About Infoplease, Part of FEN Learning. Footer last column. RSS; Contact; Advertise with Infoplease; Terms of Use* Privacy** Site Map; Partnerships; Disclaimer *
Most of the time, the International Space Station (ISS) is orbiting the Earth at an altitude of approximately 220 miles (354 km), which places it in low Earth orbit (LEO). This distance can change, however, and has varied from 205 miles (330 km) to a planned maximum of 248 miles (400 km).
So in the same 6 minutes it would take to free fall 640 km (400 miles), the ISS moves 8000 km (5000 miles) horizontally. Those two motions occur simultaneously, and the result is a smooth circular orbit. At higher altitudes gravity is weaker, and less horizontal speed is required to maintain orbit.