Space shuttle Endeavour is prepared for launch as the Rotating Service Structure (RSS) is rolled back at the launch pad, at the Kennedy Space Center in Cape Canaveral, Florida April 29, 2011. [Photo/Agencies]

CAPE CANAVERAL, Fla. - NASA is pushing back from May 8 to May 10 its target for the already delayed launch of space shuttle Endeavour on its last flight to the International Space Station, officials said on Monday.

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NASA had planned to launch Endeavour on its 25th and final mission on Friday but a failed heater in one of the spaceship's hydraulic power generators prompted managers to call off the flight about four hours before liftoff.

On Sunday, NASA managers decided to replace a suspect electronics box that routes power to the heaters on the auxiliary generator. The replacement required an extensive and time-consuming retest of the 70 to 80 impacted shuttle systems, initially pushing back the launch to no earlier than May 8.

But after assessing overnight progress, managers decided on Monday that May 10 was a more realistic target launch date, NASA spokesman Kyle Herring said.

A final decision about whether to attempt launch on that date will be made on Friday, Herring said.

The shuttle is carrying a $2 billion Alpha Magnetic Spectrometer particle detector and a pallet of spare parts to the space station.

The six-man crew, led by commander Mark Kelly, the husband of convalescent US congresswoman Gabrielle Giffords, is scheduled to spend up to 16 days in orbit preparing the station for operations after the US shuttle fleet's retirement, which is scheduled for this year.

After Endeavour's mission, NASA plans one more cargo run of supplies to the station aboard sister ship Atlantis before ending the 30-year-old program.

Kelly and his crew returned to the Johnson Space Center in Houston on Sunday to resume training.

Kelly's wife, Giffords, the Arizona Democrat badly injured in a shooting in January, expects to return again to the Florida spaceport to watch her husband's launch, the congresswoman's office said on Monday.

Giffords, who traveled to Florida for last week's launch attempt, returned to Houston's TIRR Memorial Hermann Hospital, where she is undergoing extensive rehabilitation after being shot through the head.

President Barack Obama met Giffords, and the shuttle crew, at the Kennedy Space Center on Friday.

The Jan 8 shooting outside a Tucson, Arizona, grocery store killed six and injured 12 others besides Giffords. She has not been seen publicly since the attack.