12/17/2007 - 9:28 AM - UPDATE: In order to give their staff some time off over the holidays, NASA has pushed the shuttle's launch date back again, this time to January 10. If they dalay much longer, the launch of Atlantis could impact the timeline for 2008's remaining shuttle launches. NASA has a pretty limited lifespan for these shuttles, which are supposed to be retired by 2010, so any delay in launching missions this year could have serious repercussions.
12/10/2007 - 8:11 AM - UPDATE: Still unable to find and correct the fuel sensor glitch, NASA has decided to postpone the launch until January 2, 2008. Doing so will hopefully give their people time to figure out why the sensors are failing (or replace them with a different set that will hopefully work better).
12/08/2007 10:26 AM - UPDATE: NASA has added a further delay, but odds are looking pretty good for a launch tomorrow. These sensors are a four-piece backup system, and when they fueled the shuttle on Thursday only two of the four registered. NASA's rules call for at least three to be functioning in order to launch, but they may relax that rule. They are also planning to shorten their launch window from the normal five minutes to just one minute to conserve a little extra fuel. The reason is that the sensors in question are designed to shut off the engines after fuel gets pretty low, and this way if they fail to shut off there will be a little bit more fuel left at the end of the burn.
12/07/2007 8:09 AM - UPDATE: It's not going to be today, either. NASA is going to spend a little time trying to figure out how to fix the wiring to the sensors. If they can't come up with a solution quickly, they may just launch tomorrow, anyway. These sensors are redundant systems, so not having them won't impact the launch unless the primary systems fail.
So the weather was perfect, but the shuttle wasn't. Two of four low-level fuel sensors on the Atlantis' external fuel tank malfunctioned, prompting a delay of at least 24 hours. Hopefully they'll get things fixed and launch the shuttle tomorrow.