NASA Presses Ahead With Key Valve Tests

NASA is performing tests around the country this week to determine whether suspect main propulsion system valves might endanger shuttle Discovery and seven astronauts during launch of an upcoming International Space Station assembly mission.

Due back by Friday, the results will factor into a decision on whether to press ahead toward a tentative launch date of Feb. 22, stand down to conduct still more testing, or redesign the valve.

A valve redesign would delay the Discovery flight for months, triggering a serious ripple effect in the schedule to launch nine final missions before shuttle fleet retirement in 2010.

Senior shuttle program managers will tag-up with engineers today for a status report. Testing is being carried out at Johnson Space Center in Houston, Stennis Space Center in Bay St. Louis, Miss., Marshall Space Flight Center in Hunstville, Ala., Glenn Research Center in Cleveland, Ohio, and the White Sands Test Facility in New Mexico.

NASA engineers want to determine whether a crack in a gaseous hydrogen flow control valve could liberate debris that would puncture two-inch lines that run between the shuttle's three main engines and the liquid hydrogen tank within its 15-story external tank.

The tests are geared toward establishing how large a piece of debris might be created and how much, if any, damage the debris might do to the tubing.

NASA engineers have been working on the issue since one of three gaseous hydrogen flow control valves in Endeavour's main propulsion system failed to operate as intended during its launch last November.

NASA had planned to launch Discovery on Thursday but delayed the flight because engineers were uncertain whether a crack in one of the valves might create deadly debris.

Similar to small pop-up lawn sprinklers, the gaseous hydrogen flow control valves are key to keeping pressure within the shuttle's external tank at proper levels during an 8 1/2-minute climb into orbit.

More than 500,000 gallons of liquid hydrogen and liquid oxygen are fed into the shuttle's three main engines in flight. The engines consume propellant at a rate that would drain a backyard swimming pool within 25 seconds.

Proper pressure is required to make certain the giant tank doesn't rupture. It's also key to ensuring a steady flow of propellant into the main engines as the tank is emptied.

Sensors detected higher-than-normal pressures in the liquid hydrogen reservoir inside Endeavour's tank last November. The faulty valve opened without computer commands to do so. Two other gaseous hydrogen valves compensated and Endeavour zoomed into orbit without consequence.

Post-flight inspections showed the failed valve had cracked. Engineers are concerned that sharp debris could cut into gaseous hydrogen tubing, causing a pressure drop -- and a potential engine shutdown -- in flight.

Shuttle program managers aim to meet Friday to review test data. The status report today will show whether engineers will be able to present solid flight rationale to senior managers on Friday. If not, a tentatively scheduled flight readiness review on Feb. 18 and launch on Feb. 22 might be pushed back.

Discovery will haul up a 31,000-pound girder that will cap the starboard end of the station's central truss. The segment is equipped with a fourth and final set of massive American solar wings.

The added electrical power is a key factor in plans to expand the size of resident station crews from three to six in May.

ABOUT THE IMAGES: Click to enlarge the latest still image from live video feeds in the Launch Complex 39 area at NASA's Kennedy Space Center.