Five chassis. One for Sebastian, one for Mark, one for whoever crashes his, and two test cars back at home. This is how Red Bull makes sure the RB9s won't fall apart.
In the final part of Red Bull Racing's behind the scenes videos, we learn how they measure every tiny detail to make sure it can take what the drivers throw at them on the track. The inspectors use x-rays, ultrasound and lasers to go through every micron of the cars: