Using a formula derived from the Lynden-Bell-Kalnajs theory of angular
momentum exchange, we study the angular momentum loss of a satellite
galaxy which is moving on a nearly circular, co-planar orbit around a
disc galaxy. Using this formula, estimates of the orbital decay time a
re computed for several different galaxy models. The results are then
compared with the corresponding results from numerical simulations, an
d are found to be in agreement for the satellite sizes under study. Th
e main difficulty in applying the decay formula is the fact that the d
ecay time varies as the square of the satellite softening parameter, w
hich is difficult to determine accurately. However, we find that it ca
n be chosen in the same way in all cases we have studied. For our mode
ls, the dynamical friction of the disc is shown to be significantly la
rger than that of the halo.