One of the flow control valves, which are part of the space shuttle’s main propulsion system, suffered damage during the November 2008 flight of Endeavour, when gaseous hydrogen began flowing from one of the shuttle’s engines at higher rate than normal.

 

The problem was that if the mission would launch with a broken valve, it could cause a rupture in the gaseous hydrogen line, which would then result in a loss of pressure to the external hydrogen tank, and in a main engine shutdown.

 

Another concern was that the damaged valve could cause an over pressurization of the hydrogen tank, which would force open a vent line that could expel hydrogen on an oxygen-filled area.

 

On Friday, the Flight Readiness Review team confirmed the mission is ready for takeoff, after assessing all the risks associated with the mission, and completing all necessary procedures.

 

Regarding the valve issue, John Shannon, Space Shuttle Program manager, said in a statement: “This is one of those problems requiring a lot of work. It was a little premature before today. The signs were there that we were safe, but the teams went off and came up with definitive data to prove it.”

 

The Discovery mission will carry three more astronauts to the International Space Station, as part of the expanded crew of six that the station now supports. The mission members will also deliver to the station a final set of solar arrays and the S6 truss segment, to complete the backbone of the station, all needed to support a larger crew on the ISS.