2 large pieces of space junk have a 'high risk' of colliding

A dead satellite and an old rocket part, each roughly the size of a small car, have about a 10 percent chance of smashing into each other soon.

By Dan Falk
Published 15 Oct 2020, 20:07 BST
Some 29,000 human-made objects larger than 3.9 inches are believed to be circling Earth, presenting a ...

Some 29,000 human-made objects larger than 3.9 inches are believed to be circling Earth, presenting a threat to future missions to space.

Photograph by NASA

Two pieces of space junk, each about the weight of a compact car, are predicted to have a close encounter tonight some 620 miles above Earth. If they collide—and experts are putting the odds at greater than 10 percent—the smashup would create a cloud of debris that could jeopardise other satellites and spacecraft for decades.

The two objects are a defunct Russian navigation satellite launched in 1989 and a spent Chinese rocket part from a 2009 launch. Calculations by LeoLabs, a California-based company that tracks objects in low-Earth orbit, peg the moment of closest approach at 1.56 a.m. BST on October 16 above the southern Atlantic Ocean, just off the coast of Antarctica. The combined mass of the two objects is about 6,000 pounds, and their relative speed will be about 33,000 miles an hour, according to LeoLabs.

If the two objects don’t collide it will be another near-miss—one of a handful that happen every year—with the objects likely getting within about 40 feet of one another, by LeoLabs’ estimate. These two pieces of space junk are particularly large, however. The third stage of the rocket—the upper part that separates from lower stages and flies all the way into orbit—measures about 25 feet long. The satellite measures 16 feet long, with a boom used to stabilise the spacecraft extending almost 56 feet.

If they smash head-on, it would create two big clouds “that will spread out into a shell of debris around the Earth,” says LeoLabs CEO Daniel Ceperley. And because of the objects’ altitude, the debris would “be up there for centuries” before burning up in the atmosphere.

The long boom on the Russian satellite also raises the possibility of a glancing blow rather than a head-on collision. The results of an impact like that are harder to predict, says Jonathan McDowell, an astronomer at the Harvard-Smithsonian Centre for Astrophysics in Cambridge, Massachusetts.

Still, “there’s no threat to the Earth,” McDowell says. “These will be small debris pieces that will completely burn up in the atmosphere. Most of them aren’t going to come down for decades anyway, and when they do, they’ll completely burn up.”

The International Space Station (ISS) is also in no immediate danger. The ISS orbits at an altitude of about 250 miles, “safely below” the altitude where the debris would potentially be unleashed. There would “probably not be a big risk to the ISS in the near term,” McDowell says. But over many years, bits of debris could drift down to the space station’s orbit. “It would increase the amount of ‘rain’ failing on it,” he says.

The ISS has had to manoeuver out of the way of space debris to avoid damage on three occasions this year, including a near miss less than a month ago.

The potential debris field would pose a danger to any craft passing through, including satellites on their way up to a higher geosynchronous orbit (about 22,000 miles above Earth), or any satellites above that are being deorbited into the atmosphere to burn up.

Litter in space

The space around Earth is getting more and more crowded. In all, some 29,000 human-made objects larger than 3.9 inches are believed to be circling Earth, which means the danger of space collisions is greater than ever. Demand for more and better internet access is steadily increasing the population of satellites. For example, private firm SpaceX has launched several hundred of its Starlink communication satellites into low-Earth orbit, and thousands more are planned.

One of the worst space equipment collisions happened in February 2009, when the operational Iridium 33 communications satellite collided with a defunct Russian military satellite, Kosmos 2251, above Siberia. The crash unleashed some 1,800 pieces of space debris that are still being tracked, and it increased the total amount of debris in low-Earth orbit by about 10 percent, McDowell says.

“We have no space traffic rules to mitigate these concerns over safety,” says Moriba Jah, an orbital mechanics researcher at the University of Texas, Austin, who developed ASTRIAGraph, a crowdsourced space traffic monitoring system. Unless we develop a better system for avoiding collisions, cascading space junk could limit access to orbit. “We’re on that path, unless we do something different.”

To date, most of the data about the trajectories of these objects has come from the U.S. military. The Space Surveillance Network, part of the U.S. Space Force, uses a global array of telescopes to track everything larger than a grapefruit. However, with the growing use of low-Earth orbit for commercial purposes, the Office of Space Commerce, part of the Department of Commerce, is preparing to play a larger role in tracking what’s above our heads, as are private companies such as LeoLabs.

Ceperley points out that most of the U.S.’s military radar installations were built during the Cold War “to look for missiles coming over the north pole.” Before LeoLabs opened its tracking station in New Zealand, he says, there was little surveillance of the Southern Hemisphere’s skies. (The company also operates stations in Alaska and Texas.)

NASA, for its part, established an Orbital Debris Program in 1979—but it only tracks the agency’s own spacecraft, not the many thousands of other objects orbiting our planet. The Department of Defence provides advance warning to NASA, as well as to companies and countries around the world, if it detects that spacecraft are in danger of being hit.

Ceperley says his company will know the end result of today’s encounter a couple of hours after the moment of closest approach. That’s when the two objects—or what’s left of them—are to pass over LeoLab’s New Zealand tracking station.

As more satellites are launched to space, more close calls and, ultimately, more collisions, are inevitable, Ceperley says. “These things are happening, and they’re happening more frequently—and we need to figure out how to deal with them.”

Dan Falk (@danfalk) is a science journalist based in Toronto. His books include The Science of Shakespeare and In Search of Time.

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