Pointing-error simulations of the DSS-13 antenna due to wind disturbances

Accurate spacecraft tracking by the NASA Deep Space Network (DSN) antennas must be assured during changing weather conditions. Wind disturbances are the main source of tracking errors. The development of a wind-force model and simulations of wind-induced pointing errors of DSN antennas are presented. The antenna model includes the antenna structure, the elevation and azimuth servos, and the tracking controller. Simulation results show that pointing errors due to wind gusts are of the same order as errors due to static wind pressure and that these errors (similar to those of static wind pressure) satisfy the velocity quadratic law. The presented methodology is used for wind-disturbance estimation and for the design of an antenna controller with wind-disturbance rejection properties

Robust motion control of nonlinear quadrotor model with wind disturbance observer

This paper focuses on robust wind disturbance rejection for nonlinear quadrotor models. By leveraging on nonlinear unknown observer theory, it proposes a nonlinear dynamic filter that, using sensors already on-board the aircraft, can estimate in real-time wind gust signals in the three dimensions. The wind disturbance is then treated as input to the PD controller for a quick and robust flight pathway in presence of disturbances. With this scheme, the wind disturbance can be precisely estimated online and compensated in real-time. Hence, the quadrotor can successfully reach its desired attitude and position. To show the effective and desired performance of the method, simulation results are presented in Matlab/Simulink and ROS-enabled Gazebo platform

Geometric Adaptive Control for a Quadrotor UAV with Wind Disturbance Rejection

This paper presents a geometric adaptive control scheme for a quadrotor unmanned aerial vehicle, where the effects of unknown, unstructured disturbances are mitigated by a multilayer neural network that is adjusted online. The stability of the proposed controller is analyzed with Lyapunov stability theory on the special Euclidean group, and it is shown that the tracking errors are uniformly ultimately bounded with an ultimate bound that can be abridged arbitrarily. A mathematical model of wind disturbance on the quadrotor dynamics is presented, and it is shown that the proposed adaptive controller is capable of rejecting the effects of wind disturbances successfully. These are illustrated by numerical examples

Robust Input Shaping for Sway Control of an Overhead 3D Crane

This paper presents a robust input shaping control of an overhead 3D crane. Control of a crane in the presence of wind disturbance during payload hoisting is extremely challenging, as hoisting with wind disturbance causes high unwanted payload sway, which makes payload positioning difficult to achieve. Two robust input shaping techniques are presented, the zero vibration derivative-derivative (ZVDD) and extra insensitive (EI) shapers. Simulations using a nonlinear 3D overhead crane model were performed and the performances of the two robust input shapers are compared. In these investigations a wind disturbance force of magnitude 0.3 N is considered for the robustness test, in addition different payload mass were tested. It is predicted that the method can be very useful in reducing the complexity of closed-loop controllers for both tracking and sway control

Wind Disturbance Suppression in Autopilot Design

Environmental conditions affects ship’s course. Hence, it affects velocity, and efficiency of fuel consumption, which is an important research topic nowadays. Therefore, it is important to take it into account in the design of ship’s autopilots. In this paper a method is proposed to compensate for wind’s influence, which is based on wavelet transform by introducing the so called wavelet anti-filter. The anti-filter is added to the feed-forward branch of the classic autopilot design scheme, which consists of feedback loop and PID controller. The anti-filter branch represents a modification of the classic scheme

On the He II Emission In Eta Carinae and the Origin of Its Spectroscopic Events

We describe and analyze Hubble Space Telescope (HST) observations of transient emission near 4680 {\AA} in Eta Car, reported earlier by Steiner & Damineli (2004). If, as seems probable, this is He II $\lambda$4687, then it is a unique clue to Eta Car's 5.5-year cycle. According to our analysis, several aspects of this feature support a mass-ejection model of the observed spectroscopic events, and not an eclipse model. The He II emission appeared in early 2003, grew to a brief maximum during the 2003.5 spectroscopic event, and then abruptly disappeared. It did not appear in any other HST spectra before or after the event. The peak brightness was larger than previously reported, and is difficult to explain even if one allows for an uncertainty factor of order 3. The stellar wind must provide a temporary larger-than-normal energy supply, and we describe a special form of radiative amplification that may also be needed. These characteristics are consistent with a class of mass-ejection or wind-disturbance scenarios, which have implications for the physical structure and stability of Eta Car.Comment: 47 pages (including all appendices, tabs, & figs), 9 figures, 3 tables; submitted to Astrophysical Journal (2005 March 29), accepted for publication in Ap