Planar reentry equations
The planar reentry equations are the equations of motion governing the unpowered reentry of a spacecraft, based on the assumptions of planar motion and constant mass, in an Earth-fixed reference frame. == Definition == The equations are given by:where the quantities in these equations are: V {\displaystyle V} is the velocity γ > 0 {\displaystyle \gamma >0} is the flight path angle h {\displaystyle h} is the altitude ρ {\displaystyle \rho } is the atmospheric density β {\displaystyle \beta } is the ballistic coefficient g {\displaystyle g} is the gravitational acceleration r = r e + h {\displaystyle r=r_{e}+h} is the radius from the center of a planet with equatorial radius r e {\displaystyle r_{e}} L / D {\displaystyle L/D} is the lift-to-drag ratio σ {\displaystyle \sigma } is the bank angle of the spacecraft.