Yuri Usachev, right, and Steven Lindsey clean up a water leak near the newly installed airlock

Currently, they have to exit the station via a docked shuttle. The new door will mean exterior work can be done on the platform at anytime - universal fittings ensure both American and Russian spacesuits can be worn.

A depressurisation test has been run to see that the door's systems are working properly.

Astronauts expect to be able to use the door itself by the end of the week.

The American space agency (Nasa) has already extended the mission by a day because of time wasted trying to fix small but persistent leaks on the ISS.

Mandatory earplugs

One leak, in a coolant line, has been fixed, but another, more difficult leak in air pressure has stumped astronauts and ground controllers alike.

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

Mission control finally told the eight crew members - the five astronauts from the docked Atlantis shuttle and the three members of the ISS Expedition Two team - to simply cap the faulty valve so that it could be replaced at a later time.

"We have active cooling, we have active life support, we have lights on in there," lead flight director Paul Hill said. "Everything else is going fine, we just have a few of these early quirks we need to get out of the system."

The astronauts have not complained of fatigue. So far, their only complaint has been the noise made by an air pump on the airlock, which was so loud it has driven them out of the adjacent module.

"Earplugs are mandatory," said astronaut Susan Helms, who has lived more than four months on the station.

The third spacewalk, which will be the first from the airlock itself, is scheduled now to take place on Friday. The return to Earth of Atlantis, originally set for early Monday, will now take place early on Tuesday.

The airlock will make depressurisation easier