It was the most politically complex space exploration initiative ever: Five government agencies spread across the globe would join forces to build a research station in low orbit. It was a noble notion. To make the International Space Station a reality, though, one-time rivals (particularly the United States and Russia) had to put aside decades of intense political tension—while surmounting enormously complicated, delicate technical achievements.

“There’s no room for politics when you’re working in space,” International Space Station astronaut Michael Barratt told the BBC. “It’s a sacred place. The world may call it diplomacy, but we just call it the space program.”

For the teams tasked with building what would be the largest structure ever sent to space, the variety of stakeholders exacerbated the already-challenging construction specs. “American engineering was using imperial units; the Russians and Europeans used metric—there had to be a convergence and a common set of standards,” David Baker, a former NASA engineer, told the BBC. “The project used a common digital workplace and was one of the first examples where teams from all over the world, speaking different languages, could work on exactly the same thing.”

82 HRS, 22 MIN

Amount of time Russian astronaut Anatoly Solovyev has spent on his 16 spacewalks—both record-setting feats

5 miles

(8KM) Distance the space station travels every second

925­,335 LB

(419,725 KG) The space station’s mass

16

The number of sunrises and sunsets an astronaut on the space station sees each 24-hour period

Parts were built in separate countries, with sections of the station launched into space and then assembled in orbit. It took more than 40 spaceflights to build the station, which has been continuously occupied since 2000. The station flies in low orbit at an average altitude of 248 miles (400 kilometers), hurtling at a speed of roughly 17,500 miles per hour (28,000 kilometers per hour)—fast enough to circle the globe every 90 minutes.

More than 200 astronauts from 18 countries have visited the station, conducting more than 2,500 scientific experiments covering everything from microbiology and physics to astronomy and meteorology. Among the central goals is a better understanding of the effects of low gravity—What does it do to cells and tissue? What does it do to the brain?—which could help unlock a future of human space travel to Mars and beyond.