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_{D} = \frac{1}{2} ρ C_{d} A v^{2}

where $ρ$ is the air density, $C_{d}$ is the drag coefficient, $A$ is the frontal area, and $v$ is the velocity.

The acceleration due to drag is then

a_{D} = \frac{F_{D}}{m} = \frac{ρ C_{d} A v^{2}}{2 m}

In aerodynamic theory, the factor

B = \frac{C_{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{ρ_{0} B}{2} = \frac{ρ_{0} C_{d} A}{2 m}

thus reducing the expression for the acceleration due to drag to

a_{D} = \frac{ρ}{ρ_{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 $0.15696615 kg / (m^{2} \cdot R_{Earth})$ . 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

↑ "BSTAR Drag Term". Retrieved November 8, 2022.
↑ Kelso, T.S. "Frequently Asked Questions: Two-Line Element Set Format". Retrieved November 8, 2022.
↑ Hoots, Felix R.; Roehrich, Ronald L. (December 1980). SPACETRACK Report No. 3 Models for Propagation of NORAD Element Sets (PDF) (Report). Retrieved November 8, 2022.
↑ Vallado, David A., and Paul J. Cefola. "Two-line element sets-Practice and use." 63rd International Astronautical Congress, Naples, Italy. 2012.

[1] "BSTAR Drag Term". Retrieved November 8, 2022.

[2] Kelso, T.S. "Frequently Asked Questions: Two-Line Element Set Format". Retrieved November 8, 2022.

[3] Hoots, Felix R.; Roehrich, Ronald L. (December 1980). SPACETRACK Report No. 3 Models for Propagation of NORAD Element Sets (PDF) (Report). Retrieved November 8, 2022.

[4] Vallado, David A., and Paul J. Cefola. "Two-line element sets-Practice and use." 63rd International Astronautical Congress, Naples, Italy. 2012.