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.

View of the ATV from a camera on the space station. Credit: NASA TV/Spaceflight Now

Filled with trash and liquid waste, the ATV undocked from the space station's Russian Zvezda service module at 0855 GMT (4:55 a.m. EDT) as the complex flew 260 miles over Kazakhstan.

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.

With the Soyuz docking Nov. 7, the space station will host nine astronauts and cosmonauts from Russia, the United States, Europe and Japan for nearly four days, before Yurchikhin, Nyberg and Parmitano leave and return to Earth on Nov. 10, U.S. time.

In the meantime, the ATV will head to a re-entry over the South Pacific Ocean at approximately 1200 GMT (8 a.m. EDT) Saturday. Engineers expect most of the spacecraft to disintegrate during re-entry, but a few fragments may reach the ocean surface. Officials will caution pilots and mariners in the area to steer clear of the re-entry zone.

It will take a few days to position the ATV about 75 miles beneath the space station for re-entry, allowing astronauts and automated cameras on the complex to monitor the fiery plunge, an act officials say will help calibrate data on future atmospheric entries.

Monday's undocking of ATV 4 occurred as Europe's fifth and final Automated Transfer Vehicle is set to arrive at its launch site in Kourou, French Guiana, on Tuesday.

Massimo Cislaghi, ESA's ATV 5 mission manager, said the ship carrying the spacecraft is moored offshore Kourou at Devil's Island awaiting proper tidal conditions to continue into port.

The fifth ATV left its EADS Astrium factory in Bremen, Germany, earlier this month for the overseas journey to South America. Keeping with the tradition of naming ATVs for figures in European science, ATV 5 is named for Georges Lemaitre, a Belgian cosmologist and father of the Big Bang theory.

ATV 5 flight hardware is traveling in three containers, along with about 80 boxes of ground support equipment to help engineers ready the spacecraft for launch. In Kourou, technicians will install cargo into the ATV's pressurized compartment, attach the ATV's cargo carrier to its service module and solar arrays, and mount the spacecraft atop its Ariane 5 launcher.

Cislaghi said the launch of ATV 5 is targeted for the second half of June 2014.

The ATV 5 mission will wrap up the ATV program, which launched its first mission to the space station in 2008, followed by flights in 2011, 2012 and the ATV 4 mission this year.

ESA and Astrium are developing a service module based on the ATV to fly with NASA's Orion crew capsule on an unmanned test flight around the moon in 2017. Europe is also providing service module components - and may lead the module's development - for a crewed Orion mission in 2021.

NASA says the 2021 mission will rendezvous with an asteroid towed by a robotic spacecraft from deep space into an orbit around the moon.