Commander James Halsell Jr had used both orbital-manoeuvering engines for the ride home.

Commander James Halsell was congratulated on the mission

The left engine seemed to have a stuck valve during the climb to orbit on 19 May, but flight controllers later concluded the valve was fine and a bad sensor was to blame.

After the hectic pace of the past 10 days, the astronauts said they would have liked an extra day or two in space with little to do.

"As one person who is getting mentally prepared to spend six months up here, I think any extra day is a good thing," said Susan Helms, a future space station resident.

New batteries

Susan Helms and Russian crewmate Yuri Usachev had the most important job of the mission: replacing four bad batteries inside the international space station.

The seven-member crew also furnished the ISS with a new antenna, construction crane, fire extinguishers, smoke detectors and fans, and boosted the complex into a higher orbit.

Atlantis undocked from the space station on Friday

Susan Helms and astronaut James Voss said they were impressed with the space station, which next year will become their home.

"I think it's a place, after being here for about a week, that I'll be able to live for 5� months," Mr Voss said during a news conference late on Saturday.

Before anyone can move in, the Russians must launch the Zvezda service module and its life-support systems.

It is due in July after more than two years of delay.

Even if it is postponed again, the space station is now equipped to fly solo through the end of this year.