CAPE CANAVERAL, Fla. - NASA aims to give the space shuttle Endeavour a fifth shot at launching into orbit today after being waylaid by a series of unfortunate events for more than a month.
Endeavour is slated to launch Monday evening at 6:51 p.m. EDT (2251 GMT) from Kennedy Space Center here with only a 40 percent chance of good weather expected. Approaching lightning and thunderstorms in the area are a risk to thwart the launch.
Endeavour almost got off the ground on Sunday, but was foiled at the last minute by storms too close to the shuttle's emergency landing site here. Though the weather wasn't a constraint for liftoff, Kennedy's Shuttle Landing Facility must be clear within a 20 nautical mile radius in case an emergency forces the shuttle to make an abort landing.
"Scrubs aren't fun, and I've been in this situation before," said Endeavour commander Mark Polansky late Sunday via the microblogging Web site Twitter, where he is chronicling the mission as @Astro_127. "You just have to roll with it."
The weather outlook for the coming days only appears to worsen as time goes on, with a sea breeze potentially pushing thunderstorms near the launch site.
Endeavour has until July 14 to launch before it must stand down to allow an unmanned Russian cargo ship to dock at the space station. If the mission does not get off the ground by then, NASA may negotiate with Russia for more time, or wait until the shuttle's launch window opens up again on July 27.
An earlier launch attempt this week was also spoiled by Florida's erratic weather. A violent lightning storm struck near the launch pad on Friday, and NASA was forced to delay Endeavour's flight a day so engineers could ensure the shuttle had suffered no damage.
Endeavour's STS-127 mission was delayed twice by a potentially dangerous hydrogen gas leak from the shuttle's external fuel tank, though that issue has since been successfully repaired.
Endeavour and its seven-astronaut crew are slated for a 16-day assembly mission to the International Space Station. Polansky and his crew will deliver an outdoor experiment porch for the Japanese Kibo laboratory, a cache of spare supplies and a new long-duration station crewmember - NASA astronaut Tim Kopra — to the orbital outpost. Kopra is set to start a stint as a flight engineer on the outpost's six-man Expedition 20 crew.
Rounding out the crew are Canadian astronaut Julie Payette and NASA astronauts Doug Hurley, Chris Cassidy, Tom Marshburn and Dave Wolf. The astronauts plan an ambitious visit to the station with five spacewalks and elaborate robotic work.
Endeavour's flight will be NASA's third shuttle mission of the year.
SPACE.com is providing continuous coverage of STS-127 with reporter Clara Moskowitz at Cape Canaveral and senior editor Tariq Malik in New York. Click here for mission updates and SPACE.com's live NASA TV video feed. Live launch coverage begins at 1:30 p.m. EDT (1730 GMT).