The odds of a space-junk crash this evening (Jan. 29) aren't as slim as we had thought, it turns out.
Two dead satellites — the Infrared Astronomical Satellite (IRAS) and the Gravity Gradient Stabilization Experiment (GGSE-4) — will zoom past each other today in the skies above Pittsburgh, analyses by California-based company LeoLabs indicate.
As of Tuesday (Jan. 28), LeoLabs' calculations suggested that the two craft would miss each other by from 43 feet to 285 feet (13 to 87 meters) at closest approach, which will occur at 6:39 p.m. EST (2339 GMT). And the probability of a smashup was quite low — just 0.1%.
But the latest outlook isn't quite so rosy. Additional calculations suggest that the two objects will miss each other by a mere 39 feet (12 m), LeoLabs announced via Twitter this morning. And the chance of an impact is now back up around 1%, as LeoLabs had calculated earlier this week — but might even be as high as 5%.
"Since we learned that GGSE 4 has a deployed 18-m boom and we do not know which direction it is facing relative to IRAS, this changes the assumptions used in computing collision risk," company representatives explained in a tweet this morning.
"Adjusting our calculations to account for larger object sizes (by increasing our combined hard body radius from 5 m to 10 m), this yields an updated collision probability closer to 1 in 20," they wrote in another tweet.
4/ Adjusting our calculations to account for larger object sizes (by increasing our combined Hard Body Radius from 5m to 10m), this yields an updated collision probability closer to 1 in 20.January 29, 2020
The nearly 2,400-lb. (1,090 kilograms) IRAS, a joint project involving NASA, the Netherlands and the United Kingdom, launched in January 1983 to study the heavens in infrared light. Its mission ended 10 months later.
GGSE-4, which weighs just 190 lbs. (85 kg), was lofted in 1967 and ceased operations in 1972. The little satellite was a U.S. National Reconnaissance Office craft that collected signals intelligence, according to Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics who keeps tabs on many of the objects circling Earth. And GGSE-4 was just a cover name; the satellite's true moniker was POPPY 5B, McDowell said.
We should hope that IRAS and GGSE-4 sail safely past each other Wednesday evening. Both are hurtling through space at more than 32,000 mph (51,500 km/h), and a collision would generate a new swarm of debris in sun-synchronous orbit, a valuable patch of space occupied by many spacecraft.
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Mike Wall's book about the search for alien life, "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), is out now. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.