Discovery will lift off no earlier than May 30 , NASA says . Space is concerned about a valve in the main engine . This will be the shuttle 's 28th mission to the international space station . The shuttle will deliver the final shipment of solar panels for the station .
Discovery will lift off no earlier than February 19 , NASA says . Space agency concerned about a valve in the main engine . This will be the shuttle 's 28th mission to the international space station . The mission will deliver the final set of solar arrays for the station .