Shuttle launch delayed until July

CAPE CANAVERAL, Fla. -- NASA has postponed the next space shuttle flight from May until July so engineers can change out suspect sensors in the ship's external fuel tank.

The critical fuel sensors are designed to make sure the shuttle's three main engines shut down before the 15-story tank runs out of propellant during launch. An early cutoff could prevent the shuttle from reaching orbit. A late shutdown with a dry tank could seriously damage the spacecraft.

One of four liquid hydrogen sensors in the tank that shuttle Discovery will use for the next launch gave a reading that was slightly abnormal during recent electrical testing at NASA's Michoud Assembly Facility in New Orleans. That led to the discovery that some sensors have slightly loose wire attachments because of manufacturing problems and routine handling of the tank.

"This is what we call a Criticality One, life or death, kind of a situation," said Wayne Hale, NASA's shuttle program manager.

So mission managers decided yesterday to swap out all four sensors in Discovery's tank at the Kennedy Space Center. The work means the next window for launch will be July 1 to 19.

Problems with the sensors have dogged the shuttle program in recent months. Before Discovery's launch in July, a sensor gave false readings during a tank test. After the tank was replaced because of an unrelated problem, another sensor failure scrubbed a launch attempt.

Engineers never definitively pinpointed the problem. All four sensors worked properly during Discovery's July 26 countdown and climb to orbit.