(AP) -- Shuttle Discovery and its crew of seven aimed for a Saturday afternoon touchdown at NASA's spaceport to wrap up a successful space station construction mission.
At midmorning, Mission Control said favorable weather was expected. But experts were keeping close watch on the clouds and wind.
The seven astronauts are winding up a 13-day mission highlighted by the successful installation and unfurling of the space station's last pair of solar wings. The $300 million addition brought the orbiting outpost up to full power, a vital part of NASA's plan to double the space station population and boost the amount of science work in a few months.
Discovery is bringing back former space station resident Sandra Magnus. Saturday marked her 134th day in orbit; she was launched back in mid-November.
The shuttle also is ferrying five months' worth of science samples from the space station, mostly blood, urine and saliva collected by its crew members. As many vials as possible were stuffed into the shuttle freezer, with the rest put in ice packs.
Also coming back for NASA scientists: four to five liters of recycled water that had been the astronauts' own urine and sweat. The water was produced after Discovery delivered a new urine processor that fixed the recycling machine.
NASA hopes to have the water samples tested within a month. If the toxicology results are good, the three space station residents will be given the all-clear to start drinking the recycled water up there.
The space station, meanwhile, got more guests Saturday with the arrival of a Russian Soyuz capsule, just three days after Discovery's departure.
Two of the newcomers - an American and a Russian - will swap places with commander Mike Fincke and cosmonaut Yuri Lonchakov, who have been in orbit six months.
Billionaire space tourist Charles Simonyi, a former Microsoft executive, also flew up on the Soyuz for a 1 1/2-week visit.
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Explore further: NASA fuels Discovery for mission to space station