The International Space Station (ISS) is a $100 billion (£80 billion) science and engineering laboratory that orbits 250 miles (400 km) above Earth.
It has been permanently staffed by rotating crews of astronauts and cosmonauts since November 2000.
The space station is currently home to two Russians, three Americans and one Japanese.
Research conducted aboard the ISS often requires one or more of the unusual conditions present in low Earth orbit, such as low-gravity or oxygen.
The International Space Station (file photo) is a $100 billion (£80 billion) science and engineering laboratory that orbits 250 miles (400 km) above Earth
ISS studies have investigated human research, space medicine, life sciences, physical sciences, astronomy and meteorology.
The US space agency, Nasa, spends about $3 billion (£2.4 billion) a year on the space station program, a level of funding that is endorsed by the Trump administration and Congress.
A U.S. House of Representatives committee that oversees Nasa has begun looking at whether to extend the program beyond 2024.
Alternatively the money could be used to speed up planned human space initiatives to the moon and Mars.