Today marks the 20th anniversary of the first long-term mission to the International Space Station, known as Expedition 1. Ever since then, there have always been a handful of humans living and working in orbit on the ISS — a continuous presence of people in space.

Prior to that mission, most of NASA’s human spaceflight program revolved around launching relatively quick, weeks-long trips to orbit on the agency’s Space Shuttle. But in the mid-1990s, NASA began sending its astronauts to space for much longer trips to live on Russia’s old Mir space station. Once the US, Russia, and their international partners started piecing together the International Space Station, NASA started sending some of its astronauts to stay for months at a time beginning in 2000 — and there have been people on board ever since.

As part of Expedition 1, a crew of three astronauts launched to the space station on October 31st, 2000, on board a Russian Soyuz rocket. The flight carried two Russian cosmonauts — Yuri Gidzenko and Sergei Krikalev — and NASA astronaut Bill Shepherd, who docked with the ISS two days later on November 2nd. The trio would stay for four and a half months until March, leaving after a new crew of three came to the station aboard Space Shuttle Discovery for the start of their more than five-month stay. Their mission was aptly named Expedition 2.

NASA has been celebrating this big moment with press events from astronauts currently on board the ISS — part of Expedition 64 — as well as a virtual round table with the original members of Expedition 1. Today, the space agency will air a series of specials about the construction of the International Space Station, highlighting the research that’s been done on board the lab over the last 20 years. Tune in at 1PM ET to get a history lesson about how we’ve kept people 250 miles above Earth continuously since 2000.