As Gravity made clear to the general public, it’s getting crowded in Earth orbit. In the nearly 57 years since Sputnik’s launch on October 4, 1957, Earth has seen a cloud of human-created objects continue to grow, expanding like dandelion fluff around our planet. In 2014, there’s good and bad news on the subject.

Some good news is that Gravity’s makers seized on a plausible scientific disaster scenario—the Kessler syndrome, an expanding cascade of space debris—and amped the volume up to 11 for dramatic purposes. The filmmakers kept only as much science as they felt like keeping, as movie-makers have done before. (The China Syndrome did it with nuclear meltdowns in 1979, for instance.) The actual science detailing how a Kessler-type situation would unfold presents a more nuanced picture than Gravity.

The bad news is that the Kessler syndrome isn't merely some science-fictional theory hyped by Gravity. In a true case of Kessler syndrome, the density of orbital objects becomes so great that collisional cascading is triggered, and one initial collision generates ever more smash-ups among ever greater quantities of space junk. We’ve already reached the point where the growth of debris in low Earth orbit (LEO) has become self-sustaining. Human access to space might eventually become impossible.

“The Kessler Syndrome is a mathematical singularity," said Darren McKnight, a member of a recent National Academies panel on NASA’s meteoroid and orbital debris program. "Based on the equations, we’ve already passed the critical density.”

Recent real-world events support McKnight's evaluation. In January 2007, a Chinese “hit-to-kill” ASAT (anti-satellite) demo generated more than 2,317 trackable items of debris as well as an estimated 150,000 untrackable pieces 1 cm or larger and one million pieces 1 mm or larger. In February 2008, the US shot down a dying satellite for purported safety reasons. One year later, the first accidental hypervelocity collision between two satellites—a dead Russian Cosmos satellite and a functioning US Iridium—occurred. And in 2011, the US National Academy of Sciences stated that orbital junk in two bands of LEO space—the 900 to 1,000km (620 miles) and 1,500km (930 miles) altitudes—already exceeded the necessary density.

Force before facts

Again, there's good news. Active debris removal is technically challenging, but potential solutions exist. Things like "laser brooms," electrodynamic tethers, nanosatellites, solar sails, space grapples, and tugs are being considered (more on these to come). Some of these technologies even exist as more than prototypes, although they’re sequestered away under military control.

The bad news is that our international space policy and governance lag behind our technologies. Orbital debris has reached its current disastrous status largely because during the last decade—and there’s no other way to put this—a giant pissing contest has played out in orbit between factions in the US and Chinese militaries.

“Almost every Air Force general I talk to says, ‘We’re going into space.’ For them, that really is the ultimate high ground, and they’re bedazzled by the technology—concepts like Rods from God and bombers that rise into orbit then drop directly down on a country with no overflight requirements—and their hopes that this will somehow validate strategic bombardment," said John Arquilla, a Pentagon consultant and professor at the US Naval Postgraduate School. "Unfortunately, an arms race in space will only create a catastrophe for everybody, including themselves. The simple fact of the matter is that you can destroy or cripple things in orbit far more easily than put them up there.”

The Chinese proved this handily with their 2007 ASAT test. In one shot, they fragmented one of their own 750-kilogram satellites, creating a 20-percent increase in total debris. Not to be outdone, the US Air Force demonstrated its superior ASAT prowess a year later by knocking down a failing American satellite surgically, showing it might in theory destroy Chinese space assets without generating so much debris that its own hardware would be threatened.

In practice, this capability would be irrelevant if a conflict reached the point where both sides took potshots at each other’s satellites—the Chinese could simply try to destroy as many satellites and create as much debris as they chose. It’s hard to see the Air Force’s strategic thinking here as more than a sclerotic carryover from MAD-based nuclear deterrence doctrine. Both sides’ behavior, moreover, is especially regrettable because orbital debris growth was previously slowing. As McKnight laments: “We were doing a lot of good stuff and it was ruined in an instant.”

