Overview:Saving Hubble - Two teams of spacewalkers take on the risky mission of reviving the ailing Space Telescope. First Primates - Our most distant primate ancestors, which lived about 55 million years ago, were tree-dwellers the size of mice. Profile: Alfredo Quiñones-Hinojosa - He jumped the fence from Mexico to work as a farmhand and ended up a leading brain surgeon. Killer Microbe - A relatively benign bug becomes a highly lethal pathogen, known to U.S. soldiers as Iraqibacter.