The latency of satellite communications is primarily determined by orbital altitude, as the distance a signal must travel directly impacts the time it takes to complete a round trip between the ground and space.
The differences in latency between the three main orbital regimes are as follows:
1. Low Earth Orbit (LEO)
LEO satellites operate at the lowest altitudes, typically ranging from 160 km to 2,000 km. Because they are significantly closer to Earth, the signal travel time is greatly reduced.
- Latency Figures: LEO systems offer the lowest latency, typically between 6 and 30 milliseconds (ms). Some sources estimate the range slightly higher at 30–40 ms.
- User Experience: This near-instantaneous response makes LEO ideal for real-time applications, such as voice calls (VoIP), high-speed broadband, and mobile connectivity where lag or long pauses would be disruptive.
2. Medium Earth Orbit (MEO)
MEO satellites occupy the space between LEO and GEO, usually at altitudes between 2,000 km and 35,786 km, with many (such as GPS) operating around 22,000 km.
- Latency Figures: The increased altitude results in a notable jump in delay, with latencies averaging approximately 150 ms.
- User Experience: While higher than LEO, MEO provides a middle ground often used for global navigation and systems where sub-100 ms speeds are less critical than consistent wide-area coverage.
3. Geostationary Earth Orbit (GEO)
GEO satellites are fixed at a much higher altitude of 35,786 km. At this distance, the signal path between the satellite and ground stations is extremely long.
- Latency Figures: GEO systems suffer from the highest delays. Estimates for round-trip latency range from 280 ms to as high as 600–750 ms. The one-way delay alone is roughly 135 ms.
- User Experience: These high latencies can adversely affect voice call quality and real-time data. While acceptable for fixed services like satellite TV or simple text messaging, GEO is often impractical for the dynamic, low-latency requirements of modern smartphones.
Summary of Latency and Altitude
| Orbit Type | Altitude Range (km) | Typical Latency (ms) |
|---|---|---|
| LEO | 160 – 2,000 | 6 – 40 |
| MEO | 2,000 – 35,786 | ~150 |
| GEO | 35,786 | 280 – 750 |
To understand this in practical terms, think of the “Echo Analogy”: talking through a LEO satellite is like shouting into a small room where the sound bounces back instantly; MEO is like shouting across a large hall; and GEO is like shouting at a distant mountain—you have to wait a noticeable second or two before you hear your own voice return.