'Gravity': Panel of astro-experts on the science behind the film
Warning: Spoilers ahead!
Gravity took off at the box office over the weekend, and astro-experts have been fact-checking the film’s science left and right. After Neil deGrasse Tyson took to Twitter to chime in on the film’s faults, we decided to ask a panel of experts — astronomer Phil Plait and former astronauts Leroy Chiao and Tom Jones — to give us some definitive answers to our burning questions about the film’s accuracy. And they explained everything, from the mechanics of Sandra Bullock’s spacesuit to using a fire extinguisher in space.
ENTERTAINMENT WEEKLY: Let’s start with the catastrophe that propels the film. What actually happens to debris in space? Would the chain reaction occur in real life?
LEROY CHIAO: The chain reaction is not credible. There’s orbital debris out there to be sure, and it’s something we’re concerned about. Spacecraft typically have some shielding on it to take impact up to a certain point.
TOM JONES: We built the space station with debris shields to protect from the puncture of space debris. My crew delivered the U.S. lab to the space station and it’s armored because of the threat of a catastrophe from space debris. But the chain reaction, I think, stretches the idea a bit too far. It’s not a runaway effect where everything is killed. You would not even see the debris coming as the folks did in the movie — it’s at the speed of a rifle bullet, and you would not see that.
PHIL PLAIT: Debris will move away from an explosion and each little piece will stay more or less on the same orbit. You get a cloud of debris, but over time, it expands. Usually it’s not that bad right away because satellites are specifically put on orbits that are different from other satellites.
So the way the film has the stations positioned is completely off?
PP: Oh yeah, the three objects — the Hubble, the ISS, the Chinese station — are in three completely different orbits. It’s not just that they’re in different heights, the orbits are in different shapes. It’s tilted, like two hula hoops, one inside the other and then tipped at an angle.
TJ: This is one of the biggest shortcuts the movie takes with physics, to put the three all within an orbit that lines them up, and they’re the same altitude so you can hopscotch from one to the other. They’re not in similar orbits, and in fact, you cannot jump from one to the other. You can’t just shoot your thrusters off and go visit it.
LC: The orbital planes are probably not even co-aligned, so they’re in totally different orbits and totally different altitudes.
Let’s say the disaster doesn’t occur, and instead Sandra Bullock’s character just somehow becomes untethered and goes flying through space. What would the emergency procedure be to rescue her?
TJ: Had she been on a shuttle that’s still functioning, the shuttle would fly after her and pick her up — that’s the solution we practiced for many years. But the space station is too massive to fly over and do those kinds of maneuvers, so we always wear, on the space station, an emergency jetpack that can shoot you back. But if you were hurled off at the velocity of Sandra Bullock’s character, you would need another spacecraft that’s equipped to come get you, and that’s not something we practice for, because we think it’s much easier to plan for not coming off the space station by tethering yourself carefully.
Would she, a medical doctor, have been needed for a spacewalk in the first place?
LC: It’s certainly plausible. It’s not at all uncommon for medical doctors of different backgrounds to be trained for a spacewalk, because if you show an aptitude for that, then it doesn’t matter what your background is, whether you’re an engineer like me or a medical doctor like some of my colleagues. You would be trained to do spacewalks.
Moving on to George Clooney’s character, when he’s making her share stories and talking her through their trip, wouldn’t that use more oxygen than just letting her breathe?
LC: Well, you’re right, but it’s a tradeoff. In that kind of a situation, if someone is freaking out and you think you can calm that person down by talking, then it’s worth talking. If you’re hyperventilating, then you’re using a lot of oxygen.
And he survives because of his jetpack. How does a jetpack actually work? Would it actually be able to save both of them?
LC: The jetpack, the MMU — Man Maneuvering Unit — the real thing didn’t have nearly as much fuel as was shown in the movie. First of all, he wouldn’t just be kind of flying around, making jokes and all that in the beginning and he certainly wouldn’t have enough fuel to chase after somebody who’d been thrown off in a different direction, and change orbits and make it to another station. The fuel for that was compressed nitrogen, and it’s not a very efficient fuel. We used the MMU in the early days of the shuttle program to put grappling fixtures on satellites. An MMU could actually operate for several hours but it’d be very slow, deliberate maneuvers, not like how he was in the beginning of the movie, just flying around. He’d run out of gas pretty quickly just doing that.
TJ: That device, the MMU, was a reality back in 1985, but the one he wears has a limited range. That machine was retired so we currently don’t have one.
Later, Clooney’s character is forced to let go to save Bullock’s. Could he have survived? How does the physics work in that scene?
PP: Yeah, that scene was the one scene in the whole movie where I kind of went, “I have a hard time forgiving this.” He did not have to die, basically. She’s stopped, there’s nothing pulling on him now, it’s not like she’s hanging from a tree holding on to his wrist. There’s no force on him, all she had to do was very gently pull on the tether and he would have come floating up to her, and instead he just unbuckled.
