NASA Analyzes Gravity's Trailer for Space Walking Realism

By Wesley Fenlon

Alfonso Cuaron's Gravity strives for realism, but it takes a couple big liberties with space to tell an exciting story.

Alfonso Cuaron's Gravity, releasing this Friday, has garnered near-universal praise for its depiction of astronauts struggling to survive a catastrophe in space. From its trailers, Gravity also looks like one of the most realistic depictions of movement in microgravity and NASA hardware put to film. Naturally, Ars Technica decided to sit down with one of NASA's experts to analyze just how true-to-life the film is. Instead of watching (and spoiling) the whole film, they scrutinized Gravity's extended trailer and found a lot to be impressed with--and a few things that are completely impossible.

NASA's Zeb Scoville is the EVA (extravehicular activity) task force leader at NASA's neutral buoyancy lab. He knows a thing or two about space walks. When he watched the trailer with Ars, he had high praise for Gravity's depiction of NASA equipment. Cuaron consulted with astronauts and the production based its designs off of NASA photographs to make them as close to the real thing as possible. When Sandra Bullock's character is repairing the Hubble Telescope, Scoville told Ars "They've got Sandra Bullock in foot restrains on the end of the robotic arm—we have the same foot restraint, and there's a tool stanchion they show behind her, and that's right out of the Hubble repair book!"

Gravity's creative liberties come into play with how the astronauts use their equipment. For starters, Clooney uses a jetpack in space that never existed, though it looks similar to NASA's manned maneuvering unit, or MMU. But the MMU was discontinued in the 1990s, and they're too bulky to see use on the International Space Station. And Clooney's jetpack seems to offer far, far more mobility--and fuel--than the real thing. Clooney makes quick directional changes and moves at higher speeds than an MMU would be capable of.

Quoting Ars Technica: " 'Very Superman,' laughed Scoville. 'You could do that about once, before you blow all your propellant. Very, very expensive propellant-wise to have high acceleration and quick changes in speed and direction.' Scoville informed me that when training astronauts for EVA, especially when working on the SAFER backpacks, they have a saying: 'If you feel like you're moving at a snail's pace, you're doing it right.'

'There's also a lot of nonintuitive things that come into play with orbital dynamics,' he continued. 'Like, with how you fly, relative to a vehicle in low Earth orbit. It's not necessarily a point-and-shoot type thing. Orbital dynamics affect the trajectory, and so you really just want to do a couple of small pulses and then see what direction it takes you in. For the big 'lay on the gas' moves and the tumbling—well, technically feasible, but you'd run right out of prop.' "

As Clooney rescues Bullock from the Hubble Telescope, there's one problem that dwarfs everything else shown in the trailer: the fact that they travel from Hubble to the International Space Station. The station and telescope are in completely different orbits around the Earth.

"The space shuttle couldn't go from Hubble to ISS," said Scoville. "When we did the last Hubble servicing mission, we were concerned about what to do if there was tile damage—could we fly to the ISS? The answer was no, never. The shuttle didn't have enough propellant to be able to fly from Hubble to ISS. The plane changes there are monstrously expensive."

Ars offers an in depth explanation of the physics involved in traveling from one to the other, but in short: changing altitude and orbital inclination requires burning a ton of fuel. Clooney would need a magic jetpack to pull that off.

Still, the liberties Gravity takes are fitting from a storytelling perspective. It mostly gets the small details right, and Ars delves into some of those details in the full talk with NASA. Check it out for more on the dangerous debris Clooney has to dodge and the physics of scooting around in microgravity.