The first module of the International Space Station was sent into orbit 20 years ago. It was the Russian-made Zarya, a "Functional Cargo Block" — also known as FGB. Zarya came in at 19,000 kilograms (41,000 pounds) and was 12 meters (39 feet) long. It was commissioned and paid for by America and built by a Russian space company. It was the start of two decades of international cooperation.

The International Space Station is home to an international crew of six people, who also work there. It travels at a speed of five miles per second (8kps), orbiting Earth every 90 minutes. Eight solar arrays provide power to the station and make it the second brightest object in the night sky after the moon. You don't need a telescope to see it.

This was the ISS's first long-term crew: American astronaut William Shepherd (center) and his two Russian fellow workers, cosmonauts Yuri Gidzenko (left) and Sergei Krikalev (right). They moved into the ISS on November 2, 2000, and stayed for 136 days.

On average, space station crews, also known as expeditions, stay in space for about five and a half months. Some crew members, however, have broken that record — for example, NASA astronaut Scott Kelly (photo) and Roscosmos cosmonaut, Mikhail Kornienko. They lived and worked in space for a whole year.

This is Canadian astronaut Chris Hadfield strumming his guitar on the ISS at Christmas 2012. Since 2000, crew members and Space Flight Participants (self-financed space tourists) have come from 18 different countries. The most have come from the USA and Russia. Other teams have included people from Japan, the Netherlands, Italy, France, Germany, Brazil and South Africa.

Crew members and supplies arrive at the ISS via transfer vehicles and space freighters. This photo shows space shuttle Atlantis, which operated until 2011, docking onto the space station. These days, astronauts arrive at the ISS in a Soyuz capsule.

There have been more than 210 spacewalks — "EVA" in astronaut terms — at the ISS since 2000. This photo shows astronaut Mike Hopkins on a spacewalk on December 24, 2013.

The ISS has several robotic arms. This one, Canadarm2, is 57.7 feet (17.58 meters) long when fully extended, and has seven motorized joints. It can lift 220,000 pounds (100 tons), which is the weight of a space shuttle orbiter. This photo shows astronaut Stephen K. Robinson anchored to Canadarm2's foot restraint.

Crew members spend about 35 hours per week conducting research. On his first mission, dubbed "Blue Dot," German ESA astronaut Alexander Gerst observed and analyzed changes to the human body that occur in microgravity. Gerst's second mission at the ISS started in June 2018. In October 2018, he became the first German astronaut to command the ISS.

When their time at the ISS is over, astronauts are taken away in a Soyuz capsules. They fall to Earth with a parachute to ease their landing. Welcome home!