From Video Game Music Preservation Foundation Wiki
Fugue is the song from Kiloblaster (DOS).
In Episode 1: Death of a Startship, it is heard in Level 13 (pictured), 14 and 15 but later repeats in Level 28, 29 and 30.
In Episode 3: The Final Battle, it is reused in Level 16, Level 17 and Level 18.
The filenames of the track are SONG_3.KB1 and SONG_7.KB3 (the last digit in the file extensions is the number of the episode using the song).