This is a very nice idea! But way too hard imo. To make it easier, putting some planets around the main path to catch you in case you go off-course (so it's not instant game over at the first mistake) would be nice, and maybe add visual effects to assist your aim, like some sort of quadrant around the planets to show the range of angles you can launch at.
The constant speed buildup without any way of slowing down is also a problem because it makes it basically impossible to aim properly after a while, and then you're screwed. To solve this problem, why not borrow some ideas from real physics? Angular speed is inversely proportional to the radius of the revolution. ;) But just making the planets bigger and bigger as you go doesn't seem very practical so maybe you could add a way to actually slow down. Maybe collisions with asteroids in asteroid belts or something.