Not a Redundant System (Score 0)

Two of the sensors are used to detect low levels of liquid hydrogen propellent, the other two low levels of liquid oxygen. The sensors are used to make sure that the main shuttle engines shut down properly prior to the sudden loss of fuel. The sensors are also most likely placed at key points, where the liquid oxygen and hydrogen feeds into the TWO main engines. Each engine has to be supplied with each propellent, and the sensors are designed to protect each engine. Two propellents per engine for two engines equals FOUR SENSORS Accessing this area is difficult, and NASA is very unlikely to launch with a faulty sensor. Especially when they had this same sensor anomally appear on a previous fill test, BUT WERE UNABLE TO DUPLICATE THE PROBLEM. NASA swapped parts and continued with the scheduled launch after another fill test FAILED to reproduce this sensor anamoly. After today they will be looking very closely at this. Their launch window ends July 31st. We'll find out today before 5pm EST what they are planning on doing.