Putting a bounty on orbital debrisby Jeff Foust
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| The key for any remediation effort, explained Carroll, is to focus not on small objects but much larger ones—intact satellites and upper stages—that, if they collide with another large object, can create a thousands of objects. |
Mitigation alone, however, isn’t sufficient to solve the orbital debris problem in the long run. Slowing the rate of growth of the debris population still means that the number of objects orbiting the Earth continues to grow. What’s talked about less frequently is orbital debris remediation: the removal of debris objects. Remediation is considered far more technically challenging than mitigation, which primarily requires spacecraft and rocket upper stages left in orbit to be designed such that they don’t explode or otherwise shed debris. Somehow capturing or deorbiting debris is commonly thought to be beyond the scope of what’s feasible today.
Or is it? At a session of the NewSpace 2009 conference, organized by the Space Frontier Foundation and held at NASA’s Ames Research Center in Mountain View, California last week, several speakers outlined ways that technology largely available today could be used to address at least part of the orbital debris problem. Moreover, the panel also proposed an innovative way to get companies interested in tackling the challenge.
The key for any remediation effort, explained Joe Carroll of Tether Applications, Inc., is to focus not on small objects but much larger ones—intact satellites and upper stages—that, if they collide with another large object, can create a thousands of objects, as the Iridium-Cosmos collision this year illustrated. “There are going to be nearly as many ‘large-large’ collisions—of objects between 25 kilograms and 8 tons—as there are ‘small-large’, and much more than there are ‘small-small’,” he said, explaining that this was because of the much greater collisional cross-section of larger objects.
“The key issue is that a large-large collision creates a couple thousand pieces of debris, and a small-large creates a couple,” he continued. “The real problem—the 800-pound-gorilla problem—is large-large collisions.”
Carroll’s solution for removing some of the large objects in low Earth orbits is through electrodynamic tethers. “An electrodynamic tether is simply a wire in a magnetic field in a plasma,” he explained. “If you flow a current through it, you get a force that’s at right angles to the wire and at right angles to the magnetic field.” A vehicle concept he described, using a thin tether ten kilometers long and with two kilowatts of electrical power, would generate enough force to change its orbit by hundreds of kilometers per day.
Carroll envisions using such tethers to deorbit those large objects, pushing them down to low orbits that will decay in a matter of weeks or months, then raising itself and moving on to another object. A single tether system, itself weighing only about 100 kilograms, could deorbit objects in low Earth orbit at the rate of about one per week. That low mass, he added, means the tethers could easily be launched as secondary payloads on other vehicles. “Twelve of them could clear out the problem… in about five years,” he said. “It’s not reduce the rate of growth [of debris], it’s get rid of most of the big stuff.”
The electrodynamic tether approach doesn’t work well for objects in geosynchronous orbit (GEO) because of the Earth’s magnetic field isn’t as strong. However, the lower orbital velocities of GEO make using chemical or electric propulsion more feasible, said Dennis Wingo, who was chief technology officer for Orbital Recovery Corporation, a venture that proposed using spacecraft to latch onto GEO satellites to extend their life.
| “If you had a cascade event in GEO that rendered GEO useless,” Wingo warned, “it would probably cost on the order of a couple trillion dollars in GNP over the next couple of decades while we tried to figure out how to clean it up.” |
Keeping GEO relatively clean is essential to maintaining the long-term viability of that orbit for communications and other applications. While guidelines are in place to require spacecraft to boost themselves up several hundred kilometers into a “graveyard” orbit at the end of their lives, every year spacecraft fail or are otherwise abandoned in GEO, a key example being the DSP 23 early warning satellite that failed in GEO last year and is now drifting through the GEO arc, posing a small but non-zero collision risk to other satellites.
Wingo said there was a risk that a collision between two large GEO satellites could create a cascade of debris that could threaten the hundreds of other satellites there. “If you had a cascade event in GEO that rendered GEO useless,” he warned, “it would probably cost on the order of a couple trillion dollars in GNP over the next couple of decades while we tried to figure out how to clean it up.”
Wingo also said that vehicles that could help move spacecraft out of GEO could also serve a very different market: salvage. “There’s well over half a million kilos’ worth of hardware in GEO,” he said. “There’s big solar arrays, there’s transponders: you could actually go up there and bring some of this stuff together, create a big transponder park, recycle this hardware,” he said.
While the potential economic benefits of either salvaging GEO satellites and/or getting paid by satellite operators to boost their satellites from GEO at the end of their lives might yet allow a business plan to close for companies interested in this market, attorney Jim Dunstan proposed an alternative concept. He took as his inspiration the little-known Universal Service Administrative Company (USAC), a non-profit corporation that administers the Universal Service Fund. That fund collects fees from telecommunications companies (usually in the form of surcharges on customers’ bills) and disperses it to companies and organizations providing services in rural areas or to low-income consumers.
Dunstan proposed a similar approach, with the government levying a fee on launch vehicle and spacecraft operators based on the spacecraft mass, orbital inclination, and other key parameters. The fees would be escrowed by a corporation similar to USAC. This company would, in turn, place “bounties” on objects in orbit based on their size that the risk that they posed. US companies would be eligible to collect the bounties if they deorbited or otherwise safed the objects. (Foreign companies would not be eligible since it would be a US program, Dunstan explained, but he said he could see other countries establishing similar programs.)
While the bounty fund would not come from taxpayer dollars, Dunstan said there would still be a government role in licensing the “bounty hunters” and making sure they can operate safely in orbit, setting up insurance requirements, and indemnify the bounty hunters for any losses above their required insurance level (a system analogous to launch insurance requirements and indemnification.)
Dunstan said he’s still working the numbers on this proposal, but notes that USAC collects and distributes $4 billion a year, and companies already pay the FCC $120,000 a year for communications satellite licensing, even though there’s very little regulatory overhead once the satellite is launched and operating. “That’s my project for the next few months: to talk with the user side and the potential bounty hunter side and see if there is a happy medium, see if we can come up with a program that doesn’t cost the government money but would provide economic incentive.”
| “So we want to deal with this problem before it gets any worse,” Carroll said. “It’s a problem we didn’t have to deal with in 1957, but we do have to deal with now.” |
Any such approach, though, does raise questions about space weaponization: any system that can remove a useless object from orbit, as one questioner noted, can also remove a useful object from orbit. “It is a sticky issue,” Wingo admitted. “If you have an open system where you tell everyone what you’re doing and allow everyone to look at it, I think you can get it through.”
“What I’m doing is a garbage truck. It could be a lethal weapon,” said Carroll. “But, if the company’s registered, if they’re paid to remove garbage and they could lose their registration and their paycheck if they use it as a lethal weapon, there’s less to worry about.”
A solution to those concerns, Carroll suggested, is to start first with only US objects, later expanding to those of US allies as well. Over time, “maybe the Russians and the Chinese would go along with a couple of debris removals, just to see if it works,” he said.
Whatever technical, political, and business issues there are, getting a handle on the debris problem beyond existing mitigation measures may be essential to the long-term future of both government and commercial space ventures. “As it is now, we’ve had one large-large collision in 50 years,” Carroll said. If the population of objects in orbit continues to increase at a linear rate, the collision frequency could become one in every 5 to 15 years. “So we want to deal with this problem before it gets any worse,” he said. “It’s a problem we didn’t have to deal with in 1957, but we do have to deal with now.”