For a spacecraft such as the Space Shuttle, the Mir, a Soyuz Capsule or the International Space Station to maintain an orbit around the Earth at relatively low altitudes (anywhere from approximately 175 to 575 kilometers [~95 to 310 nautical miles]) it must travel at approximately 32,500 km/hour (~17,500 nm/hr). At these altitudes and at this velocity it takes about 90 minutes to circle the Earth once, so every 45 minutes the astronauts and cosmonauts onboard see a sunrise and a sunset, a total of 16 each every 24 hours.
