Earth's Orbital Neighbourhood

As of early 2026, there are roughly 13,000 active satellites in Earth orbit. But that number only tells part of the story. There are also around 40,000 pieces of tracked debris larger than 10 centimetres - spent rocket bodies, defunct satellites, fragments from collisions and anti-satellite weapon tests. Below the tracking threshold, there are an estimated 130 million pieces of debris larger than 1 millimetre.

The number of active satellites has roughly tripled since 2020, driven almost entirely by mega-constellations. SpaceX's Starlink alone accounts for over 6,000 satellites, with plans for 42,000. OneWeb has around 630. Amazon's Project Kuiper plans 3,236. The character of space has fundamentally changed in half a decade.

Low Earth Orbit (LEO, 200-2,000 km). The most crowded zone. Satellites here complete an orbit in roughly 90 minutes and move at about 7.8 km/s. This is where the ISS flies (408 km), where Starlink operates (550 km), and where most Earth observation and scientific satellites work. Low altitude means high resolution and low latency, but also atmospheric drag that limits satellite lifetimes to a few years without propulsion.

Medium Earth Orbit (MEO, 2,000-35,000 km). Home to the navigation constellations. GPS orbits at 20,200 km (12-hour period), Galileo at 23,222 km, GLONASS at 19,130 km. These altitudes are chosen because the orbital period creates a repeating ground track that ensures global coverage with a minimum number of satellites. MEO is also used by some communications constellations like O3B.

Geostationary Orbit (GEO, 35,786 km). The unique altitude where orbital period exactly matches Earth's rotation. A satellite here appears motionless in the sky, making it ideal for communications and weather observation. The GEO belt is a finite resource - there are only 360 degrees of longitude, and satellites need to be spaced at least 0.1 degrees apart to avoid radio interference. GEO slots are allocated by the ITU and are geopolitically valuable.

In 1978, NASA scientist Donald Kessler described a scenario in which the density of objects in orbit becomes high enough that collisions between them generate more debris than natural decay can remove. Each collision produces thousands of fragments, each capable of triggering further collisions. Beyond a critical density, the process becomes self-sustaining - a cascading chain reaction that could render entire orbital shells unusable for generations.

This is not a theoretical concern. In 2009, a defunct Russian military satellite (Cosmos 2251) collided with an active Iridium communications satellite at a relative speed of 11.7 km/s. The collision produced over 2,300 trackable fragments. In 2007, China destroyed one of its own weather satellites with an anti-satellite missile, creating over 3,500 pieces of trackable debris - many of which remain in orbit and will continue to pose collision risks for decades.

Switch to the density view to see the problem visually. The LEO shell is alarmingly dense. The question facing the space industry is whether it is possible to operate tens of thousands of satellites in LEO without triggering a Kessler cascade, and what happens to the satellites that fail before they can be deorbited.

The US Space Surveillance Network maintains a catalogue of every trackable object in Earth orbit, updated continuously using ground-based radar and optical telescopes. Each object's orbit is summarised as a Two-Line Element (TLE) set - a compact, standardised format containing six orbital elements plus drag parameters.

TLE data alone does not tell you where a satellite is. To compute the position at any given time, you need a propagation algorithm. This visualisation uses SGP4 (Simplified General Perturbations 4), the standard algorithm developed by the US military in the 1980s. SGP4 accounts for Earth's oblateness (the J2 effect), atmospheric drag, solar radiation pressure, and lunar/solar gravitational perturbations. It is accurate to within a few kilometres for LEO satellites over a span of a few days.

The TLE data shown here comes from CelesTrak, a service operated by Dr T.S. Kelso that redistributes NORAD catalogue data in accessible formats. It is updated several times daily and is the primary source for civilian satellite tracking worldwide.

Select the Starlink constellation to see the scale of it. Thousands of satellites in coordinated orbital planes, each plane tilted at 53 degrees, spaced evenly around the globe. The geometry is deliberate: the orbital planes are arranged so that every point on Earth between 53°N and 53°S always has multiple satellites overhead.

The GPS constellation, by contrast, uses just 24 satellites in six orbital planes at 20,200 km altitude. The much higher orbit means each satellite covers a larger area, but the signal takes longer to arrive and the satellite cannot provide broadband internet (the entire purpose of Starlink requires low latency, which requires low altitude, which requires thousands of satellites).

Select different constellations to compare their structures. Navigation constellations (GPS, Galileo, GLONASS) all use similar medium-orbit geometries with different plane counts and inclinations. Iridium uses six planes in near-polar orbit at 780 km. OneWeb uses higher-inclination planes at 1,200 km to cover polar regions that Starlink misses.