10 Years Ago, a Stunning Sci-Fi Thriller Exposed a Growing Threat to Space Exploration
A decade after Gravity, the risk of Kessler syndrome is higher than ever.
Gravity is the spectacular record of a simple space mission going awry. First-time spacefarer and medical engineer Dr. Ryan Stone (Sandra Bullock) and veteran astronaut Matt Kowalski (George Clooney) are conducting a spacewalk to retrofit the Hubble Space Telescope when a Russian missile launch violently detonates an old satellite to decommission it. The detonation instead spawns a swarm of high-speed debris that rains on their space parade.
Perhaps any inhabitants of the International Space Station who had seen Gravity felt a chilling case of deja vu in November 2021 when a Russian missile test detonated a Soviet intelligence satellite. Astronauts aboard the ISS sheltered in their transport craft in case debris debilitated the station.
No one was hurt, nothing was damaged, and life aboard the ISS returned to normal two days later. But the incident highlights that Gravity’s scenario is a real threat — and one growing in risk as more satellites crowd Earth’s orbit, raising the chance of a collision or worse. Researchers from a range of fields agree that the current state of Earth's orbit is on course for a disaster much like that in the film.
“The fear is rational,” says Michael Runnels, an assistant professor of law at California State University, Los Angeles, who studies the risks posed by orbital debris.
What is Kessler syndrome?
Scientists have a name for the events in Gravity: Kessler syndrome. In 1978, two NASA researchers — astrophysicist Donald J. Kessler and engineer Burton G. Cour-Palais — predicted that, as Earth’s orbit became more crowded, satellites would invariably cross paths and crash into each other at high speeds. One crash would spawn a cloud of shards and detritus, spreading out.
“The fear is rational”
The result: more collisions and more debris. Debris would beget more debris, and more debris would beget even more debris until Earth’s orbit would be choked off by a ring of razor-sharp detritus speeding faster than bullets. Neither crewed space flights nor uncrewed satellites nor missions to other worlds would be safe.
When Kessler and Cour-Palais conceived this idea in the 1970s, the entire world launched about 100 to 150 objects into space every year, the majority of which were satellites being sent into Earth’s orbit. In 2022, we launched more than 2,400. (We can credit SpaceX’s Starlink network for a large proportion of them.)
Most satellites just stay up there, even after their tasks end or they’re deactivated. ESA estimates that around 10,590 satellites, dead or alive, now orbit Earth. In 2009, one of those dead satellites, a dormant Russian communications satellite, inadvertently slammed into a satellite telephone relay above Siberia. The collision spawned thousands of tiny shards that are even now swirling in orbit.
Even those are just a small drop in a pool composed of tens of thousands more. ESA estimates there are a million objects between 1 and 10 centimeters in diameter — and 130 million between 1 millimeter and 1 centimeter. That number, scientists think, is growing. Scientists don’t have the technology to track all that debris; they can only model it with computers.
“If we don’t do anything in the next 50 years, I think Kessler syndrome will be true,” says John Crassidis, an engineer at the University at Buffalo.
With every passing year, human civilization becomes ever more dependent on the satellites we’ve put out there — everything from telecommunications to weather forecasting to climate monitoring. “We already engage in the space economy, even if we don’t think of it,” says Nodir Adilov, an economist at Purdue University. Debris — and Kessler syndrome — places all that at risk.
How do we prevent it?
Some economists suggest that satellite operators pay a fee for putting their craft in orbit, similar to a carbon tax. Adilov and other economists have proposed a new type of bond: A satellite operator pays for the bond and, only after they safely dispose of their satellite — perhaps by letting it burn up in Earth’s atmosphere — they will recoup the payment with interest.
In 2022, the U.S. Federal Communications Commission adopted a rule mandating comms satellite operators safely dispose of their craft within five years of mission completion.
Runnels wants to go further and make Earth’s orbit subject to more stringent environmental regulation: forcing satellite operators to disclose what materials are in their craft, for instance, and mandating constant position tracking.
“While space might be practically infinite, the orbital space around our planet is not,” Runnels says. “We should regulate it as a finite space, as we do the oceans, as we do the air.”
And with the U.S. responsible for launching most satellites — when Starlink is filled out, as many as 90 percent of the satellites in orbit will have been launched from the U.S. — he believes it is that country’s government that ought to take the lead.
But it’s clear that preventing future debris will not be enough. Models show that, even if we stop placing satellites in orbit today, the amount of debris will keep on increasing. “At some point, you need debris removal to actually bend the curve,” Adilov says.
In 2025, ESA plans to launch a mission called ClearSpace-1 that will use a four-armed robot to capture a 220-pound spacecraft part and move it. A March 2023 NASA report recommended nudging debris into a “graveyard orbit” outside those most often used by satellites, either by physically tugging it or (as NASA recommends) pushing it with lasers.
Even though engineers have not yet proven that they can make any of these methods work at the scale they need, researchers agree that some kind of top-down effort is necessary — that this isn’t something satellite operators can be trusted to do themselves.
“The potential of our species to become a multi-planetary species cannot be outsourced to ‘I hope Elon Musk does the right thing,’” says Runnels.