Exact and Inexact Methods for the Daily Management of an Earth Observation Satellite

The daily management of an observation satellite like Spot, which consists in deciding every day what photographs will be attempted the next day, is of a great economical importance. But it is a large and difficult combinatorial optimization problem, for which efficient search methods have to be built and assessed. In this paper we describe the problem in the framework of the future Spot5 satellite. This problem can be formulated as a Variable Valued Constraint Satisfaction Problem or as an Integer Linear Programming Problem. Within the VVCSP framework, exact methods to find an optimal solution, like Depth First Branch and Bound or Russian Dolls search and approximate methods to find a good solution, like Greedy Search or Tabu search have been developed and experimented on a set of representative problems. Comparison is also made with results obtained by running the Linear Programming environment CPLEX on the corresponding linear models. The conclusion addresses some lessons which can be drawn from this overview.