Fuel Tank Sensors Will Be Replaced

ANN REALTIME REPORTING 03.14.06 1610 EST: NASA today announced the launch of the space shuttle Discovery -- the second since the program's return to flight after the 2003 Columbia disaster -- has been delayed until at least July. Shuttle Program Manager Wayne Hale said he told his shuttle prep team today that the delay was brought about by the discovery of faulty sensors in the shuttle's external tank.

"We wish it had worked out differently, but it's of course, first and foremost that we fly safely," Hale said during a briefing from the Johnson Space Center in Houston.

Discovery will now launch no earlier than July 1st.

In his televised briefing, Hale detailed the ongoing saga of external fuel tank problems -- including the delamination of foam from the tank, which caused the Columbia disaster and threatened Discovery during its latest launch last July. Ironically, however, it wasn't the foam issue that forced today's delay of the May launch.

Instead, it was the discovery of faults in the four low-level fuel sensors inside the external tank itself.

The fuel sensors -- known as ECO, or engine cut-off sensors -- are important to the mission, because they monitor propellant levels and are responsible for ensuring the shuttle's main engines shut down at the proper speed needed to reach orbit, and stay on its assigned course.

As Aero-News reported last week, one of those sensors had been reading slightly low -- which could have shut off fuel flow to the engines sooner than needed, potentially compromising the shuttle's ability to reach orbit. There is also the chance an abnormal reading could cause the engines to run at an excessively high rate, when they should actually shut down -- a scenario that arose during the earliest days of shuttle testing.

Almost the exact same type of problem also cropped up during last year's return-to-flight mission on Discovery. After a glitch was detected in one of the fuel tank sensors for that flight, NASA ultimately decided to launch in spite of the risk. All four sensors performed flawlessly for that launch... but NASA doesn't want to take any chances this time around.

Despite the delay, NASA still hopes to launch three shuttle missions before the end of 2006 -- although the timeframe, already compressed, has now been narrowed even further.

"We should still be able to get three missions in this year," Hale said, "but we don't have the details on that yet."

FMI: www.nasa.gov