Lyric discussion by Seryll 

Cover art for Spaceman lyrics by Harry Nilsson

I don't want to be that guy that says every 70s song is about drugs but, for this one I think its about "shooting up" to the moon, taking drugs to get high etc (shoot up heroin etc). Shoot em up to the moon. He wanted to have a good run, heard itd be fun, but he had taken enough and didn't want the drugs anymore.

My Interpretation