LC: Yeah, that was a horribly inaccurate thing. They stopped, so there’s nothing else pulling on him. There was no reason he had to let go. He would not have kept going the way he did. The physics on that is totally wrong.
What about the fire extinguisher? Is that scene possible?
PP: I don’t know how much pressure the fire extinguishers on the ISS have, but yeah, you could use it to propel yourself. It would be super hard because first of all, you’re facing the wrong way, and the other thing is if you’re holding it right over your center of gravity, your midsection, it’s going to cause you to spin. So I was like, “Hmm, it’s plausible, but not probable.” But you could do it.
LC: It is theoretically possible, but that whole scenario was pretty far-fetched. First of all , that hatch doesn’t exist on the Soyuz that she opened, and if she were to get it open and blown out into space, using that fire extinguisher to maneuver and slow down, well, the fire extinguisher’s not going to have much in it, and you’re going to exhaust it pretty quickly. You have to be really lucky to make it all work. It’s like jumping off an airplane to catch another airplane.
TJ: When she uses it inside the space station and it bangs her off the wall, that’s accurate, that would have happened. Outside, it would be much more difficult. She’d go tumbling head over heels and never get herself back on the proper orientation to fire herself in the right direction.
Would using the soft landing jets on the Soyuz have worked to get her to the Chinese station?
TJ: Isaac Newton won’t let you do that. You fire your rockets and you speed up and that raises your altitude to a higher orbit, and then you slow down at a higher altitude and you fall farther behind.
Tell me about her spacesuit. Do you have to take it off immediately when you get inside the station?
LC: Once you get back inside the station, you do want to take your suit off because it’s a lot easier to move around of course, and the suit’s pretty big and bulky and cumbersome — you can bump into a lot of things. Having said that, it’s a lot harder to take your suit off than shown in the movie.
What’s the actual process of taking the suit off like?
LC: The procedure is quite involved. It’s probably, I would say, close to an hour or so unassisted. It’s certainly not like changing clothes. It looks like she just kind of unzipped that. And also, you’re not wearing what she’s wearing underneath, you’re wearing a full liquid cooling garment.
TJ: It’s not that quick and it’s not that easy. You’re wearing a lot more clothing than Sandra wears, and to survive in the spacesuit, you need a cooling garment that’s laced with water-filled tubes to keep you cool, otherwise you would die from the heat. In the movie she presses a couple of quick buttons and it comes off. She takes the suit off like taking off a pair of blue jeans, but it’s more a half an hour process.
What did the movie get right?
PP: The thing it got right the best was just the view. It was just incredible. I did work with Hubble for 10 years for my degree and the thought of it up close and everything was beautiful, they did a great job with that. The stars in the sky were right. She swooped past several constellations that were pretty recognizable, like Taurus and a couple of others.
LC: They obviously did a lot of homework in looking at the hardware, the tools and the suits. The inside and the outside of the ISS looked pretty good, and they paid a lot of attention to the lighting of the Earth and how the sun appears, so they created a nice framework for the look and feel of doing a spacewalk and being in space, even if a lot of the physics and orbital mechanics were totally wrong. They did a good job of giving an impression of what it’s like being outside doing a spacewalk. Everyone who’s done a spacewalk, our secret fear is we’re somehow going to get in that situation, get thrown off the station, and here we are tumbling away pretty much to certain death as you run out of oxygen, so I mean, it hits a fear that everybody who’s done a spacewalk has thought about. That’s part of why it works.
TJ: Two things they did a really good job on were the beauty of the Earth set in space and the views that astronauts have. The real thing’s even lovelier, but that was a pretty good depiction of how lovely the Earth and the sky and the sunrise, the sunset, the moonrise and all that was very well done — I was applauding. The other part they did well was the depiction of the space station and the way the objects moved in weightlessness. I really liked the hyperrealism in the film. Those wonderful long camera shots were impressive and of course, that’s the way we would experience it.
Where would you rank the film in terms of accuracy among other films set in space?
LC: Gravity‘s pretty good, it’s in a different category than 2001, but it’s closer to Alien, even though there are no monsters or anything. To my engineer friends and my astronaut colleagues, I always say, “Look, they got a lot wrong, but if you focus on the story, it’s a good story.”
TJ: In the last 20 years, it’s the best space film by far in terms of accuracy. It’s not perfect, and we just discussed why, but you’d have to go all the way back to 2001 before you’d find a movie that paid more attention to accuracy than this one did and was depicted in such realistic terms.
PP: 2001: A Space Odyssey and Contact would be the two I always rank very highly. Gravity is definitely below those, but it makes up a lot of points for trying super hard and getting stuff right where it could, so it ranks pretty well for that. All the mistakes were minor, so it’s definitely better than Armageddon or Deep Impact.