This paper presents a fault-tolerant method for estimating the angular rate of uncontrolled bodies in space, such as failed spacecrafts. The bodies are assumed to be free of any sensors; however, a planned mission is assumed to track several features of the object by means of stereo-vision sensors. Tracking bodies in the space environment using these sensors is not, in general, an easy task: obtainable information regarding the attitude of the body is often corrupted or partial.The developed method exploits this partial information to completely recover the attitude of the body using a basis pursuit approach. An unscented Kalman filter can then be used to estimate the angular rate of the body.
Space Debris removal is a critical issue related to space research. One of the key requirements for a removal mission is the assessment of the target rotational dynamics. Ground observations are not sufficient for reaching the accuracy level required to guide the chaser spacecraft during the capture maneuver. Moreover, the guidance and control strategy for the chaser to approach the target is a critical aspect of such missions. This paper present simulation results of two complementary methods, one for estimating the entire rotational dynamic state of the target, and the other for accurately controlling the approach maneuver. In particular, the information coming from the identification and prediction of the actual motion of the rotation axis of the target is exploited by the second method for aligning the docking interface of the chaser with that axis at the instant of capture. The dynamic estimation is based on Kalman filtering in an original combination with compressive sampling techniques for making the method robust to failures of the observation sensors. The guidance of the chaser is based on a model predictive control law. The combined simulation of the employment of the methods has revealed the feasibility of the global approach.
I. .IntroductionNE of the main concerns in the space field is the high number of objects orbiting the Earth in orbits of interest for the accomplishment of scientific and communication missions. Currently, more than 10000 objects bigger than 10 cm take up Low Earth Orbit (LEO) and Geosynchronous Earth Orbit (GEO) [1].
This article proposes a parallel kinematic solar tracker designed for driving high-concentration photovoltaic modules. This kind of module produces energy only if they are oriented with misalignment errors lower than 0.4°. Generally, a parallel kinematic structure provides high stiffness and precision in positioning, so these features make this mechanism fit for the purpose. This article describes the work carried out to design a suitable parallel machine: an already existing architecture was chosen, and the geometrical parameters of the system were defined in order to obtain a workspace consistent with the requirements for sun tracking. Besides, an analysis of the singularities of the system was carried out. The method used for the singularity analysis revealed the existence of singularities which had not been previously identified for this kind of mechanism. From the analysis of the mechanism developed, very low nominal energy consumption and elevated stiffness were found. A small-scale prototype of the system was constructed for the first time. A control algorithm was also developed, implemented, and tested. Finally, experimental tests were carried out in order to verify the capability of the system of ensuring precise pointing. The tests have been considered passed as the system showed an orientation error lower than 0.4°during sun tracking.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.