A spaceship is traveling at a velocity of 0.8c (where c is the speed of light) and is approaching a planet that has a mass of 2 x 10^29 kg. Using the principles of special relativity, calculate the relativistic mass of the spaceship as it approaches the planet, and the gravitational force acting on the spaceship as it comes within 100,000 km of the planet's surface. Show all calculations and include the value of the gravitational constant (G) in your answer.