Thanks for playing!
There are definitely at least two mechanics, they are just very close nit together. You can think like this: Would there still be a "game" if one of them was removed? Yes, you could have a game without the enemy ships, just having to travel between the stars (although this wouldn't be fun). You could also have a game were the objective wasn't to visit all the stars, but rather survive for long enough or something else entirely.
You could also see the space stations themself as a mechanic, they aren't 100% necessary but add a lot to the strategic depth.