Learning Reference Governor for Constrained Spacecraft Rendezvous and Proximity Maneuvering

On reference governor in iterative learning control for dynamic systems with input saturation

A novel concept of cost-effective active debris removal spacecraft system

This paper describes the second iteration in the development of a simulation tool that provides trade-offs of avionic architectures for future Active Debris Removal (ADR) space missions.

This paper describes a learning-based approach to operating safety-critical control systems. A reference governor is an add-on scheme used to guard the nominal system against violation of pre-specified constraints by modifying set-point commands. A learning algorithm is developed in this paper to evolve the reference governor parametrization to gradually improve its performance in terms of response speed. In particular, the learning algorithm does not rely on an explicit model of the control system, i.e., it is model-free, and guarantees constraint satisfaction for all time, both during and after learning. The approach is applied to a case study of ground vehicle rollover avoidance to illustrate its functionality and characteristics.

This paper presents the concepts for a new family of holonomic wheeled platforms that feature full omnidirectionality with simultaneous and independently controlled rotational and translational motion capabilities. The authors first present the "orthogonal-wheels" concept and the two major wheel assemblies on which these platforms are based. The authors then describe how a combination of these assemblies with appropriate control can be used to generate an omnidirectional capability for mobile robot platforms. Several alternative designs are considered, and their respective characteristics with respect to rotational and translational motion control are discussed. The design and control of a prototype platform developed to test and demonstrate the proposed concepts is then described, and experimental results illustrating the full omnidirectionality of the platform with decoupled rotational and translational degrees of freedom are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

This paper mainly addresses the formation control problem for a group of tail-sitters in transition flight between forward and vertical flight. A robust formation control method is proposed to achieve the aggressive time-varying formation subject to nonlinear dynamics and uncertainties. For each tail-sitter, the proposed control method results in a composite controller that includes a trajectory tracking controller and an attitude controller to achieve the translational and rotational motion control, respectively. It is proven that tracking errors of the proposed global closed-loop system can converge to a given neighborhood around the origin in a finite time. Finally, the simulation studies for multiple tail-sitters to accomplish the time-varying formation in transition flight are presented to show the effectiveness of the proposed control strategy.

Controller Design for a 1000 MW Ultra Super Critical Once-through Boiler Power Plant

This article proposes an integrated optimal control strategy for a servicing spacecraft in proximity operations on a target in space. The relative position vector between the servicing spacecraft and the target is required to direct towards the docking port of the target while the attitude of the two bodies must be synchronised without exciting large flexible vibrations. The control of translational, rotational and flexible motions is formulated in one unified optimal control framework in which the tracking errors in relative position and attitude, and flexible structure vibrations can be minimised simultaneously using one cost function. This formulation results in a highly nonlinear system that poses a challenging control problem. The nonlinear optimal control technique is employed to design a closed-form feedback control law for this nonlinear control problem by finding an approximate solution to the Hamilton–Jacobi–Bellman (HJB) equation through a perturbation process. The closed-form controller offered by this approach is easy to implement onboard especially for this problem with a large state-space. Numerical simulations including the six degrees-of-freedom rigid body dynamics and coupled flexible structure dynamics are performed to demonstrate the effectiveness of this control formulation even under large moment of inertia uncertainties.

Obstacle Avoidance Considering Robot's Size for an Autonomous Omni-directional Mobile Robot by Simultaneous Control of Translational and Rotational Motions

This paper proposed an integrated optimal control strategy for a servicing spacecraft in proximity operations on a target in space. The relative position vector between the servicing spacecraft and the target is required to direct towards the docking port of the target while the attitude of the two bodies must be synchronized without exciting large flexible vibrations. The control of translational, rotational, and flexible motions is formulated in one unified optimal control framework in which the tracking errors in relative position and attitude, and flexible structure vibrations can be minimized simultaneously using one cost functional. This formulation results in a highly nonlinear system that poses a challenging control problem. The θ nonlinear optimal control technique is employed to design a closed-form feedback control law for this nonlinear control problem by finding an approximate solution to the Hamilton-Jacobi-Bellman (HJB) equation through a perturbation process. The closed-form controller offered by this approach is easy to implement onboard especially for this problem with a large state-space. Numerical simulations including the six degree-of-freedom rigid body dynamics and coupled flexible structure dynamics are performed to demonstrate the effectiveness of this control formulation even under large moment of inertia uncertainties. -D

In this paper, a two-level reconfiguration action is used to design an Active Fault Tolerant Control (AFTC) system. The first level of the procedure is triggered when the impact of the fault on the system performance is limited. The reconfigurable controller is updated by the new post-fault system model. At the second level a dynamic reference modification based on Reference Governor (RG) is proposed. The idea consists of modifying the set-point or reference according to the allowable performance degradation and the system constraints which become more strict after fault occurrence in order to avoid any actuator saturation and ensure system stability. The effectiveness of the proposed solution is illustrated by a wind turbine example subjects to actuator faults and constrained on the actuator dynamic ranges.

Control of proton exchange membrane fuel cell system breathing based on maximum net power control strategy

This paper aims at improving the contouring accuracy in biaxial position control systems. A quadratic cost functional consisting of the contour error is formulated including both axes of the system. Linear constraints on the motor voltages and currents are considered. Modeling of the driving motors including the often neglected current dynamics enables precise position control. Even constraints on the contour error can be considered, e.g. to meet manufacturing tolerances. This so called model predictive contouring control is employed in a control structure consisting of a reference governor which adapts the path reference in order to meet constraints and a subordinate unconstrained controller for precise tracking of the reference. This flexible structure is simple to tune and makes it possible to decouple the computationally complex optimization from the subordinate controller.

Autonomous proximity operations to explore small solar system bodies (asteroids and comets), servicing of aerospace vehicles, and active space debris removal, are likely to increase in the future with NASA’s Asteroid Redirect Mission and Grand Challenge, and planned activities in autonomous rendezvous/proximity operations (ARPO) and active debris removal. Autonomous navigation is essential for these applications. The concept proposed here is to have a single stable estimator for the naturally coupled translational and rotational motion of an observed object from only vision-based, infra-red or lidar measurements, without needing a dynamics model for this object, during proximity operations. This estimator can also be used to improve an existing dynamics model. This avoids the need for measurements from external sources, like GPS, which is anyway not available for proximity operations near asteroids or comets. It also avoids mishaps due to changes in sensors and estimation schemes used during close proximity operations between spacecraft, as witnessed during the DART and Orbital Express missions. Attitude and translational motion of spacecraft, asteroids and comets are dynamically coupled through natural effects like gravity as well as control forces and torques for spacecraft. This coupling can also be used to estimate the mass and gravity parameters of the asteroid/comet.

Space debris, such as abandoned rocket bodies, defunct satellites, and space rocks, poses an ever-increasing risk to satellites and spacecraft, threatening the long-term security and stability of the space environment. Active debris removal has become a critical task for the spaceflight community. Traditional rigid manipulators for capturing debris are heavy and lack adaptability, often causing unwanted collisions during interactions with fragile objects. This paper presents a novel lantern-like manipulator actuated by smart materials, capable of shape deformation via shape memory alloys (SMAs) and variable stiffness modulation using polycaprolactone (PCL). Experimental results demonstrate the manipulator’s ability to capture non-cooperative targets with irregular shapes, offering a promising solution for compliant active debris removal in future space missions.