Click for video report. NASA is continuing to gas up Atlantis after a critical-but-troublesome fuel sensor system passed initial tests deemed key to proceeding with plans to launch the shuttle at 2:45 p.m. EST.
The 15-story tank now is 40 percent full. Four fuel-level sensors that failed back in December now appear to be working properly. Under NASA launch rules, three of the four must be operating in order to commit a shuttle and its crew to flight.
The so-called Engine Cutoff Sensors serve as a key back-up system for shutting down the shuttle's main engines in flight. A sensor failure could lead to a premature engine shutdown, triggering an unprecedented emergency landing attempt. And a failure also could allow the engines to run dry and break apart in flight -- a catastrophic failure mode.
The four sensors were immersed in liquid hydrogen just after 6 a.m. and then a series of tests began about 20 minutes later. NASA Launch Commentator George Diller reported that all four sensors appear to be operating properly.
NASA engineers will continue to monitor sensor system circuits. Another state-of-health check will come at the end of fuel-loading operations -- around 8:20 a.m. -- and then a final test would be conducted when NASA enters a planned T-9 minute hold around 2 p.m. today.
A NASA Fact Sheet on the sensors is here: ECO-sensor fact sheet. .
NASA TV coverage of the tanking operation is being webcast live here in The Flame Trench. Simply click the link below the image above to launch our NASA TV viewer.
A cold front is continuing to drift toward the central Florida area, and it is expected to bring rain, and possibly thunderstorms, to NASA's shuttle launch site around mid-afternoon.
NASA managers are hanging on to hopes that the front will slow or stall, leaving skies over Kennedy Space Center clear enough for launch at 2:45 p.m.
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