Europe's fourth Automated Transfer Vehicle backed away from the International Space Station on Monday, firing thrusters to vacate the outpost's safety bubble and begin positioning itself for a destructive re-entry Saturday.

The spaceship's Russian docking system pushed the vehicles apart, then the ATV's rocket jets fired to accelerate its rate of departure, exiting the space station's "keep-out sphere" a few minutes after undocking.

In the minutes before undocking, controllers oversaw the activation of the ATV's flight systems, navigation computer and the unlatching of hooks connecting the European spaceship to the space station.

The undocking marked the end of a 134-day stay at the space station since the ATV arrived June 15 with seven tons of cargo, including food, experiments, spare components, water, oxygen and rocket fuel.

About the size of a London double-decker bus, the ATV was responsible for maintaining the space station's orbit during its four-month mission, boosting the outpost's orbit to counter the minuscule effects of atmospheric drag.

Astronauts replaced the cargo delivered to the space station with trash stowed inside the ATV's pressurized compartment. Liquid waste was pumped inside the ATV's fluid tanks.

Named for Albert Einstein, the ATV carted away 4,761 pounds of refuse for the fall back into the atmosphere, according to NASA.

The undocking cleared the way for three members of the station's six-person crew - Fyodor Yurchikhin, Karen Nyberg and Luca Parmitano - to relocate their Soyuz TMA-09M spacecraft to the aft port of the Zvezda module, which was vacated by the ATV's departure.

Yurchikhin, Nyberg and Parmitano will strap into their Soyuz spacecraft Friday, undock from its current location on the Rassvet module, and fly around to line up for a docking on Zvezda. The activity should take less than 30 minutes.

The Soyuz relocation will clear the way for three more crew members to dock at the space station Nov. 7, just hours after launching from the Baikonur Cosmodrome in Kazakhstan.

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European cargo freighter undocks from space station