Exponentially convergent velocity observer for an electrodynamic tether in an elliptical orbit
Hao Wen, Zhengong Zhu, Donging Jin, Hayan Hu
Abstract: This Note presents a nonlinear observer to estimate the un-measured attitude velocities of the EDT system orbiting in an inclined elliptical orbit. The dynamics of an EDT system, which is time varying by nature in the case of an elliptic orbit, is transformed into a special state-space representation via a transformation of coordinates, such that the velocity observer can be established on the basis of the immersion and invariance principle. As a result, the design of the velocity observer is recast as a state observer problem of the transformed state-space system. The proposed velocity observer demonstrates analytically the exponential convergence of the estimation errors, irrespective of the electric current inputs. Thus, the velocity observer can be adapted for control laws using different electric current profiles. Furthermore, the performance of the pro-posed scheme is numerically evaluated via two case studies, which are subject to the same system parameters but different actuating conditions. The current is switched off in the first case and set to be a constant in the second case. The simulation results of both cases demonstrate a smooth and rapid convergence of the estimated velocities to the true values, even in the presence of measurement noise. The proposed method is demonstrated with a simple dumbbell model of the EDT system to verify the aforementioned concepts. Further extension is required to handle a flexible tether, such that the EDT dynamics could be more precisely addressed. （期刊无摘要，此摘要为该文简介）
原文链接: https://arc.aiaa.org/doi/abs/10.2514/1.G001532
