Dynamics in the centre manifold of the collinear pointsof the Restricted Three Body Problem

This paper focuses on the dynamics near the collinear equilibrium points L 1;2;3 of the spatial Restricted Three Body Problem. It is well known that the linear behaviour of these three points is of the type centercentersaddle. To obtain an accurate description of the dynamics in an extended neighbourhood of those points, two diierent (but complementary) strategies are used. First, the Hamiltonian of the problem is expanded in power series around the equilibrium point. Then, a partial normal form scheme is applied in order to un-couple (up to high order) the hyperbolic directions from the elliptic ones. Skipping the remainder we have that the (truncated) Hamiltonian has an invariant manifold tangent to the central directions of the linear part. The restriction of the Hamilto-nian to this manifold is the so-called reduction to the centre manifold. The study of the dynamics of this reduced Hamiltonian (now with only 2 degrees of freedom) gives a qualitative description of the phase space near the equilibrium point. Finally, a Lindstedt-Poincar e procedure is applied to explicitly compute the invariant tori contained in the centre manifold. These tori are obtained as the Fourier series of the corresponding solutions, being the frequencies a power expansion of some parameters (amplitudes). This allows for an accurate quantitative description of these regions. In particular, the well known Halo orbits are obtained.