TRANSLUNAR HALO ORBITS IN THE QUASI-BICIRCULAR PROBLEM Miquel Angel Andreu and Carles Simo Dept. de Matematica Aplicada i Analisi, Universitat de Barcelona, Gran Via 585, 08007 Barcelona (Spain). E-mails: mangel@maia.ub.es, carles@maia.ub.es Abstract: The Quasi-bicircular Problem (QBCP) is a four body problem where three masses are revolving in a quasi-bicircular motion (that is, a coherent motion close to bicircular), the fourth mass being small and not influencing the motion of the three primaries. The Earth-Moon-Sun-Spacecraft case is considered and the Hamiltonian which governs the motion of the fourth mass is derived. That is a Hamiltonian with three degrees of freedom depending periodically on time. One application of this model has been the computation of quasi-periodic translunar Halo orbits. These orbits have been obtained using a continuation method starting at the Halo orbits of the RTBP. The Halo orbits of the QBCP are refined to Halo orbits of the Solar System using a Parallel Shooting method and JPL ephemeris.