Uncontrolled Target Research Articles

Contextual cueing during lethal force training: How target design and repetition can alter threat assessments

ABSTRACT Lethal force training requires individuals to make threat assessments, which involves holistic scenario processing to identify potential threats. Photorealistic targets can make threat/non-threat judgments substantially more genuine and challenging compared to simple cardboard or silhouette targets. Unfortunately, repeated target use also brings unintended consequences that could invalidate threat assessment processes conducted during training. Contextually rich or unique targets could be implicitly memorable in a way that allows observers to recall weapon locations rather than forcing observers to conduct a naturalistic assessment. Experiment 1 demonstrated robust contextual cueing effects in a well-established shoot/don’t-shoot stimulus set, and Experiment 2 extended this finding from complex scene stimuli to simple actor-only stimuli. Experiment 3 demonstrated that these effects also occurred among trained professionals using rifles rather than computer-based tasks. Taken together, these findings demonstrate the potential for uncontrolled target repetition to alter the fundamental processes of threat assessment during lethal force training.

Space Robot Performance During Tangent Capture of an Uncontrolled Target Satellite

Space Robot Performance During Tangent Capture of an Uncontrolled Target Satellite

Pose Tracking Control for Spacecraft Proximity Operations Using the Udwadia–Kalaba Framework

This paper develops an analytical dynamics-based approach for simultaneous position and orientation tracking control of a chaser spacecraft with respect to an uncontrolled target. The control requirements are formulated as holonomic or nonholonomic constraints, which are expressed as linear and angular acceleration constraints. The complete six-degree-of-freedom formulation of the Udwadia–Kalaba-based pose tracking controller generating exact real-time control forces and torques is presented. For design purposes, the method assumes a precise knowledge of the system parameters and states, along with perfect control action by the actuators. The exponential convergence of the constraint dynamics is proven using the Lyapunov stability theory. Simulation results demonstrate exponentially stable position and orientation tracking for close-proximity operations in perturbed low Earth orbits. Finally, the controller is experimentally validated using the Spacecraft Proximity Operations Testbed at Carleton University.

Microfibrillated cellulose films containing chitosan and tannic acid for wound healing applications

The effectiveness of tannic acid as antimicrobial and wound healing for burns have been shown for a century; however, uncontrolled target dosage may result in undesirable side-effects. Remarkably, tannic acid polyphenols compounds crosslinked with polymeric materials produce a strong composite containing the beneficial properties of this tannin. However, investigation of the crosslink structure and its antibacterial and regenerative properties are still unknown when using nanocellulose by mechanical defibrillation; additionally, due to the potential crosslink structure with chitosan, its structure can be complex. Therefore, this work uses bleach kraft nanocellulose in order to investigate the effect on the physical and regenerative properties when incorporated with chitosan and tannic acid. This film results in increased rigidity with a lamellar structure when incorporated with tannic acid due to its strong hydrogen bonding. The release of tannic acid varied depending on the structure it was synthesised with, whereas with chitosan it presented good release model compared to pure cellulose. In addition, exhibiting similar thermal stability as pure cellulose films with antibacterial properties tested against S. aureus and E. coli with good metabolic cellular viability while also inhibiting NF-κB activity, a characteristic of tannic acid.

Optimal Real-Time Approach and Capture of Uncontrolled Spacecraft

An optimal real-time neural-network-based controller for an on-orbit service mission is proposed. The problem can be mathematically formulated as a complex optimal control problem due to the coupling nature of the orbit, the attitude, and the manipulator of the chaser spacecraft. A hierarchical optimization procedure is developed to efficiently solve the problem by recursively applying three optimization modules. The relative motion characteristics and the decoupled wrist–arm feature are used to transform the solved optimal solutions into easier learnable samples. A series of deep neural network (DNN) controllers are designed to learn from these samples. The performances of the trained network controllers are analyzed by altering the number of learned trajectories and the structure of networks. Simulation results illustrate that the designed DNN controllers can successfully guide a chaser to approach and capture an uncontrolled target with tolerable errors.

