It’s hard to know why anyone thought “Lucy in the Sky,” a drama about an astronaut’s fall, would make a good movie. Was it the appeal of outer space, with its beauties, mysteries and infinite possibilities? Or was it the faintly exotic if rather basic romance that blows up so many lives? Was it the diapers?

Inspired by real events, as movies like to say, “Lucy” selectively draws on the bleak story of Capt. Lisa M. Nowak , an astronaut who earned national notoriety in 2007 when she was arrested after attacking Colleen Shipman , an Air Force captain she saw as a romantic rival. Nowak was charged on several counts, including attempted kidnapping; later, she was charged with attempted murder. It was wild and weird. She had gone full-on Jason Bourne for the attack, dressed in a wig and a trench coat, and armed with a BB gun, a steel mallet and a buck knife. But all that anyone cared about were the diapers she said she wore on a long, futile drive the night of the assault.

Some of this makes it into “Lucy in the Sky,” which takes curious liberties (no diapers) with the real story to not much point. Its main draws are Natalie Portman, who plays a sympathetic variation on Nowak called Lucy Cola ; and Jon Hamm as her swaggering heartbreaker, Mark Goodwin, another astronaut. In their shared and individual scenes, these nicely synced performers create an emotional and psychological foundation for the story that holds your attention even as the rest of the movie collapses around them. It’s a dispiriting mess and waste of talent, sunk by a lack of focus, misguided choices and insistently unproductive, at times incoherent clashing tones.