WASHINGTON -- With a slow and determined pace, NASA's shuttle Atlantis rolled out to its Florida launch site Thursday, where the spacecraft is slated to rocket towards the International Space Station (ISS) in one month's time.

Atlantis reached Pad 39A at the Kennedy Space Center in Cape Canaveral, Florida at 3:09 p.m. EST (2009 GMT) after a six-hour trip from NASA's cavernous 52-story Vehicle Assembly Building (VAB) via the agency's massive crawler carrier [image].

"This is a significant milestone and it brings us one step, or I should probably say roll, closer to the launch of Atlantis," Cathy Koerner, NASA's lead flight director for the shuttle's STS-117 mission. "We are very excited and looking forward to continuing assembly of the International Space Station."

Commanded by veteran spaceflyer Rick Sturckow, Atlantis' STS-117 crew [image] is slated to launch towards the ISS at 6:43 a.m. EDT (1043 GMT) on March 15, kicking off a series of five NASA shuttle missions to continue space station assembly over the next 12 months.

The astronauts plan to deliver two starboard ISS truss segments, a pair of new solar arrays and help retract an older solar wing on the mast-like Port 6 truss -- a counterpart to one folded away in a December shuttle flight -- during three spacewalks planned for their 11-day mission [image].

"I'm nervous about retracting solar arrays," Mike Suffredini, NASA's ISS program manager, said of the upcoming mission. "I think that will be probably one of those things we will spend probably a little more time on than we think we will today."

The upcoming shuttle flight could run two days longer than planned and include a fourth spacewalk to handle any unexpected glitches in either the Port 6 solar wing retraction or the Starboard 3/Starboard 4 (S3/S4) truss [image] delivery or deployment, Suffredini said.

Atlantis' STS-117 mission will mark NASA's third flight dedicated solely to ISS construction since the 2003 Columbia accident. It is the first of 13 planned orbiter missions, with three extras possible to haul spare parts and cargo, to complete ISS assembly by 2010, when NASA plans to retire its shuttle fleet to make way for the Orion Crew Exploration Vehicle and its Ares rockets.

ISS: Much Assembly Required

Joining Sturckow on the STS-117 mission are Atlantis shuttle pilot Lee Archambault and mission specialists James Reilly, Steven Swanson, Patrick Forrester and Danny Olivas. Their spaceflight will help prime the ISS for to support new modules and international laboratories slated for launch later this year.

"We have a tremendous amount of work that we're going to be doing for the International Space Station program," NASA shuttle program manager Wayne Hale said during Thursday's mission briefings, who called NASA's next year of orbiter missions "extremely ambitious."

In addition to delivering the new S3/S4 solar arrays, NASA shuttles are due to ferry a new starboard spacer section of the station's main truss, the Node 2 hub for future modules, and the European Space Agency's Columbus laboratory later this fall to be followed by the first part of Japan Aerospace Exploration Agency's Kibo laboratory.

In between those shuttle flights -- which are currently targeted to launch June 28 (STS-118), Aug. 26 (STS-120), sometime this fall (STS-122 with Columbus) and Dec. 8 (STS-123 with the first Kibo segment) -- some four unmanned Russian cargo ships, the first automated European resupply vehicle and two Soyuz spacecraft with new ISS crews will visit the orbital laboratory, station managers said.

"We've spent many, many years preparing for this and training for this," Suffredini said. "The partner elements are ready to go fly."

But Hale stressed that the planned launch schedule will always be susceptible to delays, especially those due to safety. Case in point: Atlantis' rollout to Launch Pad 39A today was delayed one day from a planned Feb. 14 departure so engineers could remove a faulty solid rocket booster pressure sensor that shorted out, Hale said.

"If we don't launch on the 15th, if we launch on the 16th, on the 18th or on the 20th then so be it," Hale said. "We don't want to let schedule drive us to do something dumb."

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