Editing Spacecraft flight dynamics (section)

===Aerodynamic force===
[[Aerodynamic force]]s, present near a body with a significant atmosphere such as [[Earth]], [[Mars]] or [[Venus]], are analyzed as: [[lift (force)|lift]], defined as the force component perpendicular to the direction of flight (not necessarily upward to balance gravity, as for an airplane); and [[drag (physics)|drag]], the component parallel to, and in the opposite direction of flight. Lift and drag are modeled as the products of a coefficient times [[dynamic pressure]] acting on a reference area:{{sfnp|Anderson|2004| pp=257–261}}
<math display="block">\mathbf{L} = C_L q A_\text{ref}</math>
<math display="block">\mathbf{D} = C_D q A_\text{ref}</math>

where:
*''C''<sub>''L''</sub> is roughly linear with ''α'', the angle of attack between the vehicle axis and the direction of flight (up to a limiting value), and is 0 at ''α'' = 0 for an axisymmetric body;
*''C''<sub>''D''</sub> varies with ''α''<sup>2</sup>;
*''C''<sub>''L''</sub> and ''C''<sub>''D''</sub> vary with [[Reynolds number]] and [[Mach number]];
*''q'', the dynamic pressure, is equal to 1/2 ''ρv''<sup>2</sup>, where ''ρ'' is atmospheric density, modeled for Earth as a function of altitude in the [[International Standard Atmosphere]] (using an assumed temperature distribution, [[hydrostatic pressure]] variation, and the [[ideal gas law]]); and
*''A''<sub>ref</sub> is a characteristic area of the vehicle, such as cross-sectional area at the maximum diameter.