Space Shuttle Atlantis to Launch Tonight

Seven NASA astronauts are poised to launch into orbit tonight aboard the shuttle Atlantis to haul vital new solar arrays to the International Space Station (ISS).

Commanded by veteran spaceflyer Rick Sturckow, Atlantis' STS-117 crew is set to rocket spaceward at 7:38 p.m. EDT (2338 GMT) from NASA's Kennedy Space Center in Florida after months of delay.

"This crew is very excited," Sturckow said this week of the planned space shot. "We've spent a long time training for this mission."

Sturckow and his STS-117 crewmates will deliver a pair of massive, girder-like truss segments and new solar wings to the starboard side of the ISS during their planned 11-day mission.

Joining Sturckow aboard Atlantis will be shuttle pilot Lee Archambault and mission specialists Patrick Forrester, Steven Swanson, Danny Olivas, James Reilly and Clayton Anderson. A late addition to the STS-117 mission, Anderson will stay aboard ISS to relieve NASA spaceflyer Sunita Williams as a member of the outpost's Expedition 15 crew.

Weather forecasts predict an 80 percent chance of favorable conditions at liftoff today, though mission managers will keep a close watch for afternoon thunderstorms anticipated around Atlantis' Pad 39A launch site, Kathy Winters, NASA's shuttle weather officer, has said. ?

Long road to launch day

Launch day for shuttle Atlantis comes after three months of delay prompted by a freak hail storm that damaged the orbiter's foam-covered fuel tank in late February.

Atlantis was on track for a planned March 15 liftoff before the hail storm struck, etching thousands of dents and divots into the foam insulation around the orbiter's 15-story fuel tank. The damage delayed the STS-117 mission to allow time for engineers to perform an unprecedented repair job.

"The team is really pumped to get this done this time," NASA launch director Mike Leinbach said of today's planned launch. "Team Atlantis is ready to go."

While NASA shuttle missions have been delayed by hail damage before, the scale of repair work for STS-117 -- engineers studied or patched up some 4,200 areas of damage -- outweighed those of past flights.

Bringing the power

In addition to the Expedition 15 astronaut swap, the STS-117 crew plans to stage at least three spacewalks outside the ISS to install the outpost's new trusses and solar arrays.

Weighing in at about 17.5 tons, the $367.3 million integrated Starboard 3/Starboard 4 (S3/S4) truss segments are tipped at one end by two solar arrays that, once unfurled next week, will have a wingspan of about 240 feet (73 meters).

The S3/S4 arrays are the third of four U.S.-built power plants bound for the ISS and are vital for the orbital laboratory's continued expansion. Once installed, the new solar wings will help provide enough power to support new modules and international laboratories scheduled for launch over the next eight months.

"What we're doing is bringing up the starboard set of arrays," Reilly said in a NASA interview. "[T]hat's the foundation for the power supply that will now allow us truly to become an integrated International Space Station with the European and the Japanese labs."

During the STS-117 mission, shuttle and ISS astronauts will also help coax an older solar wing into its storage boxes so its central truss segment can be moved during a future spaceflight.

"Essentially, we are ready for launch and are excited to get into the final throes of the countdown," Robbie Ashley, NASA's STS-117 payload mission manager, said Thursday. "It's an exciting time for the space station and for all of us."

NASA will provide live coverage of the launch of space shuttle Atlantis on NASA TV beginning at 1:30 p.m. EDT (1730 GMT) today. Click here for SPACE.com's shuttle mission updates and NASA TV feed.

• SPACE.com Video Interplayer: Space Station Power Up with STS-117
• STS-117 Power Play: Atlantis Shuttle Crew to Deliver ISS Solar Wings
• The Great Space Quiz: Space Shuttle Countdown
• Complete Shuttle Mission Coverage