Fuel Sensors Force NASA to Delay Launch

By Traci Watson

With less than a week of launch window left, NASA decided to delay the next attempted liftoff of shuttle Atlantis to no earlier than Saturday, after a recurrent fuel-sensor problem scrubbed Thursday’s launch.

If Atlantis doesn’t blast off before Dec. 14, it will have to wait until early 2008. NASA officials are eager for Atlantis to lift off this year because the shuttle’s cargo, a European laboratory, is five years late getting to space.

NASA might set aside its launch requirement that three of the four fuel sensors be functional if it finds that such a move wouldn’t drastically raise the safety risk, launch integration manager LeRoy Cain said.

Shortly after Thursday’s launch was canceled, NASA managers said they would try getting Atlantis off the ground today. Later, they opted to give engineers another day of troubleshooting. There is a 40% chance that Saturday’s weather will force another delay.

The sensors that forced Thursday’s cancellation have delayed launches four times in the past two years, leading NASA chief Michael Griffin to refer to them jokingly as “launch prevention devices.”

Four sensors form a system to monitor the amount of hydrogen fuel in the shuttle’s fuel tank. During the loading of the shuttle’s fuel Thursday, two of the four sensors gave erroneous readings in a routine test. Sensor malfunctions could have grave results:

*If the sensors signal that the tank is empty when it still contains fuel, the shuttle’s engines would shut down and the spacecraft would not reach orbit.

*If the sensors indicate that the tank still has fuel in it when it is actually empty, the engines would keep running, potentially tearing the shuttle apart.

Cain said the problem seems to be in the circuitry connecting the sensors to the shuttle’s main computers. He said the astronauts may be able to do manual maneuvers that would make up for sensor malfunctions. If so, Atlantis may be able to launch without a fix. (c) Copyright 2005 USA TODAY, a division of Gannett Co. Inc.