Atlantis is on a week-long visit

The $164m airlock will simplify the currently complex depressurisation process.

The installation took place during the first of three spacewalks planned for the orbiter's week-long visit.

The second and third outings, on Tuesday and Thursday, will feature the attachment of four high-pressure gas tanks needed to operate the airlock.

Atlantis docked with the ISS early on Saturday above South America.

Universal connections

Up until now, whenever astronauts on the ISS have needed to go outside the platform, they have had to go through a docked space shuttle. Unlike the orbiter, the station does not have a proper airlock to allow astronauts to safely make the transition from a pressurised environment to the vacuum of space.

Airlock spec

Material - Aluminium Length - 5.5 metres Diameter - 4 metres Weight - 6,064 kilograms Volume - 34 cubic metres Cost - $164 million, including gas tanks

The Joint Airlock Module (Jam) will make the presence of a shuttle unnecessary. What is more, its universal fittings mean it will not discriminate among spacesuits.

Unlike the shuttle's airlock, where the communications system and connections for oxygen and coolant will only accept American suits, the $164m Jam will eventually accept Russian connections as well.

Three-bedroom house

"Once the airlock is installed, the hatches between a visiting space shuttle and the space station can remain open," said Mike Hawes, Nasa Deputy Associate Administrator for the Space Station.

"This is important because in previous missions we've had to open and close the hatches several times to maintain correct pressure during spacewalks. Now, we'll be able to keep those doors open, providing greater efficiency during joint orbital activities."

The Jam, which measures four metres (13 feet) across and 5.5 metres (18 feet) in length, is anchored to the ISS with the help of the station's advanced Canadarm2, which was added to the platform in April.

The airlock's installation completes Phase Two of the space station's construction, which began in 1998 with the arrival of the Russian-built Zarya base block in orbit.

The platform represents 424 cubic metres of living space - a greater volume than a conventional three-bedroom house.