The distance you travel is determined by which engine you choose and how much power you assign to it. That's the first two clicks (click to start, click again to set the power). On the way back you're trying to click one final time (third click) in the center green spot. Anything outside of that becomes a "targeting computer error". It ranges from 0.5, 1.0, 1.5, and so on. That gets multiplied against the "Solar Winds". That in turn then get multiplied against the engine's possible deviation and that's applied to the final power.
The terrain also affects the final power. Even if you have 100% power with no error, being on a really crappy terrain (like a sticky slime planet) will only let you travel a maximum of 65%. So if the maximum power is 200 ly (lightyears), the maximum it will travel is 130 ly.
The course is always between 600-800 ly long and a random number of land types. There's some fine tuning to do, some overall design direction, and figuring out how to work the upgrade systems... but the core is there! I'm pretty happy with it now.