Generating High Quality Schedules for a Spacecraft Memory Downlink Problem

This work introduces a combinatorial optimization problem called MARS EXPRESS Memory Dumping Problem (MEX-MDP), which arises in the European Space Agency program MARS EXPRESS. It concerns the generation of high quality schedules for the spacecraft memory downlink problem. MEX-MDP is an NP-hard combinatorial problem characterized by several kinds of constraints, such as on-board memory capacity, limited communication windows over the downlink channel, deadlines and ready times on the observation activities. The contribution of this paper is twofold: on one hand it provides a CSP model of a real problem, and on the other it presents a set of metaheuristic strategies based on local and randomized search which are built around the constraint-based model of the problem. The algorithms are evaluated on a benchmark set distilled from ESA documentation and the results are compared against a lower bound of the objective function. This work describes results obtained in the framework of a research study conducted for the European Space Agency (ESA-ESOC) under contract No.14709/00/D/IM.