Decision day for Discovery

NASA shuttle managers likely will decide today whether to replace critical fuel-depletion sensors on shuttle Discovery's external tank, a move that almost certainly would prompt a launch delay until July.

Senior NASA managers will be discussing the matter at a meeting scheduled to begin at 1 p.m. EST.

One of the tank's four liquid hydrogen Engine Cut-Off (ECO) sensors produced unexpected readings during a key electrical test before the 15-story tank was shipped to Kennedy Space Center late last month.

The sensors provide a back-up means of making certain the shuttle's three liquid-fueled main engines shut down properly after an ascent into orbit.

A sensor failure could prompt a premature engine shudown, which could lead to a risky and unprecedented emergency landing attempt. A malfunction also could allow engines to run dry, potentially triggering an inflight catastrophe.

NASA has been planning to launch Discovery on the agency's second post-Columbia test flight around May 10. A launch window based primarily on daylight launch restrictions closes on May 22.

It is highly unlikely NASA could swap out the sensors -- which are located on the inside of the tank -- in time to launch during the window. Officials previously have said it could take three to four weeks to do the work.

NASA's next opportunity would come during a window that extends from July 1 to July 19.