The saga of what steps that must be taken to deal with the evolving threat of Earth-circling orbital debris is a work in progress. This menacing problem — and the possible cleanup solutions — is international in scope.
Space junk is an assortment of objects in Earth orbit that is a mix of everything from spent rocket stages, derelict satellites, chunks of busted up spacecraft to paint chips, springs and bolts. A satellite crash in February 2009, for example, marked the first accidental hypervelocity crash between two intact artificial satellites in Earth orbit. That cosmic crash created significant debris — a worrisome amount of leftover bits and pieces.
Against this backdrop of untidiness in space and the global worry among spacefaring countries it causes, experts continue to tackle the issue of exactly what to do about orbital debris. A number of rules have been pondered to address the space debris problem, from regulations that attempt to cut down on the shedding of new debris to better tracking of the human-made refuge, as well as scavenging concepts including fishing nets, lasers and garbage scows.
But how to best characterize the orbital debris dilemma, and its future, also stirs up debate and heated dialogue.
Point of no return
The clutter in Earth orbit is a situation that will continue to worsen, according to Marshall Kaplan, founder and principal of Launchspace in Bethesda, Md.
"The problem is that we've already fallen off that cliff," Kaplan told SPACE.com. "That's the reality of it and people don't want to admit that reality." [Photos of Space Junk & Cleanup Ideas]
Spending millions of dollars to retrieve space junk isn't effective, Kaplan said.
Now, ways to better track and identify space debris are being devised. Low-Earth orbit is where the main problem is — from roughly 435 miles (700 kilometers) to about 745 miles (1,200 km), he said.
"It's a serious, serious challenge," Kaplan said. "This is not a U.S. problem … it's everybody's problem. And most of the people that produced the debris, the serious offenders, like Russia, China, and the United States, are not going to spend that kind of money. It's just not a good investment."
While the creation of orbiting junk continues rise with each rocket launch, there is no market for tackling the issue directly, Kaplan said.
"We've reached the point of no return. The debris will continue to get worse in terms of collision threats … even if not another satellite were launched, the problem will continue to get worse," he added.
Speeding debris crashes
Kaplan said the frequency of collisions between active satellites and debris pieces is going to increase.
The real question, Kaplan said, is not what everyone is going to do about debris. Rather, the true question is what needs to be done about active satellites in harm's way of speeding riffraff.
"My prediction is that we are going to evacuate the areas of high debris density. It's just too dangerous to operate there. We're going to need to reinvent how we use space," Kaplan said. [Worst Space Debris Events of All Time]
In the case of large national security satellite assets, one option may be to distribute smaller satellites in lower altitudes, Kaplan added. These multiple layers of spacecraft would collectively create virtual products, such as imagery and other intelligence data. The users of this information would receive the same kind of data, but from a different satellite constellation, he said.
As one step toward that future, Kaplan is working with multiple universities to help establish new research centers on space debris and a next-generation national security space architecture.
Darren McKnight, technical director for Integrity Applications Incorporated, headquartered in Chantilly, Va., suggested that the current debate on active debris removal and the evolution of the debris environment is still developing.
McKnight said that, currently, policymakers and engineers examine environmental stability, preventing the cascading of derelict collisions from increasing exponentially over the next century. This scenario, known as the "Kessler Syndrome," is the primary metric to judge how many derelicts need to be removed and when they should be removed.
The Kessler Syndrome is one in which the density of objects in low Earth orbit is high enough that collisions between objects could cause a cascade. Each collision generates space debris, which increases the likelihood of further collisions. [Solar Sails Could Sweep Up Space Junk (Video)]
"The overall issue is that as we continue to consider active debris removal options, I question whether or not environment stability is the only metric to be tracking," McKnight told SPACE.com.
Lethal space debris
McKnight, along with company colleague Frank Di Pentino, propose that the probability of satellite failure from impact from non-trackable, yet lethal debris fragments — in the 5 millimeter to 10 centimeter size range — is a more appropriate metric. The reason is because it directly reflects harmful effects of space debris on space operations. Furthermore, these effects are likely to occur much sooner than observable manifestations of the cascading effect.
McKnight and Di Pentino's research suggests that any mitigation scheme, be it just-in-time collision avoidance, active debris removal or other methods, cannot rely on a model that does not account for projected add rates, new launches on other factors. They contend that collision rate is “not a sufficient metric” for assessing operational risk.
Wanted: A long-term plan
There is much work to do regarding orbital debris, said Donald Kessler, chair of the 2011 National Research Council (NRC) report "Limiting Future Collision Risk to Spacecraft: An Assessment of NASA's Meteoroid and Orbital Debris Programs." He is a retired head of NASA’s Orbital Debris Program Office and is a space debris and meteoroid consultant in Asheville, N.C.
Kessler said that the NRC committee that produced the report strongly felt that what was missing from the programs was a long-term strategic plan — one that outlined a path that eventually determines how manage future space operations in a way that preserves the environment.
"However, this is not simply a NASA issue … it is an international issue, and will require a carefully coordinated effort," Kessler said.
Can the space junk problem be solved?
NASA and the international community, Kessler said, "have already done enough research to know that the environment will continue to get worse if we continue on the same path … the only environmental issue to be resolved is how quickly the environment in various regions deteriorates."
The international community, through the Inter-Agency Space Debris Coordination Committee (IADC), has been very active in understanding the current environmental trends, sharing information and establishing internationally recognized mitigation requirements.
However, Kessler said that current mitigation practices are insufficient, even with 100 percent compliance. Missing in action is a plan to determine what do about the predicted worsening space environment, he said — that is, how to stop or reverse the trend of increased debris resulting from increased collisions.
Kessler added that the fundamental issues to be resolved are:
- How do we minimize the possibility of future high-velocity collisions between spacecraft and upper stage rockets?
- If we cannot eliminate that prospect, how do we clean up after a collision?
"Removal from orbit, collision avoidance, satellite servicing and repair, satellite recycling in orbit, debris storage locations, change to using a 'stable plane' at higher altitudes especially in Geosynchronous Earth Orbit (GEO) … are all possibilities," Kessler added. "Some are mutually exclusive and may not be appropriate at all altitudes, while others could combine to be more effective."
Still to be sorted out is what type of legal structure might be needed in order to implement any plan, Kessler said.
"I believe it is time that the international community takes a serious look at the future of space operations," Kessler said. "There's need to begin a process to answer these questions and determine which path will most effectively provide a sustainable environment for spacecraft in Earth orbit."
Leonard David has been reporting on the space industry for more than five decades. He is former director of research for the National Commission on Space and a past editor-in-chief of the National Space Society's Ad Astra and Space World magazines. He has written for SPACE.com since 1999.
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:
(LEFT) An image of Earth orbit and the region of space within 2,000 km of the Earth's surface to show the most concentrated area for orbital debris. (RIGHT) This image is generated from a distant oblique vantage point to provide a good view of the the larger population of objects over the northern hemisphere that is due mostly to Russian objects in high-inclination, high-eccentricity. (NASA Orbital Debris Program Office/Johnson Space Center)
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.
A 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?
(University of Colorado)
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."
-- 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.