Low-level sensors crucial to safe shuttle ascent

On two launches, sensors have shut off engines in flight for safety

http://www.msnbc.msn.com/id/8572372/

By James Oberg, NBC News space analyst

MSNBC // Updated: 1:58 p.m. ET July 14, 2005

When a low-level sensor in Discovery's propellant tank malfunctioned
during Wednesday's countdown, mission commander Eileen Collins must have had
that "déjà vu" feeling. And she would have had no objection to calling off
the launch - because the proper functioning of exactly such a sensor may
have saved her spaceship, even her life, on her previous launch in 1999.