  The orbits of satellite galaxies encode rich information about their
histories. We investigate the orbital dynamics and histories of satellite
galaxies around Milky Way (MW)-mass host galaxies using the FIRE-2 cosmological
simulations, which, as previous works have shown, produce satellite mass
functions and spatial distributions that broadly agree with observations. We
first examine trends in orbital dynamics at z = 0, including total velocity,
specific angular momentum, and specific total energy: the time of infall into
the MW-mass halo primarily determines these orbital properties. We then examine
orbital histories, focusing on the lookback time of first infall into a host
halo and pericenter distances, times, and counts. Roughly 37 per cent of
galaxies with Mstar < 10^7 Msun were `pre-processed' as a satellite in a
lower-mass group, typically ~2.7 Gyr before falling into the MW-mass halo. Half
of all satellites at z = 0 experienced multiple pericenters about their MW-mass
host. Remarkably, for most (67 per cent) of these satellites, their most recent
pericenter was not their minimum pericenter: the minimum typically was ~40 per
cent smaller and occurred ~6 Gyr earlier. These satellites with growing
pericenters appear to have multiple origins: for about half, their specific
angular momentum gradually increased over time, while for the other half, most
rapidly increased near their first apocenter, suggesting that a combination of
a time-dependent MW-mass halo potential and dynamical perturbations in the
outer halo caused these satellites' pericenters to grow. Our results highlight
the limitations of idealized, static orbit modeling, especially for pericenter
histories.
