After four previous delays, caused by concerns over the safety of three valves that control the pressure in the shuttle's fuel tanks, NASA experts decided to replace Discovery's valves with new components that should be less susceptible to cracking.
NASA said its specialists and contractor teams "are still working to identify what caused damage to a flow control valve on shuttle Endeavour during its November 2008 flight."
NASA officials are planning to hold a formal review of the valves' safety on March 6 to set an official Discovery launch date.
The Discovery's 7-man crew includes Japan's Koichi Wakata, who will replace returning ISS engineer Sandra Magnus.
Eight more flights to the station remain before the space shuttle is put into retirement in 2010 and all transport flights to the ISS switch over to Russian Soyuz and Progress spacecraft at least until 2013.
During the upcoming mission, Discovery will deliver the last set of solar wing panels to the ISS.
