ALEXANDRIA, Va. — Last month saw two high-profile events that brought widespread attention to the risks posed by space debris in low Earth orbits.
In the first, audiences worldwide were captivated by the potential impact of the defunct European Space Agency (ESA) Earth observation satellite, ESR-2’s uncontrolled reentry, with pieces as large as 115 pounds (52 kg) projected to reach the ground. In the second incident, the U.S. Department of Defense and commercial debris monitors tracked a near-miss between two non-maneuverable spacecraft—NASA’s TIMED spacecraft and the Russian Cosmos 2221 satellite.
Tensions were high for both incidents. What if the statistically unlikely happened? What if the satellites did collide? What if a surviving piece of space debris caused harm to a person, property—or worse, an aircraft?
“It’s not a situation humanity has been in before. The number of active spacecraft has quadrupled in just a handful of years,” said Caleb Henry, Senior Analyst at Quilty Analytics. In many cases, this new situation has propelled commercial innovation to push out risk on-orbit and on Earth. Still, the recent incidents serve as reminders of the improbable but not impossible worst-case space debris scenarios.
Too Close for Comfort
According to LeoLabs analysis, the near-miss of the Russian and NASA satellites on Feb. 28 could have resulted in between 2,000-7,000 new pieces of trackable debris in LEO—or as much as a 50% increase in debris. Without raising the specter of the Kessler Syndrome, the debris fragments alone would have constituted a disastrous breakup. What made the incident even more of a nail-biter was the location. The two objects were orbiting at 608 km, just a few dozen kilometers above the most populous orbital region for commercial satellites.
Darren McKnight, Senior Technical Fellow at LeoLabs, described the location as “the worst place it could have happened.” Debris would not have stayed neatly at 608 km but spread hundreds of kilometers high and low, to altitudes that would guarantee the debris stuck around for decades. “Any way you measure consequence—debris created, persistence of debris and satellites that would be affected—it kind of was a sweet spot,” he told Constellations.
As bad as the 2021 Russian ASAT test was for on-orbit safety, it was at a location where much of the debris washed out within a year. An incident at 608 km would dramatically increase the risks to satellite operators for decades. Collision risks among non-maneuverable objects would increase and so would the demand for operators to perform collision avoidance maneuvers. Over a period of just six months last year, satellites in SpaceX’s Starlink constellation had to perform 25,000 collision avoidance maneuvers. The International Space Station conducted at least four collision avoidance maneuvers in 2023, compared to just 33 performed between 1999-2022.
In the end, the TIMED and Cosmos spacecraft missed each other by a mere 20 meters (65 feet). The incident marked the seventh near miss of 20 meters or less in the last two years and highlighted the growing demands for orbital safety moving forward.
The Sky Is Not Falling, It’s Just Space Debris
Technically, the persistent risk of debris in orbit is greater than the one-time risk of falling space junk, explained McKnight, citing the classic measure of probability times consequence. At the same time, that one-time risk is not zero.
“You don’t get something for nothing,” McKnight said. “With active debris removal or removal because of high atmospheric drag, people think, ‘I’m removing risk.’ No, you’re moving it. You’re moving it from space to aviation and then to the ground.”
In the history of spaceflight, there have been no reported deaths and only a small handful of injuries from falling space debris. The ESA puts the risk at 1 in 100 billion per year that someone will be struck by space debris. A debated estimate by the U.S. Federal Aviation Association and Aerospace Corporation suggested that by 2035, there will be two injuries or deaths on the ground every two years as a result of satellite reentry. The same study found a 0.0007 per year risk of an “aircraft downing accident” in that same timeframe.
Additionally, the prospects of mega-constellation disposal have led to environmental studies on the atmospheric effects of satellites burning up on reentry. A recent ESA report found the effects to be “modest” and short-lived. Other studies have warned of ozone loss from aluminum particles and recent measurements have suggested spacecraft may be responsible for 10% of stratospheric aerosol particles containing aluminum and other metals. Scientists and government agencies have urged continued research, especially with more than 20,000 satellites planned for launch in the next decade.
Commercial Innovation to Mitigate Risk
Despite greater attention to the potential effects of satellite reentry and in-orbit collisions, the satellite industry itself remains the biggest driver of orbital safety and sustainability. “The space industry recognizes that in order for it to persist, it has to have a sustainable space environment,” Henry said.
The regulatory revisions to deorbit satellites in 5 years (down from 25 years) were led largely by industry. Even the $1.5 billion space situational awareness market shows the demand for commercial orbital safety solutions. “There’s been a good level of self-policing that has gone on, especially by the largest operators of satellite networks.”
Satellite and constellation designs have evolved in recent years to actively improve safety. Major commercial operators, including SpaceX, OneWeb and Kuiper have demonstrated maneuverability within their constellations. AI-powered or automated collision avoidance tools are also improving safety prospects in LEO. Maneuverability and onboard intelligence are quickly becoming critical features in light of the massive growth of objects in low Earth orbit. “Capacity is not just about numbers,” McKnight said. “It’s about how each of the objects can manage the risk.”
Government entities led by European and Japanese space agencies are also pioneering active debris removal in LEO with major investments in companies like Astroscale and ClearSpace. The challenges of grappling objects in orbit Currently, this is a government market with limited commercial prospects. As Henry noted, “When it comes to active debris removal, ideas abound but money doesn’t.”
There has also been a push for a more conscientious approach to satellite reentry. The ESA has been pioneering “design for demise (D4D)” technologies to ensure the breakup of satellites in the atmosphere. Controlled reentry is another method for reducing the risk of satellite debris impacting life on Earth, though the cost is much greater than uncontrolled or natural reentry. Generally, most SmallSats (180 kgs and below) will burn up fully upon reentry. At 800 – 1,000 kg and above, there is a much greater likelihood that some of that mass will survive to the ground. McKnight estimates that a piece of space debris returns on Earth at least once per week. But these are not “school-bus-sized” rocket bodies, and more often, the objects land with a “splash” rather than a “thud.”
Compared to other industries, space safety is still in its infancy. More information is still needed to understand the environmental, orbital and human risks related to debris removal in LEO. “We’re still early in this process in comparison to something like automobile safety,” McKnight noted. “I think things will evolve. Right now, we’re really in a study mode.”
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