On Earth, positrons are destroyed the moment they touch ordinary matter, so the only way to pick up the dark-matter signal, Ting says, is to search for it in the vacuum of space. Not surprisingly, the idea of launching a giant particle detector above the atmosphere generated a lot of skepticism at first. “Nobody thought this could be done in space,” he says. Ting fought for 17 years, through a space shuttle catastrophe, numerous funding challenges, and several daunting technical setbacks, to make it happen. Finally, in 2011, astronauts installed Ting’s 18,500-pound, $2-billion Alpha Magnetic Spectrometer (AMS) on the main truss of the International Space Station.