'Gravity': 7 Exclusive Behind-the-Scenes Pics

When director Alfonso Cuarón co-wrote Gravity with his son Jonás, he knew that he had a thrilling story on his hands: A medical engineer (Sandra Bullock) fights for survival after a freak accident that strands her in the depths of outer space, far from her ship and mission commander (George Clooney). What Cuarón didn't know was how he could possibly film it. ''We realized that it was impossible to do because everyone is in zero-G throughout the movie,'' he says. ''So we had to invent the technology.'' That meant developing a groundbreaking system of LED panels, computer-controlled cameras, and complicated wirework — and then digitally erasing it all in the final film to provide a believable, invisible framework for Bullock's performance, much of which she delivered while strapped to a rig in the middle of a box of computerized lights. ''If you're acting to no one and seeing nothing, you think, as an actor, I don't know what part of my body I'm going to pull this out of,'' says the actress. Judging by the roar of Oscar buzz around her performance, Bullock managed just fine — and here's a glimpse at how she and the Gravity team did it.

Inside the light box, which projected motion-controlled light onto her face, Bullock was strapped to one of several rigs that would move her body to simulate zero-gravity conditions. ''It took so long to get in and out of the rig that if they knew it would be an hour before the next setup, it was just easier and less painful mentally to stay in there,'' says Bullock. ''There were always people down below going, 'Do you want a cup of coffee? Do you need to email someone? Do you want [Bullock's son] Louis in here?' But if I had the cup of coffee, then I'd have to pee. And if they brought Louis in, then I'd be sad that I wasn't with him and he was concerned — 'Why are you in that contraption?' They were so sweet about just trying to make my time better, but everything actually just made it worse. I said, 'Just leave me alone and I'll just stay here.''' Because of Cuarón's love of lengthy takes, Bullock often had to memorize long combinations of precise movements to hit her marks at different points in the shot — more like choreography than traditional blocking. And she often had to coordinate her own moves with those of the wire rig attached to her (operated by some of the same puppeteers who brought War Horse to life on the London stage) and the camera. ''Three things had to work: the camera, the puppeteers, and my body. Once they swung you in one direction, you had to make your body do what it would do in zero-G rather than what it felt like doing. It was great synchronicity when it worked,'' she says.

While filming an underwater scene, Cuarón held his breath along with Bullock to make sure he wasn't asking too much of his star — but he soon found he couldn't match her lung power. ''Halfway through the take, I was gasping for air — and she just kept on going,'' says the director, who got worried when the actress seemed too relaxed underwater. ''At some point we were like, 'Sandy, are you okay?''' he recalls. ''And she would say, 'I'm fine! Don't ruin the take!'''

When Clooney joined Bullock on set for a few weeks of the three-month shoot, the actress says, ''It was like the party entered the room.'' And since some of their onscreen moments together are lighthearted, the pair allowed themselves to have fun between takes, especially with their behind-the-scenes soundtrack. ''George and I are literally separated at birth. I mean, musically...we would just punch up the playlist and it was music and joy and joking,'' says Bullock. ''We both love the song 'Rapper's Delight.' We'd compete to see who knows the words more. That was a daily occurrence. It still is a daily occurrence every time we're around each other.''

Shooting with cameras mounted on computer-controlled arms (a contraption that the crew nicknamed Iris) was a challenge for the actors, who had to mentally stay in the scene while machinery swirled around them. ''Here comes this seven-ton machine 30 miles an hour toward your head, and you're bolted from the chest down into this other rotating machine, and the camera will come flying into you and stop literally six inches from your nose,'' recalls Clooney (pictured above rehearsing with Bullock and Cuarón). ''And you can't duck because you're bolted in. And there are a bunch of technogeeks up there going, 'We got it!' I was like, 'I know — but if you don't, my head comes off!' It was funny. We made a lot of jokes about it.'' According to VFX supervisor Timothy Webber, the crew started giving nicknames to the different camera movements based on what they looked like. ''There was one called the ''viper strike,'' where the robot with the camera on the end would sort of shoot in, whip forward, almost look like it was biting [Sandra's] face, and then whip back again. It was quick scary to watch, but we knew it was precise and everything was checked,'' he says.

Bullock says she had to get into ''the best shape of my life'' to meet the intense physical demands of Gravity, like simulating zero-G by holding her limbs out as though they were floating during extended shots. ''I worked out so much just to make sure that I wouldn't shake when I contracted, because I was balancing. You know, your leg is pretty heavy, and I was like, 'Please don't let it shake!''' says the actress, who started training six months prior to the shoot. Even so, it wasn't always easy. ''We found a really great physio guy in London who literally came twice a week and had to put Humpty back together again,'' she laughs.

The pins sticking out of Clooney's helmet were motion-tracking devices that enabled the VFX team to monitor the movements of the actors' heads in order to match them to the CGI background and spacesuits later. The filmmakers relied heavily on ''pre-viz'' (short for ''pre-visualization,'' a process in which shots are rendered on a computer ahead of time), meaning that the actors often had to act while precisely matching their movements to the computer rendering. ''Basically everything was done in a pre-viz before you do it because they had so many pieces and moving parts that you had to try to do everything naturally while you were matching everything that was preordained a year earlier,'' says Clooney. ''So there was no improvisation, which was fine for me. Even in your actions there was no improvisation. You really had to match what you did?when you first read it and made videotapes.'' In some cases, the actors heads were the only live-action elements in a shot. Explains Webber, ''We only filmed the faces for huge amounts of the movie, and everything else was created in the computer.''

Bullock says the underwater shots were some the most fun for her — and the most nerve-wracking for the crew, who were concerned about the actress' safety. ''I think the most dangerous time for [the crew] was when we did the tank work. Because I loved it, and I sort of enjoyed seeing how long I could act underwater,'' she says. ''There were some scenes where you want to think that [my character] perished on her way up. But in a cool way, manipulating your lung expansion as you slowly go up, you gain more air — and you can [pretend to] die a little longer. So I could enjoy that. And I could hear people panicking, like, 'She's dying!' But I think that was probably a little more frightening for them because so few people could be in the water. But I loved it. You really felt like, as close to space or flying as you can get.''