An integrated guidance and feedback control scheme for steering an underactuated vehicle through desired waypoints in three-dimensional space, is developed here. The underactuated vehicle is modeled as a rigid body wi...
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An integrated guidance and feedback control scheme for steering an underactuated vehicle through desired waypoints in three-dimensional space, is developed here. The underactuated vehicle is modeled as a rigid body with four control inputs. These control inputs actuate the three degrees of freedom of rotational motion and one degree of freedom of translational motion in a vehicle body-fixed coordinate frame. This actuation model is appropriate for a wide range of underactuated vehicles including spacecraft with internal attitude actuators, vertical take-off and landing (VTOL) aircraft, fixed-wing multirotor unmanned aerial vehicles (UAVs), maneuverable robotic vehicles, etc. The guidance problem is developed on the special Euclidean group of rigid body motions, SE(3), in the framework ofgeometric mechanics, which represents the vehicle dynamics globally on this configuration manifold. The integrated guidance and control algorithm selects the desired trajectory for the translational motion that passes through the given waypoints, and the desired trajectory for the attitude based on the desired thrust direction to achieve the translational motion trajectory. A feedback control law is then obtained to steer the underactuated vehicle towards the desired trajectories in translation and rotation. This integrated guidance and control scheme takes into account known bounds on control inputs and generates a trajectory that is continuous and at least twice differentiable, which can be implemented with continuous and bounded control inputs. The integrated guidance and feedback control scheme is applied to an underactuated quadcopter UAV to autonomously generate a trajectory through a series of given waypoints in SE(3) and track the desired trajectory in finite time. The overall stability analysis of the feedback system is addressed. Discrete time models for the dynamics and control schemes of the UAV are obtained in the form of Lie group variational integrators using the discr
Re-entry guidance is one of the primary tasks of a global strike mission. Hypersonic and common aero vehicles are currently being investigated for missions like this. This paper proposes a guidance law considering not...
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Re-entry guidance is one of the primary tasks of a global strike mission. Hypersonic and common aero vehicles are currently being investigated for missions like this. This paper proposes a guidance law considering not only the constraints of terminal status and flight process, but also the avoidance of no-fly zones, to meet the requirements of a global strike mission. An improved A* algorithm is proposed first to achieve a real-time trajectory planning process. Then a dynamic optimization guidance law based on the model of a hypersonic vehicle considering single and multiple no-fly zones is founded. Numerical simulations show the robustness and rapidity of this optimization method.
Future landing and sample return missions on planets and small bodies will seek landing sites with high scientific value, which may be located in hazardous terrains. Autonomous landing in such hazardous terrains and h...
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Future landing and sample return missions on planets and small bodies will seek landing sites with high scientific value, which may be located in hazardous terrains. Autonomous landing in such hazardous terrains and highly uncertain planetary environments is particularly challenging. Onboard hazard avoidance ability is indispensable, and the algorithms must be robust to uncertainties. In this paper, a novel probability-based hazard avoidance guidance method is developed for landing in hazardous terrains on planets or small bodies. By regarding the lander state as probabilistic, the proposed guidance algorithm exploits information on the uncertainty of lander position and calculates the probability of collision with each hazard. The collision probability serves as an accurate safety index, which quantifies the impact of uncertainties on the lander safety. Based on the collision probability evaluation, the state uncertainty of the lander is explicitly taken into account in the derivation of the hazard avoidance guidance law, which contributes to enhancing the robustness to the uncertain dynamics of planetary landing. The proposed probability-based method derives fully analytic expressions and does not require off-line trajectory generation. Therefore, it is appropriate for real-time implementation. The performance of the probability-based guidance law is investigated via a set of simulations, and the effectiveness and robustness under uncertainties are demonstrated.
While common Descent and Landing strategies involve extended periods of forced motion, significant fuel savings could be achieved by exploiting the natural dynamics in the vicinity of the target. However, small bodies...
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While common Descent and Landing strategies involve extended periods of forced motion, significant fuel savings could be achieved by exploiting the natural dynamics in the vicinity of the target. However, small bodies are characterised by perturbed and poorly known dynamics environments, calling for robust autonomous guidance, navigation and control. Airbus Defence and Space and the University of Bristol have been contracted by the UK Space Agency to investigate the optimisation of landing trajectories, including novel approaches from the dynamical systems theory, and robust nonlinear control techniques, with an application to the case of a landing on the Martian moon Phobos.
This paper describes a novel lateral guidance law for an unmanned aerial vehicle using nonlinear receding horizon optimization and shows its flight test results. The guidance law uses an extended Kalman filter which e...
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This paper describes a novel lateral guidance law for an unmanned aerial vehicle using nonlinear receding horizon optimization and shows its flight test results. The guidance law uses an extended Kalman filter which estimates steady wind velocities in order to follow a pre-specified reference path defined in a ground-fixed coordinate system. The guidance law can be applied to arbitrary reference path as long as the path is represented as a differentiable function of x and y in a ground-fixed coordinate system. A small-scale research vehicle developed by the Japan Aerospace Exploration Agency is used for flight tests, and the results demonstrate the high guidance performance of the proposed method. (C) 2018 Elsevier Masson SAS. All rights reserved.
In order to improve the precision of guidance for the missile intercepting maneuvering targets, this paper proposes a sliding mode guidance law with impact angle constraints based on the equation of the relative motio...
