GMearth
terrestrial mass parameter
Standard gravitational parameterexact by definition
The terrestrial mass parameter is the product GM for the Earth, adopted by the IAU in 2015 as the nominal value of exactly 3.986004e14 m³/s². It is the constant every satellite orbit calculation starts from, since it alone fixes the period of a circular orbit at a given radius.
Watch out: Navigation and geodesy use their own slightly different values, and mixing them silently shifts an orbit. WGS 84, which GPS is built on, uses 3.986004418e14 m³/s², and the EGM2008 gravity model uses 3.986004415e14. All agree with the IAU nominal value to eight figures, and none of them should be interchanged inside one computation.
| 1 GMearth | 398,600.4 km³/s² |