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NSRC 2020

 
satellite explosion illustration
Debris mitigation guidelines have helped reduce the creation of debris through accidental satellite explosions, as illustrated above, but many argue now for the need to remove large debris objects before they can pose a debris hazard. (credit: ESA)

Cleaning up space junk


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Few people would claim that orbital debris, aka “space junk,” is not a problem for satellites and their operators. The amount of debris has been growing, punctuated in recent years by a 2007 Chinese anti-satellite (ASAT) weapon test and the 2009 collision of an Iridium satellite with a defunct Russian Cosmos satellite. The magnitude of the orbital debris problem can be debated—it is certainly unlikely to be as cataclysmically bad as depicted in the 2013 movie Gravity—but it cannot be ignored.

“Everybody who’s looked at the problem comes to the same conclusion: if we don’t start removing five to ten objects per year for the next 100 years, we’ll have an unstable environment,” Kessler said.

So far, governments have dealt with the orbital debris through mitigation: limiting the amount of new debris created. Guidelines developed in the US and widely adopted in other countries outline steps satellite and launch operators can take to reduce the creation of new debris, such as venting propellant tanks and discharging batteries to avoid on-orbit explosions that create large amounts of debris.

For some, though, mitigation is not enough. At a conference last month on the campus of the University of Maryland, organized by the school’s new Center for Orbital Debris Education and Research (CODER), attendees argued that the US government needed to do more to support orbital debris remediation: the active removal of debris, a concept loaded with technical and legal obstacles.

“Everybody who’s looked at the problem comes to the same conclusion: if we don’t start removing five to ten objects per year for the next 100 years, we’ll have an unstable environment,” said retired NASA scientist Donald Kessler in a conference keynote.

Kessler is one of the pioneers of orbital debris research. He’s also the Kessler of “Kessler Syndrome” fame: the concept that, when debris reaches a critical density in a particular orbit, it can set off a chain reaction of collisions that create more debris, eventually making the orbit unusable. (The emphasis here is on “eventually”: such a process may take decades, he notes, not the minutes depicted in Gravity.)

A few years ago, it appeared that the government was taking notice. The National Space Policy released by the Obama Administration in 2010 directed NASA and the Defense Department, for the first time, to study ways to “mitigate and remove on-orbit debris, reduce hazards, and increase understanding of the current and future debris environment.”

However, more than four years after the release of that policy, both agencies have done little in the area of debris remediation. “This past year, we’ve spent a lot of time thinking about remediation,” said Thomas Cremins, senor advisor for policy and strategy implementation at NASA, at a CODER conference session. That work, though, had focused more on early-stage technologies that could also be used for other applications, like the agency’s Asteroid Redirect Mission, than as a dedication program.

“We do not have an active debris remediation program,” Cremins said of the space agency.

Josef Koller, space policy advisor in the Office of the Secretary of Defense, said that while his office has talked with a number of companies with ideas for removing orbital debris, the DOD has instead focused primarily on orbital debris mitigation. That includes reducing the number of exemptions it grants to existing orbital debris mitigation guidelines that it grants for launches.

“The goal really is to start drawing down those granted exemptions and, by 2018, have a zero environment for granted exemptions,” he said.

“I would contend that there has been significant backsliding since 2010, since the fear of Iridium/Cosmos and the Chinese ASAT have gone away,” Dunstan said.

Some in the space community are worried that the US government, besides not following through with the intent of the policy language to develop debris remediation technologies, is not doing enough to reduce the growth of debris in general. Right now, that oversight is spread among several agencies: besides NASA and DOD oversight of their own missions, the FCC requires satellites seeking a commercial communications license to follow the debris mitigation guidelines, as does the FAA when granting commercial launch licenses.

“The FCC, at one time, was very aggressive in its enforcement” of the orbital debris guidelines, said James Dunstan, founder of Mobius Legal Group, at the conference. He cited examples in the recent past where the FCC rejected license applications because companies had not provided complete details of how they would follow debris mitigation guidelines.

That vigilance, Dunstan argued, has waned in the last couple of years. He noted that earlier this year Iridium sought to change its debris mitigation plan, which originally called for deorbiting satellites several months after the end of their lives, to the 25-year limit of the debris mitigation guidelines after it depleted the propellant on several of those satellites. The FCC approved that change.

“I would contend that there has been significant backsliding since 2010, since the fear of Iridium/Cosmos and the Chinese ASAT have gone away,” Dunstan said.

