Hoping To Avoid Trip Back To VAB

Technicians and engineers in NASA's space shuttle program plan to test the engine cutoff (ECO) sensor system onboard space shuttle Atlantis by pumping super-cold liquid hydrogen into the external fuel tank. The test is tentatively planned for December 18, and will be conducted on the launch pad at Kennedy Space Center where Atlantis remains poised for launch.

As ANN reported, NASA was forced to postpone last Thursday's scheduled launch of Atlantis, due to the problematic sensors located within the shuttle's external fuel tank. After a second launch attempt Sunday was scrubbed, NASA rescheduled the launch for no earlier than January 2, 2008.

Space Shuttle Program Manager Wayne Hale said additional instruments will be used during the test to pinpoint the problem that led to false readings during two previous countdown attempts for Atlantis.

The companies that built the pieces of the space shuttle are conducting tests at other facilities to help determine a cause, Hale said.

"This is part of broad-ranging effort," Hale said.

NASA hopes the on-pad test will pinpoint the cause of the recurring malfunction of the four ECO sensors within the tank, and determine a fix is possible without sending Atlantis back to the Vehicle Assembly Building for a more thorough teardown. Such a move would likely delay launch for months... throwing NASA's tight shuttle launch schedule into total disarray.

"We have a high degree of confidence of pinpointing the location of where we are having problems," Hale told The Houston Chronicle. "Once we know the location — and there is about 100 feet of wiring with several connectors and sensors at the end -- we will be able to concentrate on our go-forward efforts, presumably put together a fix, and go fly."

The ECO sensors detect when levels of hydrogen within the external tank run low, and send a signal to shut off the orbiter's three main engines before fuel runs out. Continuing to operate the engines without fuel would lead to a catastrophic failure; likewise, cutting off the flow of fuel too soon would lead to a launch abort.

Two sensors malfunctioned during last Thursday's countdown; NASA's launch standards require three of the four sensors to be operational at time of launch. A third sensor mysteriously failed as NASA began loading hydrogen into the tank Sunday morning.

FMI: www.nasa.gov