Imagine a world in which workers providing crucial services such as weather forecasting and global broadband Internet had to do their jobs while dodging bullets on an active shooting range. At the very least, you’d probably worry about their well-being, right?
This isn’t actually a make-believe scenario: the world we’re imagining is our own, the shooting range is Earth’s orbit, and the at-risk “workers” are satellites there (as well as crewed vehicles and habitats) threatened by skyrocketing amounts of space junk. Nearly 70 years have passed since the onset of the space age with the launch of Sputnik 1, the first artificial satellite. And in that time, the heavens above have become cluttered with thousands of spent rocket bodies, dead spacecraft and sizable pieces of hardware, all circling our planet at dangerously high speeds.
The U.S. Air Force monitors roughly 25,000 pieces of trash in low-Earth orbit (LEO), the busiest and most crowded region, which encompasses orbits of 2,000 kilometers or less in altitude. Current telescopes and radar technology limit the smallest trackable pieces to approximately 10 centimeters across, about the size of a bagel. Everything else—and there’s quite a lot of it, mostly in the form of millions of paint flecks and bits of spacecraft—is too small to be presently cataloged but can still pose extreme hazards. This so-called lethal nontrackable debris can travel around Earth at speeds of about 10 kilometers per second, or more than 22,000 miles per hour, meaning that even an otherwise-unnoticeable speck will pack a potent wallop. Indeed, in 2016, when a millimeter-sized piece of debris struck a solar panel of the European Space Agency (ESA) satellite Sentinel-1A, the impact was so strong that it punched a 40-centimeter hole in the panel and tilted the satellite askew. The risk to humans isn’t negligible either. Mere weeks ago a decommissioned Russian satellite broke into more than 100 large fragments that prompted astronauts on the International Space Station to take shelter, an incident that may have been the result of a collision with a similar uncataloged piece of debris.
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“There’s a lot of them. They’re not tracked. And they’re dangerous,” says astrophysicist Jonathan C. McDowell regarding the tiny pieces of space junk. “At orbital velocities, even quite a small object is really gonna smack you.”
Without a clear way for anyone to see all that tiny debris, it’s impossible to alert satellite operators of imminent, potentially catastrophic collisions—let alone to know the true scale of the threat.
But that may soon change. The U.S. government is now trying to develop a real-time monitoring capability for the millions of ultrasmall pieces of space junk—that is, from 10 centimeters down to a millimeter in size—throughout low-Earth orbit and even beyond. Called the Space Debris Identification and Tracking (SINTRA) program, the effort involves more than 100 scientists across a dozen institutions. As a key first step, SINTRA is leveraging supercomputers and artificial intelligence algorithms trained on extensive archival data to detect the telltale signatures created by tiny, fast-moving debris. Examples include fleeting bursts of light sparked when two pieces of junk collide and faint, wavelike plasma wakes in Earth’s electrically charged upper atmosphere made by debris streaking through, both of which scientists suspect can be used to help track and study the hazardous flotsam.
To support that work, researchers at the Naval Research Laboratory (NRL) in Washington, D.C., will soon seek to replicate some of these effects by accelerating fragments of common satellite materials such as aluminum, silicon and aerospace-grade plastic to hypervelocity speeds inside a large vacuum chamber. The results—including specific frequencies at which the lightninglike bursts occur, the amount of time they last and the rate at which clouds of dust form and expand in the aftermath of collisions—can then be used to better train the algorithms. This will ensure the team can unearth more of the myriad past collisions that were inadvertently recorded in the archives. And the eventual outcome could be a massive daily operation to track minuscule debris by the millions and create a new early-warning system for possible collisions with working satellites.
“It’s a reflection of how both our challenges and our capabilities have grown that one can think of doing this,” says McDowell, who is not involved with the SINTRA program. “It’s a lot of work to go to the next order of magnitude in space tracking, but it has to be done.”
As part of a broader, government-wide effort to address space debris risks, SINTRA was officially launched last August by the Intelligence Advanced Research Projects Activity (IARPA), a federal organization that sponsors research projects to benefit the country’s intelligence community. “We’re trying to revolutionize how we’re looking at the problem,” says Alexis Truitt of IARPA, who leads the program. “SINTRA sits really well within that vision.”
She declined to specify the project’s cost but said driving the state-of-the-art effort “requires significant investment.” A publicly available Q&A about the program notes IARPA has historically budgeted its projects between $50 million and $100 million, with contracts for individual teams typically capped at $25 million. “At IARPA, we follow a high-risk, high-payoff model,” Truitt says, “in that we will take on considerable risk to solve hard research problems that may be too risky for our government partners to pursue otherwise.”
Tracking the Nontrackable
The outsize energies associated with even minuscule space debris smashups could prove crucial to gaining a better overall view of just how much junk is actually whirling around Earth.
Previous research has shown that when two specks of material collide at very high speed, they crumble into a cloud of charged gas and tiny fragments that creates intense bursts of light—a bit like micro thunderbolts—as it expands. The charged fragments can also generate electric pulses when they brush past each other. These emissions are strong enough to be picked up by instruments on Earth, such as radio antennas in NASA’s Deep Space Network, according to recent simulations conducted by a team at the University of Michigan as part of the SINTRA project. Following the hypervelocity experiments at NRL and subsequent algorithmic training of debris-scouting AIs, the researchers hope to spot as many as 100 small-scale collisions in space every day.
