Decision Day For Discovery's Upcoming Launch

NASA managers and engineers are meeting today to work through a fog of test data in a bid to see if they can develop a solid flight rationale to launch shuttle Discovery this month despite potential problems with critical main propulsion system valves.

The test data, growing confidence in a new test technique and a one-day slip in an Air Force launch all boost the possibility that NASA will be able to launch before a stand-down for an already planned crew rotation at the International Space Station. And a move up to March 11 is a possibility.

As it stands, Discovery and seven astronauts are tentatively scheduled to blast off from Launch Complex 39A at Kennedy Space Center at 8:54 p.m. EDT March 12 on a mission to deliver a fourth and final set of American solar wings to the international outpost.

NASA must launch Discovery by March 13 to complete its planned 10-day stay at the station and then depart 72 hours before the March 25 launch of the Expedition 19 crew and returning space tourist Charles Simonyi. Otherwise, the shuttle launch would have to be postponed until around April 7.

A United Launch Alliance Atlas V rocket is currently scheduled to blast off from Cape Canaveral Air Force Station with a new-generation U.S. military communications satellite on March 13.

Since it typically takes 48 hours to reset Eastern Range tracking and range safety systems between the launches of different vehicles, the March 13 launch date raises a potential conflict.

But Mother Nature entered the picture earlier this week and the matter appears as if it will resolve itself.

Cold temperatures and high winds forced a delay in the transfer to Launch Complex 41 of the Wideband Global SATCOM spacecraft to be launched aboard the Atlas.

Col. Michael Moran, commander of the Atlas Group at Air Force Space & Missile Systems Center and deputy mission director, said the soonest the launch could take place as a result is March 14.

NASA managers are engineers are wading through extensive test data and analyses that have been done since one of three gaseous hydrogen flow control valves failed during Endeavour's successful launch last November.

About the size and shape of pop-up lawn sprinklers, the valves regulate the flow of gaseous hydrogen into the shuttle's external tank during the nine-minute flight into orbit. The gaseous hydrogen keeps pressures within the tank at proper levels as propellant within it is exhausted by the ship's three main engines.

Too little pressure could cause an engine shutdown in flight. Too much pressure in the tank could force open a separate relief valve that would dump combustible gaseous hydrogen overboard - a potentially explosive fire hazard.

Post-flight inspections on the failed Endeavour valve showed a piece of its lip cracked off. Engineers fear that debris could rupture gaseous hydrogen pressurization lines that run between the shuttle's main engines and the external tank.

Of particular concern is a 90-degree bend in the lines that is about five inches from the engines. High-velocity impact tests have shown that debris could puncture the lines in that area in a worst-case scenario. Some engineers think the area should be reinforced as a result.

NASA also has been running tests designed to determine the effectiveness of inspection techniques the agency uses to detect microscopic cracks in the valves. Engineers believe valves that have small cracks are more susceptible to failure.

The agency traditionally has used electron microscopy and dye penetration tests to detect cracks. But extensive analyses of valves in inventory have shown that small cracks have gone undetected after those tests.

NASA in the past month has been using a non-destructive technique known as an eddy current test to detect cracks. The process uses electromagnetic induction to detect subtle changes in current that are indicative of cracks.

A growing confidence in the effectiveness of eddy current testing could lead to a decision to press ahead with a formal, executive-level flight readiness review on Friday.

NASA on Tuesday installed three flow control valves on Discovery -- valves that have been tested with the new technique and found to be devoid of cracks. Two of the valves have been flown four times; the other has 12 flights.

NASA had planned to install the two four-flight valves along with one that had only five flights. But the five-flight valve was tested with the eddy current technique and showed indications of what might be tiny cracks.

The 12-flight valve is one of three 12-flight valves that had been cherry-picked from inventory and then installed on Discovery in January. The three were picked largely because they each had flown aboard Discovery before without problems. But engineers since have decided that valves with fewer flights are less susceptible to cracking.

The 12-flight valves removed from Discovery each were tested with the new eddy current technique. Two of the three passed the test and one of those was reinstalled with the two four-flight valves.

ABOUT THE IMAGE: Click to enlarge the image of shuttle Challenger moving through the fog on its way to Kennedy Space Center's launch pad 39A prior to its first flight in 1983. You can also click the enlarged image to get a bigger, more detailed view. Challenger was lost in 1986 when the vehicle exploded 73.6 seconds into its tenth flight.