Space is getting messy. The amount of debris orbiting the Earth keeps growing each year, disrupting satellites and occasionally putting astronauts in harm's way. If the problem gets severe enough, it could eventually make low-earth orbit unusable.

Scientists have been worrying about space trash since the 1970s. Humans have placed thousands of objects into orbit since Sputnik, and some of those old satellites and ejected rockets are slowly breaking apart. As pieces collide with each other at high speeds and shatter, they create more debris. Eventually, space could get saturated with high-flying trash — not entirely unlike the chaotic scenes in Alfonso Cuarón's new film Gravity.

Yet despite years of warning, the world's nations have never been able to agree on how to solve the problem. There are lots of bright ideas for cleaning up debris, but countries often wrangle over how to pay for them. So that's where economists come in.

In a recent paper, three economists argue that orbital debris is just a standard "tragedy of the commons" problem. Space is a precious commodity, and people tend to overuse it, since users don't pay the full price for the mess created by satellites. Similarly, no one country has the incentive to clean up the entire mess all by itself.

Economists typically solve this problem with what's known as a Pigouvian tax or user fee to better align those incentives. So, they ask, why not place a user fee on orbital launches to help pay for clean-up?

"User fees are a solution straight out of the Reagan era to deal with precisely these sorts of environmental issues," says Peter J. Alexander, an economist at the Federal Communications Commission and a co-author of the paper. (He helped write the paper in his spare time, not on behalf of the U.S. government.) "This is a classic commons problem."

The space-trash dilemma

The orbits around Earth are undeniably valuable. Satellites are used for everything from communications to television to Earth monitoring and military surveillance. Roughly 49 percent of satellites are in low-earth orbit, which is also where astronauts work. Another 41 percent are higher up, in geosynchronous orbit.

Yet those orbits are gradually getting clogged. The map below comes from NASA’s Orbital Debris Program Office, showing all the items humans have placed into orbit since Sputnik, including bits of satellites that have cracked apart, or old upper-launch vehicle stages:

NASA currently tracks more than 21,000 man-made objects in orbit larger than 10 centimeters, but there are also hundreds of thousands of smaller pieces circling the Earth that are harder to detect. Many of them are moving at extremely high speeds, some as fast as 22,000 mph.

That trash is starting to become a hassle. Now and again, satellites have to adjust their orbits to steer clear of passing debris. Astronauts working on the International Space Station occasionally have to scramble into their Soyuz escape capsule when metal shards fly near, just in case a piece hits the station. "A 10-centimeter sphere of aluminum would be like 7 kilograms of TNT," one NASA scientist explained. "It would blow everything to smithereens."

"There are already a lot of costs associated with the ongoing debris cloud," says Brendan Michael Cunningham, an economist at the U.S. Naval Academy and another co-author of the paper. "We have very expensive programs to track all that debris in orbit, using radar to send out early warnings to satellite operators."

The nightmare scenario would be a cascade of collisions that becomes unstoppable. Metal shards would start destroying satellites, which would create even more debris, until low-earth orbit became unusable. This is known as the "Kessler syndrome," named after NASA astrophysicist Donald Kessler who first discussed the possibility in 1978.

Fortunately, a chain reaction hasn't occurred yet, and Kessler's early prediction of apocalypse by 2000 turned out to be premature. But there are some warning signs. Back in 2009, we saw the first major collision between two intact satellites — a U.S. Iridium and an aging Russian Cosmos. The result: 2,000 extra chunks of metal flying around Earth.

major report by the National Research Council in 2011 warned that may be reaching a "tipping point" where such collisions become more common. The researchers said that space might be just 10 or 20 years away from severe problems.

"Kessler was describing an orbital Nagasaki, where everything was annihilated," says Alexander. "But there are degrees in which the environment gets degraded even before that sort of collisional cascade."

Can we clean up orbital debris?

Here's the good news: Scientists have plenty of clever schemes to deal with orbital debris, like shoving the troublesome pieces high into “graveyard orbit." Engineers at the University of Colorado have even outlined a plan to haul away junk with static electricity. (The FCC requires all newer satellites to move into graveyard orbit at the end of their lifespan, but experts say we'll also have to remove older debris to avoid disaster.)

One problem, though, is that the world's nations can't always agree on how best to handle clean-up. Current international guidelines for debris mitigation are largely voluntary, with some agencies — like NASA — more careful than others. Everyone has an incentive to keep launching satellites into space. The incentives to tidy up the aftermath are weaker.

In their paper, economists Alexander and Cunningham, along with Nodir Adilov of Indiana University-Purdue University, propose a solution: Countries should impose a fee or tax on orbital launches. The fee would be set high enough that companies and nations don't over-populate space with objects. And the revenue could fund clean-up efforts. This, they say, would be preferable to the current system of ad hoc rules and regulations on space debris.

That said, a user fee would create its own set of headaches. How does the tax get divvied up? Most of the debris currently in space, after all, was put there by the United States and Russia, with China a close third. (In 2007, China blew up one of its own satellites to show off its weapons capabilities, creating an additional 3,000 bits of debris.) Should those three countries shoulder most of the burden?

"Those are good questions," says Alexander. "The bargaining environment here has become incredibly complex. We looked at the simplest solution, which was to impose a launch fee on a forward-going basis."

What's more, getting the tax right wouldn't resolve all lingering questions. At a recent conference in Brussels, space experts pointed out that the removal of existing orbital debris involves all sorts of legal challenges. Under current law, for instance, the owners of a satellite have to give permission before anyone else can come near it. Hashing out those sorts of permissions are trickier than they sound.

But even if an international user fee wouldn't be easy to negotiate, the authors say, it's also clear that the current system is failing. "If you look at what NASA's saying, even in the absence of new launches, the amount of debris will continue to grow over the next 200 years," says Alexander.

"Up until now, we've had voluntary guidelines around launches, and the physics community is saying this is not sustainable."

Further reading:

-- Credit where due: Molly Macauley of Resources for the Future has been discussing similar solutions to orbital debris and other space issues for some time. It's worth checking out her 2003 article on the subject here.

-- Another interesting essay: Is space the final frontier of environmental disasters?

-- As mentioned above, space debris played a pivotal role in Alfonso Cuarón's new film Gravity, although that particular scenario was a little overblown. Here's a good fact-check of the movie.