Since some people were saying that there would be things hidden in the soundtrack, I played a little with "Sonic Visualiser".
In the track "Spirit", I've found a QR Code at the end:
After cleaning it:
1955 1958 1960 1961 1967 1969 1971 1977 2003 2005
What does it mean?
(It appears that others have also found it.)
Best Answer
These numbers represent years of significant space exploration achievements:
This was pointed out by swam2222 on GameFAQs, although some of swam2222's indicated milestones diverge from the ones that I've indicated here.