CAPE CANAVERAL ? Space shuttle Discovery was wheeled out of the Vehicle Assembly Building (VAB) on one of the massive crawler-transporters toward launch complex 39A ? and its final mission ? STS-133. This marks the second trip out to the launch pad for Discovery; the orbiter had to be taken back to the VAB for scans and repairs. Discovery was first wheeled out to LC 39A on Sept. 20, 2010. The Nov. 5 launch attempt was aborted due to a leaky Ground Umbilical Carrier Plate (GUCP). When engineers were checking out this problem, they discovered another, a section of popped up foam on the shuttle?s external tank. Foam has been a concern ever since a briefcase-sized piece of foam led to the loss of the shuttle Columbia in 2003. Further inspection showed that the cracks extended all the way down to the aluminum skin of the external tank. As engineers looked further more and more of these cracks were discovered around what is known as the ?intertank? region. Engineers did what repairs that they could out at the launch pad. Then the large, orange tank was filled with the super-cooled fuel that powers the shuttle into orbit. When tanking occurs, the tank can shrink by as much as half-an-inch. ; With the realization that this shrinkage could severely impact the cracks, 89 sensors were placed around this area to monitor the effect of fueling the external tank. To properly check any potential impact the tanking had, scans would need to be conducted and that meant a trip back to the VAB. So Discovery was rolled back to the VAB for X-Rays and other scans.