via MSWNBC, that faulty fuel sensor on Atlantis has postponed the next launch at least until Jan. 2nd. They will start loading fuel as a test of the system on Tuesday.
"the trouble could be anywhere in the 100 feet (30 meters) 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. A diagnostic tool known as a time-domain reflectometer will be used to track down exactly where a break in the circuitry might be located.
At the same time, engineers will conduct other tests, mostly in laboratories, to try to figure out what is causing the gauges in Atlantis’ tank to malfunction every time they’re exposed to the super-cold liquid hydrogen that fuels the shuttle."
The recalcitrant sensor has been an ongoing issue for the space agency since the Columbia tragedy. While launches have been made in the past with only three of the four sensors warking properly, NASA decided that all four must be in operation for this launch - although there is some consideration to moving back to the old rules if they cannot track down the problem.