Concurrent Proximity Control of Servicing Spacecraft With an Uncontrolled Target

This paper investigates the six-degrees-of-freedom (6-DOF) rendezvous and docking issue with an uncontrolled target for a servicing spacecraft under thruster misalignment and external disturbances. Initially, a 6-DOF relative motion dynamic model is established to depict the relative position–attitude between the servicing spacecraft and uncontrolled object (freely tumbling spacecraft). Then, an adaptive fixed-time control scheme with a novel sliding manifold is employed to accomplish the 6-DOF rendezvous (close-range) and docking mission for the servicing spacecraft. Unlike existing methods, the sliding-mode surface is designed by using the new sufficient condition to achieve the system's fixed-time convergence, and this condition reduces the conservativeness of the traditional ones with less dominated terms. Moreover, the settling time of relative translation-rotation tracking errors is guaranteed irrespective of initial motion conditions. Accordingly, the fixed-time stability of the closed-loop system is guaranteed by the rigorous Lyapunov theory analysis. Finally, numerical simulation results with various cases are implemented to verify the superiority of the presented sliding-mode control strategy.

Dual-arm coordinated capturing of an unknown tumbling target based on efficient parameters estimation

A malfunctioned satellite or other space debris is generally non-cooperative and tumbling, bringing great challenge to capture and remove it. In this paper, we propose a dual-arm coordinated capturing method based on efficient parameters estimation. Firstly, the dynamics model of a tumbling target is deduced in details. Its motion characteristics are then analyzed. Secondly, we design an efficient Hybrid Kalman Filter (HKF) by combining Extended Kalman Filter (EKF) with Unscented Kalman Filter (UKF). It effectively overcomes the shortcoming of low accuracy of EKF and long iteration time of UKF, and improves the speed and accuracy of the Kalman Filter iteration algorithm. Two movement cases of an uncontrolled target are considered: one is rotation around the principal axes of inertia; the other is rotation around arbitrary axes. Thirdly, the estimated motion and inertia parameters are used to plan the trajectories of a dual-arm space robot to capture the tumbling target. Finally, the simulation environment is created and the proposed method is verified. The simulation results show that the proposed HKF algorithm can estimate the attitude quaternion, angular velocity, and the inertia tensor (including Ixx, Iyy, Izz, Ixy, Ixz and Iyz) with higher accuracy (compared to EKF) and lower computation cost (compared to UKF); the planned trajectories of the dual-arm space robot are effectively for tumbling target capturing.

On-orbit servicing of geosynchronous satellites based on low-thrust transfers considering perturbations

The goal of this paper is to investigate the on-orbit servicing (OOS) of geosynchronous satellites based on low-thrust transfers while considering the different demands of the satellites and the effects of perturbations. One or more servicing spacecraft start from a parking orbit and service the satellites in sequence via low-thrust orbit transfers, and return to the parking orbit in the end. The different demands lead to different service requirements of time and mass, while the perturbations affect the control solution of servicing spacecraft during each transfer, and induce orbit drifts of uncontrolled target satellites during the mission. An analytical method that can efficiently calculate the fuel consumption of low-thrust transfer is proposed, and methods for evaluating the orbit drifts of uncontrolled satellites are presented. The impact of perturbations on OOS mission is investigated in detail, showing that non-negligible factors include lunisolar attraction and tessral harmonic. Based on the dynamic models, a string-based simulated annealing algorithm is adopted to schedule the OOS mission. The efficiency of the proposed dynamic models and optimization method are verified through ample simulations. Results show that it is much more efficient and reasonable to take orbit drift calculations as corrections on the scheduling result assuming no orbit drifts. The proposed models and methods make it possible to schedule the OOS mission with low-thrust transfers, while achieving high accuracy under the effects of J2 perturbation, lunisolar attracion, tesseral harmonic and solar radiation pressure.

Dual-quaternion-based modeling and control for motion tracking of a tumbling target

This paper investigates the problem of controlling a chasing spacecraft (chaser) to track and rendezvous with an uncontrolled target. Based on the actual situation, the torque-free motion of an axisymmetric prolate rigid body is employed to represent the short-term attitude motion of the tumbling target. By taking advantage of the dual quaternion's compact and efficient description of the general rigid motion, the coupled and integrated model of the 6-degree-of-freedom (6-DOF) relative motion between the chaser and the tumbling target is derived in the chaser's body fixed frame after taking full consideration of coordinate transformation. Based on the logarithm of dual quaternion, a sliding mode control (SMC) law based on the exponential reaching law and the continuous relay function is brought forward to address the problem of synchronization control of the 6-DOF relative motion. Simulation results illustrate the effectiveness of the proposed method.

