Earth has a radius of 6,357 km (at the poles) making r Earth = 6,357,000 m and the satellites have an altitude of 20,184 km making their orbit radius r GPS = 26,541,000 m. Substituting these in the above equation, with Earth mass M = 5.974 × 10, G = 6.674 × 10, and c = 2.998 × 10 (all in SI units), gives: