Astronauts assigned to fly on the U.S. space shuttle Atlantis later this month climbed into their flight suits and scrambled aboard the shuttle on Thursday for a three-hour dress rehearsal for launch.
The six-member crew hopes to be back at the Kennedy Space Center in two weeks for the start of a real countdown to the first shuttle mission in more than three years. They hope to resume construction of the $100 billion International Space Station.
"Every crew and every mission control team has to be on their game when we fly these assembly missions," Atlantis commander Brent Jett said during a media briefing at the launch pad.
"We can handle some setbacks, we can deal with some problems, but we have to perform these missions well and we have only a limited amount of time to do it," he said.
The astronauts went through launch procedures in Thursday's rehearsal, which wrapped up a three-day session that included briefings on safety and emergency evacuation procedures.
With four years left before the space shuttles are retired, NASA is under pressure to finish the station. The trusses, solar arrays and laboratories awaiting rides to space were designed to be carried only on shuttles.
Station assembly has been on hold while NASA recovered from the fatal 2003 Columbia accident, a process that finally ended with a successful flight by shuttle Discovery last month, the second of two shuttle test missions to check safety upgrades.
NASA says station construction flights can be daunting.
"All the missions between now and 2010 that involve station assembly are going to be extremely complex," Jett said. "You could probably make the case that each one is slightly more complex than the one that precedes it. We're flying hardware that has no history in space."
The Atlantis astronauts plan to install the second of the station's four sets of solar arrays and a rotary joint so the panels can track the sun. The additional power is needed for partner laboratories built by Europe and Japan, which are due to be flown to the station beginning next year.
In addition to station assembly, NASA now requires all shuttle crews to conduct time-consuming inspections of the spacecraft's heat shield to prevent another Columbia-like disaster.
Columbia broke apart as it returned through the atmosphere for landing, killing seven crewmembers. The shuttle had been struck by a piece of foam insulation that fell off its fuel tank during launch and made a hole in the heat shield on the wing.
NASA managers hope to launch Atlantis Aug. 27. A firm date is expected to be announced after a flight review next week.