Vis-viva equation

In astrodynamics vis-viva equation (also referred to as orbital energy conservation equation) is one of the fundamental and useful equations that govern the motion of orbiting bodies. It is the direct result of the law of conservation of total energy, where the sum of kinetic and potential energy is constant as the satelite moves about its orbit.

For elliptic orbits the basic form of an equation is as follows:

<math>v^2=\mu({{2 \over{r}} – {1 \over{a}}})<math>

where:

• <math>v\,\!<math> is velocity of orbiting body
• <math>r\,\!<math> is distance from orbit's focus
• <math>a\,\!<math> is semi-major axis
• <math>\mu\,\!<math> is standard gravitational parameter

See also

• Specific orbital energy

External links