Orbital mechanics in new movie, Gravity

  • In this computer generated scene, only Sandra Bullock's face is real.
  • Adapted from assembly-line robots, the IRIS motion-control camera rigs (right) used on Gravity move on six axes; a dolly track adds a seventh axis. Filmmakers played back images of Earth and space in the light box, a cube composed of 150 panels studded with more than 600 000 LEDs. Actors were clamped inside the white cage-like tilt-plus rig (centre).
Date:19 December 2013 Tags:, , , , , , , ,

How Gravity simulates free floating in space. By Steve Daly

The new space thriller, Gravity, opens with an unbroken 12-minute shot of two astronauts installing a data-gathering device on the Hubble Space Telescope. Sandra Bullock, playing a flustered medical engineer on her maiden voyage, and George Clooney, as a veteran shuttle commander on his final mission, float in zero gravity while bantering, chasing a stray bolt and marveling at the sight of Earth far below.

Then things quickly go very, very wrong. A catastrophic accident triggered by a debris field cripples the shuttle and sends the astronauts pinwheeling into space, forcing them to improvise their own rescue mission. At the core of this taut, 90-minute survival story are the physical facts of life in low Earth orbit.

Thanks to a combination of mechanical ingenuity and breakthrough visual effects, weightlessness especially is conveyed with a sense of realism unmatched by any other space-mission movie. And no previous film has depended so heavily on computer-generated animation that looks as if it’s live action. In each of Gravity’s nerve-jangling spacewalk sequences, only the heads inside the helmets are real. The spacesuits and all background elements – including the Hubble, the shuttle and the International Space Station – are rendered entirely in photo-realistic CG.

“When we started, the technology to make this film did not exist,” says Alfonso Cuarón, the director and co-writer. “It forced us to invent our own set of tools.” Adds visual-effects supervisor Tim Webber, who oversaw the work of the more than 500 people involved in both physical and CG trickery: “There was an awful lot of ‘you can’t solve this till you solve that, and you can’t solve that till you solve something else’. You just had to start somewhere and go around the loop a few times till you’d sorted it out.”

The entire film was essentially reverse engineered.

Cuarón and a team of animators at Framestore, London’s visual-effects shop, began by designing CG shots, and then a physical-shoot crew worked backwards to create live-action footage of the actors’ faces (and sometimes their bodies) that exactly matched the choreographed CG. The key to that approach was creating reliable robotic cameramen – something that motion-control set-ups had never been able to do with high consistency or ease of use.

The solution was a pioneering system called IRIS. A San Francisco company, Bot & Dolly, created it by ingeniously redeploying robotic arms originally designed for precision assembly-line tasks such as automotive welding and painting. Instead of airbrushes or blowtorches, a quartet of IRIS rigs wielded cameras, lights, props and even the actors in appropriate synchronisation. A custom computer interface translated the data from the pre-visualised CG animation shots executed in Maya software into physical camera moves on the set that captured the actors’ faces in just the right positions and sizes. (Of course, there was rarely an actual set. Mainly there were green screens and cardboard mockups for the actors’ reference.)

For some shots, the massive IRIS rigs, which weigh 1 450 kg, rolled towards the actors at speeds of up to 19 km/h. At Comic-Con last July, Bullock joked: “If that robot did decide to continue through my face, I couldn’t get out of its way.”

As much as possible, Cuarón and company tried to avoid placing the actors in wire-rig harnesses that spun them upside down to simulate weightlessness. The problem: it’s too obvious that gravity is pulling at face and body muscles. But for sequences inside the ISS, where Bullock moves horizontally as easily as a swimmer through water, there was no other option.

Attired only in a T-shirt and undies, like Sigourney Weaver’s Ripley in Alien, Bullock wore a 12-wire rig that was attached with harnesses moulded to fit her hips and shoulders. Each of the four attachment points – one on each hip and shoulder – had three wires attached to computer-controlled servomotors. These, in turn, were connected to a platform that moved along the studio ceiling and configured Bullock into various positions like a marionette. On-set puppeteers – their actual job title – supplemented pre-programmed moves with joysticks to smooth out jerkiness. Extended shots were pieced together from multiple fragmentary takes, because even someone as fit as Bullock could fight gravity convincingly for only so long. “Sandra was amazing at it,” Webber says. “She was incredibly adept at hitting her marks and miming weightlessness.”

Cuarón also placed his actors in something called the light box, an unprecedented innovation. This 2,7 m cube of LED panels was built on scaffolding to match the height of the IRIS camera rigs. Bullock and Clooney were alternately clamped inside a hip-hugging, gyrating tilt-plus contraption, also controlled by IRIS, that co-ordinated the actors’ positions with camera moves while keeping them upright but oscillating.

CG footage of the Earth, Sun and stars was played inside the cube to create intricate plays of light over the performers – and also cueing them as to where they were in space. The result of all this wizardry is a movie filled with zero-gravity shots that set a formidable new standard. But for Cuarón, “it was all for the sake of honouring this story. We wanted to make a film about facing adversity, with the possible outcome of rebirth. And to create something cathartic for the characters and the audience.” Translation: Cuarón hopes movie-goers will have a new appreciation of life after watching these space-walkers defy death in so many ways.

Watch the Gravity movie trailer

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