Final answer:
The ISS orbits Earth in the thermosphere layer of the atmosphere, at approximately 400 kilometers above the surface, where the atmosphere is thin and contains the ionosphere.
Step-by-step explanation:
The Layer of the Atmosphere Where the ISS Orbits
The International Space Station (ISS) orbits Earth in the thermosphere. This layer of the atmosphere starts just above the mesosphere, extending from about 85 kilometers (53 miles) to 600 kilometers (372 miles) above the Earth's surface. The ISS orbits at an approximate altitude of 400 kilometers (around 250 miles), which places it right within the lower part of the thermosphere. Due to the thinness of the atmosphere at this height, there is minimal aerodynamic drag, allowing satellites and the ISS to orbit efficiently. The thermosphere is also characterized by the presence of the ionosphere, a sub-region filled with ionized particles, which enables critical satellite functions including communication and GPS.