They should have used Jerry Goldsmith's alternate theme for TMP (the first one that he did that GR rejected). It's got the same sense of sweeping epic that the final TMP music did and would have lent itself well to a show about exploration. Plus, it's distant similarity to the TMP/TNG theme would have informally 'linked' it to the later productions. Unfortunate missed opportunity. But I can understand why. We all knew that more males in the 18-25 demo will watch a show with a 'cool' rock theme song, right?
I seem to recall hearing the rejected one on YouTube before and liking it.
Do you have any links - or a precise title - for Jerry Goldsmith's rejected TMP theme? I would really like to hear it!