The Mars rocket, fully fuelled and loaded, is being transported to its launch site on the far side of the Allington Bridge. The two astronauts are also inside, already strapped into their launch seats. Alas, despite being within the tolerances of the bridge, the sheer concentrated mass of the rocket causes a catastrophic failure, and the rocket plunges into the water below. While substantially undamaged by the fall, the automatic countdown clock is activated. In thirty minutes, the rockets will fire - and the astronauts will be killed!