Kepler's third law relates the period and the radius of objects in orbit around a star or planet. In conjunction with Newton's law of universal gravitation, giving the attractive force between two masses, we can find the speed and period of an artificial satellite in orbit around the Earth. Consideration is limited to circular orbits.
where is the distance from the center of the Earth (Earth's radius + altitude ), is the gravitational constant, and is the mass of the Earth.
Enrique Zeleny "Orbital Speed and Period of a Satellite"