How many times have you been lost in the ozone, drifting off to sleep or mentally calculating the decline of your 401(k) and some smart-alecky friend or spouse says to you: “Ground control to Major Tom?”

That’s just one of the many reasons that David Bowie’s “Space Oddity” is still floating around in our heads.

Today, on the 40th anniversary of its release, the song about a sad and lost astronaut stuffed “in a tin can” and cut off from communication with Earth remains as fresh and remarkable as it did in the space-race era in which it was launched.

The song was rushed into stores in England on July 11, 1969, nine days before the Apollo astronauts landed on the moon. But most American audiences never heard it until 1972, when it was released on an album of the same name.

With its eerie, outer-space theatrics, it was the first sign of Bowie’s fascination with sci-fi, and Major Tom can be seen as the spiritual godfather of Bowie’s most famous creation, the alien Ziggy Stardust.

It’s arguable, but Space Oddity is probably his best song (well, maybe after “Changes”). Bowie’s cinematic lyrics — “This is Major Tom to ground control/I’m stepping through the door/And I’m floating in a most peculiar way/And the stars look very different today” — captures almost verbatim what astronauts relayed back to Earth about the unhinged feeling of walking in space.

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Along with an orchestral, dirge-like melody and that commencement of countdown from ground control (“Check ignition and may God’s love be with you”), the song gets more and more haunting and heartbreaking. Finally, Major Tom loses radio contact and remarks with a poetic simplicity: “Planet Earth is blue and there’s nothing I can do.”

As one of the great singles of the classic rock era — and the song that made Bowie a star — it also remains one of the most hotly debated.

What inspired it? Bowie reportedly wrote it after seeing Stanley Kubrick’s 1968 film, 2001: A Space Odyssey. But some critics see it as Bowie’s metaphor for drug addiction.

So, what did happen to Major Tom? In 1980, Bowie wrote “Ashes to Ashes”, in which ground control gets a call from Major Tom (or “the action man”). He says he’s found love and “I’m happy, hope you’re happy, too.” Perhaps as an indication of how bleak things had gotten since the space-race optimism of the ’60s, ground control concludes: “Ashes to ashes, funk to funky/We know Major Tom’s a junkie.”

Other views of Major Tom: Peter Schilling wrote the 1983 New Wave song “Major Tom (Coming Home)”, in which Tom hurtles to Earth but ground control thinks he’s dead. In 2003, K.I.A. came out with “Mrs. Major Tom” in which she addresses her lost love and concludes: “You didn’t burn up, my Major Tom/You just burnt out.”

But the song has never burnt out, really. Cat Power sang it in a recent TV car commercial. It inspired a character in the trippy sci-fi movie The Fountain. And Bowie is releasing a digital EP with four versions of the song on July 20 to coincide with the moon-landing anniversary.

Finally, in movie theaters this weekend is Moon, about a man on a lone mission in space who encounters problems getting home. Sound like Major Tom?

Well, it was directed by Duncan Jones. That’s the name he goes by now, anyway. As a kid, he was known as Zowie Bowie. That’s right, the son of Major Tom’s creator, the former David Jones.

Things still float in a most peculiar way, don’t they?