of the most prominent symbols of american military power. david martin, cbs news, the pentagon. >> sargent: leading and inspiring so many. congratulations, commander. straight ahead on the "cbs weekend news," caught on camera: parts of a massive cliff collapses on two boats in brazil. the arctic tundra is melting fast as rising temperatures transform the once-reliably frozen landscape. and later, nasa completes the unwrapping of its next great telescope.