This paper presents methodology for the computation of whole sets of heteroclinic connections between iso-energetic slices of center manifolds of center × center × saddle fixed points of autonomous Hamiltonian systems. It involves: (a) computing Taylor expansions of the center-unstable and center-stable manifolds of the departing and arriving fixed points through the parameterization method, using a new style that uncouples the center part from the hyperbolic one, thus making the fibered structure of the manifolds explicit; (b) uniformly meshing iso-energetic slices of the center manifolds, using a novel strategy that avoids numerical integration of the reduced differential equations and makes an explicit 3D representation of these slices as deformed solid ellipsoids; (c) matching the center-stable and centerunstable manifolds of the departing and arriving points in a Poincaré section. The methodology is applied to obtain the whole set of iso-energetic heteroclinic connections from the center manifold of L 2 to the center manifold of L 1 in the Earth-Moon circular, spatial Restricted Three-Body Problem, for nine increasing energy levels that reach the appearance of Halo orbits in both L 1 and L 2 . Some comments are made on possible applications to space mission design.