Fifteen years ago today, the Russian Space Agency launched the first component of the International Space Station into orbit. The piece was a pressurized module called Zarya, which means sunrise. Two weeks later, the U.S. shipped their own ISS component, Unity, on the shuttle Endeavour. Piece by piece, the station was assembled with parts from various countries. Humans didn't arrive until October 31, 2000, when one NASA astronaut and two Russian cosmonauts traveled to their new orbiting home. There have been 37 expeditions since then, and ISS inhabitants have logged nearly 1,100 hours in spacewalks.