Saw the film Gravity yesterday. It got a lot of things right, but there are a few places where the writers got the science wrong. Obviously, this post contains spoilers.
The entire plot starts when Russians blow up one of their own satellites, creating a fast moving debris cloud. This cloud impacts other satellites, which break apart, and the cloud spreads. This is called a Kessler Effect, after Donald Kessler. This expanding debris cloud takes out many satellites, among them communications, the ISS, and a Chinese space station, and the space shuttle Explorer, where the action starts. Except, the cloud takes out communication satellites and the Explorer right away. The comm satellites would be in an orbit of over 22,000 miles, and the Explorer at LEO, roughly 350 miles. There’s no way both would be affected at the same time; it would be one or the other.
The two surviving astronauts use an MMU to get to the International Space Station (ISS). But again, the ISS is in a very different orbit than the Hubble Space Telescope; it’s about 100 miles closer to the Earth. So getting to the ISS by using a mostly used up MMU isn’t feasible. The MMU just wouldn’t be able to provide enough Δv to get two people to the ISS.
Once they’ve gotten to the ISS, they’re out of propellant, and have to stop themselves. They end up with Dr. Stone caught in parachute shouds and holding a tether that Lt. Kowalski is hanging from. But they’re in microgravity, and there’s no reason they would be hanging. Once their relative velocities have been canceled out, they should have been able to gently pull themselves back to the ISS. Thus, there’s no reason for Kowalski to sacrifice himself.
At this point, Dr. Stone’s oxygen has run out, and she’s rebreathing her air. She lasts over five minutes with carbon dioxide building up and each breath with less oxygen. In a high stress situation with an elevated heartbeat. I don’t buy her lasting that long without passing out.
At the end of the film, Dr. Stone has managed to get to the Chinese station. But this station is already entering the Earth’s atmosphere. There just isn’t any reason for any recently used space station to be falling into the atmosphere. If it’s supposed to be falling in because it’s been hit by debris, any impacts that would slow it down enough to enter the atmosphere would destroy it in the process.
As a side note, back in 2007, the Chinese did use a missile to blow up one of their own satellites. By 2010 97% of the debris created was still orbiting the Earth. That’s over 3000 pieces of junk, or over 20% of all tracked objects in LEO.
Don’t get me wrong, I enjoyed the film. And my suspension of disbelief was only broken a few times.