They actually thought it would be easy.
When film director Alfonso Cuarón, now 51, and his screenwriter son, Jonás, began work on their latest project, “Gravity,” they figured they’d be done in a few months.
The film focused on just two characters, a male and female astronaut who get stranded in orbit after their shuttle is destroyed by space debris. And after all, the Cuaróns reasoned, two characters is easier than a sprawling cast.
The action also takes place in just a handful of locations, meaning the number of sets would be limited. Piece of cake.
“Then,” says Jonás, 30, with a sigh, “four and a half years later, we’re still working on it.”
The problem was that the movie — opening Friday — became as technically complex as an actual mission in space.
The filmmakers discovered that they’d made a “huge miscalculation” about the amount of work needed to pull off their vision. The process would require simulating zero gravity, recreating the dim, flickering light of space and pushing actors to their breaking point.
The project began simply enough. In 2009, Jonás and Alfonso (who also directed “Y Tu Mamá También” and “Harry Potter and the Prisoner of Azkaban”) began kicking around ideas for the most adverse situation into which they could possibly put a character.
“What we came up with was an astronaut spinning into the void,” Jonás says. “We grabbed onto that image because it was so terrifying. The script [came] from that.”
The Cuaróns built a story around something called the Kessler syndrome, a hypothetical domino-like scenario in which space junk collides with orbiting objects, creating more space debris, which then destroys more space objects, creating still more debris. Ultimately, everything in Earth’s orbit is destroyed.
In “Gravity,” astronauts Ryan Stone (Sandra Bullock) and Matt Kowalski (George Clooney) are repairing the Hubble telescope when rubble from a blown-up satellite damages their shuttle, leaving them desperate for a way back to Earth.
Because nearly the entire movie is set 372 miles above the Earth’s surface, the Cuaróns spent many hours researching the reality and physics of space travel.
The first draft of the script was given to scientists and astronauts for fact-checking. In an early version, Clooney’s spacesuit springs a leak, leading to a ticking-clock scenario in which he has only a few seconds before he runs out of air.
“We talked to an astronaut, and he said, ‘Ah, come on. All you’d do is grab some gaffer tape and put it on top of the puncture,’ ” Jonás says.
Here’s how the Cuaróns pulled off the movie’s most jaw-dropping — and, it turns out, incredibly realistic — scenes:
Silence is more dramatic than deafening explosions.
The lack of air in space means there’s no sound. One of the risks the filmmakers took was to make a movie that is partially silent. You hear the actors’ voices over their characters’ radios, but you don’t hear, say, debris smashing into the shuttle — even though you see the mind-blowing chaos as it happens.
In another scene, Bullock uses an electric drill to remove bolts. The sound is like a low rumble, closer to a vibration. “If you’re touching an object, it carries, but then you’re not technically hearing with your ears, you’re hearing with your body,” Jonás says.
Zero-gravity is possible with the help of Broadway.
Understanding zero gravity was one thing. Executing it was another. The production team originally considered using the so-called Vomit Comet — a plane that flies in a parabolic pattern, allowing for a few seconds of weightlessness.
The technique was used to shoot 1995’s ”Apollo 13” but was deemed unsuitable for “Gravity,” in part because Alfonso likes long takes: The first 13 minutes is a single shot, and three shots make up 30 minutes of the film’s 90-minute run time.
“It adds to the immersion, which is so much a part of the film,” says producer David Heyman. “You feel like you’re there.”
Simulating zero G was accomplished through a variety of techniques, including CG and wire work. Bullock was strapped into a 12-line pulley system operated by puppeteers from the play “War Horse.” It allowed her to appear to float through the air in scenes set inside the space station.
Scenes set in outer space were accomplished mostly using computers. In some cases, the actors’ faces remain the only “real” element in the shot, and lighting them proved another challenge. Simulating the way light hits a person’s face in space, especially while said person is spinning, is impossible with conventional lighting.
At London’s Shepperton Studios, the production built what was called the Light Box, a 20-by-10- foot structure with an interior composed of 4,096 LED bulbs.
To create the sensation of being lost in space, drive your actors to the brink of madness.
Bullock was shut inside, alone, for hours on end.
“I went inside, and I’m glad I only spent five minutes,” Heyman says. “Not recommended. It’s disorienting, isolating and uncomfortable.”
Bullock and Clooney were also jammed into spacesuits. The replicas were lighter than actual NASA suits, so to simulate the bulk of the real thing, both actors wore rubber restriction suits under their outer costumes. The rubber constrained mobility, only allowing the actors to raise their arms to a certain degree, for example.
To make up for the hardship on the stars, the production team built a calming garden beside Bullock’s trailer and a playground for her son, Louis. Clooney was built a custom tiki bar in his trailer.
“If I was cracking under the pressure [in the box, Alfonso] would radio someone to go get Louis,” Bullock told “Access Hollywood” of her young son. “But I couldn’t get out to hold him, which was frustrating. It was like…torture.”
Critics have already lined up in praise of “Gravity.” The Post’s Lou Lumenick predicts Oscar nominations for Bullock and Clooney, at the very least. Forbes called it the “movie experience of the year,” and Time said it was “cinema’s future.”
Perhaps most important, it’s also getting a pass from real astronauts.
“The visuals were spectacularly good. I don’t know how you did it,” Canadian astronaut Chris Hadfield said at the Toronto Film Festival premiere.
A man who’s been to space left scratching his head. Not bad.