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!

On June 16 1963, skilled Russian parachutist Valentina Tereshkova became the first woman in space, finishing 48 orbits of the earth in her space capsule Vostok 6. It would be almost 20 years until another woman left Earth's atmosphere — Svetlana Savitskaya in 1982 on the Soyuz T-7 mission. A crater on the Moon is named after Tereshkova who now sits as a member of Russia's parliament, the Duma.

NASA selected Shannon Lucid, Margaret Seddon, Kathryn Sullivan, Judith Resnik, Anna Fisher, and Sally Ride as their first female astronaut candidates in January 1978. A number of American women passed the astronaut selection process in the early 1960s but were not eligible to go into space because they had not completed military jet test pilot training — a career that was unavailable to women.

The first American woman in space was due to go on a third mission before the infamous Challenger disaster cut short her training in 1986. But Sally Ride made history by using robotic arms to retrieve satellites in her first two missions and later devoting her life to helping girls excel in math, science and engineering, according to President Barack Obama. She died from pancreatic cancer in 2012.

Inspired by Sally Ride, Mae Jemison — physician, teacher, Peace Corps volunteer and founder of two technology companies — became the first African-American woman in space when she embarked with the Endeavor in September 1992 to conduct bone cell experiments. As chief of the 100 Year Starship program she hopes to make human flight beyond the solar system possible this century.

Chiaki Mukai (center) trained as a doctor in Japan and went on to become the first Japanese woman to leave the earth, conducting multiple medical experiments in microgravity environments allowing for the study of aging in space. Her two voyages in 1994 and 1998 also allowed her to support the deployment of the Hubble Space Telescope.

Kalpana means "creativity" or "imagination" in Sanskrit. After becoming the first Indian-born woman to go to space, Kalpana Chawla's first mission was to deploy satellites to study the surface of the Sun in 1997. But after her second mission was delayed three years before taking off in 2003, Chawla's Columbia shuttle broke up on re-entry into the Earth's atmosphere, killing the entire crew.

Becoming a multi-millionaire entrepreneur by the age of 32 might be enough for most people, but in September 2006 Anousheh Ansari also became not only the first Iranian-born astronaut in space but also the first ever female private space explorer. After arriving at the International Space Station, she saw earth: "So peaceful, so full of life."

As the first female commander of the International Space Station, Peggy Whitson also holds another slightly daunting record — almost 666 days in space, the longest length for any woman. After numerous spacewalks, Whitson returned to Earth last in 2017 after 289 days on the multi-national mission, also making her the oldest woman to go to space.