The science is sloppy, the sentimentality is sloppier in “The Space Between Us,” a sci-fi romance pairing up agreeable leads in a cut-and-paste script.

Sci-fi buffs — imagine “Capricorn One” without the suspense, “Starman” without the pathos, all shot on sets left over from “The Martian.”

It stumbles, staggers and sputters out of the gate, and only comes to life after an hour of blundered, banal back story.

Asa Butterfield (“Hugo,” “Ender’s Game”) is Gardner, the first child born on Mars. Nobody knows it. His mother, the mission commander of the first team colonizing the Red Planet, “made a mistake.” Yeah, the script is that tone deaf. And she died in childbirth upon landing.

We’ve seen all that, the cover-up that the visionary (Gary Oldman) who financed the mission and NASA started, heard the speech about a damaged Earth climate that prompted the effort a solid hour of preliminaries.

And then, abruptly, the kid grows up and as a teen is shown flirting with his email pen pal. Britt Robertson (“Tomorrowland,” “The Longest Ride”) plays a rebellious orphan who lives in Colorado and is named Tulsa. Gardner he lives uh, in New York. And he’s, uh, sick. Rare disease. That’s why he can’t come see her.

The world doesn’t know he’s on Mars, how could she? But hormones being hormones, Gardner is ready to fly. Sure, his bones aren’t dense enough and his heart and body aren’t used to working in Earth’s gravity. But science can fix that. They still can’t talk about him with anyone, but one surgery and one spaceflight later, Gardner is on Earth and giving NASA the slip in search of the one girl who will give him the time of day, and the father he’s never met.

“What’s your favorite thing about Earth?” he asks one and all. How does he feel? “Heavy.” Being an alien, he’s got all this Earth stuff — colors, smells, courtship, banter, gravity — to figure out.

“Sorry, he doesn’t speak ‘sarcasm.'”

And NASA? They’re scared to death word will get out, or the kid will die, or something.

Director Peter Chelsom, who voices the obligatory cute robot on Mars (Centaur), did “Serendipity” and “Funny Bones” and more recently, “Hector and the Search for Happiness.” He should know how to make this work.

But the first laughs in the movie show up when Robertson arrives, the first sparks of life are in her spunky/testy scenes with Butterfield. That’s an hour in. The film has already been stillborn.

Butterfield has the right frail, pale, spindly and wide-eyed look of a child raised in low gravity. The camera just loves the perky, animated Robertson. Oldman always gives fair value. And Carla Gugino is well-cast as the scientist/mother figure who looks after Gardner on Mars.

But the screenwriters should have binge-watched “The Martian” before this went in front of the cameras, instead of stealing action beats and story arc from “Starman” and Capricorn One.” The many science blunders might not have mattered had they simply started the film with the only reason to see it — young love, and the obstacles to it.

It’s the space before “The Space Between Us” that is the a fatal blow to the movie.

MPAA Rating:PG-13 for brief sensuality and language

Cast: Asa Butterfield, Britt Robertson, Gary Oldman, Carla Gugino

Credits:Directed by Peter Chelsom, script by Allan Loeb (screenplay), Stewart Schill. An SFX release.

Running time: 2:00