NASA delays space shuttle launch a fourth time

CAPE CANAVERAL, Florida -- Space shuttle Discovery's launch date remained uncertain after a marathon meeting Friday by senior NASA officials at Kennedy Space Center.

They could not agree to launch the year's first mission next Friday, as tentatively planned, and a mid-March time frame was under consideration.

Throughout the day, managers and engineers discussed ongoing concerns about a critical set of shuttle valves that have delayed the flight several from its original Feb. 12 target date.

The three pop-up valves regulate the flow hydrogen gas from each of the shuttle's main engines to its rust-colored, 15-story external tank.

That allows the tank to maintain proper pressure as liquid hydrogen propellant is burned during the 8.5-minute climb to orbit.

If pressure rises too high or sinks too low, or if a fragment from a broken valve punctures the gas line, the results could be catastrophic for the shuttle's seven astronauts.

The potential problem emerged during Endeavour's launch in November, when a small piece of a valve broke off.

No harm was done, but engineers worried about how likely another failure was and how big a fragment could break off.

Weeks of extensive tests across the country ensued to study the consequences of one or more broken valves, and to better understand the cause of the breakage.

Managers on Friday were deciding whether the risk was low enough to proceed with at least one flight while continuing to study the problem.

Seven astronauts are set to install the space station's final set of huge American solar array wings, completing its power supply.