How's this for the mother of all crummy jobs?

Three years alone on the back side of the moon. No live contact with mother Earth. No one to talk to except a ubiquitous computer named Gerty. Almost nothing to do but monitor a remote surface-mining operation and carry out occasional vehicular forays into the monochromatic landscape.

Why would civilian astronaut Sam Bell accept such a job? Why would anyone take such an assignment?

"Moon" never answers that question, which is disappointing but not disappointing enough to seriously dent the movie's considerable appeal.

That's because Sam's monotonous existence is shaken by the mysterious appearance of his own clone. Sam and the audience are left to figure out where the double came from, how he reached the lonely outpost on the far side of Earth's neighbor in space and what he plans to do there.

"Moon" is the feature debut of Duncan Jones, who directed the movie and co-wrote it with Nathan Parker. Scuttlebutt holds that it was filmed on London sound stages for $5 million, which wouldn't cover the catering on a sci-fi opus out of Hollywood. If so, it can be said that the effects of shoestring budgeting are evident neither in the look of "Moon" nor in its acting.

Sam's moon station successfully mingles high tech with the comfy, littered look of home. It's a relief from the sterility and whiz-bang special effects more typical of space movies.

Gerty, voiced by the distinctive tones of Kevin Spacey, manages to be both solicitous and vaguely menacing and looks more like a dental X-ray machine than the robotic, all-knowing computer it is.

The acting in "Moon" can be summed up in two words: Sam Rockwell. He plays both Sams in what is essentially a one-man show, and he makes a terrific job of it. His Sam Bell is by turns sane and mad, lucid and hallucinatory, lonely, stir crazy and content to whittle his model village and spritz the plants in his indoor garden.

"Moon" sideswipes halfheartedly at the themes of corporate greed and conspiracy. But those ideas, like the question of why a man would willingly imprison himself in such profound isolation, are left underdeveloped.

At bottom, the movie is an unpretentious sci-fi tale well told and a showcase for the appreciable acting skills of Sam Rockwell.