Rocket man by Elton John?
T-rex probably sing some sci-fi, but nobody knows what they're singing about.
Imagine by John Lennon is quite sci-fi.
And that crap song they keep playing on rock stations: "The chances of anything coming from mars, are a million to one..." I don't know what it's called. Neither do I want to.
The purple people eater (great Halloween song) by.... uh... the big bop or something? That's classic sci-fi.
So's sweet transvestite, The time warp, etc. from the Rocky Horror picture show.