Shuttle undergoes second tank test

CAPE CANAVERAL, Fla. – NASA conducted a second fueling test Friday on space shuttle Discovery to figure out why sensors and valves did not work properly during a previous run-through.

The test was in preparation for the launch of Discovery in July on the first shuttle flight since the Columbia disaster nearly 2 1/2 years ago. Discovery’s external tank was filled with 500,000 gallons of liquid hydrogen and oxygen, and a countdown was simulated.

Everything went without a hitch this time, but engineers were still unsure why the liquid hydrogen sensors gave intermittent readings and why a pressurization relief valve opened and closed more times than normal during last month’s test. The sensors act like fuel gauges that notify the shuttle’s main engines to shut down when propellants reach a certain level. The valve opens and closes to ensure the liquid hydrogen stays at the correct temperature.

NASA Administrator Michael Griffin, who took NASA’s top job last month and visited Kennedy Space Center on Friday, said he did not believe there were any major hurdles to returning the shuttle to flight.

“I’ve seen just the normal bumps in the road that you have to get past, especially when you haven’t flown in two years and several months,” he said.

The second test came days before Discovery will be rolled back into the hangar to replace its tank with a safer, updated model. Also, a heater will be installed on the new tank to prevent the buildup of ice once the super-cold fuel is pumped in.

Engineering tests found that ice falling off the tank could be as dangerous as the chunk of foam insulation that doomed Columbia.

The danger of ice and the sensor-and-valve problems prompted NASA to postpone Discovery’s launch from late May to mid-July.