Question: Calculate the gain of gravitational potential energy of a satelite of mass 200kg between launching and when it is in orbit at a height of 1.2 * 10^6m above the earth's surface. (R=6.4*10^6) I approach this question using the equation V=-GM/r . Since the mass of Earth is not given here, I assume it is 6*10^24. So, I calculate the gravitational potential at the Earth's surface and at 1.2*10^6 m and find the difference. I get the answer of 1.9*10^9. But the actual answer is 1.7*10^6.