The U.S. space agency has announced the space shuttle Endeavour will not launch for its final mission before Friday, because of electrical problems.
NASA officials said Sunday that the faulty switch box that prompted them to scrub Friday's launch will take several days to fix. They also said the next launch attempt must wait until after the planned launch of a military satellite Friday.
Technicians say the switch box in the engine compartment powers a heating system designed to protect a fuel line from freezing in space.
After Sunday's announcement the Endeavour crew headed from the Kennedy Space Center in Florida back to Houston, where they will undertake a few more days' training.
Endeavour and its six-person crew are to deliver a $2 billion scientific instrument to the International Space Station. The instrument is designed to search for cosmic rays throughout the universe
The mission is the 25th and final one for Endeavour, which will be decommissioned and put on permanent display at a science center in Los Angeles after returning to Earth.
NASA's 30-year space shuttle program is expected to end in June after the shuttle Atlantis makes its final trip to the space station.