SNAP is an N-body high fidelity trajectory propagation program developed at NASA's Glenn Research Center. Early versions of SNAP were used to support the ELV program to verify launch vehicle injection accuracy. As SNAP was further developed, it was written to perform interplanetary trajectory analysis. As an N-body code, SNAP can model trajectories about the nine planets and the Sun, as well as virtually any natural satellite in the solar system. Force models that are included in SNAP are central body gravitation with NxN harmonics, other body gravitation with NxN harmonics, solar radiation pressure, atmospheric drag (for Earth Orbits), and spacecraft thrusting including shadowing (finite or impulsive). Trajectories are propagated using a Runge-Kutta Fehlberg single step method with variable step-size control. SNAP is not written for any specific mission and is intended to be used for most any interplanetary mission.