Published: Jan 11, 2011 9:42 PM EST
Updated: Jan 11, 2011 6:43 PM EST

CAPE CANAVERAL, Fla. (AP) - NASA says it finally knows what caused the cracking in space shuttle Discovery's fuel tank.

Discovery's final voyage has been on hold since November. If the remaining repairs go well, the shuttle could fly to the space station as early as Feb. 24.

Shuttle program manager John Shannon said Tuesday a combination of inferior material and assembly issues is to blame. Potentially dangerous cracks occurred in five aluminum alloy struts in the center of the tank. Those have been patched. Technicians will reinforce the dozens of remaining struts as a safety precaution.

NASA refused Tuesday to discuss the flight status of astronaut Mark Kelly, the husband of Rep. Gabrielle Giffords. He's supposed to command an April shuttle flight.

(Copyright 2011 by The Associated Press. All Rights Reserved.)