July 26 called possible for shuttle launch

Fuel-sensor problem still baffles engineers


CAPE CANAVERAL, Fla. - Space shuttle Discovery could launch as early as July 26 despite a fuel sensor problem that continues to perplex NASA engineers.

Technicians have replaced wiring, checked systems and swapped out hardware in an effort to pinpoint the glitch that on Wednesday scrubbed the first shuttle launch attempt since 2003. So far, they haven't found or reproduced the failure.

If two more days of troubleshooting aren't successful, mission managers are considering a July 26 test that would fill the shuttle's external fuel tank with its super-cold propellants. That test could be part of a countdown for launch if engineers make progress this week.

Another scenario is a launch attempt the next day if the tanking test goes well and the failure doesn't reappear. NASA managers are trying to keep all of their options open and get Discovery off the ground before the current launch window ends July 31.

The glitch involves a backup safety system.

Usually, the shuttle's flight computers turn off the three main engines when the ship has picked up enough speed to reach the right orbit. But the cut-off sensor system shuts down the engines first if the fuel supply gets too low.

There are four cut-off sensors inside the bottom of the external fuel tank's liquid hydrogen reservoir. In addition to the one that failed during a test in Wednesday's countdown, two of the same type of sensor also malfunctioned in a preflight test of a different fuel tank in April.

The Orlando Sentinel is a Tribune Publishing newspaper.

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