CAPE CANAVERAL, Fla., March 15 (UPI) -- NASA scientists discussed options Monday following a problem that occurred during the weekend when space shuttle Discovery's aft fuel tanks were being vented.

"The Right Reaction Control System … fuel helium tank pressure unexpectedly decreased in unison with the … fuel propellant tank when the fuel tank was vented," NASA said in a statement. "This indicates that at least one of the two parallel helium isolation valves is leaking or is remaining in the open position when it is expected to be closed."


The two helium system regulators, a primary and a secondary, will be tested to verify they are functioning correctly. Scientists said both regulators are "downstream" of the isolation valves, and help to maintain helium pressure to the fuel tank. Knowing whether the regulators are operating correctly is a key factor for managers who must decide whether to proceed with launch preparations. The test is expected to occur late this week.

NASA said managers now expect to move Discovery's STS-131's payload to Launch Pad 39A starting at 12:01 a.m. EDT Friday.

Officials said the launch -- the 33rd shuttle mission to the International Space Station -- is still set for April 5 at 6:21 a.m. EDT, with a few days of contingency left in the schedule to make that liftoff date.