Online calculator to find the orbital radius given the satellite orbit period and planet mass. When a satellite travels in a geosynchronous orbit around the Earth, it needs to travel at a certain orbiting radius and period to maintain this orbit. The satellite mean orbital radius calculator uses the Kepler's third law equation to estimate orbital radius. The law states that the ratio of the squares of the orbital period for 2 planets is equal to the ratio of the cubes of their mean orbit radius.