Dynamical Substitutes of the Libration Points for Simplified Solar System Models G. Gomez, J.J. Masdemont and J.M. Mondelo Abstract. The purpose of this paper is to develop a methodology to generate simpliŻed models suitable for the analysis of the motion of a small particle, such as a spacecraft or an asteroid, in the Solar System. The procedure is based on applying reŻned Fourier analysis methods to the time{dependent functions that appear in the di®erential equations of the problem. The equations of the models obtained are quasi{periodic perturbations of the Restricted Three Body Problem that depend explicitly on natural frequencies of the Solar System. Some examples of these new models are given and compared with other ones found in the literature. For two of these new models, close to the Earth{Moon system, we have computed the dynamical substitutes of the collinear libration points.