Editing Spacecraft flight dynamics (section)

===Gravitation===
The gravitational force that a celestial body exerts on a space vehicle is modeled with the body and vehicle taken as point masses; the bodies (Earth, Moon, etc.) are simplified as spheres; and the mass of the vehicle is much smaller than the mass of the body so that its effect on the gravitational acceleration can be neglected. Therefore the gravitational force is calculated by:

<math display="block">\mathbf{W} = m \cdot g</math>

where:
*<math>W</math> is the gravitational force (weight);
*<math>m</math> is the space vehicle's mass; and
*<math>r</math> is the radial distance of the vehicle to the planet's center; and
*<math>r_0</math> is the radial distance from the planet's surface to its center; and
*<math>g_0</math> is the [[gravitational acceleration]] at the surface of the planet
*''g'' is the [[gravitational acceleration]] at altitude, which varies with the inverse square of the radial distance to the planet's center:{{sfnp|Kromis|1967| p=11:154}} <math display="block">g = g_0\left(\frac{r_0}r\right)^2</math>