When last we tuned in, Endeavour was getting set to carry seven astronauts and the final hardware for Kibo, Japan's laboratory module, to the space station. But as technicians filled the shuttle's external fuel tank, a leak appeared in the fixture that sends excess hydrogen away from the launch pad to be burned at the end of a flare stack.
Hydrogen gas poses a significant threat of explosion.
The leak appeared during fuel-up June 12, and it failed to clear up -- as it had several times in the past -- when ground controllers opened and shut the fixture's valve several times. Mission managers nixed the launch and tried to replace what they thought were the balky components. They used the same approach to repairing the fixture that solved a similar problem with Discovery in March.
By June 16, technicians had repaired (or so they thought) the fixture and NASA began filling the hydrogen tank again in preparation for a June 17 launch. But the leak appeared again and wouldn't go away.
Up to now, NASA pressure-tested the fixtures before fueling, and the fixtures passed the test. But those tests occurred at room temperature, not at the chilly temperatures the fixtures face during fueling. Mission managers didn't require tests that involved actually filling the tank with liquid hydrogen.
This time they did. And the leak failed to reappear.
The problem? A slight misalignment between the portion of the fixture on the side of the external fuel tank and the portion at the end of the umbilical hose that connects to the tank.
Engineers will continue to look at the results just to be sure that they haven't missed anything, according to launch director Peter Nickolenko. But based on today's results, "our next step is to move forward toward a launch on the 11th of July," he said during a post-test briefing.