Washington, Nov 24 (DPA) Two astronauts from the space shuttle Atlantis ended the mission's third and last spacewalk after successfully installing an oxygen tank on the outside of the International Space Station (ISS).

The spacewalk on Monday lasted five hours and 42 minutes for astronauts Robert Satcher Jr and Randy Bresnik, who also performed other maintenance upgrades.

Atlantis is scheduled to begin its return journey to Earth on Wednesday, with touchdown at Cape Canaveral expected on Saturday.

The Atlantis brought thousands of kilogrammes of extra supplies to the ISS as the shuttle programme enters its expected final year in 2010.

The shuttle delivered two platforms with 12,360 kilogrammes of spare parts, which were installed on the outside of the station. Most of the gear was installed using the robotic arm, but some pieces were physically bolted on by spacewalkers.

As the first of several flights devoted largely to delivering spare parts, this mission was laden with the highest-priority items.

The so-called Express Logistics Carriers contain a variety of crucial parts: Gyroscopes that help keep the ISS at the proper altitude in space; an extra hand for the station's robotic arm; a gas tank for providing oxygen to the airlock during spacewalks; parts for the station's cooling system.

The retirement deadline of the shuttle is fast approaching with just five more launches scheduled and one year left to go in the programme.

NASA is at work on developing the next generation spacecraft with an eye on returning humans to the moon or travelling to Mars and beyond. But full support for the plans is still pending in the halls of government.

If the programme goes forward, it would carry the crew on top of the rocket in a configuration that recalls the Apollo moon missions and which engineers say is safer than the space shuttle design, following the explosion of the Columbia in 2003.