The International Space Station Just Avoided a Collision With Space Junk

A four-minute maneuver by a docked, unmanned European spacecraft pushed the ISS out of the path of a hand-sized chuck of space debris

International Space Station

Space debris in orbit pose a serious threat: A fleck of paint can travel nearly 17,900 miles per hour and cause major damage if it slams into a satellite. In Alfonso Cuarón’s Gravity, this threat blooms to its most extreme in a cascade of collisions between satellites that eventually wipes out even the International Space Station. 

Although the nitpicking on that film’s science made clear that satellites orbit at different altitudes and couldn’t all be taken out at the same time, collision threats are real

In fact, the International Space Station just had to do an emergency maneuver to dodge a hand-sized chunk of the Russian Cosmos-2251 satellite on October 27, reports the European Space Agency. Fortunately, the agency’s unmanned Georges Lemaître Automated Transfer Vehicle — which ferries supplies to the station from earth — was docked to the ISS. It fired its thrusters for four minutes to raise the 463-ton space station by one kilometer and out of the space junk’s path.

The errant satellite piece is one of the remnants from a 2009 collision between the then-deactivated Russian Cosmos-2251 and a U.S. Iridium satellite. While several entities track space debris in order to prevent collisions (most satellites can move out of the way) making accurate predictions are tough.

“The main problem here is the data quality for the data representing the satellites locations,” Bob Hall, Technical Director of Analytical Graphics, Inc., told Universe Today in 2009. That company analyses potential collisions every day, but uncertainty riddles these calculations. That fateful 2009 collision wasn’t even in the top-10 collisions predicted for that day.  

"While many collision threats are spotted at least days before impact," writes Elizabeth Howell for Universe Today, "occasionally ground networks aren’t able to see a piece until 24 hours or less before the potential impact." The Cosmos shard was spotted just six hours before it would pass within 2.5 miles of the ISS’s position.

The space junk cascade phenomenon is named Kessler Syndrome after the man who discovered it could happen, explains Corrinne Burns, writing for The Guardian. Donald Kessler, an astrophysicist who worked for NASA, first applied his calculations about meteorite collisions to satellites in 1978. "The results of those calculations surprised me – I didn't realize it could be that bad," he told The Guardian in 2013. "But it's building up as I expected. The cascade is happening right now – the Kosmos-Iridum collision was the start of the process. It has already begun." (Kosmos or Cosmos spellings are used by different publications.) Burns writes:

Kessler syndrome isn't an acute phenomenon, as depicted in [Gravity] – it's a slow, decades-long process. "It'll happen throughout the next 100 years – we have time to deal with it," Kessler says. "The time between collisions will become shorter – it's around 10 years at the moment. In 20 years' time, the time between collisions could be reduced to five years."

The increasing risk of collision has prompted the ESA to sign an agreement with the U.S. Strategic Command in order to communicate more and reduce the collision threat, reports the space news site SenThe European Space Agency typically has to "preform four to six debris avoidances each year, and this number has been increasing," Jenny Winder writes. The CryoSat-2 satellite — which measures the thickness of polar ice sheets — had to avoid a fragment of Cosmos-2251 on October 7. 

This recent maneuver wasn’t the first time the ISS had to deal with the remains of the 2009 collision, or other space debris, but it was remarkable because it was executed within a fairly short time window.

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