Explanation for my top picks:
1: A.e.r.o - The Sloan Great Wall
Every time i listen to this, i imagine a spaceship crashing down on a lifeterra. The start is bad, but that is the only complaint i have.
2: Akira - The Blithering Heigths
This just feels very exploration-y
3: A.e.r.o - Kepler 186F
I just love A.e.r.o
music, this one has start, but it is awesome.
4: Astropilot - Hidden Planet
This just feels like it was made by A.e.r.o, and it just feels very space-y.
5: Lokijar - Black Hole
This song is the song that i feel does the most for Space Engine, because of it's uniqueness. It also feels awesome listening to this while exploring a scorched planet.
My LEAST favorite is AstroPilot - Inverted Worlds. It's just... boring, as well as not being very space-y, at least compared to other SE music.
Space is too big to understand, so do not try to understand.