A single satellite in low Earth orbit can only see a small part of the planet at any moment and passes over each location for just a few minutes. To provide continuous coverage, operators combine many satellites into a constellation. Constellations now drive a large share of global launch demand.
How constellations are designed
A constellation is described by the number of orbital planes, the number of satellites per plane, the altitude and the inclination of the planes. More satellites give better coverage and shorter revisit times, but they also increase cost and the number of launches required.
Typical applications
- Broadband communications: large constellations in low Earth orbit provide internet access with low latency.
- Navigation: systems such as Galileo and GPS use constellations in medium Earth orbit so that several satellites are visible from any point on Earth.
- Earth observation: constellations of imaging or radar satellites reduce the time between two observations of the same place.
- Internet of Things: small satellites collect data from sensors and devices on the ground.
Deploying a constellation
Satellites of one orbital plane are often launched together and then spread out along the orbit. Moving satellites into different planes is expensive, so each plane usually needs its own launch or a transfer vehicle. Operators therefore plan launch campaigns carefully, combining dedicated launches for whole planes with rideshare launches for replacements.
Replenishment and end of life
Satellites in low orbits have limited lifetimes and must be replaced regularly. Constellation operators need a steady stream of launches and a reliable plan for deorbiting old satellites, which is increasingly required by regulators.
Related reading
- LEO, MEO and GEO Satellites Compared: Altitudes, Uses and Examples
- Ariane 6 Books Its Largest Order Intake Yet: Amazon Leo Adds Six Ariane 64 Launches
- Space Situational Awareness: How Satellites Avoid Collisions
Sources
- ESA: Types of orbits
- ESA: Space debris by the numbers
- ESA: Galileo, a constellation of navigation satellites
- GPS.gov: Space Segment
Cover image: Earth at night photographed from the International Space Station. Credit: NASA (iss040e117958), public domain.