Low Earth Orbit (LEO) is a concept defining the region of space closest to Earth, typically encompassing altitudes from approximately 160 kilometers up to 2,000 kilometers above the surface. It is the lowest altitude at which a stable orbit can be formed, as anything lower than about 160 km experiences rapid orbital decay due to atmospheric drag. The concept's practical use began with the launch of Sputnik-1 by the Soviet Union in October 1957, which demonstrated the feasibility of placing a man-made satellite into orbit. LEO solved the problem of requiring immense energy and cost for satellite placement, as it demands the lowest amount of energy for a satellite to achieve orbit compared to higher regions.
A satellite in LEO must travel at an extremely high orbital velocity, around 7.8 kilometers per second (or 17,500 miles per hour), to counteract Earth's gravity and maintain its path. This speed allows a satellite to complete an orbit in about 90 to 128 minutes, meaning it circles the Earth roughly 16 times per day. Because of its proximity, LEO provides the lowest communication latency (signal delay) and is ideal for applications requiring high-resolution Earth observation and imaging. The International Space Station (ISS) and the Hubble Space Telescope both operate within LEO.
LEO is fundamentally connected to other orbital concepts, primarily Medium Earth Orbit (MEO), which ranges from 2,000 km to 35,786 km and is used for navigation systems like GPS, and Geostationary Earth Orbit (GEO), which is exactly 35,786 km above the equator and is used for broadcast services. A major recent change in LEO is the proliferation of mega-constellations like Starlink and OneWeb, which use hundreds or thousands of small satellites to provide global broadband internet. This rapid expansion has significantly increased the concern over space debris and the risk of collisions, a phenomenon known as the Kessler syndrome, making the long-term sustainability of the LEO environment a critical international issue.