Increased Worries Abound About Orbital Debris

Low earth orbit (LEO), particularly between 600 and 1,200 kilometers, is "approaching the point of a catastrophic situation," with high probability of some kind of collision in the next decade or so as traffic there increases, said Marshall Kaplan, principal of space consultancy Launchspace. "So far ... we have been lucky."

LEO between 600 and 900 kilometers is home of the biggest debris problem and collision risk, and that's where both the 2009 collision between Iridium's Iridium 33 satellite with Russia's Kosmos-2251 and China's 2007 anti-satellite test involving its FY-1C weather satellite happened, said Brian Weeden, Secure World Foundation program planning director. It's also home to LEO constellations such as Iridium, Iridium Next, Orbcomm, DigitalGlobe and NASA's A-train, he said.

Weeden said the other big concern is under 500 kilometers. That's where all sustained human spaceflight happens, including the International Space Station (ISS). Debris doesn't stay there for long because of the high atmospheric drag, meaning a smaller collision probability, but there's particular concern because such a collision could endanger human lives, he said.

Asked about the viability of the orbital plane where the Iridium 2009 collision happened, CEO Matt Desch emailed that orbital planes "don’t work that way." Debris from that crash "went up, down, left and right, and over time spread out across many planes," he added. "There may be more of it at the impact altitude of 783 km [where the collision occurred], but that’s just a statistical variation."

Desch said there may be more debris at any altitude, but it's not a consideration when selecting an altitude for one of its satellites due to safeguards by the operations of the Combined Space Operations Center at Vandenberg Air Force Base in California. He said Iridium "work[s] to take care" of the orbital altitude of its satellites by de-orbiting old ones when no longer in use. It "doesn't want other operators "to 'pollute' our neighborhood by creating more debris out of either willful actions (or lack of them), or design deficiencies in which their satellites become uncontrollable and end up becoming debris magnets and additional debris creators over tens or hundreds of years,” he continued.

There's a growing concern about geostationary (GEO) orbit. Secure World's Weeden said the traditional thinking was that collision risks there were low because most objects are moving in the same direction and there's a relative lack of debris compared with LEO. "New research is challenging that notion," he said. "There might actually be more of a threat from small, untracked space debris in GEO than we thought."

Modeling shows satellites pushed another few hundred kilometers out after the end of their use could drift back someday, said John Crassidis, University of Buffalo professor. He said GEO satellites need to be put in graveyard orbits even further out than now: "They're not staying up forever."

Orbits and orbital planes where satellite mega constellations are planned to launch "are most definitely more in jeopardy" of debris and collisions stemming from the density and traffic, said Shagun Sachdeva, Northern Sky Research senior analyst. She also cited the danger of Kessler syndrome. That's when debris collides with satellites or other debris, resulting in further debris, raising higher the likelihood of further collisions. Rather than different regulatory approaches for different orbits or orbital planes, regulation needs to take a standardized approach since debris can fly across different planes and orbits, making different rules for different planes "inefficient and futile in the long run," Sachdeva said.

Crassidis said the LEO congestion danger -- driven at least in part by the anticipated numbers of nanosatellites to be launched in coming years, none of them with propulsion capabilities -- is exacerbated by the lack of international standards on LEO procedures. Parts of LEO in 50 years could become "useless," he said. He said there needs to be better tracking capabilities of what's already in orbit, plus requirements that LEO satellites have some form of technology that can be used to bring them down within a few years.

The FCC NPRM proposes any LEO non-geostationary orbit (NGSO) constellation planned above 650 kilometers specify why it chose that particular orbit and describe its relevant characteristics, such as the presence of existing debris. The NPRM said a constellation 650 kilometers or lower will generally re-enter the atmosphere within 25 years, but going higher means it will stay up for significantly longer. Those applicants seeking to go higher also should have propulsive de-orbit capabilities, the FCC proposes. The NPRM proposes it might be in the public interest for new constellations to avoid deploying in areas more populated with debris, and asks whether the agency should require an additional disclosure from applicants about orbit selection based on those debris risks or assurances about how the applicant plans to reduce those risks.

McGill's Jakhu said any policy approach must have zero tolerance for debris. There also needs to be thought given to means for removal of existing debris, he said: There aren't no-go orbits today. "There will be" soon, given the smallsat traffic expected to be seen in the 400 to 600 kilometer orbital range, he said.

Space-going nations have discussed multilateral approaches for years through the U.N. Peaceful Uses of Outer Space and Inter-Agency Space Debris Coordination committees -- made up of various national space agencies, including NASA. The U.N.-developed guidelines are voluntary and lack a system for monitoring compliance, Jakhu said.