NASA managers today decided to stage a second tanking test next weekend or shortly after to troubleshoot problems with the shuttle Discovery's external fuel tank. The shuttle then will be hauled back to the Vehicle Assembly Building where engineers will attach the ship to a different set of boosters and a fresh external tank, officials said late today.
The external fuel tanks I think showed more problems than just ice buildups that caused this last delay. Apparently there were reports that sensors that detect the level of fuel in the external tank were malfunctioning. What's interesting is that this spaceflight now article is suggesting that a new set of boosters will be attached. I can't understand the intent here. The SRB's and the External Fuel Tank as far I understood were completely seperate systems.
During the tanking test last month, two of four hydrogen sensors inside the tank, which are used to control the main engine shutdown sequence when the shuttle reaches space, failed to operate properly. Engineers have not yet pinned down what caused the problem, but all four must be operational for a launch to proceed.
There were some suggestions that the new heater system installed on the external fuel tank may be interfering with these sensors. If that's true when they connect the new tank in a week's time they may see the same problems. In which case it would be back to the drawing board and the shuttle flight would be delayed further.
The launch window is based on an internal NASA requirement to launch at least the first two post-Columbia missions in daylight. But the issue is complicated by a requirement to also ensure the external tank separates half a world away in enough light to allow documentary photography.
This requirement I think was seen as being the easiest solution to the problem of tiles falling off the shuttle. However I still believe NASA could have easily used some sort of magnetic sensors to detect the presence of every tile on the Space Shuttle. I'm not sure if it would be easier or harder than what NASA is doing now, but I bet if the Shuttle were to be redesigned that's exactly the approach NASA engineers would take to solving this problem.