NASA plans sixth shuttle launch attempt

The shuttle is now set to lift off at 6:03 pm (2203 GMT) Wednesday from NASA's Kennedy Space Center at Cape Canaveral, Florida, with the US space agency saying there is only a 40 percent chance of unfavorable weather conditions this time.

"Well, this isn't the tweet I hoped to send, but it's just not easy to launch a shuttle," shuttle commander Mark Polansky wrote on the micro-blogging website Twitter. "We're fine in spite of this, and we'll hope for Wed."

A launch was also being considered for Thursday, the last possible date before interfering with the July 24 lift-off of the Russian cargo craft Progress to the ISS, launch integration manager Mike Moses told reporters.

Although Russian space officials have accepted the Thursday launch option, Moses noted that it would force NASA to abort the fifth spacewalk planned for Endeavour's mission to the ISS.

If the shuttle does not take off on Wednesday or Thursday, the next launch window would begin on July 26.