NASA has postponed the Discovery STS-119 mission to the International Space Station while it ponders a possibly troublesome hydrogen flow control valve.
The agency explains that the shuttles have "three flow control valves that channel gaseous hydrogen from the main engines to the external fuel tank" - one of which was damaged on Endeavour's STS-126 gig last November.
NASA last Friday decided that "more data and possible testing are required" before a launch, and is additionally looking into "the consequences if a valve piece were to break off and strike part of the shuttle and external fuel tank".
Bill Gerstenmaier, associate administrator for Space Operations at NASA Headquarters in Washington, said: "We need to complete more work to have a better understanding before flying. We were not driven by schedule pressure and did the right thing. When we fly, we want to do so with full confidence."
STS-119 will, when it eventually gets off the ground, deliver the final sets of solar arrays to the ISS to enable it to accommodate a permanent crew of six. NASA elaborates: "The set of solar arrays that the STS-119 crew will be bringing up includes two solar array wings, each of which has two 115-foot-long arrays, for a total wing span of 240 feet, including the equipment that connects the two halves and allows them to twist as they track the sun.
"Altogether, the four sets of arrays can generate 84 to 120 kilowatts of electricity - enough to provide power for more than 40 average homes. Since the three existing arrays can handle the majority of the station's day-to-day operational and life support needs, the newest solar array will double the amount of power available for scientific research."