NASA will next week fill the fuel tanks of space shuttle Atlantis for a third time, in an attempt to resolve sensor glitches which have led to two aborted launches.

A first scheduled lift-off was last week cancelled due to the failure of two of the four sensors which monitor liquid hydrogen levels in the vessel's fuel tank. A second slated attempt on Sunday to get Atlantis into orbit fell victim to the same problem.

Of the first incident, NASA explained: "On Thursday morning, two of the four engine cutoff, or ECO, sensors inside the liquid hydrogen section of the tank failed a routine prelaunch check. Following the launch postponement, the tank's liquid oxygen and liquid hydrogen were drained.

"While the tank was being emptied, engineers monitored and collected data on the liquid hydrogen sensors that failed. During that process, another sensor gave a false reading, indicating that the tank was 'wet', when it was dry."

NASA's caution is based on the fact that faulty sensors could allow the shuttle's liquid hydrogen tanks to "run dry", potentially triggering a catastrophic explosion.

The remedial plan, according to Reuters, is to "splice jumper cables into about 100 feet of wiring that runs between fuel sensors in the shuttle's tank and the ship's engine compartment". These cables will be hooked up to instruments to monitor the electrical circuits, and hopefully locate the problem.

Programme manager Wayne Hale told reporters: "We think we have a high degree of confidence of pinpointing the location where we're having our problem."

If he's right, NASA has rescheduled Atlantis for a 2 January launch to carry the European Space Agency's Columbus laboratory to the ISS. ®

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