"The launch of Discovery on the STS-124 mission is targeted for May 31," NASA announced after the shuttle moved to its launch pad at the Kennedy Space Center (KSC) in Florida.

Commanded by veteran astronaut Mark Kelly, Discovery's seven-astronaut crew is set to deliver the main part of Japan's Kibo module to the International Space Station (ISS) on STS-124.

"We're really excited to be within 30 days (of liftoff)," Kelly told reporters. "We're looking forward to the next three weeks of training and then the launch."

Discovery crew plans to perform three spacewalks to install and outfit the 11-meter long Kibo during their 13-day construction mission.

Kelly and his crewmembers plan to head to KSC next week to rehearse launch day activities aboard Discovery. Their spaceflight will mark NASA's third shuttle mission of up to five planned for the year.