BSTAR

BSTAR is a way of modeling aerodynamic drag on a satellite in the simplified general perturbation model 4 satellite orbit propagation model. Traditionally, aerodynamic resistance ("drag") is given by : F_\text{D} = \frac{1}{2} \rho C_\text{d} A v^2 where \rho is the air density, C_\text{d} is the drag coefficient, A is the frontal area, and v is the velocity. The acceleration due to drag is then : a_\text{D} = \frac{F_\text{D}}{m} = \frac{\rho C_\text{d} A v^2}{2m} In aerodynamic theory, the factor : B = \frac{C_\text{d} A}{m} is the inverse of 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: : B^* = \frac{\rho_0 B}{2} = \frac{\rho_0 C_\text{d} A}{2m} thus reducing the expression for the acceleration due to drag to : a_\text{D} = \frac{\rho}{\rho_0} B^* v^2 As it can be seen, B^* has a unit of inverse length. For orbit propagation purposes, there is a field for BSTAR drag in two-line element set (TLE) files, where it is to be given in units of inverse Earth radii. The corresponding reference air density is given as 0.15696615\text{ kg}/(\mathrm{m}^2 \cdot R_\text{Earth}) .…

BSTAR is a way of modeling aerodynamic drag on a satellite in the simplified general perturbation model 4 satellite orbit propagation model. Traditionally, aerodynamic resistance ("drag") is given by F_\text{D} = \frac{1}{2} \rho C_\text{d} A v^2 where \rho is the air density, C_\text{d} is the drag coefficient, A is the frontal area, and v is the velocity. The acceleration due to drag is then a_\text{D} = \frac{F_\text{D}}{m} = \frac{\rho C_\text{d} A v^2}{2m} In aerodynamic theory, the factor B = \frac{C_\text{d} A}{m} is the inverse of 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: B^* = \frac{\rho_0 B}{2} = \frac{\rho_0 C_\text{d} A}{2m} thus reducing the expression for the acceleration due to drag to a_\text{D} = \frac{\rho}{\rho_0} B^* v^2 As it can be seen, B^* has a unit of inverse length. For orbit propagation purposes, there is a field for BSTAR drag in two-line element set (TLE) files, where it is to be given in units of inverse Earth radii. The corresponding reference air density is given as 0.15696615\text{ kg}/(\mathrm{m}^2 \cdot R_\text{Earth}) . One must be very careful when using the value of B^* released in the TLEs, as it is fitted to work on the SGP4 orbit propagation framework and, as a consequence, may even be negative as an effect of unmodelled forces on the orbital determination process. ==References==

Text derived from https://en.wikipedia.org/w/index.php?oldid=1171641465 under CC BY-SA 4.0; modifications have been made.