NASA officials have postponed the target launch date for the space shuttle Discovery yet again because they say they do not know what caused support beams on the shuttle's fuel tank to crack. NASA now says Discovery will not blast off on its final mission until December 17 at the earliest.
Shuttle managers have decided that more tests and analysis must be done before giving Discovery the go-ahead for its final launch.
Engineers are still working to understand what caused cracks on two 6.5- meter-long, U-shaped aluminum support brackets on the shuttle Discovery's external tank. The cracks were found on November 5 while Discovery was being filled with liquid oxygen on the launch pad, in anticipation of a launch that day.
In the past, inspectors have found cracks and successfully repaired them at the assembly plant. But, Shuttle Program Manager John Shannon told reporters at Johnson Space Center in Houston, Texas, Wednesday that this time the situation is different.
"You know, this is the first time it happened at the launch pad, so we have some kind of a process-escape that allowed this to get to the launch pad in the first place," said Shannon.
NASA says the cracks were repaired while the shuttle was on the launch pad, and Shannon said it is now a matter of risk assessment.
"What is the risk that something else could have gotten through our process and gotten out to the launch pad?" he asked.
This is set to be Discovery's final mission. NASA is retiring its shuttle fleet next year and is encouraging the development of commercial human spaceflight vehicles.