NASA's Mission Management Team has delayed launch of the shuttle Atlantis on a critical space station assembly mission to at least Jan. 2 to troubleshoot intermittent electrical problems with low-level hydrogen fuel sensors that derailed launch attempts Thursday and again today.

The shuttle's current launch window closes Dec. 13 because of space station power and temperature issues related to the lab's orbit. The window reopens Dec. 30, but NASA managers do not want to conduct a launch campaign during the end-of-year rollover because of countdown software issues.

Given the subtle nature of the problems with the engine cutoff - ECO - sensors at the base of Atlantis' external tank, managers concluded there was not enough time to attempt repairs before the current launch window expires.

Telemtry indicates a possible open circuit somewhere between an electronic unit in the shuttle's engine compartment and the sensors themselves. While the box is accessible at the launch pad, much of the wiring that runs through the belly of the shuttle and into the tank - not to mention the sensors - cannot be easily inspected or replaced.

But as of this writing, no decisions have been made about whether to attempt any repair work at the pad or whether it makes more sense to haul Atlantis back to the Vehicle Assembly Building where the tank can be removed.

In the meantime, flight controllers informed space station commander Peggy Whitson and her crewmates of the launch delay and told her she and Tani may be asked to carry out a spacewalk later this month to inspect a problematic solar array rotary joint on the right side of the lab's main power truss.

If Atlantis had gotten off the pad during the current window, NASA managers planned to add a fourth spacewalk to the shuttle mission to carry out the solar alpha rotary joint - SARJ - inspection.

Because of recently discovered contamination in the massive gear-driven joint, used to rotate outboard arrays to keep them face on to the sun, the starboard SARJ has been locked in place pending additional analysis.

NASA needs to fix the joint and restore it to normal, or near normal, operation before a sophisticated Japanese research module can be launched in April.

Additional coverage for subscribers:
VIDEO: POST-SCRUB INTERVIEW WITH LAUNCH DIRECTOR PLAY
VIDEO: LAUNCH OF ATLANTIS SCRUBBED AGAIN PLAY
VIDEO: HYDROGEN SENSOR NO. 3 FAILS PLAY
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