The heaviest satellite ever built is the International Space Station (ISS). As of 2021, it has a total mass of about 925,000 pounds (419,000 kg).
The ISS is a collaboration between NASA, the Russian Space Agency, the European Space Agency, and other international partners. The ISS is primarily used for scientific research in fields such as biology, physics, and meteorology.
It is also used as a testing ground for new technologies and as a platform for observing the Earth. The ISS orbits the Earth at an altitude of about 250 miles (400 km) and is visible from the ground during certain times of the night. It has been continuously occupied since November 2, 2000 and is expected to remain in operation until at least 2030.