“You better know what you want to do before somebody else knows it for you,” Charlie Farmer warns a young kid in the new Polish brothers film The Astronaut Farmer. Farmer (Billy Bob Thornton) is an almost-astronaut who tries to make it to space on his own, with a rocket built in his barn.

“I went to Mark one day and said what if a guy built a rocket in his barn?” explains Michael Polish, at a roundtable with The Muse, half of the identical-twin-filmmaking-duo responsible for the movie. After years of being doubted for their own ambitions, the brothers created a film about a guy who takes the unconventional route to realize his dreams. The Astronaut Farmer came from the idea of making a space travel story that was more personal, about a regular guy who wants to orbit the planet.

Except that Farmer isn’t a regular guy, he’s the heroic, sacrifice-it-all-for-the-dream type. The Astronaut Farmer has the feel of an inspirational movie based on a true story, but it’s complete fiction. Virginia Madsen, who plays Farmer’s wife Audie, has the countenance of either a saint or a crazy person — perhaps St. Dympna, patron saint of the insane.

As Farmer gets closer and closer to achieving his goal, it begins to tear his family apart. He tries Audie’s nerves, taking his kids out of school to serve as his mission control, drawing overwhelming media attention, attracting heat from the feds and spending every last penny the family has reserved for emergencies (like food). Pretty much everyone in the town, and soon in the country, thinks the would-be space cadet is out of his mind.

But Charlie Farmer is no Lance Bass. He’s a really smart guy who wants to prove something, not just a fantasist daydreaming in his barn. Farmer’s heroic resolve drew Thornton to the film.

“I’d always wanted to do like a Jimmy Stewart movie, like Mr. Smith Goes to Washington — sort of a triumphant movie with the common man fighting against the system,” the actor says.

He could easily relate to Farmer, who gets sick of being told what to do. “Hollywood has a very narrow vision. It’s not a very creative place. There’s a lot of creative people there, but the people who run it aren’t,” he says.

The Polish brothers based the character on their own father, who never discouraged his sons fom their dreams. “Everything I know now is from my father, not really school,” Michael said. While being harassed by the world for his renegade-rocketeering, Farmer proves to his kids that they can do anything they want.