Defunct Satellite and Rocket Stage Nearly Collide in Potential ‘Worst-Case Scenario’

Defunct Satellite and Rocket Stage Nearly Collide in Potential ‘Worst-Case Scenario’

An old rocket body and military satellite — large pieces of space junk dating back to the Soviet Union — nearly smashed into each other on Friday morning, in an uncomfortable near-miss that would’ve resulted in thousands of pieces of debris had they collided.

LeoLabs, a private company that tracks satellites and derelict objects in low Earth orbit, spotted the near-collision in radar data. The company, which can track objects as tiny as 10 centimetres in diameter, operates three radar stations, two in the U.S. and one in New Zealand.

The two objects whizzed past each other at an altitude of 984 kilometres on the morning of Friday, January 27. LeoLabs “computed a miss distance of only 6 metres with an error margin of only a few tens of meters,” the company said in a tweet.

That is unbelievably close, as Harvard-Smithsonian astrophysicist Jonathan McDowell conveyed in a graphic posted to Twitter. The SL-8 rocket body (NORAD ID 16511), specifically its second stage, has been in space since 1986, while the Cosmos 2361 military satellite (NORAD ID 25590), known as Parus, launched to low Earth orbit in 1998. A collision between the two objects would have produced thousands of new debris fragments that would have lingered in Earth orbit for decades.

The conjunction happened in an orbital “bad neighbourhood” located between 950 and 1,050 km above the surface, according to LeoLabs. This band has “significant debris-generating potential” in low Earth orbit “due to a mix of breakup events and abandoned derelict objects,” the company explained in a series of tweets. The so-called bad neighbourhood hosts around 160 SL-8 rocket bodies along with their roughly 160 payloads launched decades ago. LeoLabs says around 1,400 conjunctions involving these rocket bodies were chronicled between June and September 2022.

LeoLabs describes this type of potential collision between “two massive derelict objects” as a “worst-case scenario,” saying it would be “largely out of our control and would likely result in a ripple effect of dangerous collisional encounters.” Indeed, a collision on this scale would most certainly accelerate the ongoing Kessler Syndrome — the steady accumulation of space debris that threatens to make portions of Earth orbit inaccessible.

Related story: What to Know About Kessler Syndrome, the Ultimate Space Disaster

Near-misses in space are becoming increasingly common, whether it’s conjunctions between defunct satellites or clouds of debris that threaten the International Space Station. Avoidance manoeuvres are now a steady fixture for satellite operators, with SpaceX, as an extreme example, having to perform over 26,000 collision avoidance manoeuvres of its Starlink satellites from December 1, 2020 to November 30, 2022.

In addition to focusing on collision avoidance, LeoLabs recommends the implementation of debris mitigation and debris remediation efforts. This could take the form of sensible guidelines having to do with the removal of satellites once they’re been retired, as well as the introduction of debris removal technologies.

More: The FCC Wants a 5-Year Deadline to Deorbit Defunct Satellites

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