High above the Earth, the rubbish from a hundred space missions is floating around and around in serene peace. Or is it?

By Alex Hale

'NASA' Space junk

Kessler Syndrome is the big bad guy in the recently released 3D sci-fi movie extravaganza Gravity. As Dr Ryan Stone (Sandra Bullock) finds out to her peril, this syndrome is actually a space agency’s worst nightmare that could mean the end of all current and future space missions. This is not a Hollywood-created fictional catastrophe, and it may already be happening.

Imagine the space around the earth; it’s filled with man-made objects. Since humans started going to space half a century ago, we have sent up more than 2,500 satellites and filled the rest of the area with a veritable smorgasbord of space junk like nose-cones, rocket bodies, hatch covers and other odds and ends. The US Strategic Command is tracking more than 13,000 pieces of space junk larger than 10cm and has suggested that there could be more than a million bits of debris larger than a marble. This may not sound too bad but when the average speed of objects in low earth orbit (closer than 1,200 miles to earth) is about 20,000mph, a hunk of metal 10cm across could punch a fairly substantial hole in just about anything. Near misses and minor damage are a fairly regular occurrence for the space going communities of the world; NASA reports a few near misses to their satellites every year.

So what would happen if a satellite were to be hit by a particularly large piece of debris? Or worse, two defunct and uncontrolled satellites were to collide?  This would create a huge cloud of debris that could endanger many others. A domino effect could spread throughout low earth orbit, destroying anything in its path and creating an impassable cloud of hyper-speed bullets surrounding the earth. Satellites that would be affected include spy satellites, weather systems, space stations and some communications satellites (the majority of communication satellites usually hang out at around 22,000 miles from earth so, unlike in the film, they wouldn’t be at risk. Don’t panic, your Facebook selfies are safe). The debris would all burn up in the atmosphere eventually, but that could take a hundred years, and you can forget about leaving Earth for the moon or Mars in that time.

Surely, though, this is just a worst case scenario? Well NASA scientist Donald J. Kessler, who proposed the theory in 1978, has said that “the cascade process can be more accurately thought of as continuous and as already started, where each collision or explosion in orbit slowly results in an increase in the frequency of future collisions.” Even astrophysicist Neil deGrasse Tyson, whose jokey criticisms of Gravity’s science are well publicised, agrees that “The film #Gravity depicts a scenario of catastrophic satellite destruction that can actually happen.”

It’s all well and good attempting to predict these apocalyptic events, but what’s being done about it? In Gravity, the whole thing is set off by the Russians blowing up one of their disused satellites (don’t worry, I haven’t ruined the film for you, this happens in the first five minutes) and this is a technique that was tried briefly in the real world. Of course, it caused fears that what the film illustrates so well would actually happen. The best way to deal with the big bits, like old satellites, would be to send a rocket up there to tow them to a safe area, whether that be back to Earth or out into deeper space where they can’t hurt anything. Other methods suggested include using disintegrating lasers, recycling the junk into new satellites or using the elegantly named CleanSpace One project to grapple the pieces together into a big ball and pull them back to earth.

So Gravity may not depict Kessler Syndrome perfectly, and the keen eyed physics students amongst you may notice a few other minor errors.  In the end, though, the film is fiction and these are all in service to the story.  In reality, an astronaut’s day doesn’t make great spectator sport and you can’t blame the director for throwing in a few scientific discrepancies to get your heart racing.  It certainly works: shot through with a core of hard science, Gravity defines heart racing, spectacle cinema.