When Alfonso Cuaron was first planning his marooned-in-space drama "Gravity," the filmmaker imagined an action-drama set in orbit, most of it with just a single character who would be weightless for the entire picture. It would be filmed using his signature long, continuous shots.

But there was one big problem: As fellow director David Fincher warned Cuaron and his cinematographer, Emmanuel "Chivo" Lubezki, the technology to make that movie simply didn't exist yet. He advised them to wait five years.

"We were stubborn, (and) said we're going to make it work," Cuaron tells Variety. "But you know what? David was right. It took us 4½ years."

"Gravity," which opened the Venice Film Festival to great fanfare -- and early Oscar buzz -- and will screen at Telluride and Toronto on its way to an Oct. 4 release, is as much of a game-changer, in its way, as "Avatar" was. Perhaps that's fitting, since "Avatar" director James Cameron, whose pal Cuaron screened the fi lm for him four weeks ago, is among the picture's most ardent champions.

"I was stunned, absolutely floored," he says. "I think it's the best space photography ever done, I think it's the best space film ever done, and it's the movie I've been hungry to see for an awful long time."

SEE ALSO: Alfonso Cuaron's Signature Style Offers Unique Viewing Experience

Cameron, surprisingly, said it wasn't the cutting edge technology that impressed him; it was Cuaron's uncompromising vision and tenacity in getting the picture made as he wanted it, and star Sandra Bullock's preparation for and performance of a highly challenging role. "What is interesting is the human dimension," Cameron says. "Alfonso and Sandra working together to create an absolutely seamless portrayal of a woman fighting for her life in zero gravity."

The 91-minute picture -- unusually short in today's world of two-hour-plus tentpoles -- follows two spacewalking astronauts, commander Matt Kowalsky (George Clooney) and mission specialist Ryan Stone (Bullock), whose journey becomes a fight for survival when a fusillade of debris cripples their shuttle, kills a shipmate and leaves them stranded in space. As they make their way to the Intl. Space Station and beyond, searching for a lifeboat, it falls to Stone, on her first space expedition, to find a way back to Earth despite a terrifying series of setbacks.

A lot is riding on "Gravity" for Bullock, the filmmakers and their studio backer, Warner Bros., which bankrolled the risky mission at approximately $100 million. For producer David Heyman, it is the first picture he's steered since the blockbuster "Harry Potter" series. For Cuaron, it's his first since 2006's sci-fi thriller "Children of Men," and by far his most challenging outing. For Bullock, it's the first time the Oscar winner has toplined a CG-heavy sci-fier, let alone carried an entire picture on her own for most of its length.

Even with so much at stake, though, Cuaron stayed true to form, eschewing a tried-and-true approach to filmmaking in favor of breaking creative and technological barriers to bring a highly emotional story to the fore.

Photo by Julian Broad
"Alfonso does not play it safe," says Heyman, who worked with the director on the third "Harry Potter" film, "Prisoner of Azkaban," the darkest, and according to many the most daring, of the series. In "Gravity," Cuaron and his team tackled unproven techniques and digital technologies aimed at transporting audiences into weightless space.

"There was no way to rely on anything we knew before this film," Bullock says. "No character was like Stone, no film set was ever like these sets, not one member of this crew had ever done this before. We all were doing something that had never been done before."

"Gravity" began to tug at Cuaron after his screenwriter son Jonas asked him for notes on a struggle-for-survival script he was writing, "Desierto." The elder Cuaron had a few notes, but liked the script's stripped-down narrative.

"What I really wanted to do is something in which, in a single through -line, you can play and juggle with different things and motifs and serious subject matter without stopping the action," Cuaron says. "I said (to Jonas), 'I would love you to help me do something like that,' and he got excited (and said), 'OK, let's do something together.' "

SEE ALSO: Warner Bros. Plots Careful 'Gravity' Launch

They soon settled on a theme they wanted to explore: "Adversity and the possibility of rebirth as an outcome of adversities," explains the director.