The space shuttle Discovery has undocked from the International Space Station (ISS) to head back to Earth after a week on a milestone construction mission that has doubled the capacity of the orbiting laboratory.
The mission astronauts installed a fourth set of solar panels, completing the power plant needed to double the station's electrical generating capacity. The power allows the station to sustain six long-term residents instead of the current crew of three, and more occupants could arrive as early as May.
The shuttle crew completed three spacewalks during its mission, including installation of the last solar panels.
Discovery was to fly around the ISS, taking the first photos of the station with its newly deployed solar wings.
"Godspeed, thanks for making us symmetrical, giving us more power and all the other wonderful things you did for us," ISS commander Mike Fincke said as Discovery departed Wednesday.
Discovery will pass a Russian Soyuz mission on its way back to Earth. The Soyuz will launch Thursday with two more ISS crew members and space tourist Charles Simonyi, a co-founder of Microsoft taking his second flight in space. Cosmonaut Gennady Padalka and US astronaut Michael Barratt will replace Yury Lonchakov and Fincke.
The shuttle is carrying scientific experiments conducted aboard ISS and samples from a machine designed to turn urine and sweat into drinkable water, NASA officials said.
Discovery delivered a new machine after an earlier version kept breaking on an earlier shuttle mission. NASA will take about a month to analyse the sample to make sure the water is safe before the expansion of the ISS crew to six.
Separately, controversy has emerged over the naming of a new room at the International Space Station that will provide extra space for the expanded long-term crew.
The name contest applied to Node 3, a cupola to be delivered in February 2010 that will offer astronauts an "unrivaled" panoramic view of Earth and space. The cupola will also house the controls station for the giant ISS robotic arm.
Thinking to engage the public in the naming process, NASA invited people to vote on names for the room on its website. It had an epic identity in mind, such as Serenity or Legacy.
But the US space agency also invited write-ins and was surprised to find the top vote-getter was TV comedian and political satirist Stephen Colbert.
Colbert, star of "The Colbert Report" on the cable channel Comedy Central, suggested to his fans that they rush to the website and cast their votes. The Colbert name won, according to the Houston Chronicle, but it wasn't yet known whether NASA would honour the write-in campaign.
In the contest rules, NASA says it will consider the voting results but would not be bound by them.
"NASA reserves the right to ultimately select a name in accordance with the best interests" of the space programme, it said.
In fact, the website indicates that one of its preferred names, Serenity, was in the running to win the contest.
Other popular names in the write-in were Gaia, the earth goddess; Xenu, a character in Scientology mythology who was dictator of a "Galactic Confederacy" that adherents believe brought human beings to Earth 75 million years ago; and Ubuntu, the spirit of reconciliation anchored in the Bantu languages of southern Africa.
Discovery leaves behind Japanese astronaut Koichi Wakata, the first astronaut from his country to take up long-term residence in the orbiting station.
His predecessor on the ISS crew, US astronaut Sandra Magnus, will return home with the Discovery, which is set to land Saturday in Florida.