Low Earth orbit

Lore & Background

Low Earth orbit is defined by orbital period and eccentricity, though many sources use altitude. The altitude of an object in elliptic orbit can vary significantly, and even circular orbits vary by up to 30 km due to Earth's oblateness. The LEO region is distinct from LEO orbits: highly elliptical orbits may pass through the region but are not in LEO, and sub-orbital objects can reach the region but re-enter the atmosphere. This distinction is important for collision analysis.

Reader's Guide

Low Earth orbit is significant because it requires the least energy for satellite placement, provides high bandwidth and low communication latency, and allows easier crew access and servicing. LEO is used for communication, Earth observation, and satellite internet constellations. However, LEO satellites have a small field of view, requiring large constellations for continuous coverage. Atmospheric drag causes orbital decay, especially below 300 km, requiring periodic re-boosting or replacement.

Did You Know?

• The International Space Station orbits at about 400 to 420 km and decays by about 2 km/month, requiring re-boosting a few times a year.
• The oldest piece of space debris in LEO is the Vanguard 1 satellite and its third-stage.

Defining the Middle Band

What makes this band conceptually interesting is that its lower boundary is not a physical phenomenon but a convention agreed upon by the orbital mechanics community, while its upper boundary is anchored to something far more concrete: the altitude at which a satellite completes one revolution in exactly 24 hours, matching Earth's own rotation. Every satellite dwelling in this middle region circles the planet in less than a full day, with the fastest circular orbits at the lowest MEO altitudes completing a lap in approximately two hours. The region goes by several names depending on context—mid Earth orbit, intermediate circular orbit, or simply MEO—but all refer to the same swath of space. It is a transitional zone, neither hugging the atmosphere nor locked in step with the planet's spin, and that in-between quality shapes both its engineering challenges and its applications.

Forces and Hazards in the Middle

Operating in MEO means contending with a suite of non-gravitational forces that nudge satellites off their ideal paths. Solar radiation pressure stands out as the dominant perturbing influence, constantly pushing on any surface exposed to sunlight. Beyond the Sun's push, engineers must account for Earth's reflected light—albedo—tiny thrust from navigation antennas, and thermal effects arising when a spacecraft re-radiates absorbed heat. These forces are individually small but collectively demand continuous station-keeping. The environment also carries a more severe threat: the Van Allen radiation belts, two zones of energetic charged particles concentrated above the equator, thread through the MEO region. Without purpose-built shielding, these particles can degrade or destroy onboard electronics. The combination of persistent mechanical perturbations and a hazardous radiation environment makes MEO a demanding operational theater, one where every design choice must balance mass, power, and survivability against the mission's communication or navigation goals.

Navigation, Broadcasting, and the New Broadband Era

MEO has become the preferred altitude for global positioning constellations. More recently, MEO has entered the broadband conversation.

The Debris Problem and Orbital Permanence

Perhaps the most sobering aspect of the MEO region is the permanence of objects once placed there. Space debris in medium Earth orbit stays practically permanently in orbit around the planet, never decaying away as it might in lower altitudes. This means every defunct satellite, spent stage, or collision fragment becomes a long-term resident in a region already populated by operational navigation and communications constellations. The debris population does not stop at the MEO boundary; it extends upward into the lowest high Earth orbits, the same altitude band where geostationary satellites are parked in so-called graveyard orbits after their useful lives end. The result is a continuous corridor of residual objects stretching from the upper edge of MEO into the geostationary belt. For operators maintaining GPS, GLONASS, Galileo, BeiDou, and the newer broadband constellations in this altitude range, the persistent clutter elevates the importance of collision avoidance and long-term orbital sustainability to a degree that distinguishes MEO from both lower and higher orbital regimes.