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In order to improve the precision of guidance for the missile intercepting maneuvering targets, this paper proposes a sliding mode guidance law with impact angle constraints based on the equation of the relative motion of the missile and the target in a 2D plane. Two finite-time convergent guidance laws are proposed based on the nonsingular terminal sliding mode, while, two exponential convergent guidance laws involving dynamic delay are developed through applying the higher-order nonsingular terminal sliding mode. The simulations denote that, in all the four scenarios of the target＇s maneuvering, the guidance laws are able to inhibit the chattering phenomenon of the sliding modes effectively; and from an expected aspect angle, the missiles could attack the targets with high precision and fast speed.
Process knowledge is a vital prerequisite for employees to execute organizational processes successfully in the course of their daily work. However, the lack of process knowledge, especially concerning novice users, a...
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Process knowledge is a vital prerequisite for employees to execute organizational processes successfully in the course of their daily work. However, the lack of process knowledge, especially concerning novice users, and the need for support pose a challenge to employers. Inspired by research on spatial knowledge and navigation, we conceptualize three process knowledge types addressing the needs of employees during their process execution. On the basis of these process knowledge types, we derive three theoretically grounded design principles for process guidance systems to support employees' process execution. We instantiate the design principles and evaluate the resulting artifacts in a laboratory experiment and in a subsequent field study. The results demonstrate the positive effects of process guidance systems on users' process knowledge and process execution performance. Our study contributes to research and practice by proposing a new conceptualization of process knowledge and a nascent design theory for process guidance systems that builds on theories of spatial knowledge and navigation, as well as decision support research.
Enhancing precision has been the essential goal for ballistic rockets since the beginnings of this aircraft class. In the past, ballistic rockets impact point precision deteriorated at the same time as range was exten...
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Enhancing precision has been the essential goal for ballistic rockets since the beginnings of this aircraft class. In the past, ballistic rockets impact point precision deteriorated at the same time as range was extended, specially for those rockets which were nonpropelled and nonguided amid the greater part of their trajectories. Once that inertial and Global Navigation Satellite System (GNSS) navigation and guidance systems were introduced, precision was unlinked from range increments. The fundamental issue for these inertial and GNSS strategies (hybridized or not) is the enormous errors on attitude and position determination during last phases of flight as the movement is governed by aerodynamic forces and moments, which feature a deeply nonlinear character. Choosing another kind of low-cost sensors, independent of accumulative errors and precise on terminal guidance, for example, quadrant photodetector semi-active laser, is crucially essential. Hybridization of nonlinear algorithms, such as extended Kalman filter, joining measurements from sensors such as GNSS, inertial measurement units and photodetectors are described in this paper to be utilized on modified proportional navigation techniques and novel control methods. The results are tested on rocket nonlinear flight simulations in order to prove the accuracy of proposed algorithms.
Solid rocket motors expect to remove the thrust termination mechanism to increase the strength of structure and reduce the cost, which induce new difficulties and challenges to ascent guidance. This paper presents an ...
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Solid rocket motors expect to remove the thrust termination mechanism to increase the strength of structure and reduce the cost, which induce new difficulties and challenges to ascent guidance. This paper presents an ascent guidance algorithm for small solid launch vehicles (SSLVs) which shut off by fuel exhaustion. A pointing algorithm is tailored for the baseline guidance algorithm of SSLVs with constraints of the velocity vectors and the position vectors. Subsequently, an energy management technique is developed for dissipating the extra energy that the solid rockets have when shutting off by fuel exhaustion. The energy management technique primarily allocates the energy to different sub-stages, while an attitude control energy management method is applied to the dissipation of the excess energy at one stage. Finally, the proposed guidance algorithm is verified by Monte Carlo simulations in which the dispersions of vehicle mass, operation temperature of motors and aerodynamic coefficient as well as random wind shear are considered. The testing results demonstrate the capability, strong robustness and excellent performance of the proposed guidance algorithm. (C) 2018 Elsevier Masson SAS. All rights reserved.
A dynamic model of a high-speed instrument rotor bearing is established, in which the parched oil lubrication is considered. The machine for dynamic test of the cage is designed to measure the cage centroid trajectory...
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A dynamic model of a high-speed instrument rotor bearing is established, in which the parched oil lubrication is considered. The machine for dynamic test of the cage is designed to measure the cage centroid trajectory, and there comes a good agreement between the experimental results and the theoretical results. Based on the dynamic model, the force and motion of bearing cage under different conditions is analyzed, for instance, inner ring rotates with inner ring guidance (TRIG), inner ring rotates with outer ring guidance (IROG), outer ring rotates with inner ring guidance (ORIG), and outer ring rotates with outer ring guidance (OROG). Considering of ring guidance mode and rotation mode, the cage movement is investigated through the decomposition of the force on the cage. It is found the direction of cage-guide ring friction force has a significant effect on the cage whirl. When the cage is guided by rotated ring, the direction of cage-guide ring friction force is same as that of the cage whirl, and the cage movement is relatively stable;When the cage is guided by fixed ring, the direction of cage-guide ring friction force is opposite to that of the cage whirl, and the instability of the cage increases. The cage is more stable when the inner ring rotation is relative to the outer ring rotation. The instability of the cage whirl speed will cause fluctuations in the whirl radius of the cage.
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