this is easily hawkwind's most famous song, so i am not expecting to surprise anyone with their big hit... but i was just watching a documentary about the band and they explained that a "silver machine" is a bicycle. i had always assumed it was about a rocketship and some metaphysical LSD experience about soaring through the cosmos, but no... it is about being really happy, riding around on a bicycle. the joy of riding a bike. that's it. i think i like the song a lot more now.
also in the documentary, lemmy claimed that he was the only one who could sing the high notes in the studio and that is why he was the one to sing it - by default. sometimes these things just work out for the best on their own.