Constellations
A satellite constellation is a group of satellites working together to provide coverage or services that a single satellite cannot. The arrangement of orbital planes, the number of satellites per plane, and the relative spacing between them determine the constellation's coverage, revisit time, and network topology.
Walker Constellations
Most LEO constellations use a Walker pattern — a regular arrangement where all orbital planes share the same inclination and altitude, and satellites are evenly spaced. Two variants exist:
- Walker Delta — orbital planes are spread evenly around the full 360° of RAAN. This provides global coverage. Used by most LEO constellations including Starlink, Iridium, and the LeoDOS default configuration.
- Walker Star — orbital planes are spread over 180° of RAAN (half the circle). Satellites in adjacent planes travel in opposite directions at the poles, creating a "seam" where relative velocities are very high. Used when coverage is needed primarily at specific latitudes.
A Walker constellation is described by three numbers: T/P/F where T = total satellites, P = number of planes, and F = the phasing parameter (how satellites in adjacent planes are offset from each other). For example, Iridium is 66/6/2.
Constellation Parameters
- Number of planes — how many orbital planes. More planes provide better coverage between planes but require more RAAN spread.
- Satellites per plane — how many satellites in each plane. More satellites per plane reduce the gap between consecutive passes over the same ground point.
- Altitude — higher orbits see more of Earth's surface per satellite (larger footprint) but with lower resolution. Also affects orbital period, atmospheric drag, and radiation exposure.
- Inclination — determines which latitudes are covered. A 53° inclination covers latitudes up to ±53°. A 97° (near-polar) inclination covers the entire globe.
- Phasing (F) — the relative angular offset between satellites in adjacent planes. Affects how evenly the constellation covers the ground. F=0 means satellites in adjacent planes are aligned; F=1 means they are offset by one satellite spacing.
- RAAN spacing — the angular separation between orbital planes. In a Walker Delta with N planes, this is 360°/N by default, but can be customized.
Real Constellations
| Constellation | Operator | Satellites | Planes | Altitude | Inclination | Purpose |
|---|---|---|---|---|---|---|
| Starlink | SpaceX | ~6,000+ | Multiple shells | 540–570 km | 53°, 70°, 97° | Internet |
| OneWeb | OneWeb | 648 | 12 | 1,200 km | 87.9° | Internet |
| Iridium | Iridium | 66 | 6 | 780 km | 86.4° | Voice/data |
| Kuiper | Amazon | 3,236 | Multiple shells | 590–630 km | 30°, 42°, 52° | Internet |
| Iris² | EU/ESA | ~290 | TBD | MEO + LEO | TBD | Secure comms |
| Telesat | Telesat | 298 | 6 + 5 | 1,015–1,325 km | 99°, 37° | Internet |
LeoDOS's default configuration uses 20 planes × 72 satellites at 550 km and 87° inclination — similar in scale to OneWeb and Iridium.
Topology
A Walker Delta constellation forms a 2D torus network. Each satellite has four ISL neighbors (north, south within the same plane; east, west to adjacent planes). The topology wraps around in both dimensions. This regular structure enables efficient routing with predictable hop counts.