Ongoing concerns held by NASA scientists about the external fuel tank trigger a second test.
An initial tanking test done on April 14 showed problems with a couple of hydrogen sensors and a pressure relief valve. A subsequent test showed the sensors working properly, but the pressure relief valve cycled 13 times, which was more than expected.
In the initial test, the valve also cycled 13 times, indicating the tank repressurizing each time. NASA scientists expect to see this happen 8 or 9 times; greater than 13 times could indicate a fuel leak.
A diffuser in the tank may be the problem, and a different one that has been flight tested will be installed as a replacement.
Also, scientists want to check the wheels of the massive mover that carries the shuttle to the launch pad from the Vehicle Administration Building, to ensure no cracks are present.
NASA could conduct a third tanking test, but that might push Discovery out of its July launch window and delay the mission a third time.
One solution implemented by NASA engineers intends to minimize the risk of ice forming on one part of the tank, where it could potentially fall off on launch and hit the shuttle.
A heater has been placed on a joint on a line that carries supercooled liquid oxygen to the engines from the tank. This project appears to be functionally successful.
“We have tested it, and the heaters will be fully certified,” Sandy Coleman, external tank project manager, said. “The bellows heater will eliminate the ice in the area completely.”
David Utter is a staff writer for Murdok covering technology and business. Email him here.
