They said more tests and analysis are needed before proceeding with the launch of the STS-133 mission to the International Space Station.
The Program Requirements Control Board met Thursday and reviewed engineering evaluations associated with cracks on two 21-foot-long, U-shaped aluminium brackets, called stringers, on the shuttle's external tank.
They are planning to conduct an instrumented test on the external fuel tank and structural evaluations on stringer test articles to determine if the analysis is correct.
Details and timelines for the tanking test are in work, but plans call for temperature and strain gauge measurements in the intertank region near the top of the tank during the test.
A team of engineers and technicians will inspect the tank for evidence of any foam cracking as it would on an actual launch day. The test also will verify the integrity of repairs to the Ground Umbilical Carrier Plate, which leaked an unsafe amount of gaseous hydrogen during Discovery's Nov. 5 launch attempt.
Engineers will continue to search for the root cause of the stringer cracks through data analysis and tests, including placement of manufacturing defects in separate stringers to demonstrate structural integrity in an effort to duplicate the same type of failure that occurred in November.
NASA will review and analyze the data from the tests before setting a launch date. Because of Discovery's delayed launch, the earliest opportunity for the lift-off of the final scheduled shuttle mission, STS-134 on Endeavour, is April 1. (ANI)