On-Orbit Center Of Mass Relocation System For A 3U Cubesat

This paper describes the design and simulation tests of a system that uses a set of three internal shifting masses (ISMs) that can be displaced along three orthogonal axes, with the purpose to re-adjust the center of mass (CoM) in a nanosat. This procedure will reduce the magnitude of the on-orbit external disturbing torques, re-locating the CoM as close as possible to the geometrical center of the spacecraft. This implementation decreases the power needed to keep the attitude stable along time. Angular rates and angular accelerations, provided by an IMU, are employed by the onboard computer that executes the algorithm for the estimation of the CoM and the magnitude of the displacements needed on every sliding element. The disturbance torques considered were: solar pressure, aerodynamic drag and gravitational gradient. In every control loop CoM deviation is estimated using a recursive least square (RLS) method, the magnitude of the displacements of each ISM is calculated and moved accordingly. In the next step on-board computer identifies the new position of the CoM and the magnitude of the displacements, until the CoM position is within the threshold range, from the geometric center of the spacecraft, established in � 5 mm. Feasibility of the CoM estimation, and relocation system was performed through numerical simulations using Matlab Simulink considering a 3U Cubesat nanosatellite dynamic model.

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