The “good stuff” came about in large part thanks to Donald Kessler's landmark 1978 paper, "Collision Frequency of Artificial Satellites: The Creation of a Debris Belt." That sufficiently impressed NASA that it had Kessler head an Orbital Debris Program. By the early 1980s, following that program’s recommendations, NASA had McDonnell-Douglas design its Delta boosters so that once their missions end, they vent any energy left (as residual fuel or in their batteries) to prevent debris-generating explosions, then drop into a decaying orbit and burn up in Earth’s atmosphere. Subsequently, this approach to passivation became standard operating procedure internationally.

As such, we wouldn’t be where we are with orbital debris in 2014—that is, facing Kessler-type growth—if international policy and governance had reigned in US and Chinese military knuckleheadedness. As we examine the challenge’s technical scope and potential solutions, we should remember that no technological fix, however brilliant, will matter much without international agreements that prevent the creation of debris.

Risk management

Even without such an agreement, the problem of orbital debris is a problem of risk management in a context and scale that’s unprecedented. Any solutions must factor in the following questions: What are the different categories of threat posed by orbital debris? How much time do we have and what should we prioritize? And what potential debris removal technologies might we have in our toolbox?

In terms of threats, the nearly instantaneous cataclysm Gravity depicts has almost zero chance of happening. The film’s scenario, an ASAT test at the same altitude as the International Space Station, would actually play out very differently in the real world. After the initial event, the likelihood of the ISS encountering any debris would be extremely low (at 10 seconds afterwards as low as 4×10-11) unless the ISS hit the debris cloud full on. Thereafter, the ISS’s chances of encountering the expanding cloud would grow but remain low (reaching 4×10-6 per orbit six months later) as debris increasingly dispersed and some of it burned up in Earth’s atmosphere.

A single impact on the ISS would also be far likelier than the multiple debris impacts that tear through it in Gravity. After all, though China’s 2007 ASAT test smashed a 750-kilogram satellite into a vast number of fragments, none of them have managed to collide with another tracked object since.

Any real-world Kessler-style cascade would be a slow-grinding, exponential process, probably requiring two to four decades to really kick in. If current debris growth is sustained, McKnight reckons, it’ll be 2035 before there’ll be, say, one collision involving a large object occurring annually in LEO. The bad news, McKnight adds, is that the current growth rate may not hold: the situation has become non-linear (he uses the term "mathematical singularity").

“Before the Iridium 33 and Cosmos 2251 collision in 2009, those two objects’ potential conjunction wasn’t rated as even one of the 150 most likely that day,” he said. “It wasn’t even the likeliest collision for an operational Iridium satellite.” Nevertheless, when those two satellites smashed into each otherat a combined speed of 42,120 kilometers per hour (26,172mph), the result equaled over six years of typical debris growth. Hence, we entered potential "black swan" territory.

Thanks to this situation, any technical solutions to the problems of orbital debris have to begin with improved space situational awareness, or SSA.

At least, that's the case according to Richard Crowther, the UK Space Agency’s Chief Engineer. He heads that country’s delegations to various UN and EU committees on orbital debris. Beyond preventing collisions, Crowther said better tracking of near-Earth space is vital for other reasons. “If treaties require removing spacecraft when their working lives end, we need to measure compliance. If an anomaly is encountered in orbit, we have to differentiate between natural phenomena and hostile actions.”

The US recognized the importance of SSA early, Crowther noted, yet even the American system has gaps over Earth’s Southern Hemisphere. Other nations have far more limited coverage, as good SSA requires a globally distributed, integrated network of radars and telescopes. Unfortunately, SSA remains primarily the province of national militaries, so there’s a reluctance to share data (the US being the exception) even when it’s in everybody’s interests. “The data largely is out there, but those who possess it tend to keep it to themselves," Crowther said. He believes we won’t come to grips with orbital debris until an international data-sharing arrangement lets us understand the totality of what’s up there.