In a 2016 YouTube video, Elton John said,

It was a pretty easy song to write the melody to, because it’s a song about space, so it’s quite a spacious song.

Bernie Taupin, on the same video, said,

It was inspired by a story by Ray Bradbury, from his book of science fiction short stories called The Illustrated Man. In that book there’s a story called ‘The Rocket Man,’ which was about how astronauts in the future would become sort of an everyday job. So I kind of took that idea and ran with it.

In a 2013 interview with Rolling Stone, Elton John said:

The first huge single that I had. ‘Your Song’ was a hit; ‘Rocket Man’ was a big hit. It had an acoustic guitar on it, it was a different song for me – it was a simpler sound. I’d moved into a house, I was becoming successful, I was so confident, musically. Everything was to do with the music – touring, recording, radio interviews, photo shoots and ‘What are we going to do next?’"