Manipulation of uncooperative rotating objects in space with a modular self-reconfigurable robot

Abstract

The following thesis is a feasibility study for the controlled deployment of robotic scaffolding structures on randomly tumbling objects with low-magnitude gravitational field for use in space applications such as space debris removal, spacecraft maintenance and asteroids capture and mining. The proposed solution is based on the novel use of self-reconfigurable modular robots performing deployments on randomly tumbling objects as a task-driven reconfiguration or manipulation through reconfiguration. The robot design focused on its control strategy which used a decentralised modular controller with two levels. One high-level behaviour-based component and one low-level component generating commands via a constrained optimisation using either a linear or a non-linear model predictive control approach and constituting a novel control method for rotating objects via angular momentum exchanges and mass distribution changes. The controller design relied on modelling the robot modules and the object as a rotating discretised deformable continuum whose rigid part, the object, was an ellipsoid. All parameters were normalised when possible and disturbances, sensors and actuator errors were modelled respectively as biased white noises and coloured noises. The correctness of the overall control algorithm was ensured. The main objective of the MPC controllers was to control the deployment of a module from the tip of the spinning axis to the plane containing the object’s centre of mass while coiling around the spinning axis and ensuring the object’s rotational state tracked a reference state. Simulations showed that the nonlinear MPC controller should be preferred over a linear one and that, for a mass ratio of the object’s to the module’s equal to 10000, the nonlinear MPC controller is best suited to stability maintenance and meets the deployment requirement, suggesting that the proposed solution would be acceptable for medium-size objects such as asteroids