Awesome but not well known Composer Carl Nielsen and if you like Holsts Planets or a good 2001 vibe listen to this and think about the sun coming up slowly...
For those deep space missions far away from kerbal i like to listen to Mahlers 10 Symphony or Phillipp Glass
What also works well is this Playlist of Civilization 4s modern era music with a couple of great songs
Or for more modern music id recommend motion trio - stars