NASA order more repairs for Discovery fuel tank

NASA has ordered additional repairs to space shuttle Discovery after more cracks were discovered in the ship's fuel tank, but the flight remains targeted for early February, officials said.

The shuttle's cargo run to the International Space Station, one of the final missions before the United States ends the 30-year-old shuttle programme, has been on hold since November 5 when a hydrogen fuel leak scuttled a launch attempt. Technicians later found a 21-inch (53-cm) long crack in the foam insulation that covers the tank, a potential debris hazard for launching.

Further investigation revealed underlying cracking in structural supports, the cause of which has not been determined.

X-rays of the backside of the tank, completed this week, showed additional cracks in three more of the aluminum lithium tank support structures, Kennedy Space Center spokesperson Allard Buetel said late on Thursday.    

Those cracks will be repaired while managers consider if additional modifications to the tank will be needed, work that could delay the scheduled February 3 launch to later in the month.

The shuttle fuel tanks have been a top safety issue for NASA since the 2003 Columbia accident, which killed seven astronauts. A piece of foam insulation broke off Columbia's tank during launch and smashed into the ship's wing.

The damage caused the shuttle to break apart as it flew through the atmosphere for landing 16 days later.

NASA redesigned the tanks after the accident and developed new in-flight inspection procedures.    

NASA is ending its space shuttle programme in 2011 after two or three more missions to complete the space station, a $100 billion project of 16 nations that has been under construction 220 miles (354 km) above the planet since 1998. Russia already has taken over the job of transporting crew members to and from the outpost - at a cost of $51 million a seat - in anticipation of the shuttles' retirement.

NASA is also investing in commercial companies with the hope that private industry will be ready to provide launch services for astronauts by about 2015.