Overview

Low Earth orbit, commonly abbreviated LEO, refers to the band of Earth-centered orbits that begin just above the atmosphere and extend to a few thousand kilometres altitude. Different sources set the upper limit at different heights, but a widely used boundary is shown in the definition commonly applied by engineers and astronomers. In practical terms LEO includes satellites from a few hundred kilometres up to about 2,000 kilometres above the surface; see also general altitude discussions at altitude references.

Characteristics and orbital mechanics

Objects in LEO travel at high speeds to balance Earth's gravity: typical orbital velocities are several kilometres per second and orbital periods range from roughly 90 minutes at very low altitudes to a few hours near the top of the LEO band. Orbital shape and behaviour depend on parameters such as eccentricity and orbital period. Atmospheric drag acts on low-altitude satellites and causes gradual orbital decay, so many operational spacecraft require occasional boosts to maintain altitude.

Uses and typical examples

LEO is favored when proximity to Earth is important or when shorter communication delays are desired. Common uses include:

  • Earth observation and remote sensing: weather monitoring, land and resource imaging, and environmental surveillance.
  • Communications constellations: networks of small satellites providing broadband services, which exploit the lower latency of LEO compared with higher orbits.
  • Scientific instruments and space telescopes that need to be above the atmosphere but do not require extremely high altitudes; many are placed in LEO to reduce launch costs and simplify operations — see space telescopes.
  • Crewed platforms and stations: the International Space Station and similar habitats operate in LEO to support human access and resupply.
  • Small satellites and educational CubeSats: lower launch energy makes LEO the common choice for experimental and university missions, including many of the satellites referenced as satellite examples.

History and development

LEO was the venue for the earliest artificial satellites and human spaceflight. The first generation of orbital missions demonstrated the feasibility of operating spacecraft in low orbits and laid the foundation for decades of Earth observation, telecommunications, and human exploration. Over time technological advances reduced launch costs and enabled the proliferation of small satellites and large constellations, changing the operational and regulatory landscape for LEO operations.

Advantages, challenges and distinctions

Benefits of LEO include lower launch energy than higher orbits, reduced signal latency, and better spatial resolution for imaging. Challenges include atmospheric drag at the lowest altitudes, shorter operational lifetimes without stationkeeping, increased collision risk as the number of objects rises, and the need for debris mitigation. LEO differs from medium and geostationary orbits chiefly in altitude, orbital period, and typical operational roles; it remains the most accessible region of near-Earth space for science, commerce and human activity, and is often described in broader policy and outreach materials as an area of active growth and concern about sustainability in space — see general context at outer space references.

For further technical background and mission examples consult introductory and technical sources via links such as orbital period resources and general overviews at LEO information. Historical mission lists and modern constellation reports are widely available for readers seeking detailed timelines and inventories.