ABSTRACT
The effects of orbital drag are typically significant at low Earth orbits with altitudes less than 500–600 km, where the atmospheric density is still significant. This chapter focuses on the specification and prediction of the neutral density and the issues that face the community in doing so. It discusses all the factors that affect orbital drag in more specific terms. An assumption commonly made in empirical models of orbital drag is that of diffusive equilibrium, in which the atmospheric constituents are assumed to have reached a steady state. The most substantial limitations in the successful specification and prediction of neutral density and orbital drag are the inherent errors in all the empirical models and measurement-derived densities and the complete lack of absolute validation of such measurements. The goals in the field of space weather impact on orbital drag are to specify and forecast drag with high accuracy.