Safe path planning for free-floating space robot to approach noncooperative spacecraft

In order to eliminate plume impingement on the target satellite, a free-floating space robot (also known as a chaser), which has the advantage of executing on-orbit service, is always used. This paper develops a path planning method for a safe rendezvous of chaser with a noncooperative target satellite in orbital coordinates. Safety principles for rendezvous in terminal approaching phase are proposed. Grasp points on the target satellite are analyzed and classified into two categories, and a moving ellipse trajectory is adopted to approach a rotating and uncontrolled target satellite. This method guarantees that the chaser can successfully escape if unexpected error occurs or capture fails. The simulation results show that, with this novel autonomous rendezvous method, the chaser can approach the noncooperative target satellite along the designated trajectory in any quadrant of the orbital plane.

Modelling and Optimal Control of a Docking Maneuver with an Uncontrolled Satellite

AbstractCapturing disused satellites in orbit and their controlled reentry is the aim of the DEOS space mission. Satellites that ran out of fuel or got damaged pose a threat to working projects in orbit. Additionally, the reentry of such objects endangers the population as the place of impact cannot be controlled anymore. This paper demonstrates the modelling of a rendezvous szenario between a controlled service satellite and an uncontrolled target. The situation is modelled via first order ordinary differental equations where a stable target is considered. In order to prevent a collision of the two spacecrafts and to ensure both satellites are docked at the end of the maneuver, additional state constraints, box contraints for the control and a time dependent rendezvous condition for the final time are added. The problem is formulated as an optimal control problem with Bolza type cost functional and solved using a full discretization approach in AMPL/IpOpt. Last, simulation results for capturing a tumbling satellite are given.

Rotational motion-damper for the capture of an uncontrolled floating satellite

This paper discusses a method for damping the angular momentum of an uncontrolled target satellite in order to make it easy to capture using a chaser-satellite-mounted robotic arm. During the capture operation of an uncontrolled floating target, it may be difficult for the arm to grapple it directly because of the target’s nutation or tumbling. In this paper, the authors propose a contact/push-based control method using a cushion-type damper in order to absorb the rotational motion. The scenario is as follows: (1) a cushion-type damper is attached to the end-effector of the arm, (2) the arm softly pushes the damper on a selected point on the target, and (3) the contact force between the damper and the target causes the angular momentum of the target to decrease. The validity and feasibility of the proposed method are verified through numerical simulations.

接触・押し動作を利用した非協力衛星の角運動量減衰制御

This paper discusses a method for damping the angular momentum of an uncontrolled target satellite in order to make it easy to capture using a chaser-satellite-mounted manipulator. During the capture operation of an uncontrolled floating target, it may be difficult for a manipulator to grapple it directly because of target nutation or tumbling. In this paper, we propose using a cushion type damper in order to absorb the rotational motion. The scenario is as follows: 1) a cushion type damper is attached to the end-effector of the manipulator, 2) the manipulator softly pushes the damper on carefully selected points on the target, and 3) the contact force between the damper and the target causes the angular momentum of the target to decrease. The validity and feasibility of the proposed method are verified through numerical simulations.

Rotational-Motion-Damper for Capture of an Uncontrolled Floating Satellite

This paper discusses a method for damping the angular momentum of an uncontrolled target satellite in order to make it easy to capture using a chaser-satellite-mounted manipulator. During the capture operation of an uncontrolled floating target, it may be difficult for a manipulator to grapple it directly because of target nutation or tumbling. In this paper, the authors propose using a cushion type damper in order to absorb the rotational motion. The scenario is as follows: 1) a cushion type damper is attached to the end-effector of the manipulator, 2) the manipulator softly pushes the damper on a selected point on the target, and 3) the contact force between the damper and the target causes the angular momentum of the target to decrease. The validity and feasibility of the proposed method are verified through numerical simulations.