After a string of vexing delays, NASA is once more preparing the space shuttle Endeavour for what will be its sixth launch attempt late Wednesday.

The browbeaten shuttle has been trapped on the ground by a series of weather delays and a gas leak that has since been fixed.

NASA is hoping Wednesday will bring a much-needed break in stormy weather and allow Endeavour to lift off at 6:03 p.m. EDT (2203 GMT) from a seaside launch pad here at the Kennedy Space Center.

In the meantime, ground crews must replace an unattached plastic cover on one of the shuttle's 44 small thrusters used for minor course corrections.

The cover, made of a material called Tyvek, keeps moisture out of the thruster nozzle while the shuttle is on the ground.

Without the cap, rainwater could seep into the thruster and freeze, rendering it useless once Endeavour reaches space.

• Click here for more photos.

• Click here for astronaut Mark Polansky's Twitter page.

• Click here for all news on the space shuttle program.

• Click here for NASA's live video feed.

• Click here to visit FOXNews.com's Space Center.

Endeavour's STS-127 mission is a busy construction flight to the International Space Station. The spaceflyers plan to deliver spare parts and a new exposed science platform for the station's Japanese Kibo laboratory.

Endeavour's crew is taking some down time today. The astronauts plan to spend time with family and friends, and commander Mark Polansky and pilot Doug Hurley are scheduled to practice landing the space shuttle by flying modified Gulfstream aircraft.

Thruster cover fix on tap

The thruster cover work for Endeavour involves moving the giant Rotating Service Structure scaffolding into place around the shuttle to gain access to the nose, where the exposed thruster is located.

Workers will inspect the area for moisture, vacuum any water out if necessary, then reapply the cover with an adhesive that takes a while to dry.

"There is a process so it takes on the order of about four hours to go through and do that," Nickolenko said. "While we have the Rotating Service Structure around the vehicle, the intention is to replace all of those Tyvek covers, in essence to reset our clock. We require that the covers be replaced after seven days."

If Endeavour succeeds in launching Wednesday, its STS-127 mission should not be adversely affected.

Though some activities will have to be rearranged to allow for an earlier space station undocking time than planned, to make way for the arrival of a Russian unmanned cargo craft, the shuttle mission should not have to give up on any of its goals, shuttle mission management chair Mike Moses said.

However, if Endeavour's launch must be pushed to Thursday, the 16-day mission may have to lose at least one spacewalk.

"I think that would definitely be our last try," Moses said. "We want to be smart about it. This is a very complicated mission, it's very aggressive, very full. And we don't want to just, without a lot of forethought, change things up."

After Thursday, the next chance for Endeavour to launch comes July 26.

Copyright © 2009 Imaginova Corp. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.