The task of scheduling communications between satellites and ground control stations is getting more and more critical since an increasing number of satellites must be controlled by a small set of stations. In such a congested scenario, the current practice, in which experts build hand-made schedules, often leaves a large number of communication requests unserved. We report on our experience in the design of an optimization-based support tool at the European Space Agency. We propose a tight time-indexed formulation of the problem able to include several complex technological constraints. A non-standard Lagrangian heuristic is then devised which provides near-optimal solutions of a set of largescale test problems arising in the forthcoming GALILEO constellation. The heuristic shows numerical stability and robustness adequate for practical implementation. The resulting tool is used by the Italian reference operator for GALILEO system management and is currently under testing at the European Space Agency.
The aim of this work is to propose a solution approach for a capacitated lot sizing and scheduling real problem with parallel machines and shared buffers, arising in a packaging company producing yoghurt. The problem has been formulated as a hybrid Continuous Set-up and Capacitated Lot Sizing Problem (CSLP-CLSP). A new effective two stage optimisation heuristic based on the decomposition of the problem into a lot sizing problem and a scheduling problem has been developed. An assignment of mixture to buffers is made in the first stage, and therefore the corresponding orders are scheduled on the production lines by performing a local search. Computational tests have been performed on the real data provided by the company. The heuristic exhibits near-optimal solutions, all obtained in a very short computational time.
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