This educational HD video shows how the International Space Station works and operates. In Earth's orbit, NASA Astronaut Sunita (Suni) Williams tours and describes how International Space Station's internal structure is divided into two pressurized modules, the Russian Orbital Segment (ROS) and the United States Orbital Segment (USOS). The ESA (European Space Agency) also uses the International Space Station for research and experiments. The International Space Station maintains an orbit with an altitude of between 330 and 435 km (205 and 270 mi) by means of re-boost maneuvers using the engines of the Zvezda module or other visiting spacecraft. It completes 15.54 orbits around the earth per day. Sunita Lyn "Suni" Williams is an American astronaut of Indian-Slovenian descent and holds records for total spacewalks and spacewalk time by a woman.