The space shuttle Endeavour will not blast off at the beginning of the week as NASA had hoped, and the space agency on Sunday once again postponed the launch saying that it will not fly before May 8.

NASA said its administrators decided that it would not be possible to begin the next-to-last shuttle mission on Monday, the earliest possible day another launch try could be made after the original launch on Friday was postponed due technical difficulties.

Technical teams are scheduled to meet on Monday to try and set a new launch date.

The second launch try had been scheduled for Monday, which would have been a 72-hour postponement after a problem in two of the heaters in the shuttle's auxiliary power unit was detected.

The problem in the unit, which performs key functions for the spacecraft's control and landing systems, forced officials to postpone the launch, which was to have been attended by President Barack Obama and Arizona Rep. Gabrielle Giffords, the latter of whom is recovering and undergoing intensive therapy after being shot in the head in January in an assassination attempt and whose husband Mark Kelly heads the shuttle mission.

NASA said that technicians began testing the systems associated with the heaters on Saturday afternoon and continued with that task into the night.

The test results indicated that the problem is localized in the ALCA-2 element of the shuttle.

The teams are working on a plan to replace the control box and any hardware linked to the defect.

The mission's six astronauts quickly left Florida for the Johnson Space Center in Houston, Texas, for a few days of "additional training" before returning to Cape Canaveral for a new launch attempt.

The crewmembers' families will also return home, C.J. Karamargin, the spokesman for Giffords, said in a communique that the congresswoman was already back in Houston, but she will return to Florida for the launch.

Spanish Science and Technology Minister Cristina Garmendia planned to watch the takeoff on Friday, given that Spain contributed to developing the Alfa-2 Magnetic Spectrometer, or AMS-2, on board the craft, but she left Florida a few hours after the launch postponement due to scheduling problems.

Once launched, the flight will be the 134th shuttle mission, 25 of which have been made by Endeavour. It will be the 36th shuttle mission to the International Space Station.

During the 14 days of the mission, the astronauts are scheduled to make four spacewalks to set up experiments, refill the radiators with ammonia and deploy support platforms on the shuttle's robotic arm, along with other tasks.