CAPE CANAREVAL, Florida, the United States, July 13 (Xinhuanet) --Technical problem with Discovery's liquid fuel sensor has forced a delay of the shuttle launch Wednesday, with NASA engineers still trying to resolve the problem and a NASA decision on the time of next launch attempt to be yet made.

    The US space agency is assessing the situation. It is unknown how long it will take technicians to fix the problem and the delay of shuttle launch could be days. The launch window runs from July 13 to 31. NASA announced it will give a press conference at 4:30 p.m. EDT to provide details.

    An announcement of the time for the next launch attempt is expected. The technical problem was found about one hour before the planned launch at 3:51 p.m. EDT (1951 GMT), and a couple of hours after the fuelling that loaded the shuttle's external fuel tank with supercold liquid oxygen and hydrogen.

    The fuelling had been about an hour later than planned as a result of a problematic heater that was quickly fixed.

    There are two sensors for liquid oxygen and two sensors for liquid hydrogen in the fuel tank. The troubled sensor was one of the two for liquid hydrogen. The malfunction of the sensor could lead to incorrect readings about how much liquid hydrogen was consumed in the tank, threatening the safety of the flight. The unexpected event gives a setback in NASA's return-to-flight effort.

    NASA has made many major safety improvements over the past two and a half years at the recommendation by the Columbia accident investigation board. NASA Administrator Michael Griffin said Tuesday NASA has done everything it needs to do to ensure a safe flight.

    Griffin said a safe flight is "utterly crucial" for NASA, for the nation, and for the US space program.

    NASA's shuttle flight, which is currently consisting of Discovery, Atlantis and Endeavor, has been grounded since the Columbia midair disintegration in Feb. 2003, in which all seven astronauts aboard were killed. Enditem