Practical Implementation of Attitude-Control Algorithms for an Underactuated Satellite

The challenging problem of controlling the attitude of satellites subject to actuator failures has been the subject of increased attention in recent years. The problem of controlling the attitude of a satellite on all three axes with two reaction wheels is addressed in this paper. This system is controllable in a zero-momentum mode. Three-axis attitude stability is proven by imposing a singular quaternion feedback law to the angular velocity trajectories.Two approaches are proposed and compared to achieve three-axis control: The first one does not require angular velocity measurements and is based on the assumption of a perfect zero momentum, while the second approach consists of tracking the desired angular velocity trajectories. The full-state feedback is a nonlinear singular controller. In-orbit tests of the first approach provide an unprecedented practical proof of three-axis stability with two control torques. The angular velocity tracking approach is shown to be less efficient using the nonlinear singular controller. However, when inverse optimization theory is applied to enhance the nonlinear singular controller, the angular velocity tracking approach is shown to be the most efficient. The resulting switched inverse optimal controller allows for a significant enhancement of settling time, for a prescribed level of the integrated torque

A Matheuristic Approach For Planning Interrelated Voyages With Separation Requirements In Maritime Transportation

Roll-on/Roll-off (RoRo) vessels represent the primary source for transport- ing vehicles and other types of rolling material over long distances. How- ever, comparatively little operational research has been done on RoRo ship- ping, suggesting there is room for improvement. In this thesis, I focus on the single trade ship routing and scheduling problem (STSRSP) in RoRo- shipping. This problem considers which ports a voyage should visit along a trade route, which vessels should be deployed for a given voyages, as well as where and when these vessels should load and unload goods. In the STSRSP, the objective is to minimize the total cost of all activities, while satisfying contractual requirements Hansen et al. (2018). Efforts to solve mathematical formulations of this problem with standard MIP solvers have shown that the run time is prohibitively large for direct use in opera- tional level decisions. Hence, the purpose of this thesis have been to create a heuristic that can be used to reduce the time used to solve single instances of the STSRSP to within an acceptable accuracy. In this thesis, I propose a new solution method to solve the STSRSP. The solution method uses a matheuristic approach that divides the problem into several parts, combining both mathematical models to determine routes and vessel assignment, as well as a heuristic for placing the contracts on voyages. Finally, a service level search is implemented to make sure the separation requirement is satisfied. Computational results show that the matheuristic has the potential to solve STSRSP instances within very short time limits

Passivity Based Adaptive Attitude Control of a Rigid Spacecraft

An adaptive control scheme for the attitude control of a rigid spacecraft is derived using a linear parameterization of the equation of motion. The tracking error is described with the Euler parameter vector. Global convergence of the tracking error to zero is shown using passivity theory. This allows for the use of time-varying positive definite feedback gain matrices, and the results can easily be extended to other passive parameter update laws