“What was she thinking?” the nation wondered in 2007 as former astronaut Lisa Marie Nowak got arrested for a truly bizarre act of obsession. “Lucy in the Sky” admirably tries to get into the head of its thinly fictionalized protagonist, Lucy (Natalie Portman), but can’t stick the landing. Or, really, the takeoff. Trying for humane drama but landing somewhere nearer basic-cable shtick, it asks a bowl-cut Portman to deliver accusatory lines like, “I read your emails while you were in space!” with a straight face.

The fairly solid premise of the film, from feature debut director Noah Hawley, is that traveling to space fundamentally changes a person, a claim echoed by many a real astronaut. In the case of the film’s Lucy Cola, it finds her grasping for meaning in her mundane suburban life, including a tepid marriage to nice guy Drew (Dan Stevens). Distraction comes nicely packaged in the form of Jon Hamm as fellow astronaut Mark, an “action figure on a motorcycle,” as Drew wryly observes, and soon Mark and Lucy are hot and heavy — until he falls for another colleague (Zazie Beetz) and drops Lucy like a hot moon rock.

Portman is always consummately watchable, and she tries her best to telegraph the utter existential confusion engulfing Lucy at work and in love. But the film around her is simply not up to her level. My favorite unintentionally funny moment came when, in the deepest throes of delusion, she stocks up before attempting a kidnapping, in a supermarket section offering rope, knives, duct tape and wigs. The only thing not in the Abduction Aisle? Puzzlingly, the adult diapers that made this a news story in the first place.