NASA will fill the space shuttle Atlantis's fuel tank next week in hopes of cracking a vexing fuel gauge problem that led to back-to-back launch delays, the agency said Tuesday.
The trouble could be anywhere in the 30 metres of wiring between the four gauges at the bottom of the fuel tank and the shuttle itself, in any of the connectors or even in the sensors themselves, said shuttle program manager Wayne Hale from Kennedy Space Center in Florida.
At the same time, engineers from the U.S. space agency will conduct other tests, mostly in laboratories, to try to figure out what is causing the gauges in Atlantis's tank to malfunction every time they're exposed to the super-cold liquid hydrogen that fuels the shuttle.
Last Thursday and again Sunday, some of the gauges failed as the shuttle's external fuel tank was being loaded. Both times, the countdown was halted and the launch called off.
NASA is aiming for liftoff no earlier than Jan. 2 for Atlantis's mission to deliver the European lab Columbus to the International Space Station, Hale said. He noted that the launch date "could definitely be a little bit later than that."
"I am very concerned about team fatigue," he said during a news conference. "When we talk about no earlier than Jan. 2, part of the discussion is not only how quickly can we troubleshoot and fix this problem, but what is prudent to allow our folks to have a few days with their families, and rest and recuperate."
Fuelling test next Tuesday
The four so-called engine cutoff sensors are part of a backup safety system that prevents the shuttle's main engines from running on an empty fuel tank, a potentially catastrophic situation. They have malfunctioned off and on over the past two years, ever since shuttle flights resumed following the Columbia tragedy.
Hale was reluctant to discuss possible options if engineers cannot discover a cause for the problem, or whether the launch team might stick to the rule put in place for Sunday's launch attempt, requiring all four gauges to work. Before then, only three gauges had to function before a liftoff.
For next Tuesday's fuelling test, NASA will cut into the system's wiring and install jumper cables leading to the test equipment out on the launch pad.
The test equipment — a device that sends out timed pulses — is commonly used by telephone and cable companies to track open circuits or other problems in their lines. NASA has used it before, but never as part of a shuttle fuelling test, Hale said.
The astronauts at the space station, meanwhile, are expected to conduct a spacewalk that day to shed more light on a flawed solar rotary joint. Two of Atlantis's crew were supposed to go out and fully inspect the joint; officials want to move up the work now that the shuttle flight is off until January.
The joint controls the movement of a set of solar wings and, until it is fixed, cannot be used in the automatic mode to turn the wings toward the sun. It's filled with steel grit because of grinding parts and may require several spacewalks next year to fix it.
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