You probably don’t remember what you were doing on Nov. 2, 2000, but astronaut Bill Shepherd and cosmonauts Yuri Gidzenko and Sergei Krikalev likely do.
That was the day they climbed aboard the International Space Station (ISS), becoming its very first inhabitants—and beginning a streak for the station that reached 15 straight years of occupancy early Monday eastern time.
Shepherd, Gidzenko and Krikalev—who were aboard for four months—were members of what was known as the Expedition 1 crew. Last July 22, Expedition 45, including American astronaut Kjell Lindgren, cosmonaut Oleg Kononenko and Japanese astronaut Kimiya Yui, took off from the Baikonur Cosmodrome in Kazakhstan to begin their own station stay.
In all, 220 people from 17 countries have lived aboard the ISS since 2000. During those 15 years, the station has made 87,600 revolutions of the Earth—give or take the odd leap day. Oh, and in case anyone’s counting, the crews have eaten approximately 26,500 meals—so far.
The ISS was little more than three pressurized modules, some supplies and a couple of solar wings to help keep it powered on the day the first crew climbed aboard. Today, the station is a flying piece of cosmic infrastructure the size of a football field, containing 15 pressurized modules, which afford the astronauts as much habitable space as a six-bedroom home. It weighs 1 million pounds (454,000 kg), runs on 3.3 million lines of software code and required 115 launches just to carry all of its components up to orbit.
A lot has changed on Earth too in the last 15 years. When the station welcomed its first three visitors, Bill Clinton was rounding out the last few months of his presidency; Christina Aguilera’s “Come on Over Baby (All I Want is You)” topped the singles charts; Meet the Parents reigned at the box office; Miley Cyrus—who, history records, would later learn to twerk—was three weeks away from celebrating her eighth birthday; and the New York Mets had just lost the World Series, falling four games to one to the crosstown New York Yankees. (So some things haven’t changed in 15 years.)
What hasn’t changed in all that time is the purpose of the station: To conduct basic research in biology, botany, materials manufacturing and more, without the so-called “forcing function” of gravity, which disguises and distorts how systems behave in a more pristine state. As human beings look increasingly toward long-term, deep-space missions—especially a two-and-a-half year, round-trip journey to Mars—the station is increasingly important in determining how the human body can withstand such sustained periods of weightlessness.
Astronaut Scott Kelly and cosmonaut Misha Kornienko are currently seven months through a one-year stay in space, volunteering as real-time test subjects for many of those biomed experiments. Scott’s identical twin, Mark, a retired astronaut, is back on Earth, serving as a perfect control subject to whom Scott’s physical changes can be compared over the course of the year.
TIME has been following Scott’s journey since well before he left Earth, and will continue after he returns, in our A Year in Space video series. The latest episode, titled “Welcome Aboard,” will be launched on the same Nov. 2 anniversary that the station celebrates 15 years of occupancy. This installment takes viewers inside the Soyuz spacecraft itself as Kelly and his crewmates flew to orbit, and explores how difficult it is to perform the cosmic sharpshooting needed to guide a ship to a docking with the station—an exercise that requires two machines to find one another in tens of millions of cubic miles of orbital space, with a margin of error measured in millimeters.
Going live at the same time as Episode 5 is TIME.com’s interactive Space Station Tracker, which can show you where the ISS is at any moment, along with its altitude, its speed and when it will next pass over your town. Space travel has always been dangerous, difficult and deadly serious. And sometimes, as the ISS has shown for a decade and a half now, it’s just plain glorious too.
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