For SGP4 and SDP4 users, the mean motion is first recovered from its altered form and the drag effect is obtained from the SGP4 drag term (B*) with the pseudo-drag term being ignored. The value of the mean motion can be used to determine whether the satellite is near-Earth or deep-space (and hence whether SGP4 or SDP4 was used to generate the element set). From this information the user can decide whether to use SGP4 or SDP4 for propagation and hence be assured of agreement with NORAD predictions.
The SGP8 and SDP8 models have the same gravitational and atmospheric models as SGP4 and SDP4, although the form of the solution equations is quite different. Additionally, SGP8 and SDP8 use a ballistic coefficient (B term) in the drag equations rather than the B* drag term. However, compatible predictions can be made with NORAD element sets by first calculating a B term from the SGP4 B* drag term.
At the present time consideration is being given to replacing SGP4 and SDP4 by SGP8 and SDP8 as the NORAD satellite models. In such a case the new NORAD element sets would still give compatible predictions for SGP, SGP4, and SDP4 users and, for SGP8 and SDP8 users, would give agreement with NORAD predictions.