  We present an updated model for the evolution of the orbits of "orphan
galaxies" to be used in the SAG semi-analytical model of galaxy formation and
evolution. In cosmological simulations, orphan galaxies are those satellite
galaxies for which, due to limited mass resolution, halo finders lose track of
their dark matter subhalos and can no longer be distinguished as self-bound
overdensities within the larger host system. Since the evolution of orphans
depends strongly on the orbit they describe within their host halo, a proper
treatment of their evolution is crucial in predicting the distribution of
subhalos and satellite galaxies. The model proposed takes into account the
dynamical friction drag, mass loss by tidal stripping and a proximity merger
criterion, also it is simple enough to be inexpensive from a computational
point of view. To calibrate this model, we apply it onto a dark matter only
simulation and compare the results with a high resolution simulation,
considering the halo mass function and the two-point correlation function as
constraints. We show that while the halo mass function fails to put tight
constraints on the dynamical friction, the addition of clustering information
helps to better define the parameters of the model related to the spatial
distribution of subhalos. Using the model with the best fit parameters allows
us to reproduce the halo mass function to a precision better than 5 per cent,
and the two point correlation function at a precision better than 10 per cent.
