Extreme conditions surround the International Space Station’s scientific work, to say the least. It takes a rocketship to get there. Construction required more than 1,000 hours of people using spacesuits. Astronauts must balance their scientific work with the need to repair stuff when it breaks (like an ammonia coolant leak this past spring.)

But amid these conditions, despite what could have been show-stoppers to construction such as the Columbia shuttle tragedy of 2003, and in the face of changing political priorities and funding from the many nations building the station, there the ISS orbits. Fully built, although more is being added every year. The first module (Zarya) launched into space 15 years ago tomorrow. Humans have been on board continuously since November 2000, an incredible 13 years.

The bulk of construction wrapped up in 2011, but the station is still growing and changing and producing science for the researchers sending experiments up there. Below are some of the milestones of construction in the past couple of decades. Did we miss something important? Let us know in the comments.