Introduction
Have you noticed that your GPS works better in an open field than in a city with tall buildings? The reason has everything to do with where the satellites are and how they move.
Medium Earth Orbit (MEO): The Home of GNSS
Most GNSS satellites live in Medium Earth Orbit:
- Altitude: 19,000–23,000 km above Earth
- Orbital period: About 12 hours
- Why this altitude: Balance between coverage and signal strength
Orbital Parameters by System
| System | Altitude | Orbital Planes | Inclination |
|---|---|---|---|
| GPS | 20,180 km | 6 | 55° |
| GLONASS | 19,130 km | 3 | 64.8° |
| Galileo | 23,222 km | 3 | 56° |
| BeiDou | 21,528 km | 3 | 55° |
Key terms:
- Orbital planes: Rings around Earth at different angles
- Inclination: Tilt relative to equator (higher = better polar coverage)
Why Satellites Move Across the Sky
- Satellite orbits at ~14,000 km/h
- Earth rotates underneath
- From your view, satellites rise in East and set in West over several hours
How Many Satellites Are Visible?
Depends on your latitude:
- Equator: Good visibility, satellites often overhead
- Mid-latitudes (US/Europe): Excellent coverage (optimized here)
- Polar regions: GLONASS and BeiDou provide better coverage
The Horizon Problem
Satellites near the horizon cause issues:
- Longer path through atmosphere = more error
- Higher risk of signal bounce (multipath)
- More likely to be blocked
Professional Tip: Set an "elevation mask" to ignore satellites below 10–15° for better accuracy.
Vital Points
- GNSS satellites live in Medium Earth Orbit (~20,000 km up)
- Different constellations use different orbits for optimal coverage
- Satellites move across the sky completing two orbits per day
- Your latitude affects which satellites you see
- For best results, get a clear view of the sky