Two days ago, the EU Space Surveillance and Tracking (EU SST) initiative warned of a possible collision on Friday between two orbiting objects, but it now appears they passed each other without incident.

The two chunks of space junk are identified as OPS 6182 (1978-042A), a defunct US meteorological satellite, and SL-8 R/B (1981-041B), a rocket body launched in 1971 by the former Soviet Union to deliver a satellite into orbit.

Initially, EU SST estimated the chance of collision at above 1 per cent, and by Thursday, that figure had been revised upward to more than 20 per cent. The abandoned pieces of equipment were initially expected to come within 10m of each other, an uncomfortably small gap given the possible consequences.

But a few hours before the time of closest approach, that figure was subsequently revised to about 21m while the impact chance remained the same.

Were the two objects to cross paths and collide, EU SST estimates that the impact would produce more than four million fragments. “More than 400 of the fragments generated by the potential collision would be larger than 20cm,” the space program said.

A similar near-miss occurred last year when IRAS (13777), the decommissioned NASA space telescope launched in 1983, and GGSE-4 (2828), an old US Naval Research Laboratory satellite, passed each other in the night.

Illustration of lots of satellites in space around Earth

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The time of closest approach, 17:18 UTC, April 9, 2021, came and went as the two objects appear to have passed by one another.

Nonetheless, the risk posed by debris from satellite collisions remains an area of significant concern. A 2009 Iridium-Cosmos collision is said to have introduced over 3,000 fragments large enough to be tracked, and perhaps 30,000 smaller pieces. And the 2007 Fengyun-1C anti-satellite missile test is said to have put about 2,200 trackable fragments and 25,000 non-trackable bits into orbit [PDF].

EU SST says there are more than a million space debris objects larger than a centimiter in width cluttreing in Earth’s orbit, putting space-based projects at risk. At the speeds these objects are traveling they could easily take out fragile space hardware.

In the 2017 NASA Transition Authorization Act, Congress said, “orbital debris poses serious risks to the operational space capabilities of the United States” and called for “an international commitment and integrated strategic plan are needed to mitigate the growth of orbital debris wherever possible.”

One cleanup option NASA has considered is space lasers [PDF]. So we have that to look forward to. ®

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