NASA plans tanking test Tuesday

Atlantis waits at the pad for a launch no earlier than Jan. 2.

NASA plans a tanking test next week to try to figure out why fuel sensors in the bottom of shuttle Atlantis' external tank are not working properly.

Under the plan, crews at the Kennedy Space Center would fuel the shuttle Tuesday, with some additional instruments, to try to repeat a fuel sensor malfunction that forced scrubs of two space shuttle launch attempts last week.

"If the erroneous conditions repeat, which is what we think will happen, we can capture the location," said shuttle program manager Wayne Hale.

The instruments are similar to those used by television cable companies when they test their lines, Hale said. Instruments will be spliced into five wires that are about 100 feet long and will be reached through the orbiter's aft.

Hale said Atlantis will launch no earlier than Jan. 2, but the agency must fix the sensor problem before setting a firm date. NASA managers and engineers worked out the plan in meetings this morning.

Hale said he is working to give the team some time off Christmas Eve, Christmas Day and perhaps some additional time off for holiday rest. Decisions about time off could come after the tanking test.

Launch attempts were scrubbed Dec. 6 and 9, due to faulty readings from the sensors that shut down the shuttle's main engines if fuel runs low. The sensors have never been used in flight.

The sensor problem has resurfaced after two perfect launches. If the cause of the sporadic malfunctions can't be found, NASA might formulate a launch criteria that allows a launch when one or more of the redundant sensors isn't working.

"If we come to a place where we're less than confident of our fix, we would re-address the criteria," said Hale.

While a short-term team proposed the tanking test, a long-term team will look at broader solutions.

NASA engineers have speculated that the sensors work and the problem is caused by connectors that fail when cooled by liquid hydrogen. However, Hale said the entire system would be tested to avoid missing any possible cause.

Atlantis is scheduled to ferry a European laboratory module to the space station and tentatively perform a fourth spacewalk to inspect a damaged solar array rotary joint.

However, spacewalkers at the ISS have been tasked to inspect the solar joint next week.