After eight days together, the return crew of the space shuttle Discovery will bid goodbye to the astronauts remaining on the International Space Station. The hatches between the spacecraft and the station would be sealed today afternoon (Washington time), and three hours later, Discovery will undock.
It will be bringing back five months' worth of scientific experiment from the space station. These include blood, urine and saliva samples of the station astronauts, which will remain in the station freezer until the last possible moment to keep them as cold as possible.
The shuttle is also bringing back four to five litres of recycled water made from astronauts' urine and condensation. NASA wants to make sure the water is safe before space station astronauts start drinking it.
Discovery and its crew of seven are due back at the Kennedy Space Center in Florida on Saturday. The station, a project of 16 nations under construction for more than 10 years, is scheduled to be finished in 2010.
NASA has up to nine more missions planned to the space station, as well as a final servicing call to the Hubble space telescope, before it retires the shuttle fleet in 2010.
On Tuesday, the crews of the space station and Discovery received a phone call from US President Barack Obama, along with a group of schoolchildren and members of Congress, whose questions the astronauts tried to answer.
He said he and the other adults were just as excited as the kids to speak with the crew, adding that he was proud of the US astronauts, but also of the international cooperation in the building and operation of the space station.
Obama himself peppered the crew with questions. "Do you guys still drink Tang up there?" he asked at one point, referring to the powdered, orange-flavoured drink consumed by earlier US astronauts.
It was Obama's first chance to chat with an orbiting US space shuttle crew since he took office in January, and he was clearly enjoying it. Obama is the fifth US president to have spoken with shuttle crews aboard an orbiting space station, NASA said.
"Obviously we're really proud of the exciting work that our US astronauts are doing," Obama said. "But one of the things that is wonderful about this is that it's an international space station. I know we have Japanese and Russian counterparts on board. That's a spirit of cooperation we can apply not just on space, but on the ground as well."
Station commander Mike Fincke told Obama that the space station does a lap around Earth every 90 minutes, and that inhabitants get to see 16 sunrises and sunsets every 24 hours.
'Spacious and comfortable'
Japanese astronaut Koichi Wakata and Russian cosmonaut Yury Lonchakov emphasised their nation's role in the mission and need to work together on scientific endeavours.
At a press conference from space later on Tuesday, Wakata, who is the newest crew member of the ISS and the first Japanese astronaut to live at the station long term, detailed his first views of his new home. "My first impression is the space station interior is so big and I would love to stay here as long as I can," he said. "The interior is so big and very comfortable to live in."
For Discovery's crew, Tuesday was mostly a day of rest after they completed three spacewalks to deploy a new set of solar arrays and other construction tasks to prepare the $100 billion station for a six-person crew - double its current size.