  The overlapping of mean-motion resonances is useful for low or
zero-propellant space mission design, but while most related prior work uses a
planar CRTBP model, tours of multi-moon systems require using resonances
affected by two moons. In this case study, we investigate Jupiter-Ganymede
unstable 4:3 resonant orbits in a concentric circular restricted 4-body
Jupiter-Europa-Ganymede model. We show that despite their high order, secondary
resonances between the 4:3 orbits and Europa have a large effect, including
11/34, 12/37, 23/71, and 25/77. Computing newly generated objects inside the
secondary resonances definitively confirms their overlap, which causes a
complete structural change of the higher-energy unstable 4:3 orbits whose
manifolds are most useful for low-TOF orbit transfers. We believe this
phenomenon is general, with major implications for resonant orbit use in tour
design.
