BSTAR is a way of modeling aerodynamic drag on a satellite in the SGP4 satellite orbit propagation model.
Traditionally, aerodynamic resistance ("drag") is given by
where
The acceleration due to drag is then
In aerodynamic theory, the factor
is called the ballistic coefficient, and its unit is area per mass. Further incorporating a reference air density and the factor of two in the denominator, we get the starred ballistic coefficient:
thus reducing the expression for the acceleration due to drag to
As it can be seen,