrodynamic tether. • Developed coupled multiphysics model for orbit boost by electrodynamic tether. • Derived close-loop current-potential relation of electrodynamic tether. • Demonstrated orbital boost efficiency by dynamic simulation. [ABSTRACT FROM AUTHOR]

Five electrodynamic tether simulators (BETsMA v2.0, DYNATETHER, EDTSim, FLEX, and TeMPEST) have been cross-verified by running and analysing simulations of increasing complexity. A set of ten simulations without any tether was run to test the orbital propagators and the implementation of the perturbation force due to the non-sphericity of the Earth and its non-homogeneous mass distribution. The environmental models of the five codes and their implementation were then cross-verified by analysing the evolution of the magnetic field and the plasma and atmospheric densities. The electric modules of the simulators for electrodynamic tethers working in the passive mode, i.e., the routines in charge of computing the current and the voltage profiles along the tethers as well as the Lorentz force, were compared by running simulations with bare tethers. Configurations with an ideal electron emitter (zero potential drop), a real emitter, and a resistor and an ideal emitter were considered, as well as round and tape tethers. The electric models of BETsMA, EDTSim, FLEX, and TeMPEST, which assumed a straight tether, were also compared with the result of DYNATETHER for curved tethers. The consistency of the five simulators as a whole was tested by preparing performance maps with the deorbit time versus orbit inclination for a reference scenario and considering tape and round electrodynamic tethers. Although they implement different models and make different assumptions, the results of the five codes are consistent for the full simulation campaign. The simulation data and the software to visualize them are available in a public repository. • We present a systematic study to cross-verify 5 electrodynamic tether simulators. • An international collaboration of universities and an agency performed this work. • The simulation results are available in a public repository. • This work may serve as a valuable source of information for the tether community. [ABSTRACT FROM AUTHOR]

Abstract This paper investigates the stable orbital transfer of a climber in a partial space elevator system in circular orbits. The elevator includes a main satellite, an end body, and a climber, which are connected by two straight, inextensible, massless and variable length tethers. Derived from system dynamics, two closed-loop velocity control strategies are proposed to regulate the tethers' deploying and retrieving speeds directly to control the Coriolis forces acting on the climber and the end body directly. The stable region of the control strategies is analyzed, and the effectiveness of the proposed strategies is demonstrated by numerical simulation. Simulation results show that the newly proposed strategies effectively minimize the libration of a partial space elevator system during the orbital transfer of the climber and the system states successfully approach to the desired equilibrium by the end of the orbital transfer. Furthermore, the proposed deployment/retrieval control strategies can be converted to tension control laws easily. Highlights • Studied stable orbital transfer of a partial space elevator in circular orbits. • Developed velocity control strategies to suppress libration of elevator. • Controlled velocities by regulating tether deployment and retrieval rates. [ABSTRACT FROM AUTHOR]

This paper investigates the dynamic characteristics a three-body tethered satellite system in large elliptic orbits and the control strategy to suppress the libration of the system in orbital transfer process. The system is modeled by a two-piece dumbbell model in the domain of true anomaly. The model consists of one main satellite and two subsatellites connected with two straight, massless and inextensible tethers. Two control strategies based on the sliding mode control are developed to control the libration to the zero state and the steady state respectively. The results of numerical simulations show that the proposed control scheme has good performance in controlling the libration motion of a three-body tethered satellite system in an elliptic orbit with large eccentricity by limited control inputs. Furthermore, Hamiltonians in both states are examined and it shows that less control input is required to control the libration motion to the steady state than that of zero state. [ABSTRACT FROM AUTHOR]

This paper presents two transitions between microstrip and stripline in Low Temperature Co-fired Ceramic technology, including a vertical transition and a coplanar transition for millimeter-wave application. These interconnects are simulated and optimized by a three-dimensional electromagnetic field simulator. Simulation results show that the return loss of microstrip to stripline vertical transition is less than −22 dB, and insertion losses are greater than 0.5 dB up to 35 GHz, and greater than 1 dB up to 40 GHz. Similarly, the return loss of the coplanar transition is less than −32 dB and insertion loss is better than 0.5 dB. LTCC test structures were fabricated and the performance of all transitions was successfully validated by scattering parameter measurements up to 40 GHz. [ABSTRACT FROM AUTHOR]

A novel concept of a looped tether transportation system with multiple rungs (L-TTS-R) is proposed for highly efficient payload transfer in space. In addition to two huge platforms connected by two parallel tethers with multiple moving climbers, some rigid rungs are evenly distributed between the two tethers in L-TTS-R to suppress the libration movement of the system and to reduce or avoid the risk of collision between climbers and tethers in the process of payload transportation. To establish an accurate model of L-TTS-R in the framework of multibody system dynamics, the gradient deficient beam elements of the absolute nodal coordinate formulation (ANCF) are used to mesh two tethers. The sliding joint based on ANCF is introduced to build up the contact interaction model between tethers and climbers. The generalized forces acting on the L-TTS-R, for example, the gravitational force and the elastic force, are derived in brief. The generalized-alpha method is used to solve the dynamics equations of the constrained flexible multibody systems. Some representative examples are given to validate the effectiveness of the proposed L-TTS-R model for space payload transfer missions and to assess the influence of rungs on the system libration suppression, the climber collision risk avoidance, the relative oscillation and pitching motion of platforms, and the tether tensions. The numerical results reveal that the L-TTS-R shows distinct effects on suppressing the overall libration of the system, reducing or even avoiding the risk of collision between climbers and tethers and decreasing significantly the oscillating magnitudes of the relative distances between two platforms, and these effects are more visible with increasing the number of rungs. • A novel concept of a looped tether transportation system with multiple rungs (L-TTS-R) is proposed. • The absolute nodal coordinate formulation based beam element and sliding joint are used to establish the model of L-TTS-R. • The influence of rungs on the system dynamics is assessed. [ABSTRACT FROM AUTHOR]