text:  NASA says it must now conduct extensive testing to understand the thruster problem before it will allow Wilmore and Williams to return. The space agency plans to spend several weeks testing an identical thruster at a New Mexico facility to gather more data. The astronauts were only supposed to be in orbit for a week. They are now indefinitely delayed. They're not on their own, though. Four other Americans and three Russians are also currently working at the space station. Jeff Brumfield, NPR News.