Mean motion

Mean Motion, <math>n\,\!<math>, is a meansure of how far a satellite has progressed around its orbit, from perigee. Unless the orbit is circular, the Mean Motion is only an average value, and does not represent the instantaneous angular rate.

In databases of satellite orbital parameters the Mean Motion is typically specified in revolutions per day.

Calculation

<math>n = \sqrt{(GM/a^3)}\,\!<math>

will return units of radians/second.

where:

• <math>G\,\!<math> is the gravitational constant in m³ kg^-1 s^-2</sub>,
• <math>M\,\!<math> is the mass of the planet, in kg,

(note that <math>G\,\!<math> and <math>M\,\!<math> are typically combined to give the Standard gravitational parameter, <math>\mu\,\!<math>)

• <math>a\,\!<math> is semi-major axis in meters.