The International Space Station (ISS) ( Fig. 1 ) is a laboratory the size of a mansion, orbiting Earth at an altitude of 250 miles (400 km). It was assembled in space using modules sent into orbit in separate launches, because no rocket is powerful enough to launch such a large structure in one piece. The station features habitable areas with breathable air for astronauts, as well as airless sections housing machinery operated by robotic arms, which are accessible only via sp