A NASA quality specialist inspects wiring in the aft compartment of Discovery. Photo: NASA/KSC

The hibernating Hubble Space Telescope will have to wait yet another day before shuttle Discovery will blast off on a mission to fix the obseravtory's broken pointing system.

NASA officials announced Tuesday that Discovery's 10-day mission would be postponed again to repair damaged wiring aboard the 16-year old spaceship.

Discovery had been slated to begin its 10-day mission on Saturday at 0513 GMT (12:13 a.m. EST), nearly two months later than planned because of other wiring defects.

But the extra time spent fixing the newest wiring problem forced space agency managers to reschedule the mission for the next opportunity to send Discovery to rendezvous with Hubble, which will come at 0442 GMT on Sunday (11:42 p.m. EST Saturday night).

The latest wiring problem surfaced Monday when workers found a 1/8-inch nick in insulation covering a command relay cable attached to main engine No. 2.

On Tuesday, the entire wiring bundle that the cable was part of, called a wiring harness, was replaced. The bundle contained between 20 and 30 wires, NASA spokesman Bruce Buckingham said.

The damaged cable is used to send commands from the shuttle's main computers to the engine controller. Feedback information to verify the commands were accomplished is then relayed through the cable from the engine controller to Discovery's computers.

Later Tuesday night, shuttle engineers were planning to run a flight readiness test on the engine. The test involved sending commands through the new wiring harness to gimbal the engine nozzle. The bell-shaped nozzle must gimbal properly in order to steer the shuttle during launch.

If the test goes well and no other problems arise, the three-day launch countdown will begin on Thursday at 0900 GMT (4 a.m. EST). The seven astronauts are already at Kennedy Space Center. They arrived Monday night.

"We have the time to get the work done to launch on Saturday night," Buckingham said. "If we find any more work we would have to do, then we would have to assess the impact."

Hubble has been orbiting around Earth since mid-November without making any observations of the universe because its precision pointing system shut down. Four of the craft's six gyroscopes have failed and at least three are needed to keep the telescope pointed toward stars, planets and its other celestrial targets.

Four of Discovery's seven astronauts will make four spacewalks to install six new gyroscopes and other electronics.