The European Space Agency has revealed that, last week, the International Space Station confronted its most urgent threat ever from space debris. When ground stations detected a piece of a Russian satellite on a collision course, they managed to protect the station with just hours to spare.

Stations on Earth continuously track space junk, since even a fleck of paint can cause major damage if it impacts an object while travelling at 28,800 kilometers per hour. If a piece of debris is expected to pass too close for comfort, ground teams can move the station to a safer orbit.


The calculations can take hours (this is rocket science), but fortunately, the radar network gives ample warning. Sometimes, however, a dangerous object can slip through the observation net or its erratic behavior might make accurate predictions difficult.

Such was the case last week with a piece of Russia's Cosmos-2251 satellite that had broken up after colliding with another satellite in 2009. The object, the size of a human hand, was discovered to be heading toward the space station with only six hours to spare.


All five space station agencies agreed to perform an emergency maneuver using the automated transfer vehicle (ATV) that was docked at the station. The ATVs are the expendable, unpiloted craft used for delivering supplies. Once emptied, they are gradually filled with refuse from the station, at which point they separate and their thrusters move them out of orbit to perform a controlled burn up in Earth's atmosphere.

ATVs can hold more than 10,000 pounds of propellant for their four main engines and 28 altitude control thrusters. When docked, those engines and thrusters can be used to maneuver the station.


The Georges Lemaître (above) is the ATV currently docked. The ATV Control Centre team in Toulouse, France—coordinating with control centers in Moscow, Russia and Houston—triggered a 4-minute thruster burn, providing an emergency boost of 1.8 km/h, which was enough to raise the 420-ton station by 1 km and out of harm's way. "Great care was taken to make sure that the move did not push the station into a worse orbit," the ESA stated.

The Georges Lemaître will undock and burn up in the atmosphere in February. Perhaps a moment of silence in its honor would be appropriate.