In the clean room at NASA Goddard Space Flight Center in Greenbelt Md., the Global Precipitation Measurement (GPM) mission's Core satellite is steadily taking shape. Set to measure rainfall worldwide after launch in 2014, GPM's two solar panels are the latest components currently undergoing rigorous testing before being integrated with the spacecraft, a process that began seven months ago when the main structural elements went on an unusual ride. GPM moves from the clean room to the test chamber on a dolly without wheels. Compressed air is pumped out under airpads that float the Spacecraft on...