NASA is not taking any chances with the 26-year-old Space Shuttle Discovery, which has been in orbit 38 times and is the senior citizen of the U.S. space program.

The agency on Dec. 3 postponed for the third time what was to be the final launch of Discovery until after the holidays. It originally was supposed to go Nov. 5 but was delayed until Nov. 30, again until Dec. 17, and now until next year.

The craft is now scheduled to fly no earlier than Feb. 3, 2011, to enable more testing on repairs that were made to cracked supports on the shuttle's fuel tank and to other mechanical problems that included a hydrogen leak.

Discovery has flown 38 flights, completed 5,247 orbits, and has spent 322 days in orbit. The space agency has deemed it usable for one more flight but said it is possible it may never fly again if the nagging mechanical problems aren't solved once and for all.

If the cause of the cracks isn't found and delays continue, Discovery may not make it into space before the launch of Space Shuttle Endeavor, which is planned to go Feb. 27, 2011. That mission has been designated as the final one for the 35-year-old shuttle program, which has faced budgetary issues in Congress.

NASA said Dec. 3 that it has repaired cracks on two 21-foot-long brackets that support one of Discovery's large external fuel tanks. Flight engineers found that the brackets cracked during the first loading operations for Discovery's final mission to the space station.

More time needed to find cause of cracks

More time is required for engineers to fully determine exactly why the cracks occurred, Bill Gerstenmaier, NASA's associate administrator for space operations, told reporters during a press conference Dec. 3.

All the shuttles have performed numerous missions that involve astrological, geophysical and other scientific research and repairs/assembly work on the International Space Station.

Of the all the NASA shuttles, Atlantis and Endeavor are the newest and are currently available for duty. NASA lost Challenger in 1986 and Columbia in separate accidents that claimed the lives of their crew members.

The original space shuttle, Enterprise, was a tester that flew suborbital flights for one year and was retired in 1977.