Another speaker warned against looking to the US military for leadership on the debris issue. “As far as debris mitigation is concerned, national security space does not want this role,” said James Armor, a retired Air Force major general who led the now-defunct National Security Space Office prior to his retirement at the end of 2007. The military is willing to follow debris mitigation guidelines, he said, but not take a larger role. “Do not look to national security space for leadership in this domain.”

While the government has not been investing much in debris removal efforts, the private sector has been more active. At the three-day CODER conference, several companies discussed ideas to use tugs, tethers, and lasers to move with debris of varying sizes.

One example was from Busek, a company best known for its electric propulsion technology. At the conference, Busek pitched a two-satellite tug concept involving a large satellite, called the Orbital Debris Remover (ORDER), and a microsatellite called Satellite on an Umbilical Line (SOUL). ORDER would approach a large debris object, like a defunct satellite, then release a SOUL, attached to ORDER on a tether. SOUL would grapple the debris object and ORDER would then fire its electric thrusters to tow the object either into a lower orbit for reentry, or a designated “graveyard” orbit.

A single ORDER/SOUL combination could remove 40 satellites over its life at a mission cost of as little as $80 million, said Daniel Williams, director of business development for Busek. “I think that every spacecraft deserves a SOUL,” he quipped.

Spacecraft might deserve a SOUL, or some other end-of-life deorbiting system, but getting one will be a challenge. Some of those will be technical, while others will be legal and regulatory. Those latter issues would include licensing and oversight of any debris removal activities, as well as getting approval to move specific debris objects that may be under the jurisdiction of another nation under the Outer Space Treaty.

“Right now, there is no business case for debris mitigation. You cannot rely strictly on commercial market forces to mitigate this,” Armor said.

Such would be true for a concept discussed at the conference by Claude Phipps of Photonic Associates, who proposed an orbiting ultraviolet laser that would nudge debris objects into lower orbits, accelerating their reentry. An orbiting laser would raise many eyebrows given its potential application as a space-based weapon, but Phipps suggested international cooperation, or possibly commercial versus government funding, might reduce those concerns.

Beyond the technical and legal concerns, though, is one of the business case: who pays for removing debris? Armor, now the vice president of ATK Spacecraft Systems and Services, said his company had looked at debris removal as a potential application for its ViviSat satellite servicing venture. The results were not encouraging.

“Right now, there is no business case for debris mitigation. You cannot rely strictly on commercial market forces to mitigate this,” he said.

Armor and others suggested ways to help improve the case for active debris removal. That includes direct funding of debris removal efforts, either through government contracts or through a “bounty” system where the government offers to pay a set amount to remove a specific object.

Dunstan suggested a bounty system could be funded by placing a $1 tax on every GPS chip in a smartphone. “Sooner or later it adds up to enough money that people would actually go after some of this stuff,” he said.

Dunstan also recommended that the government fund development of debris removal technologies, then transfer them to the private sector. He also recommended an indemnification regime for debris removal companies that would be similar to what exists today for commercial launches, where the government commits to pay for any damage above a certain amount that the company must insure against.

A single government agency also needs to be responsible for debris mitigation and cleanup, he argued. “Who the heck is going to regulate it? We need to determine it,” he said.

In the meantime, there may be solutions to help reduce the orbital debris problem without requiring active debris removal technologies, and their associated fiscal and regulatory challenges. In a presentation at the conference, Eric Sundberg of the Aerospace Corporation proposed a change to current guidelines that require satellites in low Earth orbit to deorbit within 25 years of their end of life. “Why do I have a 25-year rule?” he asked. “Is that relevant anymore? Probably not.”

“It’s going to be a little hard for some of us to stand back and let lawyers and policy people get involved and start telling us how to solve the problem,” Sundberg said.

Sundberg proposed an alternative approach that zoned low Earth orbit by altitude, in much the same way airspace is zoned. At higher altitudes, spacecraft would require active disposal between five and 25 years of the end of life. No spacecraft would be allowed in the “habitable zone,” the range of altitudes currently occupied by the ISS, except those actively transiting between lower and higher orbits.

At lower altitudes, where atmospheric drag keeps orbital lifetimes short, Sundberg said passive removal would be sufficient, but with a “beacon” to aid in tracking. Very low altitudes—below 200 kilometers—could be the equivalent of uncontrolled airspace, since any satellite there would have a very short life. That would be ideal, he said, for extremely small “chipsats” that are impossible to track but, deployed in that low of an orbit, would deorbit naturally in just a few weeks. “Go for it, have fun,” he said of that very low orbit.

Any solution to the orbital debris problem, Sundberg told an audience dominated by engineers and researchers, will not be technical alone. “It’s going to be a little hard for some of us to stand back and let lawyers and policy people get involved and start telling us how to solve the problem,” he said.


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