It's a sad week for space travel: acclaimed NASA administrator George Mueller (shown at right) has died at the age of 97. He was only with the agency for six years, but he's well-known for instituting key oversight changes that helped the Apollo program reach the Moon on time -- he insisted on testing complete launch systems rather than individual parts, for example. Moreover, his legacy extends well beyond that short stint. Mueller advanced initial designs for the Skylab space station, and is widely considered the "father" of the Space Shuttle thanks to his advocacy and early work. He may not be as famous as some astronauts or scientists, but his efforts reverberate throughout NASA's history. He'll be missed.
[Image credit: Keystone/Hulton Archive/Getty Images]