International Space Station
1998-present
The largest structure humans have ever built. Continuously crewed since November 2000, assembled in orbit from 40+ pieces by Shuttle and Russian rockets.
Specs
~420 t; 109 m long; ~420 km orbit; 7.66 km/s (27,600 km/h); one lap of Earth every 92.9 min; 15 partner countries.
Why it matters
It laps the Earth 16 times a day - a bright moving dot visible to the naked eye. Its orbit slowly decays from drag in the upper atmosphere and needs re-boosting: real physics, on a schedule, every year.