A new type of estimator is developed for the satellite formation to track and inspect on-orbit targets.The follower satellite in the formation works without relative sensors,and its target pointing commands are derived based on relative orbital dynamics.The centralized estimator based on truth measurement is designed,however,this estimator is proved unstable because of the lack of necessary measurement information.After that,an alternative estimator based on pseudo measurement is designed,and its observability and controllability are analyzed to qualitatively evaluate the convergence performance.Finally,an on-orbit target inspection scenario is numerically simulated to verify the performance of the estimator based on pseudo measurement.
This paper addresses the attitude control problem of a space tethered robot platform in the presence of unknown external disturbance caused by a connecting elastic tether. The tethergenerated unknown disturbance leads to tremendous challenges for attitude control of the platform.In this work, the perturbed attitude dynamics of the platform are derived with a consideration of the libration of the elastic tether, and then with the purpose of compensating the unknown disturbance, major attention is dedicated to develop a nonlinear disturbance observer based on gyros measurements, after which, an adaptive attitude scheme is proposed by combining the disturbance observer with a sliding mode controller. Finally, benefits from the observer based on an adaptive controller are validated by series of numerical simulations.
