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Sensors No. 2 and 3 have experienced intermittent failures, "which is actually good news," said NASA commentator George Diller.
Sensor No. 1 has hard-failed, "which is just what we wanted," he added. "We will be able to collect data during stable-replenish that we were expecting to get."
The intermittent failure of sensor No. 2 is new.
"We haven't seen that before on that sensor," said Diller.
Sensor No. 4 has worked perfectly today, though it malfunctioned in earlier tests.
"Now we've seen all four sensors display some sort of anomalous data," added Diller. "We just don't know what the problem is."
The external tank, once full, will be kept full several hours and emptied of 500,000 gallons of cryogenic fuel about 1 p.m.
While the tank is full, crews will enter the launch pad area to gather data. Both the liquid Oxygen and Hydrogen tanks were on track to be full about 10:15 a.m. However, liquid Oxygen pumps stopped at 10:10 for an unknown reason.
"Sensors No. 1, 2 and 3 will be the primary focus of troubleshooting," said Diller.
"Hopefully, once we get into draining the tank, we'll have some insight into whatever has been occurring," Diller said.
Diagnostic equipment will analyze the the failures, and NASA engineers hope the root cause can be found and fixed before Atlantis' planned Jan. 10 launch attempt.
Engineers have installed instruments similar to devices used by cable television companies to measure signal strength.
Shuttle program manager Wayne Hale will explain the test during a news conference no earlier than 4:30 p.m. EST.
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