International Space Station (15 nations, 1998–present)

The International Space Station, a $150 billion collaboration among 15 nations, has hosted over 3,300 experiments since its first crew arrived in November 2000, achieving over 25 years of continuous habitation. Its orbit at 408 km and 16 daily orbits enable unique studies in cancer research, fluid physics, and human physiology that cannot be replicated on Earth. Unlike shorter missions such as the Space Shuttle’s two-week flights, the ISS provides a stable microgravity platform for long-duration research. The station’s success demonstrates that international cooperation in space can transcend political divisions, setting a benchmark for future lunar and Mars outposts.