"The Astronaut Farmer" is a surefire test of our ability to believe in anyone with a dream -- including a soft-spoken Texan who figures if he points his homemade rocket in the right direction and juices it with enough fuel, he'll orbit the globe and get back home in time for dinner.

It helps us considerably that the man in the spacesuit -- a silvery "Buck Rogers"-style outfit that laces up like a set of granny boots -- is Billy Bob Thornton, the actor whose relaxed assurance can boost even the hokiest of roles.

He's Charles Farmer, an aspiring astronaut who had to jettison his career thanks to a family crisis. But in the years since, he's been running a farm -- rather ineptly -- in Story, Tex., and dreaming of making it into space. As for the rocket -- well, who needs Houston? -- he's been building it himself in the barn.

Sure, it's the corniest of conceits, but "Astronaut" delightfully taps into one of our deepest cultural values -- the one about the pursuit of happiness. And the movie's unpretentious lightheartedness, which echoes the old-fashioned, corn-fed lore of Frank Capra or even "The Andy Griffith Show," makes it blissfully easy to sign on for this good-natured voyage. Written by Mark and Michael Polish (Michael is also the director), "Astronaut" doesn't sweat the small stuff of veracity. Its willful innocence is its charm and its safeguard. And to watch it is to protect the movie -- and ourselves -- from the killjoy rules of reality.

Which is why we gamely ignore the laws of rocket thrust and atmospheric reentry, and why we practically celebrate Charles's low-tech control panel -- manned by his 15-year-old son, Shepard (Max Thieriot) -- that will supposedly guide him around the world. And it's definitely why we quietly applaud Charles's wife, Audrey (Virginia Madsen), who -- in the secular-Madonna tradition of all screen wives who stand by their dreamer husbands -- smiles and steels herself for the inevitable countdown.

After all, if "Audie" were really taking stock of the situation, the ink would be dry on the divorce papers by the end of Act 1: The farm is facing foreclosure.

The Polish brothers are best known for such eccentric, otherworldly fare as 1999's "Twin Falls Idaho," which starred the filmmakers as a pair of mystical, conjoined twins. So it's refreshing -- and certainly surprising -- to see them make the kind of traditional movie that a generation ago would be half of a Saturday afternoon double bill at the local Rialto.

Yet, leave it to the filmmakers to lace the movie with winks to their art house fans. The more conventional developments in the movie -- the FBI becoming interested in a loner who's looking to buy 100,000 pounds of rocket fuel -- are treated with arm's length wryness. One of the FBI agents is presented as an adorable, almost Disneyesque goofball. And a scene in which Charles makes an emotional speech before Federal Aviation Administration inspectors is ticklishly funny for the way he twits their humorless logic before pulling out his Capraesque trump card: A vote against Charles is one against the freedom to be American.

Most of the outstanding supporting players have earned their spurs in the indie-movie world, including Bruce Dern, Jon Gries (the nutty uncle in "Napoleon Dynamite"), Tim Blake Nelson (Delmar in "O, Brother Where Art Thou?") and longtime character actor J.K. Simmons. There's also Bruce Willis, who makes an eleventh-hour appearance as Charles's old flying pal.

The result: a PG-rated movie that's savvy about its schmaltziness yet not so postmodern that it has to let us know. Like "October Sky," the true story of a West Virginia boy who dreams of building rockets, and "Field of Dreams," the Kevin Costner baseball fable, it engenders audience goodwill with characters we care for.

The Astronaut Farmer(109 minutes, at area theaters) is rated PG for adult themes, including domestic tension and scenes of peril and some profanity.