The final launch of the space shuttle Endeavour hit yet another snag as engineers battle to resolve an electrical problem that continues to delay the mission.

The launch of the space shuttle Endeavour, originally scheduled for April 29, is being pushed back for the 2nd time  to no earlier than May 16, said NASA spokesman Allard Beutel.

If the shuttle launches on that day, liftoff would be at 8:56 a.m. EDT.

More extensive work is still needed to fix a faulty heater system in the engine compartment. The heaters keep fuel from freezing in the line, critical in preventing it from rupturing in the cold vacuum of space.

Technicians this weekend will continue to repair and retest the electrical system to determine what caused a circuit to short out.

NASA repair crews have already replaced a distribution box that shorted out a circuit supplying power to heaters for the orbiter's hydraulics system.

The NASA space shuttle was first scheduled for lift-off last Friday afternoon in its historic final flight, to deliver the $2bn Alpha Magnetic Spectrometer particle detector to the International Space Station.

Officials had expected up to 500,000 people to descend on the area for the event, including President Barack Obama and his family.

Endeavour is the second-to-last shuttle mission for the 30-year US program. Atlantis will mark the end to the program in in June and July.

NASA is winding down its space shuttle operations this summer as it tries to save money, which will leave American and European astronauts with only Russian rockets as options for going into space.

In February, the space shuttle Discovery, NASA's oldest and most travelled spacecraft, made its final voyage into space.

The country is focusing on inspiring 3rd part companies to put astronauts in orbit using privately run launch, transport and services companies.

NASA will now focus its resources on deep space exploration, such as potential landings on asteroids and, eventually, Mars.

The scrubbed also postpones what promised to be an emotional moment for the shuttle's commander, Mark Kelly.

Kelly's wife, U.S. Rep. Gabrielle Giffords, D-Arizona, traveled to Florida hoping to watch the shuttle's ascent. Giffords was shot in the head during a January 8 assassination attempt at a public event in Tucson, Arizona.

She has been recovering at a Houston rehabilitation hospital.