Suppose life would evolve on a planet near a black hole, like the water planet on Interstellar. And just like on Earth, they eventually discover a theory of relativity and also how to send a rocket away from planet/black hole and back. Could they take advantage of the huge time dilation between the surface of the planet and the rocket? Like send a computer with a complicated problem that would take years to solve on the surface, but only hours on the rocket? Isn't this "free energy" in a way? Also, if one would watch the rocket leave the surface, would they see it speed up exponentially much faster than it should, as time dilation gradually kicks in the further it gets from the black hole?