Moon, Duncan Jones, 97 mins, (15)

Bowie gave us the song, his son has directed a film that explores the greatest mystery of all – man

The new British feature Moon is an example of what I'd call existential science fiction. It follows a strain of pensive, desolate-future films in which, typically, a handful of astronauts languish in the vastness of space with only, perhaps, a wise and melancholic computer for company.

Prime examples would be Douglas Trumbull's 1972 Silent Running, and John Carpenter's 1974 debut Dark Star, which the director once called "Waiting for Godot in space". On a grander scale, there's 2001: A Space Odyssey, in which humankind contemplated its origins and ends, yet was eclipsed by a machine when it came to crises of consciousness and identity.

Another, more concise example of existential science fiction (ESF, for convenience) is a song, David Bowie's "Space Oddity", in which Major Tom ponders his lonely condition, "sitting in a tin can/far above the world". Now it happens that the director of Moon is David Bowie's son, once known as Zowie Bowie, although these days he prefers to be called Duncan Jones (well, you would, wouldn't you?).

Moon bears a tenuous relation to the song, but it owes a great deal, by way of homage, to the aforementioned ESF canon. Moon is an old-fashioned film, thematically and visually: the general conception echoes Sixties and Seventies imaginings of our future; and overall, the film has a solid, handmade look. The lunar surface scenes – a dumpy tractor-like vehicle trundling over craters and dunes – are manifestly modelled rather than CGI-programmed. If I say there's a hint of Thunderbirds or Space 1999 here, that's intended as a compliment to Moon's approachable human touch, and to the ingenuity of designers Tony Noble and Gavin Rothery.

The story is set in a near future in which energy has ceased to be a problem on Earth, all our needs supplied by a Moon-mined substance called Helium-3. Sam Bell (Sam Rockwell) is the operator of lunar mining station Sarang, alone on a three-year contract. He leads a lonely life, not least because a communications glitch prevents direct contact with Earth: he hears from his wife only in pre-recorded messages. Sam's only company is "Gerty", a solicitous computer that hangs from the ceiling: voiced by Kevin Spacey, it speaks with the reassuring, patient tones of a psychotherapist, while a screen showing a smiley face and other emoticons stands as shorthand for empathy.

After three years alone, Sam ought to be going crazy: but the only signs of burn-out are a tendency to talk to himself and to his whimsically named plants (Doug, Kathryn), and to grow his beard out until he looks like a renegade member of the Grateful Dead. Then Sam starts to see a female presence about the station. Madness? Hallucination? Or homage to Tarkovsky's Solaris, an altogether more rarefied exercise in philosophical futurism?

About half an hour in, things turn really odd. I'll try not to reveal too much, but just in case – spoiler alert! Sam wakes up to learn that he's had an accident, and that there's an identical copy of himself around the station. The other Sam is just as surprised to see him – but bizarrely, rather than react with startled horror, the two Sams just skirt around each other with wary curiosity, as if unconvinced of the other's reality, or as if their coexistence is merely some sort of ontological blip.

It's a smart touch on the part of Jones and writer Nathan Parker that the two Sams react so tentatively before coming into conflict, and that the explanation, when it arrives, is at once so matter-of-fact and so troubling in its implications. The idea of identical Sam Rockwells would have come across as a mere novelty if Moon had overplayed the GI card. In fact, the illusion of two Sams – fighting, or in one snazzy sequence, playing ping-pong – is achieved seamlessly, yet we know it's not just through clever digitals, but by means of artful shooting and editing, and terrific acting. Rockwell contrives to evoke two shades of bewilderment for two slightly different Sams: one haggard and drolly cranky, the other a scowling, clean-cut Nasa type. When the two fight, it's like a playground tussle between the class jock and the clever kid who's too sarcastic for his own good.

While it's nice to see such nuts-and-bolts science fiction again, Moon is heartening rather than an outright revelation, because so much of it is knowingly familiar, right down to the octagonal corridors that echo 2001. "Gerty", too, is a direct descendant of that film's HAL, but one of Moon's smartest twists is that, despite Spacey's ominously smooth delivery, Gerty proves not nearly as sinister as habit teaches us to expect.

Generally, Moon has plenty going for it. The design plays off the initial impression of shiny futuristic whiteness against the grubbiness and wear of objects seen close up. There are some nice, gently cruel gags (Sam wakes up to an alarm clock playing "The One and Only"); and Clint Mansell's music is as spare as John Carpenter's old DIY scores. The ending feels a little cursory, but it doesn't spoil the overall tone, which is poetic and soulful. There's a nice moment as the two Sams see the reality of their situation by the cold light of day – literally, as for the first time, the Earth is seen hovering in the sky. It's that painful, poignant moment of truth in which a spaceman realises, if you'll excuse me quoting an old song, "Planet Earth is blue/And there's nothing I can do ..."