“It’s never been done before,” says Mojtaba Akhavan-Tafti of the University of Michigan, a member of the team that conducted the recent simulations and a scientist on the SINTRA project. “This is a new field being created by this research, so you don’t have colleagues that have done this for many years to go and ask questions to.”
Similarly, scientists at SRI International, a nonprofit research institute headquartered in California, are training ground-based radars and other instruments to detect the tenuous wakes rippling through our planet’s upper atmosphere that are caused by impinging orbital debris. Finding and following these trails should allow observers to identify and localize the corresponding pieces of junk. The same team also plans to run a test using a large radio telescope at Stanford University, nicknamed the Dish, to see whether the researchers can use radar signals to map more of the tiny orbital debris.
“We are tackling some very hard problems,” Truitt says. “The debris problem is bigger than one entity could handle, so [SINTRA] is just a piece of the bigger puzzle.”
This animation from the European Space Agency (ESA) shows different types and sizes of space debris in Earth orbit, ranging from large satellites (red) and rocket bodies (yellow) to inert intact objects (green) and fragments (blue). Information about debris smaller than 10 centimeters is based on a statistical model by ESA.
Another puzzle piece that SINTRA personnel are pondering is how to handle the drastic spike in collision alerts expected from continuously tracking millions of debris objects. Satellite operators are typically notified of worrisome possible collisions a week in advance by the 18th Space Defense Squadron of the U.S. Space Force, which monitors known orbiting debris through its Space Surveillance Network. But because of the significant fuel costs for maneuvering and uncertainties from the highly dynamic orbital environment, decisions to dodge “are taken as late as possible,” usually in the final 24 hours, says Francesca Litizia, a space debris mitigation engineer at the ESA. But data that are paramount for those decisions —such as whether the objects on a potential collision course can be maneuvered and, if so, which party should swerve—are not often available or up-to-date. “Now we still have to call [satellite operators] on the phone and hope that someone replies on the other side,” says Litizia, who is not directly involved in the SINTRA program. “Of course, this is not very scalable in the future.”
“We would need to revolutionize how we provide alerts to our satellite operators,” Truitt acknowledges.
Too Much Orbital Trash
“We think that space is very large, but we ignore the fact that humans are also very good at trashing the environment,” Akhavan-Tafti says. That so much orbital trash has accumulated in less than seven decades of space activities—the blink of an eye compared with Earth’s 4.5-billion-year history—is indeed alarming. Astronomer Aaron C. Boley, who studies orbital debris as co-director of the Outer Space Institute, hopes SINTRA will create “a greater sense of awareness of what’s been done so that we can be much more careful about the way we are using low-Earth orbit.”
Multiple recent milestones offer hope for improvement. Chief among them is the 2022 ruling by the U.S. Federal Communications Commission (FCC) that shortened the period of time defunct satellites were allowed to stay in orbit according to a long-standing guideline from 25 to five years. Last year ESA followed suit with the Zero Debris Charter, a set of guidelines for its 22 member countries and the global space community to follow to become debris-neutral by 2030. India, too, has vowed to achieve debris-free missions by the end of the decade. Many scientists hope other spacefaring nations will soon apply similar practices to their own space assets. “It’s very important that these sorts of regulations exist so that everyone can benefit from the space environment,” Akhavan-Tafti says.
Any effort to clean up our orbital trash would begin with determining where the objects are, so SINTRA and other debris-detection programs seem destined to become essential enablers of future space activity. It is equally important, however, to address the fundamental problem—the thousands of large derelict spacecraft and rocket stages that created most of the smaller debris in the first place, Boley says. “That’s gonna be hard,” he adds. “These things are the size of school buses and are spinning rapidly.”
Multiple commercial debris removal services are nonetheless eager to rise to the challenge. Noteworthy among them is Astroscale, a start-up headquartered in Tokyo that was recently commissioned by the Japanese government to demonstrate its abilities by rendezvousing with and removing a defunct rocket stage from orbit. Looking ahead, in 2026 a Switzerland-based start-up named ClearSpace is scheduled to launch an ESA-funded mission to meet up with and deorbit a hefty hunk of space debris as well.
Even if such approaches prove wildly effective, Boley, Akhavan-Tafti and other scientists interviewed for this story all share a common concern: Can any effort to take out Earth’s orbital trash counteract the all-too-human tendency to maintain the status quo, treating the sky itself as a dumping ground? The lessons from history are discouraging; domains long considered too big and remote to be subject to human foibles are increasingly disrupted by them. The plastic in our oceans, pollution in our air and clear-cut wastes where forests once stood all offer mute testament to our hubris. Now something similar is unfolding again in the heavens above, and we are only beginning to grasp the implications.
“My worry is how we just continuously do this and don’t seem to learn,” Boley says. “We still have the opportunity to do something before there is a tragedy.”