Satellite drag data plays an important role in the estimation of atmospheric density and the study of thermospheric cooling and contraction. There are many ways of calculating atmospheric density, but inferring thermospheric density from satellite drag data is a relatively cost-effective way of gathering in-situ measurements. Given an initial satellite orbit, one approach is to use an orbital propagator to predict the satellite's state at some time ahead and then to compare that state with the Two-Line Element (TLE) data at the same epoch. The difference between the mean motions from consecutive TLE sets is calculated then compared to results obtained from the orbital propagator. From this an estimate of global average density can then be calculated. The validation of a new orbital propagator that will be used for this purpose is the primary focus of this paper. Here, the validation takes the form of re-entry prediction for decaying satellites.