How Iridium Works

Most of us are familiar with the way mobile phone networks work, with multiple interconnected cellular towers. As you move from one cell to another, the system automatically hands off your call seamlessly to the next tower. Iridium's satellite network functions in much the same way. The satellites are the towers, orbiting the Earth and handing off calls to each other as they pass overhead.

The Constellation

Iridium's constellation consists of 66 cross-linked operational satellites, plus six in-orbit spares. The satellites operate in near-circular low-Earth orbits (LEO) about 780 km (483 miles) above the Earth's surface.

6 Orbital Planes

11 satellites in each plane, orbits "crisscross" over the poles

17,000 mph

Satellites complete an orbit in about 100 minutes

48 Spot Beams

Each satellite projects beams ~250 miles in diameter

Cross-Linked

Satellites communicate with each other directly

Unique Cross-Link Architecture

The network is considered a meshed constellation of interconnected, cross-linked satellites so that each satellite "talks" with the other nearby satellites in front, behind and in adjacent orbits. The satellite network hands off voice or data communications automatically from one spot beam to another within the satellite footprint, and from one satellite to the next as they pass overhead.

The call is relayed from satellite to satellite around the constellation without touching ground until it is downlinked at an Iridium gateway and subsequently patched into the public switched telecommunication network (PSTN). This all happens in fractions of seconds and is completely seamless to the end user.

Why Cross-Linking Matters

This architecture is unique to Iridium and provides inherent advantages in performance and reliability over other mobile satellite services providers.

Key Advantages

  • Minimal dropped calls: The large number of fast-moving satellites with multiple overlapping spot beams minimizes missed connections, since more than one satellite is usually visible from any place on Earth.
  • Resilient network: If a single satellite is temporarily unavailable, traffic can be routed within the constellation until a spare is moved into place.
  • True global coverage: The only network that covers 100% of the Earth's surface, including polar regions, oceans, and airways.
  • Lower latency: The low-Earth orbit provides a shorter transmission path with less signal attenuation, resulting in delays of only ~50ms compared to ~250ms for geostationary satellites.
  • Smaller equipment: LEO satellites permit truly mobile user equipment with smaller antennas that require no mechanical stabilization.

Ground Infrastructure

Iridium's cross-linked, low-Earth orbit satellite constellation is supported by an extensive ground infrastructure that provides terrestrial connections for satellite voice and data calls, as well as network command, control, monitoring and technical support.

Satellite Network Operating Center (SNOC)

The SNOC is the nerve center of the Iridium space and ground network. It provides 24/7 monitoring and control over all network elements, including the satellites, ground sites and interconnections.

Gateway

The Gateway is the landing point for commercial voice and data traffic via the satellites, providing connections into the Public Switched Telephone Network (PSTN) and the Internet.

TTAC Stations

Tracking, Telemetry and Control sites route satellite health and safety information to the SNOC, provide upload commanding from the SNOC to the satellites, and serve as a delivery mechanism for satellite telemetry.