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A full degree-of-freedom Model Predictive Control approach to RendezVous and Docking missions of small satellites

Federica Mincuzzi

A full degree-of-freedom Model Predictive Control approach to RendezVous and Docking missions of small satellites.

Rel. Sabrina Corpino, Carlo Novara. Politecnico di Torino, Corso di laurea magistrale in Mechatronic Engineering (Ingegneria Meccatronica), 2021

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The use of small satellites (Cubesat) is gaining great success in the New Space Economy thanks to their small size, low cost and reduced development time. Cubesat were born in university but are now universally used. The miniaturized technologies of these small satellites are having a big development and are used even for complex missions, which include proximity maneuvers, relative navigation, observations and interplanetary transfers. One of these innovative missions involves the release of a Cubesat 12U (size 20 cm x 20cm x 30 cm), with a weight of around 20 kg, by 'Space Rider' (a new transport system and re-entry, developed by Thales-Alenia for ESA) in low-Earth orbit and the subsequent re-entry of the Cubesat into the cargo bay of Space Rider, after making observations of the outer surface of the vehicle. Cubesat’s name is SROC (Space Rider Observer Cube). This mission is very complex and delicate due to the high safety constraints and the high accuracy required for the maneuver. The specific objective of this thesis is to define a strategy of integrated control (using Non-linear Model Predictive Control) of attitude and relative position for the last part of the maneuver of Rendez-vous & Docking (RVD) of the present Cubesat (Chaser of the mission) that must dock to Space Rider (Collaborative target). This type of proximity operation requires a high level of accuracy for reaching the final position (less than cm) and for the speed in the reaching of the final point (less than cm/s) and with low values of rotation speed and misalignment angle. Is important to note the coupling between the dynamics of rotation and the relative translation between the two bodies. The control system must be robust with respect to the uncertainties of the mission and to the disturbances related to the space environment. Within the thesis has been developed a mathematical model of 12 equations that described the relative motion between the points of the two spacecraft (called docking points) that come into contact at the end of the maneuver. The definition of this system overcomes the limits of Hill’s equations that are limited to define the relative motion between the chaser’s barycenter the and target’s barycenter and allows to design a single controller for both the rotational and the translational part. The state variables are the relative attitude, the relative angular velocity, the position and relative velocity between the mechanisms placed on the mating points. As control input, instead, the torque and force generated by the Cubesat’s actuators. The design and verification of the controller’s requirements have been developed in several steps using Matlab and Simulink. The mathematical model was linearized, and the controller was designed. The consistency of the model and of the controller after a first tuning of the parameters has been verified . Then, the non-linear system has been considered and, after several modifications of the parameters of the NMPC, a first effective feedback has been obtained on the ability of the controller to meet the accuracy requirements on reaching the final point. Then, torques and forces due to aerodynamic resistance, gravity gradient and interaction with the magnetic field have been added to the system and the simulations have verified that the controller operates well even in the presence of disturbances and that works alsoin presence of uncertain parameters. In this thesis’s work has been produced a control system able to meet the performance requirements.

Relators: Sabrina Corpino, Carlo Novara
Academic year: 2021/22
Publication type: Electronic
Number of Pages: 130
Corso di laurea: Corso di laurea magistrale in Mechatronic Engineering (Ingegneria Meccatronica)
Classe di laurea: New organization > Master science > LM-25 - AUTOMATION ENGINEERING
Aziende collaboratrici: Politecnico di Torino
URI: http://webthesis.biblio.polito.it/id/eprint/21589
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